Articoli di riviste: "Radioactive tracers in physiology"

1

Minchin, Peter E. H., e Michael R. Thorpe. "Using the short-lived isotope 11C in mechanistic studies of photosynthate transport". Functional Plant Biology 30, n. 8 (2003): 831. http://dx.doi.org/10.1071/fp03008.

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Tracer techniques have been central in studies of transport in plants. In the case of carbon, the only readily available radioactive tracer has been 14C, although 11C was used for a short time before 14C could be made. Tracers have usually had to be measured by destructive harvesting of the plant, giving a practical limit to the data resolution in both time and space. A major advantage of the short-lived, positron-emitting tracers, of which 11C is one example, is that in vivo measurement is possible, giving detailed time series of tracer data in many locations and opening up powerful new techniques of data analysis. Medical applications of these isotopes have utilised both dynamic imaging and time courses of uptake or washout. Unfortunately, few plant biology laboratories have realised the potential of these techniques, possibly because of the large physics infrastructure needed. In this paper we review the concepts behind the use of these short-lived tracers in plant physiology, and illustrate with several cases where 11C was an essential tool.

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Guery, Benoit P., Steve Nelson, Nathalie Viget, Patrice Fialdes, Warren R. Summer, Elizabeth Dobard, Gilles Beaucaire e Carol M. Mason. "Fluorescein-labeled dextran concentration is increased in BAL fluid after ANTU-induced edema in rats". Journal of Applied Physiology 85, n. 3 (1 settembre 1998): 842–48. http://dx.doi.org/10.1152/jappl.1998.85.3.842.

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Several methodologies have been developed to assess alveolocapillary membrane permeability in acute lung injury. The purpose of this study was to determine the reliability of FITC-dextran compared with radioactive tracers to assess lung permeability alterations. After intraperitoneal administration of α-naphthylthiourea (ANTU, 50 mg/kg) or DMSO-ANTU vehicle, the animals were euthanized and their lungs were studied in an isolated-lung preparation. FITC-dextran or radiolabeled tracers were added to the perfusate. At 2 h the bronchoalveolar lavage (BAL) fluid from the ANTU group showed a significantly greater amount of fluorescence in the supernatant after centrifugation of BAL fluid compared with the DMSO group. Consistent results were observed with the radioactive tracers: there was an increase in extravascular albumin space and extravascular lung water compared with the control group. No cleavage of the FITC from the dextran molecule was evident by chromatography comparing samples recovered from the BAL fluid to the pure FITC-dextran molecule. In conclusion, measurement of FITC-dextran in the supernatant of BAL fluid after intravascular administration is a reliable method of assessing lung permeability changes in vivo and ex vivo.

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Sharp, P. F. "The measurement of blood flow in humans using radioactive tracers". Physiological Measurement 15, n. 4 (1 novembre 1994): 339–79. http://dx.doi.org/10.1088/0967-3334/15/4/001.

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Hopkins, Susan R., Mark O. Wielpütz e Hans-Ulrich Kauczor. "Imaging lung perfusion". Journal of Applied Physiology 113, n. 2 (15 luglio 2012): 328–39. http://dx.doi.org/10.1152/japplphysiol.00320.2012.

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From the first measurements of the distribution of pulmonary blood flow using radioactive tracers by West and colleagues ( J Clin Invest 40: 1–12, 1961) allowing gravitational differences in pulmonary blood flow to be described, the imaging of pulmonary blood flow has made considerable progress. The researcher employing modern imaging techniques now has the choice of several techniques, including magnetic resonance imaging (MRI), computerized tomography (CT), positron emission tomography (PET), and single photon emission computed tomography (SPECT). These techniques differ in several important ways: the resolution of the measurement, the type of contrast or tag used to image flow, and the amount of ionizing radiation associated with each measurement. In addition, the techniques vary in what is actually measured, whether it is capillary perfusion such as with PET and SPECT, or larger vessel information in addition to capillary perfusion such as with MRI and CT. Combined, these issues affect quantification and interpretation of data as well as the type of experiments possible using different techniques. The goal of this review is to give an overview of the techniques most commonly in use for physiological experiments along with the issues unique to each technique.

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Jødal, Lars, Pia Afzelius, Aage Kristian Olsen Alstrup e Svend Borup Jensen. "Radiotracers for Bone Marrow Infection Imaging". Molecules 26, n. 11 (25 maggio 2021): 3159. http://dx.doi.org/10.3390/molecules26113159.

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Introduction: Radiotracers are widely used in medical imaging, using techniques of gamma-camera imaging (scintigraphy and SPECT) or positron emission tomography (PET). In bone marrow infection, there is no single routine test available that can detect infection with sufficiently high diagnostic accuracy. Here, we review radiotracers used for imaging of bone marrow infection, also known as osteomyelitis, with a focus on why these molecules are relevant for the task, based on their physiological uptake mechanisms. The review comprises [67Ga]Ga-citrate, radiolabelled leukocytes, radiolabelled nanocolloids (bone marrow) and radiolabelled phosphonates (bone structure), and [18F]FDG as established radiotracers for bone marrow infection imaging. Tracers that are under development or testing for this purpose include [68Ga]Ga-citrate, [18F]FDG, [18F]FDS and other non-glucose sugar analogues, [15O]water, [11C]methionine, [11C]donepezil, [99mTc]Tc-IL-8, [68Ga]Ga-Siglec-9, phage-display selected peptides, and the antimicrobial peptide [99mTc]Tc-UBI29-41 or [68Ga]Ga-NOTA-UBI29-41. Conclusion: Molecular radiotracers allow studies of physiological processes such as infection. None of the reviewed molecules are ideal for the imaging of infections, whether bone marrow or otherwise, but each can give information about a separate aspect such as physiology or biochemistry. Knowledge of uptake mechanisms, pitfalls, and challenges is useful in both the use and development of medically relevant radioactive tracers.

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Phipps, R. J., W. M. Abraham, A. T. Mariassy, P. J. Torrealba, M. W. Sielczak, A. Ahmed, M. McCray, J. S. Stevenson e A. Wanner. "Developmental changes in the tracheal mucociliary system in neonatal sheep". Journal of Applied Physiology 67, n. 2 (1 agosto 1989): 824–32. http://dx.doi.org/10.1152/jappl.1989.67.2.824.

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We studied the postnatal development of the tracheal epithelium and mucociliary system in neonatal sheep. Secretion of macromolecules (radiolabeled with 35SO4 and [3H]-threonine), unidirectional fluxes of Cl-, Na+, and water (measured with radioactive tracers), and ciliary beat frequency (CBF) were measured in tracheal tissues in vitro. Tracheal mucus transport velocity (TMV) was measured in vivo. Sheep were studied at 0, 2, 4, 8, and greater than 24 (adult) wk after birth. In newborn sheep trachea, secretion of macromolecules was significantly elevated (cf. adults), and there was basal net secretion of Cl- under short-circuit and open-circuit conditions. This induced open-circuit secretion of Na+. Secretion of macromolecules decreased rapidly by 2 wk (by 40–50%) and was not different from adult values by 4 wk. Active Na+ absorption developed rapidly, and from 2 wk onward it predominated under open-circuit conditions, inducing net Cl- absorption. These changes in secretory function were associated with an age-related increase in TMV, whereas inherent tracheal CBF was unchanged. In sheep, therefore, the newborn's trachea has elevated secretion of macromolecules and secretes Cl- and liquid under basal conditions. Normal secretory function (a reduction in secretion of macromolecules coupled with net absorption of ions and presumably of liquid also) approaches adult function by 2–4 wk of age.

