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1
Diven, R. H., R. E. Reed e W. J. Pistor. "THE PHYSIOLOGY OF NITRITE POISONING IN SHEEP*". Annals of the New York Academy of Sciences 111, n. 2 (15 dicembre 2006): 638–43. http://dx.doi.org/10.1111/j.1749-6632.1964.tb53131.x.
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Ahmad Pampori, Zahoor, Aasif Ahmad Sheikh, Ovais Aarif, Dilruba Hasin e Irfan Ahmad Bhat. "Physiology of reproductive seasonality in sheep – an update". Biological Rhythm Research 51, n. 4 (10 dicembre 2018): 586–98. http://dx.doi.org/10.1080/09291016.2018.1548112.
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3
Fortune, J. A. "Reproductive physiology of Merino sheep: Concepts and consequences". Animal Reproduction Science 30, n. 4 (gennaio 1993): 335–36. http://dx.doi.org/10.1016/0378-4320(93)90083-4.
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4
Zhao, Pengfei, Shaobin Li, Zhaohua He, Fangfang Zhao, Jiqing Wang, Xiu Liu, Mingna Li, Jiang Hu, Zhidong Zhao e Yuzhu Luo. "Physiology and Proteomic Basis of Lung Adaptation to High-Altitude Hypoxia in Tibetan Sheep". Animals 12, n. 16 (19 agosto 2022): 2134. http://dx.doi.org/10.3390/ani12162134.
Testo completoAbstract (sommario):
The Tibetan sheep is an indigenous animal of the Tibetan plateau, and after a long period of adaptation have adapted to high-altitude hypoxia. Many physiological changes occur in Tibetan sheep as they adapt to high-altitude hypoxia, especially in the lungs. To reveal the physiological changes and their molecular mechanisms in the lungs of Tibetan sheep during adaptation to high altitudes, we selected Tibetan sheep from three altitudes (2500 m, 3500 m, and 4500 m) and measured blood-gas indicators, observed lung structures, and compared lung proteome changes. The results showed that the Tibetan sheep increased their O2-carrying capacity by increasing the hemoglobin (Hb) concentration and Hematocrit (Hct) at an altitude of 3500 m. While at altitude of 4500 m, Tibetan sheep decreased their Hb concentration and Hct to avoid pulmonary hypertension and increased the efficiency of air-blood exchange and O2 transfer by increasing the surface area of gas exchange and half-saturation oxygen partial pressure. Besides these, some important proteins and pathways related to gas transport, oxidative stress, and angiogenesis identified by proteome sequencing further support these physiology findings, including HBB, PRDX2, GPX1, GSTA1, COL14A1, and LTBP4, etc. In conclusion, the lungs of Tibetan sheep are adapted to different altitudes by different strategies; these findings are valuable for understanding the basis of hypoxic adaptation in Tibetan sheep.
5
Morand, C., C. Yacoub, C. Remesy e C. Demigne. "Characterization of glucagon and catecholamine effects on isolated sheep hepatocytes". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 255, n. 4 (1 ottobre 1988): R539—R546. http://dx.doi.org/10.1152/ajpregu.1988.255.4.r539.
Testo completoAbstract (sommario):
The purpose of this study was to characterize the glycogenolytic response to catecholamines and glucagon in isolated sheep hepatocytes. In this species, epinephrine appeared to exert its action on hepatic glycogenolysis by altering the cytosolic concentrations of both adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+. In contrast to results obtained in rat hepatocytes, glucagon failed to induce a rise in free cytosolic Ca2+ in sheep liver. Experiments on isolated hepatocytes or on liver plasma membranes showed that in sheep, glucagon was more efficient than epinephrine in promoting the production of cAMP. In the presence of glucagon or epinephrine, the activation of the glycogen phosphorylase a always appeared greater in sheep than in rat liver cells, whereas the variations in cellular cAMP were quite limited in sheep. The alpha 1- and beta-agonists (phenylephrine and isoproterenol) were alone as efficient as epinephrine in promoting phosphorylase a activation in sheep hepatocytes. All these results indicate the existence in sheep liver of a glycogen phosphorylase highly responsive to hormones.
6
Owens, J. A., J. Falconer e J. S. Robinson. "Glucose metabolism in pregnant sheep when placental growth is restricted". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 257, n. 2 (1 agosto 1989): R350—R357. http://dx.doi.org/10.1152/ajpregu.1989.257.2.r350.
Testo completoAbstract (sommario):
The effect of restricting placental growth on glucose metabolism in pregnant sheep in late gestation was determined by primed constant infusions of D-[U-14C]- and D-[2-3H]glucose and antipyrine into fetuses of six control sheep and six sheep from which endometrial caruncles had been removed before pregnancy (caruncle sheep). In the latter, placental and fetal weights were reduced, as was the concentration of glucose in fetal arterial blood. Fetal glucose turnover in caruncle sheep was only 52-59% of that in controls, largely because of lower umbilical loss of glucose back to the placenta (38-39% of control) and lower fetal glucose utilization (61-74% of control). However, fetal glucose utilization on a weight-specific basis was similar in control and caruncle sheep. Significant endogenous glucose production occurred in control and caruncle fetal sheep. Maternal glucose production and partition of glucose between the gravid uterus and other maternal tissues were similar in control and caruncle sheep. In conclusion, when placental and fetal growth are restricted, fetal glucose utilization is maintained by reduced loss of glucose back to the placenta and mother and by maintaining endogenous glucose production.
7
Snapper, J. R., e P. L. Lefferts. "Effects of aerosol histamine and carbachol on central and peripheral airflow resistance in sheep". Journal of Applied Physiology 61, n. 2 (1 agosto 1986): 760–65. http://dx.doi.org/10.1152/jappl.1986.61.2.760.
Testo completoAbstract (sommario):
Sixteen anesthetized artificially ventilated open-chest sheep were prepared with retrograde catheters to allow for measurement of dynamic compliance of the lungs (Cdyn), total airflow resistance of the lungs (RL), and central (Rc) and peripheral (Rp) airflow resistance. Twelve sheep received aerosol histamine and 12 sheep received aerosol carbachol. Eight sheep received and responded to both aerosol histamine and aerosol carbachol. Three sheep received both aerosol histamine and aerosol carbachol but failed to respond to both agents. Under base-line conditions, for the 16 sheep, 69% of total RL was located in the peripheral component, Rp, and 31% in the central component, Rc. Aerosol histamine caused only peripheral small airway changes while aerosol carbachol predominantly effected the central large airways. When aerosol histamine responsiveness, defined using Cdyn or Rp, was compared to aerosol carbachol responsiveness using Rc, a correlation was demonstrable (r = 0.84, n = 8, P less than 0.05). It is possible in sheep to cause relatively pure peripheral small airway and relatively pure central large airway changes by using different bronchoconstrictor agents. Aerosol histamine and aerosol carbachol responsiveness correlated with each other in these artificially ventilated anesthetized sheep.
8
Coggeshall, J. W., B. W. Christman, P. L. Lefferts, W. E. Serafin, I. A. Blair, M. J. Butterfield e J. R. Snapper. "Effect of inhibition of 5-lipoxygenase metabolism of arachidonic acid on response to endotoxemia in sheep". Journal of Applied Physiology 65, n. 3 (1 settembre 1988): 1351–59. http://dx.doi.org/10.1152/jappl.1988.65.3.1351.
Testo completoAbstract (sommario):
We studied the effects of a 5-lipoxygenase inhibitor, L-651,192, on the pulmonary dysfunction caused by endotoxemia in chronically instrumented unanesthetized sheep. The efficacy and selectivity of L-651,392 were tested by measuring in vivo production of leukotriene B4 (LTB4) and cyclooxygenase products of arachidonic acid after endotoxemia before and after pretreatment with L-651,392 and ex vivo from granulocytes and whole blood stimulated with calcium ionophore from sheep before and 24 h after pretreatment with L-651,392. A novel assay for LTB4 by high-performance liquid chromatography/gas chromatography/mass spectrometry techniques was developed as a measure of 5-lipoxygenase metabolism of arachidonic acid. L-651,392 proved to be an effective in vivo 5-lipoxygenase inhibitor in sheep. L-651,392 blocked the increase in LTB4 observed in lung lymph after endotoxemia in vivo in sheep as well as inhibited by 80% the ex vivo production of LTB4 by granulocytes removed from sheep treated 24 h earlier with L-651,392. Although L-651,392 blocked the increase in cyclooxygenase products of arachidonic acid observed in lung lymph after endotoxemia in vivo in sheep, the drug probably did not function directly as a cyclooxygenase inhibitor. L-651,392 did not attenuate the ex vivo production of thromboxane B2 by whole blood from sheep treated 24 h earlier with the drug. L-651,392 attenuated the alterations in pulmonary hemodynamics, lung mechanics, oxygenation, and lung fluid and solute exchange observed after endotoxemia in sheep. We speculate that 5-lipoxygenase products are a major stimulus for cyclooxygenase metabolism of arachidonic acid after endotoxemia in sheep.
9
Bujok, Jolanta, Tomasz Walski, Albert Czerski, Katarzyna Gałecka, Karolina Grzeszczuk-Kuć, Wojciech Zawadzki, Wojciech Witkiewicz e Małgorzata Komorowska. "Sheep model of haemodialysis treatment". Laboratory Animals 52, n. 2 (10 luglio 2017): 176–85. http://dx.doi.org/10.1177/0023677217718861.