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Goodman, B. E., K. J. Kim e E. D. Crandall. "Evidence for active sodium transport across alveolar epithelium of isolated rat lung". Journal of Applied Physiology 62, n. 6 (1 giugno 1987): 2460–66. http://dx.doi.org/10.1152/jappl.1987.62.6.2460.

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We have previously presented evidence that cultured alveolar epithelial cell monolayers actively transport sodium from medium to substratum, a process that can be inhibited by sodium transport blockers and stimulated by beta-agonists. In this study, the isolated perfused rat lung was utilized in order to investigate the presence of active sodium transport by intact adult mammalian alveolar epithelium. Radioactive tracers (22Na and [14C]sucrose) were instilled into the airways of isolated Ringer-perfused rat lungs whose weight was continuously monitored. The appearance of isotopes in the recirculated perfusate was measured, and fluxes and apparent permeability-surface area products were determined. A pharmacological agent (amiloride, ouabain, or terbutaline) was added to the perfusate during each experiment after a suitable control period. Amiloride and ouabain resulted in decreased 22Na fluxes and a faster rate of lung weight gain. Terbutaline resulted in increased 22Na flux and a more rapid rate of lung weight loss. [14C]sucrose fluxes were unchanged by the presence of these pharmacological agents. These data are most consistent with the presence of a regulable active component of sodium transport across intact mammalian alveolar epithelium that leads to removal of sodium from the alveolar space, with anions and water following passively. Regulation of the rate of sodium and fluid removal from the alveolar space may play an important role in the prevention and/or resolution of alveolar pulmonary edema.

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Edelman, J. L., H. Lin e S. S. Miller. "Acidification stimulates chloride and fluid absorption across frog retinal pigment epithelium". American Journal of Physiology-Cell Physiology 266, n. 4 (1 aprile 1994): C946—C956. http://dx.doi.org/10.1152/ajpcell.1994.266.4.c946.

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Radioactive tracers and a modified capacitance-probe technique were used to characterize the mechanisms that mediate Cl and fluid absorption across the bullfrog retinal pigment epithelium (RPE)-choroid. In control (HCO3/CO2) Ringer solution, 36Cl was actively absorbed (retina to choroid) at a mean rate of 0.34 mu eq.cm-2.h-1 (n = 34) and accounted for approximately 25% of the short-circuit current. Apical bumetanide (100 microM) or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) inhibited active Cl transport by 70 and 62%, respectively. Active Cl absorption was doubled, either by removing HCO3 from the bathing media or by elevating CO2 from 5 to 13%, and the increased flux was inhibited by apical bumetanide or basal DIDS. Open-circuit measurements of fluid absorption rate (Jv) and the net fluxes of 36Cl, 22Na, and 86Rb (K substitute) indicated that CO2-induced acidification stimulated NaCl and fluid absorption across the RPE. During acidification, bumetanide produced a twofold larger inhibition of Jv compared with control. Stimulation of net Cl absorption was most likely caused by inhibition of the the basolateral membrane intracellular pH-dependent Cl-HCO3 exchanger.

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Bureau, M. F., C. D. Arreto, J. Lefort e B. B. Vargaftig. "Albumin exchange and inflammatory cell recruitment in lungs of antigen-challenged guinea pigs: role of histamine". Journal of Applied Physiology 77, n. 1 (1 luglio 1994): 252–61. http://dx.doi.org/10.1152/jappl.1994.77.1.252.

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Microvascular albumin exchange and sequestration of inflammatory cells into the lungs of anesthetized guinea pigs immunized to ovalbumin were evaluated using radioactive tracers. Increased exchange of radiolabeled (*) albumin from airways to blood was noted in immunized and boosted animals under basal conditions. After the intratracheal injection of 300 micrograms of ovalbumin, an additional increase in exchange through epithelium occurred, since the rate of appearance of *albumin in blood was enhanced compared with control (140 +/- 30 vs. 54 +/- 20% in 1 h). The augmentation of lung content in extravascular *albumin compared with control (16.2 +/- 4.0 vs. 5.9 +/- 1.6%) indicates that transendothelial exchange was also facilitated. Concomitment with the sequestration of *platelets into the lungs of antigen-challenged sensitized animals (59.2 +/- 20% in 1 h), leukocytes (> 60% polymorphonuclear neutrophils) did not marginate. Histamine released during antigenic shock might promote leukocyte demargination from the vascular bed through its vasomotor effect and/or by inhibiting leukocyte activation and consequently may counteract the effects of other inflammatory mediators acting to sequester neutrophils. In confirmation, perfusion of histamine to the immunized animals induced demargination of lung leukocytes. Histamine antagonists prevented the increased exchange of *albumin through the epithelial and endothelial barriers and uncovered *leukocyte sequestration (100.7 +/- 28.9% in 1 h) in the lungs of antigen-challenged animals. Histamine antagonists may favor antigen-induced leukocyte sequestration in the lungs by preventing the effects of endogenous histamine on capillary recruitment and blood flow.

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Hong, Yet Hoi, Tony Frugier, Xinmei Zhang, Robyn M. Murphy, Gordon S. Lynch, Andrew C. Betik, Stephen Rattigan e Glenn K. McConell. "Glucose uptake during contraction in isolated skeletal muscles from neuronal nitric oxide synthase μ knockout mice". Journal of Applied Physiology 118, n. 9 (1 maggio 2015): 1113–21. http://dx.doi.org/10.1152/japplphysiol.00056.2015.

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Inhibition of nitric oxide synthase (NOS) significantly attenuates the increase in skeletal muscle glucose uptake during contraction/exercise, and a greater attenuation is observed in individuals with Type 2 diabetes compared with healthy individuals. Therefore, NO appears to play an important role in mediating muscle glucose uptake during contraction. In this study, we investigated the involvement of neuronal NOSμ (nNOSμ), the main NOS isoform activated during contraction, on skeletal muscle glucose uptake during ex vivo contraction. Extensor digitorum longus muscles were isolated from nNOSμ−/−and nNOSμ+/+mice. Muscles were contracted ex vivo in a temperature-controlled (30°C) organ bath with or without the presence of the NOS inhibitor NG-monomethyl-l-arginine (L-NMMA) and the NOS substrate L-arginine. Glucose uptake was determined by radioactive tracers. Skeletal muscle glucose uptake increased approximately fourfold during contraction in muscles from both nNOSμ−/−and nNOSμ+/+mice. L-NMMA significantly attenuated the increase in muscle glucose uptake during contraction in both genotypes. This attenuation was reversed by L-arginine, suggesting that L-NMMA attenuated the increase in muscle glucose uptake during contraction by inhibiting NOS and not via a nonspecific effect of the inhibitor. Low levels of NOS activity (∼4%) were detected in muscles from nNOSμ−/−mice, and there was no evidence of compensation from other NOS isoform or AMP-activated protein kinase which is also involved in mediating muscle glucose uptake during contraction. These results indicate that NO regulates skeletal muscle glucose uptake during ex vivo contraction independently of nNOSμ.