Testo completoAbstract (sommario):
More than two million patients received haemodialysis (HD) in 2013. Many methods for improving dialysis therapy outcomes have been tested. Nevertheless, patients continue to experience high morbidity and mortality rates. We aimed to develop an animal model of HD treatment to study methods that would prevent the adverse effects of renal replacement therapy. The study was conducted using six male Merino sheep. The animals underwent a two-step bilateral nephrectomy, and a permanent dual-lumen catheter was inserted into the jugular vein. In each animal, 10 short, daily HD treatments were conducted. The dialysis prescription was adjusted individually to each animal. Measures of dialysis adequacy (spKt/V and urea reduction ratio [URR]) were calculated for each HD treatment. All animals remained in a good clinical state during the experiment. However, a sustained decrease in red blood cell count was detected. The average URR was 0.65 ± 0.01, whereas the calculated spKt/V was approximately 1.16 ± 0.03. Neither hyperphosphataemia nor a significant decline in serum albumin concentrations were detected during the study. A sustained increase in serum potassium concentrations was detected on consecutive days of the experiment. All sheep survived the treatment and were euthanized at the end of the experiment. In conclusion, we developed a reproducible sheep model of HD treatment. The gentle nature and specific anatomical features of sheep provided easy blood access and allowed us to perform HD without pharmacological intervention. However, some differences in sheep physiology relative to human physiology must be considered when interpreting the results of the study.
10
Gopalakrishnan, G. S., D. S. Gardner, S. M. Rhind, M. T. Rae, C. E. Kyle, A. N. Brooks, R. M. Walker et al. "Programming of adult cardiovascular function after early maternal undernutrition in sheep". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 287, n. 1 (luglio 2004): R12—R20. http://dx.doi.org/10.1152/ajpregu.00687.2003.
Testo completoAbstract (sommario):
The prenatal nutritional environment influences the subsequent risk of hypertension in adulthood. Animal studies have used, generally, the rat as a model species to illustrate the association between maternal nutrient intake and blood pressure in the resulting adult offspring. No study to date has shown programming of adult cardiovascular function in the sheep through maternal dietary intervention. We therefore fed pregnant sheep to either 100% recommended intake from day 0 of gestation to term [∼147 days gestational age (dGA); controls n = 8] or to 50% recommended intake from day 0 to 95 dGA and thereafter to 100% intake (NR; n = 9). Sheep lambed naturally, offspring were weaned at 16 wk, and the male offspring were reared on pasture until 3 yr of age. At this time, cardiovascular catheters were inserted under halothane anesthesia and sheep were allowed 2–4 days recovery. Basal cardiovascular status and pressor responses to infusion of norepinephrine, angiotensin II, and captopril were then assessed alongside basal plasma concentrations of glucose, cortisol, and leptin. NR sheep were of similar birth weight to controls but at 3 yr of age had higher blood pressure before, but not after, feeding. Peripheral sensitivity to vasoconstrictor infusion was similar between dietary groups, although a reflex bradycardia was not apparent in NR sheep during norepinephrine infusion. Circulating leptin correlated well with fat mass and increased more after vasoconstrictor infusion in NR sheep. In conclusion, early NR has been shown to program aspects of cardiovascular control and adipocyte function in adult sheep.
11
Pearse, D. B., E. M. Wagner e J. T. Sylvester. "Edema clearance in isolated sheep lungs". Journal of Applied Physiology 74, n. 1 (1 gennaio 1993): 126–32. http://dx.doi.org/10.1152/jappl.1993.74.1.126.
Testo completoAbstract (sommario):
Edema may be cleared from the lung by lymphatic drainage, transudation across the visceral pleural, vascular reabsorption, and movement into the mediastinum. To determine the quantity and mechanisms of edema clearance associated with spontaneous edema formation in isolated sheep lungs, we perfused six lungs for 180 min with blood (100 ml.kg-1.min-1) at subatmospheric left atrial pressure (Pla) from a weighed reservoir. In six other lungs, Pla was increased to 20 mmHg at 30–75 min to further augment edema. Fluid drainage from the lung was fractionated into blood and water components by serial measurements of drainage and perfusate hematocrit. Changes in weight of circulating intravascular blood and extravascular lung water (EVLW) were also directly measured by dye dilution and standard gravimetric techniques, respectively. From these measurements, we calculated that 3.04 +/- 0.53 g/g blood-free dry lung of water filtered into the extravascular space during perfusion. Of this amount, 42% was reabsorbed into the pulmonary vasculature; 18% drained from the lung via lymphatics, visceral pleura, and mediastinum; and 40% was retained in the lung. Compared with low Pla lungs, transient elevation of Pla increased lung hemorrhage and the final change in reservoir weight, but the quantity and clearance of cumulative filtered water and the final values of EVLW and wet-to-dry weight ratio (WW/DW) were not altered. These results suggest that 1) significant edema clearance occurred in isolated sheep lungs, primarily by vascular reabsorption, and 2) measurements of EVLW and WW/DW under-estimated injury in the presence of lung hemorrhage and significant edema clearance.
12
Julien, M., J. M. Hoeffel e M. R. Flick. "Oleic acid lung injury in sheep". Journal of Applied Physiology 60, n. 2 (1 febbraio 1986): 433–40. http://dx.doi.org/10.1152/jappl.1986.60.2.433.
Testo completoAbstract (sommario):
Intravenous infusion of oleic acid into experimental animals causes acute lung injury resulting in pulmonary edema. We investigated the mechanism of oleic acid lung injury in sheep. In experiments with anesthetized and unanesthetized sheep with lung lymph fistulas, we measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and lymph and plasma protein concentrations. We injured the lungs with intravenous infusions of oleic acid at doses ranging from 0.015 to 0.120 ml/kg. We found that oleic acid caused reproducible dose-related increases in pulmonary arterial pressure and pulmonary vascular resistance, arterial hypoxemia, and increased protein-rich lung lymph flow and extravascular lung water. The lung fluid balance changes were characteristic of increased permeability pulmonary edema. Infusion of the esterified fat triolein had no hemodynamic or lung fluid balance effects. Depletion of leukocytes with a nitrogen mustard or platelets with an antiplatelet serum had no effect on oleic acid lung injury. Treatment of sheep before injury with methylprednisolone 30 mg/kg or ibuprofen 12.5–15.0 mg/kg also had no effects. Unlike other well-characterized sheep lung injuries, injury caused by oleic acid does not require participation of leukocytes.
13
Terry, P. B., H. A. Menkes e R. J. Traystman. "Effects of maturation and aging on collateral ventilation in sheep". Journal of Applied Physiology 62, n. 3 (1 marzo 1987): 1028–32. http://dx.doi.org/10.1152/jappl.1987.62.3.1028.
Testo completoAbstract (sommario):
We studied collateral ventilation as a function of age by measuring the resistance (Rcoll) and time constant (Tcoll) of collateral airflow in young (2–10 mo), mature (16–24 mo), and old sheep (6–13 yr). Rcoll was 0.50 +/- 0.11 cmH2O X ml-1 X min (SE) in young sheep and decreased significantly to 0.05 +/- 0.02 and 0.02 +/- 0.01 cmH2O X ml-1 X min in mature and old sheep, respectively. Tcoll was 34.4 +/- 7.9 (SE) s in young sheep and decreased to 5.7 +/- 0.9 and 10.2 +/- 3.1 s in mature and old sheep, respectively. We conclude that a marked decrease in Rcoll and Tcoll occurs between birth and maturity but changes little with further aging. In the young an increased resistance and time constant of collateral airflow may accentuate ventilation perfusion imbalance and impair the removal of secretions in disease states.
14
Flick, M. R., S. A. Milligan, J. M. Hoeffel e I. M. Goldstein. "Catalase prevents increased lung vascular permeability during air emboli in unanesthetized sheep". Journal of Applied Physiology 64, n. 3 (1 marzo 1988): 929–35. http://dx.doi.org/10.1152/jappl.1988.64.3.929.
Testo completoAbstract (sommario):
We studied the effects of bovine catalase on increased lung vascular permeability to fluid and protein during air emboli in unanesthetized sheep. Pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, lymph and plasma protein concentrations, arterial PO2, and numbers of arterial leukocytes were measured in paired experiments in which each sheep served as its own control. We found an increase in protein-rich lung lymph flow during embolization in untreated sheep, indicating an increase in microvascular permeability. When sheep were pretreated with intraperitoneal injections of catalase (50 mg/kg divided over the 24 h before air infusion), vascular pressures, arterial PO2, and leukocyte counts were not different from when the sheep were untreated, but the expected increases in transvascular fluid and protein flow during emboli were significantly attenuated (by approximately 50%). This effect required catalase enzyme activity, as demonstrated by the failure of enzymatically inactivated catalase (by reaction in vitro with aminotriazole in the presence of H2O2) or catalase vehicle (0.1% thymol in water) to affect the lung lymph response to air emboli. We conclude that H2O2 plays a role in the pathogenesis of the acute lung injury caused by intravenous air infusions into unanesthetized sheep. Because both catalase and superoxide dismutase have protected sheep lungs from air emboli-induced increased vascular permeability, a possible specific cause of microvascular barrier injury could be hydroxyl radicals formed from reactions between H2O2 and superoxide anion.