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Larsen, Erik Hviid. "Hans Henriksen Ussing. 30 December 1911 — 22 December 2000". Biographical Memoirs of Fellows of the Royal Society 55 (gennaio 2009): 305–35. http://dx.doi.org/10.1098/rsbm.2009.0002.

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Hans Ussing was born on 30 December 1911 at Sorø Academy in Denmark, where his father Dr Henrik Ussing was a lecturer and, as historian, a leading Danish folklorist. After his doctoral thesis in marine biology, Hans Ussing came to August Krogh's laboratory, where he studied protein turnover by using deuterium-labelled amino acids. After World War II, when radioactive isotopes of light elements became available for biological research, Ussing pioneered the development of epithelial physiology by introducing new concepts and theoretical tools, such as unidirectional fluxes, exchange diffusion, the flux-ratio equation, the shortcircuiting technique, solvent drag, anomalous solvent drag and the pre-steady-state flux ratio theorem. In studies on frog skin, combining electrophysiology and radioactive tracer technology, he provided the first unambiguous demonstration of active transport of sodium ions. His two-membrane hypothesis of active transport by frog skin initiated studies of epithelial transport at the cellular level in other organs and of the mechanisms of action of hormones and drugs. His discovery of paracellular ion transports bridged the physiology of high-resistance and low-resistance epithelia. With the Na + recirculation theory of isotonic transport he continued his studies of epithelial physiology until shortly before his death. Ussing's scientific research provided analytical methods and new insights of general applicability for the study of absorbing and secreting epithelia—of equal importance to biology and medicine. Hans Ussing died on 22 December 2000 after a short illness.

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Herbst, M. D., e J. H. Goldstein. "A review of water diffusion measurement by NMR in human red blood cells". American Journal of Physiology-Cell Physiology 256, n. 5 (1 maggio 1989): C1097—C1104. http://dx.doi.org/10.1152/ajpcell.1989.256.5.c1097.

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This review of water transport measurement in normal human erythrocytes attempts to harmonize discordant results obtained under diverse study conditions with two different techniques: nuclear magnetic resonance (NMR) and radioactive tracer (THO) diffusion. Natural aggregation of red cells into rouleaux appeared to cause most of the variation among results from NMR experiments. The remainder of the discrepancy was attributed to the use of inappropriate mathematical approximations of the two-site exchange equations, differences in blood storage time, and failure to adjust NMR calculations for the nonwater protons. Differences in hematocrit, frequency-magnetic field strength, or NMR pulse technique played no apparent role in the disparity among NMR reports. When these confounding factors were removed, diffusion results obtained by NMR or by influx or bulk diffusion of radioactive tracer agreed within a relatively narrow range of values. These techniques place the mean lifetime of water inside fresh normal human erythrocytes at room temperature (20-25 degrees C) between the extremes of 9.8 and 14 ms, where the uncorrected range was previously 9.8-21.7 ms. This new range of water exchange times corresponds to a range of diffusional permeability between 3.3 and 4.7 x 10(-3) cm/s.

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Petersson, Johan, Alejandro Sánchez-Crespo, Stig A. Larsson e Margareta Mure. "Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)". Journal of Applied Physiology 102, n. 1 (gennaio 2007): 468–76. http://dx.doi.org/10.1152/japplphysiol.00732.2006.

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Emission tomography provides three-dimensional, quantitative images of the distribution of radiotracers used to mark physiological, metabolic, or pathological processes. Quantitative single photon emission computed tomography (SPECT) requires correction for the image-degrading effects due to photon attenuation and scatter. Phantom experiments have shown that radioactive concentrations can be assessed within some percentage of the true value when relevant corrections are applied. SPECT is widely spread, and radiotracers are available that are easy to use and comparably inexpensive. Compared with other methods, SPECT suffers from a lower spatial resolution, and the time required for image acquisition is longer than for some alternative methods. In contrast to some other methods, SPECT allows simultaneous imaging of more than one process, e.g., both regional blood flow and ventilation, for the whole lung. SPECT has been used to explore the influence of posture and clinical interventions on the spatial distribution of lung blood flow and ventilation. Lung blood flow is typically imaged using macroaggregates of albumin. Both radioactive gases and particulate aerosols labeled with radioactivity have been used for imaging of regional ventilation. However, all radiotracers are not equally suited for quantitative measurements; all have specific advantages and limitations. With SPECT, both blood flow and ventilation can be marked with radiotracers that remain fixed in the lung tissue, which allows tracer administration during conditions different from those at image registration. All SPECT methods have specific features that result from the used radiotracer, the manner in which it is administered, and how images are registered and analyzed.

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Nagra, Gurjit, Lena Koh, Andrei Zakharov, Dianna Armstrong e Miles Johnston. "Quantification of cerebrospinal fluid transport across the cribriform plate into lymphatics in rats". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 291, n. 5 (novembre 2006): R1383—R1389. http://dx.doi.org/10.1152/ajpregu.00235.2006.

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A major pathway by which cerebrospinal fluid (CSF) is removed from the cranium is transport through the cribriform plate in association with the olfactory nerves. CSF is then absorbed into lymphatics located in the submucosa of the olfactory epithelium (olfactory turbinates). In an attempt to provide a quantitative measure of this transport,125I-human serum albumin (HSA) was injected into the lateral ventricles of adult Fisher 344 rats. The animals were killed at 10, 20, 30, 40, and 60 min after injection, and tissue samples, including blood (from heart puncture), skeletal muscle, spleen, liver, kidney, and tail were excised for radioactive assessment. The remains were frozen. To sample the olfactory turbinates, angled coronal tissue sections anterior to the cribriform plate were prepared from the frozen heads. The average concentration of125I-HSA was higher in the middle olfactory turbinates than in any other tissue with peak concentrations achieved 30 min after injection. At this point, the recoveries of injected tracer (percent injected dose/g tissue) were 9.4% middle turbinates, 1.6% blood, 0.04% skeletal muscle, 0.2% spleen, 0.3% liver, 0.3% kidney, and 0.09% tail. The current belief that arachnoid projections are responsible for CSF drainage fails to explain some important issues related to the pathogenesis of CSF disorders. The rapid movement of the CSF tracer into the olfactory turbinates further supports a role for lymphatics in CSF absorption and provides the basis of a method to investigate the novel concept that diseases associated with the CSF system may involve impaired lymphatic CSF transport.

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Marvão, P., M. G. Emílio, K. Gil Ferreira, P. L. Fernandes e H. Gil Ferreira. "ION TRANSPORT IN THE INTESTINE OF ANGUILLA ANGUILLA: GRADIENTS AND TRANSLOCATORS". Journal of Experimental Biology 193, n. 1 (1 agosto 1994): 97–117. http://dx.doi.org/10.1242/jeb.193.1.97.

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The transport of Na+, K+ and Cl- across the isolated epithelium of the eel intestine was studied using a combination of four experimental strategies: short-circuiting, measurements of intracellular potentials and ion concentrations, application of a variety of transport inhibitors and measurement of unidirectional fluxes with radioactive tracers. When short-circuited, the system performs a net transport of Cl- and Na+ towards the blood side, with a stoichiometry approaching 2, and a much smaller net transport of K+ towards the lumen. The system is totally driven by the sodium pump located in the basolateral barrier and the main coupling between the fluxes of the three ions is through the operation of a furosemide-sensitive transporter in the apical barrier, probably a 2Cl-/Na+/K+ symporter. The inhibitory effect of DIDS and picrylsulphonic acid on the short-circuit current, when added to the serosal side, suggests the presence of a sodium-dependent anionic shuttle located in the basolateral membrane. The short-circuit current is inhibited by H25, a non-specific inhibitor of the K+/Cl- symport, added to the serosal side. This effect occurs after a delay of at least 5 min and may result from the diffusion of the drug to the apical barrier, where it blocks the 2Cl-/Na+/K+ symport with much higher affinity.

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Støttrup, Nicolaj B., Steen B. Kristiansen, Bo Løfgren, Bo Falck Hansen, Hans-Henrik Kimose, Hans Erik Bøtker e Torsten Toftegaard Nielsen. "l-GLUTAMATE AND GLUTAMINE IMPROVE HAEMODYNAMIC FUNCTION AND RESTORE MYOCARDIAL GLYCOGEN CONTENT DURING POSTISCHAEMIC REPERFUSION: A RADIOACTIVE TRACER STUDY IN THE RAT ISOLATED HEART". Clinical and Experimental Pharmacology and Physiology 33, n. 11 (novembre 2006): 1099–103. http://dx.doi.org/10.1111/j.1440-1681.2006.04497.x.

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Colvin, Robert A. "pH dependence and compartmentalization of zinc transported across plasma membrane of rat cortical neurons". American Journal of Physiology-Cell Physiology 282, n. 2 (1 febbraio 2002): C317—C329. http://dx.doi.org/10.1152/ajpcell.00143.2001.

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In this study, Zn2+ transport in rat cortical neurons was characterized by successfully combining radioactive tracer experiments with spectrofluorometry and fluorescence microscopy. Cortical neurons showed a time-dependent and saturable transport of65Zn2+ with an apparent affinity of 15–20 μM. 65Zn2+ transport was pH dependent and was decreased by extracellular acidification and increased by intracellular acidification. Compartmentalization of newly transported Zn2+ was assessed with the Zn2+-selective fluorescent dye zinquin. Resting cortical neurons showed uniform punctate labeling that was found in cell processes and the soma, suggesting extrasynaptic compartmentalization of Zn2+. Depletion of intracellular Zn2+ with the membrane-permeant chelator N, N, N′, N′-tetrakis(2-pyridylmethyl)-ethylenediamine (TPEN) resulted in the complete loss of punctate zinquin labeling. After Zn2+ depletion, punctate zinquin labeling was rapidly restored when cells were placed in 30 μM Zn2+, pH 7.4. However, rapid restoration of punctate zinquin labeling was not observed when cells were placed in 30 μM Zn2+, pH 6.0. These data were confirmed in parallel 65Zn2+transport experiments.

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Bojsen-Møller, J., K. K. Kalliokoski, M. Seppänen, M. Kjaer e S. P. Magnusson. "Low-intensity tensile loading increases intratendinous glucose uptake in the Achilles tendon". Journal of Applied Physiology 101, n. 1 (luglio 2006): 196–201. http://dx.doi.org/10.1152/japplphysiol.00004.2006.

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The metabolic activity of tendinous tissues has traditionally been considered to be of limited magnitude. However, recent studies have suggested that glucose uptake increases in the force-transmitting tissues as a response to contractile loading, which in turn indicates an elevated tissue metabolism. The purpose of the present study was to investigate whether such a mechanism could be observed for the human Achilles tendon following tensile loading. Six subjects participated in the study. Unilateral Achilles tendon loading was applied by 25-min intermittent voluntary plantar flexor contractions. A radioactive tracer ([18F]-2-fluoro-2-deoxy-d-glucose) was administered during muscle action, and glucose uptake was measured by use of PET. Regions of interest were defined on the PET images corresponding to the cross section of Achilles tendon at two longitudinally separated sites (insertion and free tendon). Glucose uptake index was determined within respective regions of interest for the active and resting leg. Tendon force during voluntary contractions was ∼13% of maximal voluntary contraction force. Tendon loading induced an elevated glucose uptake index compared with that of the contralateral resting tendon in the region of tendon insertion (0.13 ± 0.05 vs. 0.09 ± 0.02; P < 0.05) and at the free tendon (0.12 ± 0.01 vs. 0.08 ± 0.02; P < 0.05). The present data suggest that tissue metabolism is elevated in the human Achilles tendon in response to low-intensity loading.

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Bertocci, Loren A., John G. Jones, Craig R. Malloy, Ronald G. Victor e Gail D. Thomas. "Oxidation of lactate and acetate in rat skeletal muscle: analysis by 13C-nuclear magnetic resonance spectroscopy". Journal of Applied Physiology 83, n. 1 (1 luglio 1997): 32–39. http://dx.doi.org/10.1152/jappl.1997.83.1.32.

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Bertocci, Loren A., John G. Jones, Craig R. Malloy, Ronald G. Victor, and Gail D. Thomas. Oxidation of lactate and acetate in rat skeletal muscle: analysis by13C-nuclear magnetic resonance spectroscopy. J. Appl. Physiol. 83(1): 32–39, 1997.—The balance between carbohydrate and fatty acid utilization in skeletal muscle previously has been studied in vivo by using a variety of methods such as arteriovenous concentration differences and radioactive isotope tracer techniques. However, these methodologies provide only indirect estimates of substrate oxidation. We used 13C-nuclear magnetic resonance (NMR) spectroscopy and non-steady-state isotopomer analysis to directly quantify the relative oxidation of two competing exogenous substrates in rat skeletal muscles. We infused [1,2-13C]acetate and [3-13C]lactate intravenously in anesthetized rats during the final 30 min of 35 ( n = 10) or 95 ( n = 10) min of intense, unilateral, rhythmic hindlimb contractions.13C-NMR spectroscopy and isotopomer analysis were performed on extracts of gastrocnemius and soleus muscles from both the contracting and contralateral resting hindlimbs. We found that 1) [13C]lactate and [13C]acetate were taken up and oxidized by both resting and contracting skeletal muscles; and 2) high-intensity muscle contractions altered the pattern of substrate utilization such that the relative oxidation of acetate decreased while that of lactate remained unchanged or increased. Based on these findings, we propose that13C-NMR spectroscopy in combination with isotopomer analysis can be used to study the general dynamics of substrate competition between carbohydrates and fats in rat skeletal muscle.