15
Kuratomi, Y., P. L. Lefferts, B. W. Christman, R. E. Parker, W. G. Smith, R. A. Mueller e J. R. Snapper. "Effect of a 5-lipoxygenase inhibitor on endotoxin-induced pulmonary dysfunction in awake sheep". Journal of Applied Physiology 74, n. 2 (1 febbraio 1993): 596–605. http://dx.doi.org/10.1152/jappl.1993.74.2.596.
Testo completoAbstract (sommario):
We studied the effects of a 5-lipoxygenase inhibitor, SC-45662, on endotoxin-induced pulmonary dysfunction in chronically instrumented unanesthetized sheep. Each sheep was studied with endotoxin alone, SC-45662 alone, and endotoxin after SC-45662 pretreatment. Endotoxin did not cause consistent increases in plasma or lung lymph concentrations of leukotriene B4 (LTB4). Ex vivo stimulation of whole blood from sheep before and after treatment with SC-45662 demonstrated no inhibition of cyclooxygenase metabolism but an approximately 80% inhibition of LTB4 production. At drug concentrations obtained in vivo, SC-45662 did not significantly inhibit in vitro A23187-stimulated whole blood thromboxane B2 production but did inhibit LTB4 production from ionophore-stimulated sheep granulocytes. SC-45662 attenuated the early changes in lung mechanics and pulmonary hypertension but did not attenuate the later increase in lung fluid and solute exchange observed after endotoxemia. We conclude that 5-lipoxygenase products are not measurably involved in the later increase in lung fluid and solute exchange observed after endotoxemia in sheep.
16
Matos, C. A. P., e D. L. Thomas. "Physiology and genetics of testicular size in sheep: a review". Livestock Production Science 32, n. 1 (agosto 1992): 1–30. http://dx.doi.org/10.1016/s0301-6226(12)80009-1.
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Kobayashi, H., T. Kobayashi e M. Fukushima. "Effects of dibutyryl cAMP on pulmonary air embolism-induced lung injury in awake sheep". Journal of Applied Physiology 63, n. 6 (1 dicembre 1987): 2201–7. http://dx.doi.org/10.1152/jappl.1987.63.6.2201.
Testo completoAbstract (sommario):
To assess the role of intracellular adenosine 3′,5′-cyclic monophosphate (cAMP), we tested the effects of dibutyryl cAMP (DBcAMP), an analogue of cAMP, on lung injury induced by pulmonary air embolism in awake sheep with chronic lung lymph fistula. We infused air (1.23 ml/min) in the pulmonary artery for 2 h in untreated control sheep. In DBcAMP-pretreated sheep DBcAMP was infused (1 mg/kg bolus and 0.02 mg.kg-1.min-1 constantly for 5 h); after 1 h from beginning of DBcAMP administration the air infusion was started. After the air infusion, pulmonary arterial pressure (Ppa) and lung lymph flow rate (Qlym) significantly increased in both groups. DBcAMP-pretreated sheep showed significantly lower responses in Qlym (2.7 X base line) compared with untreated control sheep (4.6 X base line); however, Ppa, left atrial pressure, and lung lymph-to-plasma protein concentration ratio were not significantly different between the two groups. Although plasma and lung lymph thromboxane B2 and 6-ketoprostaglandin F1 alpha concentrations increased significantly during the air infusion, DBcAMP-pretreated sheep showed significantly lower responses. Thus DBcAMP infusion attenuated pulmonary microvascular permeability induced by air embolism. We conclude that pulmonary vascular permeability is in part controlled by the intracellular cAMP level.
18
Rider, E. D., A. H. Jobe, M. Ikegami e B. Sun. "Different ventilation strategies alter surfactant responses in preterm rabbits". Journal of Applied Physiology 73, n. 5 (1 novembre 1992): 2089–96. http://dx.doi.org/10.1152/jappl.1992.73.5.2089.
Testo completoAbstract (sommario):
The effect of ventilation strategy on in vivo function of different surfactants was evaluated in preterm rabbits delivered at 27 days gestational age and ventilated with either 0 cmH2O positive end-expiratory pressure (PEEP) at tidal volumes of 10–11 ml/kg or 3 cmH2O PEEP at tidal volumes of 7–8 ml/kg after treatment with one of four different surfactants: sheep surfactant, the lipids of sheep surfactant stripped of protein (LH-20 lipid), Exosurf, and Survanta. The use of 3 cmH2O PEEP decreased pneumothoraces in all groups except for the sheep surfactant group where pneumothoraces increased (P < 0.01). Ventilatory pressures (peak pressures - PEEP) decreased more with the 3 cmH2O PEEP, low-tidal-volume ventilation strategy for Exosurf-, Survanta-, and sheep surfactant-treated rabbits (P < 0.05), whereas ventilation efficiency indexes (VEI) improved only for Survanta- and sheep surfactant-treated rabbits with 3 cmH2O PEEP (P < 0.01). Pressure-volume curves for sheep surfactant-treated rabbits were better than for all other treated groups (P < 0.01), although Exosurf and Survanta increased lung volumes above those in control rabbits (P < 0.05). The recovery of intravascular radiolabeled albumin in the lungs and alveolar washes was used as an indicator of pulmonary edema. Only Survanta and sheep surfactant decreased protein leaks in the absence of PEEP, whereas all treatments decreased labeled albumin recoveries when 3 cmH2O PEEP was used (P < 0.05). These experiments demonstrate that ventilation style will alter a number of measurements of surfactant function, and the effects differ for different surfactants.
19
Russi, E. W., W. M. Abraham, G. A. Chapman, J. S. Stevenson, E. Codias e A. Wanner. "Effects of leukotriene D4 on mucociliary and respiratory function in allergic and nonallergic sheep". Journal of Applied Physiology 59, n. 5 (1 novembre 1985): 1416–22. http://dx.doi.org/10.1152/jappl.1985.59.5.1416.
Testo completoAbstract (sommario):
We determined the effect of aerosol challenge with leukotriene D4 (LTD4) on specific lung resistance (sRL) and tracheal mucous velocity (TMV) in conscious sheep with (allergic) and without (nonallergic) Ascaris suum hypersensitivity. In allergic sheep LTD4 in concentrations of 50, 100, and 150 micrograms/ml produced dose-dependent increases in mean sRL by 44 (P = NS), 154 (P less than 0.05), and 233% (P less than 0.05), respectively. The increase in sRL produced by 150 micrograms/ml LTD4 was prevented by FPL 55712, an antagonist of slow-reacting substance of anaphylaxis. In nonallergic sheep 150 micrograms/ml LTD4 failed to elicit a significant change in sRL. In contrast to the changes in airway mechanics, concentrations of LTD4 as low as 25 micrograms/ml produced significant decreases in TMV in allergic sheep. The maximum decrease in TMV at this dose occurred 2 h after challenge; with larger doses of LTD4 (100 and 150 micrograms/ml) the maximum effect was observed 3 h after challenge. Furthermore, 150 micrograms/ml LTD4 reduced TMV in nonallergic sheep (mean decrease 43%, P less than 0.05). FPL 55712 only had a minor effect on the LTD4-induced decreases in TMV. We conclude that allergic sheep exhibit greater airway responsiveness to inhaled LTD4 than nonallergic sheep but that this difference is not evident for the concomitant changes in mucociliary transport. This suggests that the allergic state is associated with an increased responsiveness to LTD4 in tissues controlling airway caliber but not in those contributing to mucociliary function.
20
Fan, L., S. Mukaddam-Daher, J. Gutkowska, B. S. Nuwayhid e E. W. Quillen Jr. "Renal perfusion pressure and renin secretion in bilaterally renal denervated sheep". Canadian Journal of Physiology and Pharmacology 72, n. 7 (1 luglio 1994): 782–87. http://dx.doi.org/10.1139/y94-111.
Testo completoAbstract (sommario):
To further investigate the influence of renal nerves on renin secretion, the renin secretion responses to step reductions of renal perfusion pressure (RPP) were studied in conscious sheep with innervated kidneys (n = 5) and with bilaterally denervated kidneys (n = 5). The average basal level of RPP in sheep with denervated kidneys (82 ± 4 mmHg; 1 mmHg = 133.3 Pa) was similar to that in sheep with innervated kidneys (83 ± 3 mmHg). RPP was reduced in four sequential 15-min steps, to a final level of 54 ± 2 mmHg in sheep with innervated kidneys and to 57 ± 1 mmHg in denervated sheep. The renin secretion rate was increased as RPP was reduced in sheep with innervated kidneys. Baseline peripheral plasma renin activity was reduced and there was almost no response of renin secretion rate to reduction of RPP in sheep with denervated kidneys. Also, baseline renal blood flow, urine flow rate, sodium excretion rate, and potassium excretion rate were higher in sheep with denervated kidneys than those with innervated kidneys. Baseline plasma angiotensin II was similar in both groups of sheep. As RPP was decreased, plasma angiotensin II was increased in sheep with innervated kidneys, but was not significantly altered in sheep with denervated kidneys. Plasma atrial natriuretic factor was unaltered by either reduction of RPP or renal denervation. In conclusion, hormonal factors, such as angiotensin II and atrial natriuretic factor, do not account for the dramatic suppression of renin secretion in response to the reduction of RPP in sheep with bilateral renal denervation. Renal nerves are a necessary component in the control of renin secretion during reduction of RPP and may contribute to the regulation of baseline plasma renin activity and sodium excretion rate in conscious ewes.Key words: renin secretion, renal perfusion pressure, renal nerves, denervation, sheep.