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Klaesner, Joseph W., N. Adrienne Pou, Richard E. Parker, Charlene Finney e Robert J. Roselli. "Optical measurement of isolated canine lung filtration coefficients at normal hematocrits". Journal of Applied Physiology 83, n. 6 (1 dicembre 1997): 1976–85. http://dx.doi.org/10.1152/jappl.1997.83.6.1976.

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Klaesner, Joseph W., N. Adrienne Pou, Richard E. Parker, Charlene Finney, and Robert J. Roselli. Optical measurement of isolated canine lung filtration coefficients at normal hematocrits. J. Appl. Physiol. 83(6): 1976–1985, 1997.—In this study, lung filtration coefficient ( K fc) values were measured in eight isolated canine lung preparations at normal hematocrit values using three methods: gravimetric, blood-corrected gravimetric, and optical. The lungs were kept in zone 3 conditions and subjected to an average venous pressure increase of 10.24 ± 0.27 (SE) cmH2O. The resulting K fc(ml ⋅ min−1 ⋅ cmH2O−1 ⋅ 100 g dry lung wt−1) measured with the gravimetric technique was 0.420 ± 0.017, which was statistically different from the K fc measured by the blood-corrected gravimetric method (0.273 ± 0.018) or the product of the reflection coefficient (ςf) and K fc measured optically (0.272 ± 0.018). The optical method involved the use of a Cellco filter cartridge to separate red blood cells from plasma, which allowed measurement of the concentration of the tracer in plasma at normal hematocrits (34 ± 1.5). The permeability-surface area product was measured using radioactive multiple indicator-dilution methods before, during, and after venous pressure elevations. Results showed that the surface area of the lung did not change significantly during the measurement of K fc. These studies suggest that ςf K fccan be measured optically at normal hematocrits, that this measurement is not influenced by blood volume changes that occur during the measurement, and that the optical ςf K fcagrees with the K fc obtained via the blood-corrected gravimetric method.

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Dowell, R. T., e C. D. Kauer. "Uteroplacental blood flow at rest and during exercise in late-gestation conscious rats". Journal of Applied Physiology 74, n. 5 (1 maggio 1993): 2079–85. http://dx.doi.org/10.1152/jappl.1993.74.5.2079.

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The present studies were conducted to achieve three specific aims. First, techniques and procedures were developed to allow tissue and organ blood flow measurements by radioactive microsphere methodology in the conscious female rat. Second, technical aspects of the methodology were evaluated with emphasis on potential uteroplacental shunting of microspheres in the late-gestational period. Third, the above techniques and procedures were utilized to assess uteroplacental blood flow at rest and during exercise in conscious pregnant rats during the late stages of gestation, i.e., days 15, 19, and 22 of pregnancy. Results established the validity of tracer blood flow technical assumptions, and no significant increase in arteriovenous shunting of 15-microns microspheres either as pregnancy progressed or during superimposed exercise in near-term pregnant animals was detected. During the stages of pregnancy studied, cardiac output was enhanced approximately 20% near term. Marked and progressive increases in uterine blood flow were noted both in milliliters per minute and as percentage of cardiac output. Preferential placental perfusion during late-stage gestation was indicated by increased tissue flow (7 +/- 1, 84 +/- 12, 232 +/- 32 ml.min-1 x 100 g-1), increased percent cardiac output (1.7 +/- 0.1, 5.1 +/- 0.7, 11.0 +/- 1.7% cardiac output), and increased percent uterine blood flow (10 +/- 1, 59 +/- 3, 87 +/- 2% uterine flow) at days 15, 19, and 22 of gestation, respectively. Progressive maternal body weight increase during gestation enhanced exercise work intensity, as shown by heart rate and cardiac output at the end of 30 min of treadmill running at 8.5 m/min, 0% incline.

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22

Chabot, J. G., P. Walker e G. Pelletier. "Demonstration of epidermal growth factor binding sites in the adult rat small intestine by autoradiography". Canadian Journal of Physiology and Pharmacology 65, n. 2 (1 febbraio 1987): 109–12. http://dx.doi.org/10.1139/y87-022.

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The distribution of epidermal growth factor (EGF) receptors was studied in the distal portion of duodenum using light microscopic autoradiography performed at different time intervals (2–60 min) after intravenous injection of 125I-labelled EGF into adult rats. The results revealed a substantial binding of EGF to both cell types of the mucosal epithelium in duodenal crypts and villi, the columnar absorptive cells and the globet cells. Labelling was also found over few cells of lamina propria. No labelling was observed over the striated border of the duodenal mucosa epithelium. The time-course study performed in epithelial cells of duodenal crypts and villi showed that most silver grains were found at the periphery of the cells 2 min after injection. At the 7 min, silver grains were found both at the periphery and over the cytoplasm, more specifically the supranuclear region of the columnar absorptive cells. The number of grains overlying the cytoplasm of these cells was markedly reduced at 60 min. By quantitative autoradiography, maximal values were reached 7 min after the injection. Control experiments indicated that the autoradiography reaction was due to specific interaction of 125I-labelled EGF with its receptor. These results clearly indicate that EGF receptors are present in epithelial cells of the duodenal mucosa and suggest that the radioactive tracer is taken up by these cells.

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23

Salaets, Thomas, André Gie, Julio Jimenez, Margo Aertgeerts, Olivier Gheysens, Greetje Vande Velde, Michel Koole et al. "Local pulmonary drug delivery in the preterm rabbit: feasibility and efficacy of daily intratracheal injections". American Journal of Physiology-Lung Cellular and Molecular Physiology 316, n. 4 (1 aprile 2019): L589—L597. http://dx.doi.org/10.1152/ajplung.00255.2018.

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Recent clinical trials in newborns have successfully used surfactant as a drug carrier for an active compound, to minimize systemic exposure. To investigate the translational potential of surfactant-compound mixtures and other local therapeutics, a relevant animal model is required in which intratracheal administration for maximal local deposition is technically possible and well tolerated. Preterm rabbit pups (born at 28 days of gestation) were exposed to either hyperoxia or normoxia and randomized to receive daily intratracheal surfactant, daily intratracheal saline, or no injections for 7 days. At day 7, the overall lung function and morphology were assessed. Efficacy in terms of distribution was assessed by micro-PET-CT on both day 0 and day 7. Lung function as well as parenchymal and vascular structure were altered by hyperoxia, thereby reproducing a phenotype reminiscent of bronchopulmonary dysplasia (BPD). Neither intratracheal surfactant nor saline affected the survival or the hyperoxia-induced BPD phenotype of the pups. Using PET-CT, we demonstrate that 82.5% of the injected radioactive tracer goes and remains in the lungs, with a decrease of only 4% after 150 min. Surfactant and saline can safely and effectively be administered in spontaneously breathing preterm rabbits. The described model and method enable researchers to evaluate intratracheal pharmacological interventions for the treatment of BPD.

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24

Bukowiecki, Ludwik Jan. "Energy balance and diabetes. The effects of cold exposure, exercise training, and diet composition on glucose tolerance and glucose metabolism in rat peripheral tissues". Canadian Journal of Physiology and Pharmacology 67, n. 4 (1 aprile 1989): 382–93. http://dx.doi.org/10.1139/y89-062.

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The effects of cold exposure, exercise training, and diet (high fat versus high carbohydrate) on glucose tolerance and glucose metabolism in rat peripheral tissues will be briefly reviewed. Stimulation of energy expenditure by cold exposure (4 °C) or exercise training generally leads to decreased plasma insulin levels and to an improvement in glucose tolerance, suggesting that insulin action on peripheral tissues is increased when energy expenditure is stimulated. On the contrary, feeding high-fat diets to sedentary rats living in the warm (25 °C) induces hyperinsulinemia and insulin resistance resulting in a marked deterioration of glucose tolerance. Nevertheless, cold exposure reverses the diabetogenic effects of high-fat feeding, demonstrating that nutrition-induced insulin resistance is amplified in sedentary animals living at temperatures close to thermoneutrality. Radioactive tracer studies of 2-deoxyglucose uptake in peripheral tissues revealed that cold exposure synergistically potentiates the effects of insulin on glucose uptake in skeletal muscles as well as in white and brown adipose tissues. However, more recent data showed that cold exposure improves glucose tolerance and stimulates glucose uptake in starved animals (ie., in the virtual absence of circulating insulin) nearly by the same order of magnitude as in fed animals. It is therefore concluded that cold exposure, and possibly also exercise, improve glucose tolerance and stimulate glucose uptake in peripheral tissues primarily by enhancing glucose oxidation via insulin-independent pathways, and secondarily by increasing the responsiveness of peripheral tissues to insulin.Key words: insulin, brown adipose tissue, skeletal muscle, 2-deoxyglucose, diabetes.

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25

Lüscher, E. "RADIOACTIVE TRACERS IN STUDYING CLEAN SURFACES". Annals of the New York Academy of Sciences 101, n. 3 (22 dicembre 2006): 816–21. http://dx.doi.org/10.1111/j.1749-6632.1963.tb54937.x.

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26

Blet, V., Ph Berne, F. Tola, X. Vitart e C. Chaussy. "Recent developments in radioactive tracers methodology". Applied Radiation and Isotopes 51, n. 6 (dicembre 1999): 615–24. http://dx.doi.org/10.1016/s0969-8043(99)00095-0.

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27

Carroll, J., e I. Lerche. "Sedimentary radioactive tracers and diffusive models". Journal of Environmental Radioactivity 101, n. 8 (agosto 2010): 597–600. http://dx.doi.org/10.1016/j.jenvrad.2010.03.005.

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28

Alstrup, Aage Kristian Olsen, Svend Borup Jensen, Ole Lerberg Nielsen, Lars Jødal e Pia Afzelius. "Preclinical Testing of Radiopharmaceuticals for the Detection and Characterization of Osteomyelitis: Experiences from a Porcine Model". Molecules 26, n. 14 (12 luglio 2021): 4221. http://dx.doi.org/10.3390/molecules26144221.

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Abstract (sommario):

The development of new and better radioactive tracers capable of detecting and characterizing osteomyelitis is an ongoing process, mainly because available tracers lack selectivity towards osteomyelitis. An integrated part of developing new tracers is the performance of in vivo tests using appropriate animal models. The available animal models for osteomyelitis are also far from ideal. Therefore, developing improved animal osteomyelitis models is as important as developing new radioactive tracers. We recently published a review on radioactive tracers. In this review, we only present and discuss osteomyelitis models. Three ethical aspects (3R) are essential when exposing experimental animals to infections. Thus, we should perform experiments in vitro rather than in vivo (Replacement), use as few animals as possible (Reduction), and impose as little pain on the animal as possible (Refinement). The gain for humans should by far exceed the disadvantages for the individual experimental animal. To this end, the translational value of animal experiments is crucial. We therefore need a robust and well-characterized animal model to evaluate new osteomyelitis tracers to be sure that unpredicted variation in the animal model does not lead to a misinterpretation of the tracer behavior. In this review, we focus on how the development of radioactive tracers relies heavily on the selection of a reliable animal model, and we base the discussions on our own experience with a porcine model.

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29

Leong, P., e D. Manahan. "Metabolic importance of Na+/K+-ATPase activity during sea urchin development." Journal of Experimental Biology 200, n. 22 (1 novembre 1997): 2881–92. http://dx.doi.org/10.1242/jeb.200.22.2881.

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Abstract (sommario):

Early stages of animal development have high mass-specific rates of metabolism. The biochemical processes that establish metabolic rate and how these processes change during development are not understood. In this study, changes in Na+/K+-ATPase activity (the sodium pump) and rate of oxygen consumption were measured during embryonic and early larval development for two species of sea urchin, Strongylocentrotus purpuratus and Lytechinus pictus. Total (in vitro) Na+/K+-ATPase activity increased during development and could potentially account for up to 77 % of larval oxygen consumption in Strongylocentrotus purpuratus (pluteus stage) and 80 % in Lytechinus pictus (prism stage). The critical issue was addressed of what percentage of total enzyme activity is physiologically active in living embryos and larvae and thus what percentage of metabolism is established by the activity of the sodium pump during development. Early developmental stages of sea urchins are ideal for understanding the in vivo metabolic importance of Na+/K+-ATPase because of their small size and high permeability to radioactive tracers (86Rb+) added to sea water. A comparison of total and in vivo Na+/K+-ATPase activities revealed that approximately half of the total activity was utilized in vivo. The remainder represented a functionally active reserve that was subject to regulation, as verified by stimulation of in vivo Na+/K+-ATPase activity in the presence of the ionophore monensin. In the presence of monensin, in vivo Na+/K+-ATPase activities in embryos of S. purpuratus increased to 94 % of the maximum enzyme activity measured in vitro. Stimulation of in vivo Na+/K+-ATPase activity was also observed in the presence of dissolved alanine, presumably due to the requirement to remove the additional intracellular Na+ that was cotransported with alanine from sea water. The metabolic cost of maintaining the ionic balance was found to be high, with this process alone accounting for 40 % of the metabolic rate of sea urchin larvae (based on the measured fraction of total Na+/K+-ATPase that is physiologically active in larvae of S. purpuratus). Ontogenetic changes in pump activity and environmentally induced regulation of reserve Na+/K+-ATPase activity are important factors that determine a major proportion of the metabolic costs of sea urchin development.

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30

Pemper, Richard R., Michael J. Flecker, Vernie C. McWhirter e Donald W. Oliver. "Hydraulic fracture evaluation with multiple radioactive tracers". GEOPHYSICS 53, n. 10 (ottobre 1988): 1323–33. http://dx.doi.org/10.1190/1.1442410.

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Abstract (sommario):

For many years, wireline tracer surveys have been used to determine the height of fractures created during hydraulic stimulation procedures. A recent advancement in fracture evaluation technology has been to tag different stages of a fracture operation with multiple radioactive tracers, providing the capability to discern between created and propped fracture heights in one or more zones of interest. In this research, a wireline instrumentation and data analysis system is implemented to identify and separate the individual yields from multiple radioactive tracers, with an additional feature that determines whether the tracer material is inside of the borehole or distributed throughout the created fracture zone. A single postfracture pass of the logging instrument is used to accumulate gamma ray spectra at each 7.6 cm interval along a borehole. A weighted least‐squares spectrum unfolding algorithm calculates the radioactive intensities as a function of depth, while the peak‐to‐Compton down‐scatter ratio determines the proximity of the tracer material to the wellbore. Field examples illustrate the effectiveness of the system for the evaluation of multistage fracture operations.