21
Peterson, B. T., H. L. James e J. W. McLarty. "Effects of lung volume on clearance of solutes from the air spaces of lungs". Journal of Applied Physiology 64, n. 3 (1 marzo 1988): 1068–75. http://dx.doi.org/10.1152/jappl.1988.64.3.1068.
Testo completoAbstract (sommario):
Several investigators have shown that the clearance rate of aerosolized 99mTc-labeled diethylenetriamine pentaacetate (DTPA, mol wt = 492, radius = 0.6 nm) from the air spaces of the lungs of humans and experimental animals increases with lung volume. To further investigate this phenomenon we performed a compartmental analysis of the 2-h clearance of DTPA from the lungs of anesthetized sheep using a new method to more accurately correct for the effects of DTPA recirculation. This analysis showed that the DTPA clearance in eight sheep ventilated with zero end-expired pressure was best described by a one-compartment model with a clearance rate of 0.42 ± 0.15%/min. Ventilating eight sheep with an end-expired pressure of 10 cmH2O throughout the study increased the end-expired volume 0.4 ± 0.1 liter BTPS and created a clearance curve that was best described by a two-compartment model. In these sheep 56 ± 16% of the DTPA cleared from the lungs at a rate of 7.9 ± 2.9%/min. The remainder cleared at a rate similar to that measured in the sheep ventilated with zero end-expired pressure (0.35 ± 0.18%/min). Additional control and lung inflation experiments were performed using 99mTc-labeled human serum albumin (mol wt = 66,000, radius = 3.6 nm). In six control sheep ventilated with zero end-expired pressure the albumin clearance was best described by a one-compartment model with a clearance rate of 0.06 ± 0.02%/min. The clearance rate in six sheep with increased lung volume was slightly larger (0.09 ± 0.02, P less than 0.05) but was well described by a one-compartment model.(ABSTRACT TRUNCATED AT 250 WORDS)
22
Sakuma, T., J. F. Pittet, C. Jayr e M. A. Matthay. "Alveolar liquid and protein clearance in the absence of blood flow or ventilation in sheep". Journal of Applied Physiology 74, n. 1 (1 gennaio 1993): 176–85. http://dx.doi.org/10.1152/jappl.1993.74.1.176.
Testo completoAbstract (sommario):
The primary objective of these studies was to test the contribution of ventilation and blood flow to the removal of excess liquid from the air spaces and interstitium of the lung. First, after eliminating ventilation by clamping the left main bronchus in anesthetized sheep, alveolar and lung liquid clearance was not altered over 4 h compared with control sheep that were ventilated normally. Thus, removal of excess liquid across the alveolar epithelium was independent of the change in the transalveolar hydrostatic pressure gradient produced by ventilation. Second, to determine the effect of removing all blood flow to the lung, we developed a new in situ sheep lung model in which lung lymph flow was measured over 4 h with or without ventilation after the sheep had been exsanguinated. Alveolar liquid clearance, as measured by the percent increase in alveolar protein concentration over 4 h, was similar between sheep without blood flow (31 +/- 18%) compared with sheep with normal blood flow to the lungs (31 +/- 17%). Lung lymph flow contributed to only 10–15% of the clearance of the excess alveolar liquid that was transported to the interstitium, indicating that nonlymphatic pathways accounted for most of the excess lung liquid clearance in the absence of microvascular filtration. Third, because ouabain completely inhibited alveolar liquid clearance in this in situ sheep lung model, these data provide evidence that alveolar liquid clearance depends on an intact Na(+)-K(+)-ATPase-dependent pump mechanisms. Finally, this in situ model represents a unique experimental preparation that can be used to study the alveolar epithelial barrier without blood flow or ventilation for a short time (4 h) interval.
23
Parsons, G. H., P. D. Pare, D. A. White e E. M. Baile. "Airway blood flow response to eucapnic dry air hyperventilation in sheep". Journal of Applied Physiology 66, n. 3 (1 marzo 1989): 1443–47. http://dx.doi.org/10.1152/jappl.1989.66.3.1443.
Testo completoAbstract (sommario):
Eucapnic hyperventilation, breathing dry air, produces a two- to fivefold increase in airway blood flow in the dog. To determine whether airway blood flow responds similarly in the sheep we studied 16 anesthetized sheep. Seven sheep (1–7) were subjected to two 30-min periods of eucapnic hyperventilation breathing 1) warm humid air [100% relative humidity (rh)] followed by 2) warm dry air [0% rh] at 40 breaths/min. To determine whether there was a dose-response effect on blood flow of increasing levels of hyperventilation of dry air, another nine sheep (8–16) were subjected to four 30-min periods of eucapnic hyperventilation breathing warm humid O2 followed by warm dry O2 at 20 or 40 breaths/min in random sequence. Five minutes before the end of each period of hyperventilation, hemodynamics, blood gases, and tracheal mucosal temperature were measured, and tracheal and bronchial blood flows were determined by injection of 15- or 50-micron-diam radiolabeled microspheres. After the last measurements had been made, all sheep were killed, and the lungs and trachea were removed for determination of blood flow to trachea, bronchi, and parenchyma. In sheep 1–7, warm dry air hyperventilation at 40 breaths/min produced an increase in blood flow to trachea (7.6 +/- 3.5 to 17.0 +/- 6.2 ml/min, P less than 0.05) and bronchi (9.0 +/- 5.4 to 18.2 +/- 8.2 ml/min, P less than 0.05) but not to the parenchyma. When blood flow was compared with the two ventilatory rates (sheep 8–16), tracheal blood flow increased (9.1 +/- 3.3 to 18.2 +/- 6.1 ml/min, P less than 0.05) at a rate of 40 breaths/min but not at 20 breaths/min.(ABSTRACT TRUNCATED AT 250 WORDS)
24
Mukaddam-Daher, S., J. Gutkowska, B. S. Nuwayhid e E. W. Quillen. "Metabolic clearance of atrial natriuretic factor in ovine pregnancy". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 267, n. 5 (1 novembre 1994): R1413—R1420. http://dx.doi.org/10.1152/ajpregu.1994.267.5.r1413.
Testo completoAbstract (sommario):
Plasma atrial natriuretic factor (ANF) is normally released into the circulation primarily by volume expansion and atrial distension, but we have shown that plasma ANF is elevated in pregnant sheep before volume expansion. Because alterations in the metabolic clearance of ANF could lead to elevated plasma ANF levels, the present study was designed to determine the pharmacokinetics of plasma ANF in pregnant sheep. Chronically instrumented nonpregnant and pregnant sheep received intravenous injections of monoiodinated human ANF (125I-hANF). Plasma decay curves of 125I-hANF followed a biexponential function in both groups. High-performance liquid chromatography (HPLC) revealed the accumulation of smaller degradation products by 2 min postinjection, and by 30 min no intact ANF was present. Because HPLC identification of ANF and its metabolites was shown to be more efficient than precipitation with 10% trichloroacetic acid (TCA) or extraction by Sep-Pak cartridges, ANF kinetic parameters were calculated from HPLC-corrected plasma decay curves. Injected ANF was rapidly distributed in an initial distribution volume (IDV) that was expanded in pregnant sheep. Metabolic clearance rate (MCR) was greater in pregnant sheep (2.8 +/- 0.3 vs. 6.8 +/- 1.2 l/min, P = 0.002), while plasma half-life (t1/2) was not altered (2.2 +/- 0.5 vs. 2.4 +/- 0.4 min). The data demonstrate that during pregnancy, the t1/2 of ANF is not altered but the MCR of ANF is enhanced. These findings imply that plasma ANF is increased by mechanisms other than reduced clearance in pregnant sheep.
25
Blair-West, J. R., A. P. Gibson, S. J. Sheather, R. L. Woods e A. H. Brook. "Vasopressin release in sheep following various degrees of rehydration". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 253, n. 4 (1 ottobre 1987): R640—R645. http://dx.doi.org/10.1152/ajpregu.1987.253.4.r640.
Testo completoAbstract (sommario):
Restriction of the water intake of sheep to 0.5 1/day for 7-9 days increases plasma arginine vasopressin (pAVP), and voluntary rehydration causes a rapid fall in pAVP with no change in plasma osmolality. The extent of that inhibition of AVP release was assessed by comparing the decline of pAVP after drinking with pAVP disappearance curves obtained in the same sheep after stopping a constant infusion of AVP at 0.5 micrograms/h, which increased pAVP to the dehydration level. The fall in pAVP after drinking was almost identical with the disappearance curve showing that AVP release was almost completely inhibited during the 2-3 min taken for the sheep to drink 3-5 liters to satiate themselves. The response seemed, therefore, to be cued before the intake reached the satiating volume. When dehydrated sheep drank only 0.5 or 1.0 liter, in 30 s or less, pAVP again fell rapidly but only to a minimum approximately 15 min after drinking. The pAVP was unaltered in dehydrated sheep presented with water but denied access to it. Thus satiation was not necessary for rapid inhibition of AVP release after drinking, but satiation was necessary for this inhibition to be maintained. The initial inhibition was associated with falls in hematocrit and plasma total protein but not plasma osmolality. This isosmolar dilution occurred even in sheep that saw but were denied access to the water and suggests a shift of fluid from the extravascular space.
26
Wang, Sutian, Shoulong Deng, Yang Cao, Rui Zhang, Zhixian Wang, Xiaojing Jiang, Jiahao Wang et al. "Overexpression of Toll-Like Receptor 4 Contributes to Phagocytosis of Salmonella Enterica Serovar Typhimurium via Phosphoinositide 3-Kinase Signaling in Sheep". Cellular Physiology and Biochemistry 49, n. 2 (2018): 662–77. http://dx.doi.org/10.1159/000493032.
Testo completoAbstract (sommario):
Background/Aims: Phagocytosis of bacteria by monocytes/macrophages can trigger the immune response and the clearance of bacteria. This innate immune response involves Toll-like receptor 4 (TLR4). However, much remains unknown about the mechanism of TLR4-regulated phagocytosis of Salmonella enterica serovar Typhimurium (S. typhimurium) within sheep monocytes/macrophages. Here, we aimed to address these knowledge gaps by infecting transgenic sheep overexpressing TLR4 with S. typhimurium and examining the phagocytic mechanisms involved. Methods: Transgenic sheep were generated by microinjection of the constructed plasmids into fertilized eggs. Monocytes/macrophages isolated from sheep blood were stimulated with LPS and S. typhimurium. Phagocytosis-related factor expression, phagocytic ability, and adhesion were then determined. TLR4/phosphatidylinositide 3-kinase (PI3K) signaling was inhibited to investigate if this pathway is involved in changes in bacterial internalization in sheep. Results: We found that TLR4 overexpression effectively activated the PI3K signaling pathway and upregulated the expression of scavenger receptors. Additionally, actin polymerization and adhesive capacity were both enhanced in TLR4-overexpressing sheep monocytes/macrophages. TLR4 inhibition decreased S. typhimurium phagocytosis by reducing the actin polymerization and adhesive capacity of cells. Furthermore, inhibition of PI3K markedly impaired TLR4-dependent phagocytosis by restraining actin polymerization and scavenger receptor expression and reduced the adhesive capacity of the monocytes/macrophages. Conclusion: Our findings indicate that overexpression of TLR4 enhances phagocytosis through PI3K signaling and the subsequent activation of actin polymerization and scavenger receptors in sheep monocytes/macrophages infected with S. typhimurium.
27
McAllen, R. M., G. L. Pennington e M. J. McKinley. "Osmoresponsive units in sheep median preoptic nucleus". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 259, n. 3 (1 settembre 1990): R593—R600. http://dx.doi.org/10.1152/ajpregu.1990.259.3.r593.
Testo completoAbstract (sommario):
Single-unit neural activity in the lamina terminalis, a region implicated in osmoregulation, was studied in alpha-chloralose-anesthetized sheep during mild hyperosmotic stimulation (intracarotid infusions of 1.65 M NaCl, 3 M sorbitol in 0.15 M NaCl, or 3 M urea in 0.15 M NaCl, at 1 ml/min). Twelve of 121 units (9.9%) were activated significantly (by 82 +/- 52%) by 2- to 3-min infusions of 1.65 M NaCl. Eleven of these and one untested unit were excited by hypertonic sorbitol (91 +/- 40% increase). Of five units further tested with urea, two were excited (by 19 and 58%). Isotonic or hypotonic NaCl infusions were without effect (eight osmoresponsive units tested). All responsive units were in the median preoptic nucleus (MnPO; nucleus medianus). MnPO units were compared with neurohypophysial fibers (multiunit recordings). Osmotic response profiles were similar; both MnPO units and neurohypophysial fibers responded equally to hypertonic NaCl and sorbitol but less to equiosmolal urea. Both MnPO units and neurohypophysial fibers responded slowly, taking 50 and 30 s of NaCl infusion, respectively, to show significant increases and approximately 2 min to reach peak activity. Their hemodynamic responses differed, however; neurohypophysial fibers were strongly excited by nitroprusside-induced hypotension (three of three animals) but MnPO osmoresponsive units were not (zero of five units). Osmoresponsive MnPO units may contribute osmotic, but not hemodynamic, inputs to control vasopressin secretion and/or osmoregulatory responses.
28
al-Bazzaz, F. J., C. Tarka e M. Farah. "Microperfusion of sheep bronchioles". American Journal of Physiology-Lung Cellular and Molecular Physiology 260, n. 6 (1 giugno 1991): L594—L602. http://dx.doi.org/10.1152/ajplung.1991.260.6.l594.
Testo completoAbstract (sommario):
We isolated segments of sheep bronchioles (length 406 +/- 46 microns, diameter 227 +/- 53 microns, n = 27). These segments were placed in a 37 degree C bath and cannulated at both ends with glass micropipettes. The proximal end was cannulated and held by three concentrically arranged micropipettes that delivered perfusion solution by gravity. The distal end was cannulated and held by two concentrically arranged micropipettes for fluid collection. When both the lumen and the bath contained oxygenated Krebs-Henseleit buffer (pH 7.40), spontaneous potential difference (PD) was 2.46 +/- 0.39 mV, lumen negative. KCN in the bath diminished PD by 1.48 +/- 0.29 mV (P = 0.00003, n = 25). The isolated bronchiole was depolarized when the luminal solution was Na free (delta PD -1.78 +/- 0.11 mV, P = 0.00007, n = 5) or when the submucosal bath was Cl free (delta PD -2.63 +/- 0.81, P = 0.018, n = 7). In preparations pretreated with 10 microM indomethacin, 1 microM isoproterenol raised PD by 0.75 +/- 0.29 mV (P = 0.03, n = 8), whereas 0.1 mM submucosal bumetanide reduced PD by 0.21 +/- 0.04 mV (P = 0.0005, n = 8). The data show that microperfusion technique is applicable for investigating ion transport by distal bronchioles and that the bronchiolar epithelium probably has both Na and Cl conductive pathways.
29
Akabas, S. R., A. R. Bazzy, S. DiMauro e G. G. Haddad. "Metabolic and functional adaptation of the diaphragm to training with resistive loads". Journal of Applied Physiology 66, n. 2 (1 febbraio 1989): 529–35. http://dx.doi.org/10.1152/jappl.1989.66.2.529.
Testo completoAbstract (sommario):
To study the metabolic and functional changes that occur during training with inspiratory flow resistive loads, a chronically instrumented unanesthetized sheep preparation was used. Sheep were exposed to resistances ranging from 50 to 100 cmH2O.l–1.s, for 2–4 h/day, 5–6 days/wk, for a total of 3 wk. Load intensity was adjusted to maintain arterial Po2 (PaO2) above 60 Torr and arterial PCO2 (PaCO2) below 45 Torr. Training produced significant (P less than 0.05) increases in citrate synthase, 3-hydroxyacyl-CoA dehydrogenase, and cytochrome oxidase in the costal and crural diaphragm of the trained sheep (n = 9) compared with control sheep (n = 7). Phosphofructokinase did not increase. In the quadriceps, citrate synthase, 3-hydroxyacyl-CoA dehydrogenase, and phosphofructokinase did not change with training but cytochrome oxidase increased significantly (P less than 0.01). Function of the diaphragm was assessed in a subset of five sheep exposed to the same severe load 1 wk before and 2 days after the final training session. After training, sheep had a lower PaCO2 (10–40%), generated a higher transdiaphragmatic pressure (20–40%), and could sustain this level of transdiaphragmatic pressure for 0.5–2 h longer. The respiratory duty cycle was 10–15% lower, whereas minute ventilation and tidal volume were 20–30% higher in the posttraining test. We conclude that 1) training with inspiratory flow resistive loads improves the performance of the respiratory neuromuscular system and 2) the shift in enzyme profile of the diaphragm is at least in part responsible for this improvement.
30
Doerr, T. A., D. L. Rosolia, S. P. Peters, M. H. Gee e K. H. Albertine. "PGE1 inhibited PMN attachment to air emboli in vivo during infusion of ZAP without preventing lung injury". Journal of Applied Physiology 72, n. 1 (1 gennaio 1992): 340–51. http://dx.doi.org/10.1152/jappl.1992.72.1.340.
Testo completoAbstract (sommario):
Prostaglandin E1 (PGE1) treatment of neutrophils inhibits their adherence to substrates in vitro, including endothelial cell monolayers. Demonstration that PGE1 inhibits neutrophil adherence in vivo in the lung, however, is complicated by PGE1 effects on cells other than neutrophils, such as endothelial cells. To determine whether PGE1 inhibits neutrophil adherence properties in vivo, we used air emboli as intravascular targets for neutrophil attachment. Four experimental conditions were studied in anesthetized and awake sheep that were treated with 1) PGE1 and air emboli, 2) saline and air emboli, 3) PGE1 and zymosan-activated plasma (ZAP) + air emboli, and 4) saline and ZAP + air emboli. PGE1 (30 ng.kg-1.min-1) or saline was infused continuously 1 h before and 1 h during the infusion of air emboli (group 1; n = 13 sheep) or ZAP + air emboli (group 2; n = 13 sheep). The number of neutrophils (PMNs) attached to air emboli in four anesthetized sheep per condition was significantly less in sheep given PGE1 and ZAP + air emboli [8 +/- 3 (SD) PMNs/mm of embolus perimeter] than in the other three conditions (14–21 PMNs/mm; P less than 0.05). Repeated experiments in five awake sheep per group showed that PGE1 treatment did not prevent increased lung lymph protein clearance in either group compared with saline treatment. We conclude that PGE1 specifically inhibited attachment of ZAP-activated neutrophils to air emboli in vivo. The lack of pathophysiological protection suggests that PGE1-induced alterations in neutrophil attachment properties were independent of other cellular activation responses.