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31

Bramlet, Roland. "Radioactive and Stable Isotope Tracers in Biomedicine". Clinical Nuclear Medicine 18, n. 5 (maggio 1993): 455–56. http://dx.doi.org/10.1097/00003072-199305000-00027.

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32

Papastefanou, C., e C. Papastefanou. "Radioactive nuclides as tracers of environmental processes". Journal of Radioanalytical and Nuclear Chemistry 267, n. 2 (gennaio 2006): 315–20. http://dx.doi.org/10.1007/s10967-006-0050-8.

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33

Counsell, Raymond E., Marcian Van Dort e Richard Neubig. "Iodinated clonidine derivatives as radioactive imaging tracers". International Journal of Radiation Applications and Instrumentation. Part B. Nuclear Medicine and Biology 17, n. 4 (gennaio 1990): ii. http://dx.doi.org/10.1016/0883-2897(90)90117-j.

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34

Jansson, Mats, Trygve E. Eriksen e Susanna Wold. "LOT—in situ diffusion experiments using radioactive tracers". Applied Clay Science 23, n. 1-4 (agosto 2003): 77–85. http://dx.doi.org/10.1016/s0169-1317(03)00089-9.

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35

Blet, V., Ph Berne, C. Chaussy, S. Perrin e D. Schweich. "Characterization of a packed column using radioactive tracers". Chemical Engineering Science 54, n. 1 (gennaio 1999): 91–101. http://dx.doi.org/10.1016/s0009-2509(98)00217-6.

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36

Delhez, Éric J. M., Éric Deleersnijder, Anne Mouchet e J. M. Beckers. "A note on the age of radioactive tracers". Journal of Marine Systems 38, n. 3-4 (gennaio 2003): 277–86. http://dx.doi.org/10.1016/s0924-7963(02)00245-2.

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37

Gulati, R. D. "Zooplankton grazing methods using radioactive tracers: Technical problems". Hydrobiological Bulletin 19, n. 1 (novembre 1985): 61–66. http://dx.doi.org/10.1007/bf02255094.

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38

Cantone, M. C., D. De Bartolo, A. Giussani, N. Molho, L. Pirola, G. Gambarini, Ch Hansen, P. Roth e E. Werner. "Stable and radioactive tracers in Ru biokinetic studies". Journal of Radioanalytical and Nuclear Chemistry 178, n. 2 (marzo 1994): 407–15. http://dx.doi.org/10.1007/bf02039734.

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39

Campos, Armando Macias, e Gerardo Rodriguez Aranda. "Microcomputer systems for analysis of radioactive tracers data". International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes 41, n. 10-11 (gennaio 1990): 1095–102. http://dx.doi.org/10.1016/0883-2889(90)90178-j.

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40

Podglajen, Aurélien, e Felix Ploeger. "Retrieving the age of air spectrum from tracers: principle and method". Atmospheric Chemistry and Physics 19, n. 3 (8 febbraio 2019): 1767–83. http://dx.doi.org/10.5194/acp-19-1767-2019.

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Abstract (sommario):

Abstract. Surface-emitted tracers with different dependencies on transit time (e.g., due to chemical loss or time-dependent boundary conditions) carry independent pieces of information on the age of air spectrum (the distribution of transit times from the surface). This paper investigates how and to what extent knowledge of tracer concentrations can be used to retrieve the age spectrum. Since the mixing ratios of the tracers considered depend linearly on the transit time distribution, the question posed can be formulated as a linear inverse problem of small dimension. An inversion methodology is introduced, which does not assume a prescribed shape for the spectrum. The performance of the approach is first evaluated on a constructed set of artificial radioactive tracers derived from idealized spectra. Hereafter, the inversion method is applied to outputs of a chemistry–transport model. The latter experiment highlights the limits of inversions using only parent radioactive tracers: they are unable to retrieve fine-scale structures such as the annual cycle. Improvements can be achieved by including daughter decaying tracers and tracers with an annual cycle at the surface. This study demonstrates the feasibility of retrieving the age spectrum from tracers and has implications for transport diagnosis in models and observations.

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41

Wastney, M. E., I. G. Gokmen, R. L. Aamodt, W. F. Rumble, G. E. Gordon e R. I. Henkin. "Kinetic analysis of zinc metabolism in humans after simultaneous administration of 65Zn and 70Zn". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 260, n. 1 (1 gennaio 1991): R134—R141. http://dx.doi.org/10.1152/ajpregu.1991.260.1.r134.

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Abstract (sommario):

Zinc kinetics were studied and compared after oral simultaneous administration of two tracers, radioactive (65Zn) and stable (70Zn) isotope, to four normal human volunteers. Both tracers and zinc concentration were measured in plasma, red blood cells (RBC), urine, and feces for up to 78 days. Radioactive zinc was also measured by external counting over whole body, liver, and thigh. Data from each individual were analyzed using a compartmental model for zinc metabolism. Values calculated for absorption, fractional zinc excretion in urine, exchange with RBC, and secretion into gut using 70Zn data did not differ from values calculated using 65Zn data. Results show that human zinc metabolism can be investigated using stable isotopes as tracers to determine parameters of whole body zinc metabolism, including zinc absorption, excretion, and secretion.

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42

Huybers, Peter, Geoffrey Gebbie e Olivier Marchal. "Can Paleoceanographic Tracers Constrain Meridional Circulation Rates?" Journal of Physical Oceanography 37, n. 2 (1 febbraio 2007): 394–407. http://dx.doi.org/10.1175/jpo3018.1.

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Abstract (sommario):

Abstract The ability of paleoceanographic tracers to constrain rates of transport is examined using an inverse method to combine idealized observations with a geostrophic model. Considered are the spatial distribution, accuracy, and types of tracers required to constrain changes in meridional transport within an idealized single-hemisphere basin. Measurements of density and radioactive tracers each act to constrain rates of transport. Conservative tracers, while not of themselves able to inform regarding rates of transport, improve constraints when coupled with density or radioactive observations. It is found that the tracer data would require an accuracy one order of magnitude better than is presently available for paleo-observations to conclusively rule out factor-of-2 changes in meridional transport, even when assumed available over the entire model domain. When data are available only at the margins and bottom of the model, radiocarbon is unable to constrain transport while density remains effective only when a reference velocity level is assumed. The difficulty in constraining the circulation in this idealized model indicates that placing firm bounds on past meridional transport rates will prove challenging.

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43

Iijima, Yoshiaki, Hiroyuki Nitta, Ryusuke Nakamura, Koichi Takasawa, Akiko Inoue, Shigeru Takemoto e Yoshihiro Yamazaki. "Precise Measurement of Low Diffusion Coefficients Using Radioactive Tracers". Journal of the Japan Institute of Metals 69, n. 4 (2005): 321–31. http://dx.doi.org/10.2320/jinstmet.69.321.