31
Clark, T. P., e R. J. Kemppainen. "Glucocorticoid negative feedback in sheep corticotrophs: a comparison with AtT-20 corticotroph tumor cells". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 267, n. 2 (1 agosto 1994): R463—R469. http://dx.doi.org/10.1152/ajpregu.1994.267.2.r463.
Testo completoAbstract (sommario):
Early glucocorticoid feedback in sheep anterior pituitary (AP) cells was compared and contrasted with that in mouse pituitary tumor AtT-20 cells. Dexamethasone (DEX) inhibited corticotropin-releasing hormone (CRH)-stimulated adrenocorticotropin (ACTH) release in a concentration- and time-dependent manner with similar potency amongst cell types. This inhibition was mediated through type II glucocorticoid receptors and required the synthesis of new protein. However, stimulation of protein kinase C with phorbol 12-myristate 13-acetate (PMA) resulted in greater ACTH release and greater inhibition by DEX in sheep AP cells. In contrast to sheep AP cells, AtT-20 cells were insensitive to glucocorticoids when secretion was stimulated by KCl depolarization or the voltage-dependent calcium channel agonist, maitotoxin (MTX). In both cell types, CRH-, KCl-, and MTX-stimulated ACTH release was inhibited by the calcium channel blocker, nifedipine (NIF). Whereas NIF also inhibited PMA-induced ACTH secretion in AtT-20 cells, it did not in sheep AP cells. These data demonstrate that early glucocorticoid feedback is operative in sheep corticotrophs and that AtT-20 cells appear to serve as an appropriate mechanistic model for aspects of negative feedback when the CRH-protein kinase A pathway is activated but may not be appropriate when ACTH secretion is activated via other intracellular signaling pathways.
32
Broaddus, V. C., J. P. Wiener-Kronish, Y. Berthiaume e N. C. Staub. "Removal of pleural liquid and protein by lymphatics in awake sheep". Journal of Applied Physiology 64, n. 1 (1 gennaio 1988): 384–90. http://dx.doi.org/10.1152/jappl.1988.64.1.384.
Testo completoAbstract (sommario):
The contribution of the parietal pleural lymphatics to pleural liquid and protein removal is unclear. We asked two questions. What is the rate of removal of sterile, artificial hydrothoraxes in awake sheep? What percentage is removed through parietal pleural lymphatics? Three days after the placement of a rib capsule in 18 sheep, we instilled a 10 ml/kg 1.0 g/dl autologous protein solution with labeled albumin and erythrocytes through the capsule into the pleural space. Erythrocytes were used as a marker for lymphatic flow. We measured terminal pleural liquid volume and radioactivity at periods from 2 to 48 h. In three sheep, we obtained a third volume measurement at 6 h by the volume of dilution technique. We found that hydrothorax removal could be described by a linear function with a constant rate: 0.28 +/- 0.01 ml.kg-1.h-1 (mean +/- SE) for the grouped data, and 0.20, 0.28, and 0.31 ml.kg-1.h-1 for the individual sheep. At 24 h, erythrocyte clearance was 89 +/- 16% (mean +/- SD) that of liquid and albumin clearance. We conclude that in awake sheep with large hydrothoraxes, pleural liquid and protein are removed at a rate of 0.28 +/- 0.01 ml.kg-1.h-1 (mean +/- SE) and lymphatics are responsible for at least 89% of this removal.
33
Nakamura, K. T., R. A. Felder, P. A. Jose e J. E. Robillard. "Effects of dopamine in the renal vascular bed of fetal, newborn, and adult sheep". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 252, n. 3 (1 marzo 1987): R490—R497. http://dx.doi.org/10.1152/ajpregu.1987.252.3.r490.
Testo completoAbstract (sommario):
The renal hemodynamic response to renal arterial dopamine infusions was compared in unanesthetized fetal (129-137 days gestation, full term 145 days), newborn, and adult sheep. Mean arterial blood pressure and heart rate remained unchanged during intrarenal dopamine infusions. Dopamine produced dose-related decreases in mean renal blood flow velocity in all three groups. When compared with adult sheep fetal sheep were slightly more sensitive to the vasoconstrictive effects of dopamine ED50 (mean effective dose ratio: fetus/ED50 adult = 0.368 +/- 0.047, P less than 0.05). Increases in mean renal blood flow velocity were not seen at any dose given (1-16 micrograms/kg body wt in fetuses, 2-32 micrograms/kg body wt in newborns and adults) until dopamine was infused during alpha- and beta-adrenoceptor blockade. The largest mean increase in renal flow velocity was 13 +/- 3, 16 +/- 3, and 17 +/- 4% in fetal, newborn, and adult sheep, respectively. cis-Flupentixol inhibited the vasodilation. This study demonstrates the presence of renal vasodilation following renal arterial dopamine infusions in fetal, newborn, and adult sheep when renal alpha- and beta-adrenoceptors are blocked. Vasodilator responses are similar in all three groups, and increases in renal blood flow velocity are small compared with that of other experimental models.
34
Hutchison, A. A., M. L. Ogletree, J. R. Snapper e K. L. Brigham. "Effect of endotoxemia on hypoxic pulmonary vasoconstriction in unanesthetized sheep". Journal of Applied Physiology 58, n. 5 (1 maggio 1985): 1463–68. http://dx.doi.org/10.1152/jappl.1985.58.5.1463.
Testo completoAbstract (sommario):
This study examined the effect of acute endotoxemia on hypoxic pulmonary vasoconstriction (HPV) in awake sheep. Thirteen sheep were chronically instrumented with Silastic catheters in the pulmonary artery, left atrium, jugular vein, and carotid artery; with a Swan-Ganz catheter in the main pulmonary artery; with a chronic lung lymph fistula; and with a tracheostomy. Base-line HPV was determined by measuring the change in pulmonary vascular resistance (PVR) while sheep breathed 12% O2 for 7 min. Concentrations of immunoreactive 6-keto-PGF1 alpha and thromboxane B2 (TXB2) were measured in lung lymph during the hypoxic challenge. Escherichia coli endotoxin (0.2–0.5 micrograms/kg) was infused intravenously. Four hours after endotoxemia, HPV was measured. In five sheep, meclofenamate was infused at 4.5 h after endotoxemia and HPV measured again. During the base-line hypoxic challenge, PVR increased by 36 +/- 9% (mean +/- SE). There was no significant change in lung lymph 6-keto-PGF1 alpha or TXB2 levels with hypoxia. Twelve of the 13 sheep showed a decrease in HPV 4 h after endotoxemia; the mean change in PVR with hypoxia was -8 +/- 5%, which was significantly (P less than 0.05) reduced compared with base-line HPV. The infusion of meclofenamate at 4.5 h after endotoxin did not restore HPV.
35
Wei, Caihong, Mingming Wu, Chuduan Wang, Ruizao Liu, Huijing Zhao, Li Yang, Jiafan Liu et al. "Long Noncoding RNA Lnc-SEMT Modulates IGF2 Expression by Sponging miR-125b to Promote Sheep Muscle Development and Growth". Cellular Physiology and Biochemistry 49, n. 2 (2018): 447–62. http://dx.doi.org/10.1159/000492979.
Testo completoAbstract (sommario):
Background/Aims: Long noncoding RNAs (lncRNAs) are RNA transcripts that are more than 200 nt long but have little protein-coding potential. Within the last few years, thousands of lncRNAs have been identified and their functions in biological processes have begun to be understood. Although many studies havebegun to examine the functions of many noncoding RNAs, very little is known about the functions of long noncoding (lncRNA) function of livestock production and molecular mechanisms of their functions are still lackingrelated to livestock production. Methods: Expression of sheep enhanced muscularityTranscript lncRNA (lnc-SEMT) and miR-125b were examined in sheep using quantitative reverse-transcription polymerase chain reaction. Expression of Myod (myogenic determination factor), Myog (myoglobin) and Insulin-like growth factor 2 (IGF2)were examined by Western Blot.Luciferase reporter assays were performedto confirm the relationship between lnc-SEMT and miR-125b. Results: Here, we identified a novel lnc-SEMT that promote sheep myoblast differentiation in vitro and enhanced sheep muscularity in vivo. Functional analyses showed that lnc-SEMT accelerates sheep myoblast differentiation in vitro. lnc-SEMT transgenic sheep exhibit a muscle hypertrophy phenotype characterized by increased body weight, and increased the number of muscle fibers indicating that lnc-SEMT play an important role in the regulation of skeletal muscle differentiation in vivo. Our results show that lnc-SEMT acts as a molecular sponge by antagonizing miR-125b to control IGF2 protein labundance in vitro and in vivo. Conclusion: In brief, lnc-SEMT is the first example of a lncRNA could be a useful candidate for improving biological growth traits such as skeletal muscle production in sheep.
36
Peterson, B. T., e L. D. Gray. "Pulmonary lymphatic clearance of 99mTc-DTPA from air spaces during lung inflation and lung injury". Journal of Applied Physiology 63, n. 3 (1 settembre 1987): 1136–41. http://dx.doi.org/10.1152/jappl.1987.63.3.1136.
Testo completoAbstract (sommario):
A total of 22 sheep with lymphatic cannulas were used to determine if 99mTc-labeled diethylenetriaminepentaacetic acid (DTPA) clears directly from the air spaces of the lungs into the lymph vessels. Each sheep was anesthetized and ventilated with an aerosol of the DTPA for 2–5 min, and the DTPA activities in the lymph and plasma were measured every 15 min for 2 h. After the first 45 min, the average ratio of the DTPA in the lymph to that in the plasma (L/P) was 1.03 +/- 0.06 (SD) in the six control experiments and 1.11 +/- 0.05 in the six experiments in which the lungs were inflated with a positive end-expired pressure of 10 cmH2O throughout the study. Direct movement of the DTPA from the air spaces into the lymph was not necessary to account for the DTPA clearance in these experiments because the L/P ratio was not significantly different from 1.0. Eight additional sheep received intravenous infusions of air at 0.2 ml.kg-1.min-1 for 2 h to induce lung injury before depositing the DTPA. In these sheep L/P was 1.53 +/- 0.28, which was significantly higher than the value measured in the control group (P less than 0.01). We considered the possibility that the increased L/P ratio in these sheep could be due to alterations in the distribution of the blood flow to the tissue, but the L/P ratio in four sheep whose distribution of blood flow was altered by inflation of a balloon in the right pulmonary artery was 1.05 +/- 0.10, the same as the control value.(ABSTRACT TRUNCATED AT 250 WORDS)
37
Peterson, B. T., e K. D. Dickerson. "Concentration of aerosolized 99mTc-albumin in the pulmonary lymph of anesthetized sheep". Journal of Applied Physiology 68, n. 3 (1 marzo 1990): 1233–40. http://dx.doi.org/10.1152/jappl.1990.68.3.1233.
Testo completoAbstract (sommario):
We examined the lymphatic concentration of 99mTc-albumin deposited in the air spaces of anesthetized sheep to determine whether changes in the concentration reflected changes in lung epithelial function. Five control sheep were ventilated with an aerosol of 99mTc-albumin for 6 min, and the lung lymphatic concentration of the tracer was monitored for the next 2 h. During the last 45 min the lymphatic concentration stabilized at a value that was 0.03 +/- 0.01% of the estimated value in the air spaces. Pulmonary vascular hypertension, induced in seven sheep by increasing the left atrial pressure 20 cmH2O for 4 h, increased the lung lymph flow from a base-line value of 3 +/- 2 to 21 +/- 14 ml/h. This caused the concentration of the 99mTc-albumin in the lymph to double to 0.07 +/- 0.03% of the air space concentration (P less than 0.01). Lung injury induced by infusing 0.08-0.10 ml/kg oleic acid intravenously in seven other sheep increased the lymphatic concentration of the 99mTc-albumin 10-fold to 0.31 +/- 0.09% of the air space concentration (P less than 0.01). The increased tracer concentration in the sheep with pulmonary vascular hypertension could be the result of the increased lymph flow causing a diversion of tracer into the lymphatics. However, a mathematical model showed that the 10-fold increase in the lymphatic concentration in the sheep with lung injury was primarily the result of an increase in both permeability and surface area of the epithelium that participated in the transfer of the 99mTc-albumin from the air spaces into the lung tissue drained by the lymphatics.(ABSTRACT TRUNCATED AT 250 WORDS)
38
Ramchandra, Rohit, Sally G. Hood, Anna M. D. Watson e Clive N. May. "Responses of cardiac sympathetic nerve activity to changes in circulating volume differ in normal and heart failure sheep". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 295, n. 3 (settembre 2008): R719—R726. http://dx.doi.org/10.1152/ajpregu.00824.2007.
Testo completoAbstract (sommario):
Factors controlling cardiac sympathetic nerve activity (CSNA) in the normal state and those causing the large increase in activity in heart failure (HF) remain unclear. We hypothesized from previous clinical findings that activation of cardiac mechanoreceptors by the increased blood volume in HF may stimulate sympathetic nerve activity (SNA), particularly to the heart via cardiocardiac reflexes. To investigate the effect of volume expansion and depletion on CSNA we have made multiunit recordings of CSNA in conscious normal sheep and sheep paced into HF. In HF sheep ( n = 9) compared with normal sheep ( n = 9), resting levels of CSNA were significantly higher (34 ± 5 vs. 93 ± 2 bursts/100 heart beats, P < 0.05), mean arterial pressure was lower (76 ± 3 vs. 87 ± 2 mmHg; P < 0.05), and central venous pressure (CVP) was greater (3.0 ± 1.0 vs. 0.0 ± 1.0 mmHg; P < 0.05). In normal sheep ( n = 6), hemorrhage (400 ml over 30 min) was associated with a significant increase in CSNA (179 ± 16%) with a decrease in CVP (2.7 ± 0.7 mmHg). Volume expansion (400 ml Gelofusine over 30 min) significantly decreased CSNA (35 ± 12%) and increased CVP (4.7 ± 1.0 mmHg). In HF sheep ( n = 6) the responses of CSNA to both volume expansion and hemorrhage were severely blunted with no significant changes in CSNA or heart rate with either stimulus. In summary, these studies in a large conscious mammal demonstrate that in the normal state directly recorded CSNA increased with volume depletion and decreased with volume loading. In contrast, both of these responses were severely blunted in HF with no significant changes in CSNA during either hemorrhage or volume expansion.
39
Smith, Francine G., Alp Sener, Raghmeet Basati e Isam Abu-Amarah. "Renal responses to hemorrhage are age dependent in conscious sheep". Journal of Applied Physiology 96, n. 1 (gennaio 2004): 131–36. http://dx.doi.org/10.1152/japplphysiol.00492.2003.
Testo completoAbstract (sommario):
Experiments were carried out in conscious, chronically instrumented lambs ( n = 8) and young adult sheep ( n = 11) to investigate age-dependent renal responses to hemorrhage. Various parameters of renal function were measured for 1 h before and 1 h after either 10% hemorrhage ( experiment 1) or 20% hemorrhage ( experiment 2). The two experiments were carried out in random order at intervals of 2-5 days. There were no effects of 10-20% hemorrhage on renal plasma flow in either age group. Blood pressure decreased after 20% but not 10% hemorrhage in both age groups. Glomerular filtration rate and filtration fraction decreased after 20% hemorrhage in both age groups, the decrease being greater in lambs than young adult sheep. In response to 20% hemorrhage, urinary flow rate and urinary Na+ excretion rate decreased by 40 min after hemorrhage in young adult sheep but not lambs and remained decreased for 60 min; urinary chloride excretion rate showed a similar response. In lambs but not young adult sheep, free water clearance increased by 20 min after 20% hemorrhage and remained above control at 60 min. Urinary osmolality decreased at 20 min after 20% hemorrhage in young adult sheep but not lambs, returning to control levels by 40 min. These data provide new information that renal responses to hypotensive hemorrhage appear to be developmentally regulated.
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Ahmed, Tahir, Jaime Ungo, Min Zhou e Carlos Campo. "Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides". Journal of Applied Physiology 88, n. 5 (1 maggio 2000): 1721–29. http://dx.doi.org/10.1152/jappl.2000.88.5.1721.
Testo completoAbstract (sommario):
Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2,500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and “non-anticoagulant” fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered “after” the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D4, excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled “fractionated” heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.
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Dickson, K. A., S. B. Hooper, I. C. McMillen e R. Harding. "Endocrine and fluid-balance responses to amniotic and allantoic fluid loss in sheep". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 259, n. 4 (1 ottobre 1990): R745—R752. http://dx.doi.org/10.1152/ajpregu.1990.259.4.r745.
Testo completoAbstract (sommario):
Our aim was to determine fetal and maternal endocrine and fluid-balance responses to prolonged loss of amniotic and allantoic fluids in sheep. In seven sheep, amniotic and allantoic fluids were drained [379.1 +/- 20.1 (SE) ml/day] from 107 to 135.3 +/- 0.6 days of gestation (term: 145 days). The results from these sheep were compared with those from seven control sheep. Maternal water intake, urine production, and urine osmolality were not altered by fluid drainage, nor were fetal and maternal arterial blood gases, pH, or plasma osmolalities. Fluid drainage increased amniotic, but not allantoic, fluid osmolality. Maternal plasma cortisol concentration increased with fluid drainage, but maternal plasma concentrations of prolactin and arginine vasopressin were unchanged. Fluid drainage increased prolactin concentrations in fetal plasma and amniotic fluid, but fetal plasma concentrations of cortisol (hydrocortisone), arginine vasopressin, norepinephrine, and epinephrine were unchanged. Our results show that the fetus is capable of maintaining its plasma osmolality despite prolonged loss of fluid from its amniotic and allantoic sacs and that this is associated with alterations in the production rate and the composition of amniotic fluid.
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Chanana, A. D., e D. D. Joel. "Contamination of lung lymph following standard and modified procedures in sheep". Journal of Applied Physiology 60, n. 3 (1 marzo 1986): 809–16. http://dx.doi.org/10.1152/jappl.1986.60.3.809.