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44

Voss, R. "Radioactive and kinematic tracers of feedback from massive stars". EPJ Web of Conferences 19 (2012): 10004. http://dx.doi.org/10.1051/epjconf/20121910004.

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45

Armstrong, Dennis J. "An investigation of ammonia plant performance using radioactive tracers". Plant/Operations Progress 4, n. 2 (aprile 1985): 72–78. http://dx.doi.org/10.1002/prsb.720040205.

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46

Coggan, Andrew R. "Use of stable isotopes to study carbohydrate and fat metabolism at the whole-body level". Proceedings of the Nutrition Society 58, n. 4 (novembre 1999): 953–61. http://dx.doi.org/10.1017/s0029665199001263.

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Abstract (sommario):

The present review discusses the advantages and limitations of using stable-isotope tracers to assess carbohydrate and fat metabolism at the whole-body level. One advantage of stable-(v. radioactive-) isotope tracers is the relative ease with which the location of a label within a molecule can be determined using selected-ion-monitoring GC-mass spectrometry (SIM-GC- MS). This technique minimizes potential problems due to label recycling, allows the use of multiple-labelled compounds simultaneously (e.g. to quantify glucose cycling), and perhaps most importantly, has led to the development of unique stable-isotope methods for, for example, quantifying gluconeogenesis. However, the limited sensitivity of SIM-GC-MS sometimes requires that relatively large amounts of a stable-isotope tracer be used, thus increasing cost and potentially altering metabolism. At least theoretically, stable- (or radioactive-) isotope tracers can also be used in conjunction with indirect calorimetry to estimate utilization of muscle glycogen or triacylglycerol stores, thus potentially circumventing the need to obtain muscle biopsies. These calculations, however, require certain critical assumptions, which if incorrect could lead to major errors in the values obtained. Despite such limitations, stable-isotope tracers provide a powerful and sometimes unique tool for investigating carbohydrate and fat metabolism at the whole-body level. With continuing advances in availability, instrumentation and methods, it is likely that stable-isotope tracers will become increasingly important in the immediate future.

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47

Li, Zhiyan, Xianghui Li, Xudong Zhu, Shichao Ai, Wenxian Guan e Song Liu. "Tracers in Gastric Cancer Surgery". Cancers 14, n. 23 (22 novembre 2022): 5735. http://dx.doi.org/10.3390/cancers14235735.

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Abstract (sommario):

The treatment of gastric cancer mainly depends on radical gastrectomy. Determination of appropriate surgical margins and adequate lymph node (LN) resection are two major surgical steps that directly correlate with prognosis in gastric cancer. Due to the expanding use of minimally invasive procedures, it is no longer possible to locate tumors and LNs through touch. As an alternative, tracers have begun to enter the field due to their capacities for intraoperative visualization. Herein, we summarize the application of contemporary tracers in gastric cancer surgery, including isosulfan blue, methylene blue, patent blue, indocyanine green, carbon particles, and radioactive tracers. Their mechanisms, administration methods, detection efficiency, and challenges, as well as perspectives on them, are also outlined.

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48

Chang, E. C., e K. Yoshimura. "A semi-Lagrangian advection scheme for radioactive tracers in the NCEP Regional Spectral Model (RSM)". Geoscientific Model Development 8, n. 10 (14 ottobre 2015): 3247–55. http://dx.doi.org/10.5194/gmd-8-3247-2015.

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Abstract (sommario):

Abstract. In this study, the non-iteration dimensional-split semi-Lagrangian (NDSL) advection scheme is applied to the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) to alleviate the Gibbs phenomenon. The Gibbs phenomenon is a problem wherein negative values of positive-definite quantities (e.g., moisture and tracers) are generated by the spectral space transformation in a spectral model system. To solve this problem, the spectral prognostic specific humidity and radioactive tracer advection scheme is replaced by the NDSL advection scheme, which considers advection of tracers in a grid system without spectral space transformations. A regional version of the NDSL is developed in this study and is applied to the RSM. Idealized experiments show that the regional version of the NDSL is successful. The model runs for an actual case study suggest that the NDSL can successfully advect radioactive tracers (iodine-131 and cesium-137) without noise from the Gibbs phenomenon. The NDSL can also remove negative specific humidity values produced in spectral calculations without losing detailed features.

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49

Chang, E. C., e K. Yoshimura. "A semi-Lagrangian advection scheme for radioactive tracers in a regional spectral model". Geoscientific Model Development Discussions 8, n. 6 (2 giugno 2015): 4221–43. http://dx.doi.org/10.5194/gmdd-8-4221-2015.

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Abstract (sommario):

Abstract. In this study, the non-iteration dimensional-split semi-Lagrangian (NDSL) advection scheme is applied to the National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) to alleviate the Gibbs phenomenon. The Gibbs phenomenon is a problem wherein negative values of positive-definite quantities (e.g., moisture and tracers) are generated by the spectral space transformation in a spectral model system. To solve this problem, the spectral prognostic specific humidity and radioactive tracer advection scheme is replaced by the NDSL advection scheme, which considers advection of tracers in a grid system without spectral space transformations. A regional version of the NDSL is developed in this study and is applied to the RSM. Idealized experiments show that the regional version of the NDSL is successful. The model runs for an actual case study suggest that the NDSL can successfully advect radioactive tracers (iodine-131 and cesium-137) without noise from the Gibbs phenomenon. The NDSL can also remove negative specific humidity values produced in spectral calculations without losing detailed features.

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50

Argoud, G. M., D. S. Schade e R. P. Eaton. "Underestimation of hepatic glucose production by radioactive and stable tracers". American Journal of Physiology-Endocrinology and Metabolism 252, n. 5 (1 maggio 1987): E606—E615. http://dx.doi.org/10.1152/ajpendo.1987.252.5.e606.

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Abstract (sommario):

Although negative hepatic glucose production rates are physiologically impossible, they have been observed when hepatic glucose production is measured with the tracer-dilution technique during the hyperinsulinemic, euglycemic glucose clamp. Because hepatic glucose production is determined from the difference between tracer-derived glucose disposal and the known exogenous glucose infusion rate, the negative values for hepatic glucose production must result from an underestimation of glucose disposal by the tracer technique. In the current investigation, tracer-derived glucose disposal was measured in 25 subjects undergoing hyperinsulinemic, euglycemic clamps. Glucose disposal was measured with both radioactive and stable isotopes that utilize different methodologies, to determine whether discriminant metabolism of the isotopes versus methodological error leads to underestimation of tracer-derived glucose disposal. Both the radioactive and stable methodologies underestimated the exogenous glucose infusion rate during the hyperinsulinemic euglycemic clamp by 27 and 17%, respectively. Mean hepatic glucose production was -2.1 +/- 0.2 and -1.3 +/- 0.2 mg X kg-1 X min-1 as determined by the radioactive and stable isotope methodologies, respectively. Methodological error was an unlikely cause of this underestimation because it occurred with two different methodologies. The most likely explanation for underestimated rates of glucose disposal determined by the two types of isotope methodologies is discrepant metabolism of glucose tracers in comparison with unlabeled glucose.

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