Testo completoAbstract (sommario):
The sheep lung lymph fistula preparation of Staub et al. is reported to be contaminated by systemic lymph. The published estimates of contamination range from 5% (awake sheep) to 60% (anesthetized sheep). In view of these conflicting estimates, we investigated the pre- and postoperative contaminating sources, morphological and functional consequences of the proposed contamination reducing modifications, and base-line lung lymph flow in awake sheep following standard and modified cannulation procedures. Our morphological observations are not compatible with the higher estimates of contamination (25–60%). Evidence of lymph leakage from cauterized lymphatics was found. The lymphatics that appear after diaphragmatic cautery and partial resection of caudal mediastinal lymph node were found to constitute “new” contaminating sources. The lymph flow data from base-line and increased vascular pressure conditions were consistent with the reported low estimates of contamination (5%). We propose simple modifications of the standard procedure of Staub et al. which may be nearly as effective in reducing contamination by extrapulmonary lymph as the more invasive and/or traumatic modifications.
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Jensen, R. I., A. M. Carter, O. Skott e B. L. Jensen. "Adrenomedullin expression during hypoxia in fetal sheep". Acta Physiologica Scandinavica 183, n. 2 (febbraio 2005): 219–28. http://dx.doi.org/10.1111/j.1365-201x.2004.01377.x.
Testo completo
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Haouzi, Philippe, e Bruno Chenuel. "Control of arterialPCO2by somatic afferents in sheep". Journal of Physiology 569, n. 3 (dicembre 2005): 975–87. http://dx.doi.org/10.1113/jphysiol.2005.089649.
Testo completo
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Zhang, Hongying, DaLiao Xiao, Lawrence D. Longo e Lubo Zhang. "Regulation of α1-adrenoceptor-mediated contractions of uterine arteries by PKC: effect of pregnancy". American Journal of Physiology-Heart and Circulatory Physiology 291, n. 5 (novembre 2006): H2282—H2289. http://dx.doi.org/10.1152/ajpheart.00321.2006.
Testo completoAbstract (sommario):
Protein kinase C (PKC) plays an important role in the regulation of uterine artery contractility and its adaptation to pregnancy. The present study tested the hypothesis that PKC differentially regulates α1-adrenoceptor-mediated contractions of uterine arteries isolated from nonpregnant (NPUA) and near-term pregnant (PUA) sheep. Phenylephrine-induced contractions of NPUA and PUA sheep were determined in the absence or presence of the PKC activator phorbol 12,13-dibutyrate (PDBu). In NPUA sheep, PDBu produced a concentration-dependent potentiation of phenylephrine-induced contractions and shifted the dose-response curve to the left. In contrast, in PUA sheep, PDBu significantly inhibited phenylephrine-induced contractions and decreased their maximum response. Simultaneous measurement of contractions and intracellular free Ca2+ concentrations ([Ca2+]i) in the same tissues revealed that PDBu inhibited phenylephrine-induced [Ca2+]i and contractions in PUA sheep. In NPUA sheep, PDBu increased phenylephrine-induced contractions without changing [Ca2+]i. Western blot analysis showed six PKC isozymes, α, βI, βII, δ, ε, and ζ, in uterine arteries, among which βI, βII, and ζ isozymes were significantly increased in PUA sheep. In contrast, PKC-α was decreased in PUA sheep. In addition, analysis of subcellular distribution revealed a significant decrease in the particulate-to-cytosolic ratio of PKC-ε in PUA compared with that in NPUA sheep. The results suggest that pregnancy induces a reversal of PKC regulatory role on α1-adrenoceptor-mediated contractions from a potentiation in NPUA sheep to an inhibition in PUA sheep. The differential expression of PKC isozymes and their subcellular distribution in uterine arteries appears to play an important role in the regulation of Ca2+ mobilization and Ca2+ sensitivity in α1-adrenoceptor-mediated contractions and their adaptation to pregnancy.
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Morris, CA, TT Wheeler, HV Henderson, NR Towers e SH Phua. "Animal physiology and genetic aspects of ryegrass staggers in grazing sheep". New Zealand Veterinary Journal 65, n. 4 (19 marzo 2017): 171–75. http://dx.doi.org/10.1080/00480169.2017.1301229.
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Meikle, A., C. Tasende, C. Sosa e E. G. Garófalo. "The role of sex steroid receptors in sheep female reproductive physiology". Reproduction, Fertility and Development 16, n. 4 (2004): 385. http://dx.doi.org/10.1071/rd04036.
Testo completoAbstract (sommario):
Cell responsiveness to steroid hormones is related to the number and affinity of its receptors, thus factors affecting steroid expression will influence tissue sensitivity and functionality. The present review discusses the role of oestrogen and progesterone receptors in sheep female reproductive physiology. The mechanism of steroid hormone action in the target cell is introduced first; the tissue distribution, physiological functions and regulation of oestrogen receptor subtypes and progesterone receptor isoforms in ruminants are reported. The role of steroid receptors in target tissues (with emphasis on the uterus and pituitary gland) during different physiological events is addressed in an attempt to clarify oestrogen and progesterone actions in different developmental and reproductive stages: prepubertal period, oestrous cycle, pregnancy, post-partum period and seasonal anoestrus. The present review shows how the distinct reproductive stages are accompanied by dramatic changes in uterine receptor expression. The role of oestrogen and progesterone receptors in the molecular mechanism responsible for premature luteolysis that results in subnormal luteal function is discussed. Finally, the effect of nutrition on sex steroid receptor expression and the involvement on reproductive performance is reported.
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Evans, A. C. "THE PHYSIOLOGY OF THE SHEEP BLOW-FLY LUCILIA SERICATA MEIG. (DIPTERA)". Transactions of the Royal Entomological Society of London 85, n. 15 (24 aprile 2009): 363–77. http://dx.doi.org/10.1111/j.1365-2311.1936.tb00236.x.
Testo completo
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Wanner, A., M. Sielczak, J. F. Mella e W. M. Abraham. "Ciliary responsiveness in allergic and nonallergic airways". Journal of Applied Physiology 60, n. 6 (1 giugno 1986): 1967–71. http://dx.doi.org/10.1152/jappl.1986.60.6.1967.
Testo completoAbstract (sommario):
Allergic asthma is associated with airway (smooth muscle) hyperresponsiveness to several chemical mediators of anaphylaxis; however, it is not known whether this is accompanied by mucociliary hyperresponsiveness. The purpose of this study was therefore to determine if airway ciliary activity, a component function of mucociliary clearance, exhibits exaggerated responses to prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), and leukotriene D4 (LTD4) in allergic sheep when compared with nonallergic sheep, and the effects of LTD4 are direct or involve the generation of cyclooxygenase products of arachidonate metabolism. Ciliary beat frequency (CBF) was measured in a perfusion chamber with a microscopic technique using tracheal epithelial cells obtained from brushing of “allergic” (positive cutaneous reaction and previous bronchospastic response to inhaled specific antigen) and “nonallergic” (negative cutaneous reaction, no previous inhalation challenge with antigen) sheep. Mean base-line CBF was not different among the groups; PGE1, PGE2, and LTD4 induced dose-dependent increases in CBF, and these increases were not different in allergic and nonallergic sheep. At the highest agonist concentration the mean increase in CBF from base line varied between 13 and 16% (P less than 0.05). The ciliostimulatory effect of LTD4 was significantly blunted by both the sulfidopeptide leukotriene antagonist FPL-55712 and the cyclooxygenase inhibitor indomethacin. These results suggest that allergic sheep fail to exhibit ciliary hyperresponsiveness to selected chemical mediators of anaphylaxis and the ciliostimulatory effect of LTD4 depends on the activation of cyclooxygenase and possibly the generation of prostaglandins.
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Abraham, W. M., J. S. Stevenson e R. Garrido. "A possible role for PAF in allergen-induced late responses: modification by a selective antagonist". Journal of Applied Physiology 66, n. 5 (1 maggio 1989): 2351–57. http://dx.doi.org/10.1152/jappl.1989.66.5.2351.
Testo completoAbstract (sommario):
We determined whether platelet-activating factor (PAF) plays a role in allergen-induced airway responses by studying the effects of a selective PAF antagonist WEB-2086 on antigen-induced early and late airway responses in allergic sheep. In seven sheep, inhaled Ascaris suum produced significant early (282%) and late (176%) increases in specific lung resistance (sRL). WEB-2086 (1 mg/kg iv) given 20 min before antigen challenge did not affect the early response, but the peak late increase in sRL was only 37% over base line (P less than 0.05 vs. control). To study the mechanism by which PAF contributes to antigen-induced responses, we evaluated the effects of pharmacological probes on PAF-induced bronchoconstriction. Inhaled PAF (dose range 75–700 micrograms) caused reproducible (r = 0.781, P less than 0.05) increases in sRL in eight sheep. The PAF-induced bronchoconstriction was blocked by WEB-2086 (1 mg/kg iv) and by the leukotriene antagonist FPL-55712 (30 mg by aerosol); however, neither the cyclooxygenase blocker indomethacin (2 mg/kg iv) nor the histamine H1-antagonist chlorpheniramine (2 mg/kg iv) blocked the PAF response. WEB-2086, however, did not block bronchoconstriction induced by aerosol leukotriene D4, indicating that PAF acts indirectly through leukotrienes. Finally, we determined whether PAF could induce late airway responses. Inhaled PAF produced an immediate increase in sRL in all seven sheep tested, but late airway responses were observed in only three of the seven sheep.(ABSTRACT TRUNCATED AT 250 WORDS)