Dissertations / Theses on the topic 'Natriuretic peptide hormones'

Plant natriuretic peptides (PNP) are novel peptides which, like in vertebrates, have been shown to have a function associated with water and salt homeostasis. Two PNP-encoding genes have been identified and isolated from Arabidopsis thaliana, namely; AtPNP-A and AtPNP-B. In this study, the focus was on PNP-B, which has not been extensively studied. Bioinformatic analysis was done on the AtPNP-B gene. This included the bioinformatic study of its primary structure, secondary structure, tertiary structure, transcription factor binding sites (TFBS) and its relation to other known proteins. The AtPNP-B gene was shown to be a 510 bp long, including a predicted 138 bp intron. AtPNP-B was also shown to have some sequence similarity with AtPNP-A and CjBAp12. The TFBS for AtPNP-B and OsJPNP-B were compared and they comprised of TFBS that are related to water homeostasis and pathogenesis. This suggested two possible functions; water stress and homeostasis and a pathogenesis related function for PNP-B. Following bioinformatic analysis, the heterologous expression of the AtPNP-B was attempted to investigate whether the AtPNP-B gene encoded a functional protein and to determine the functional role of PNP-B. However, expression was unsuccessful. An evolutionary study was then carried out which revealed that there were some plants without the intron such as, rice, leafy spurge, oilseed rape, onion, poplar, sugar cane, sunflower and tobacco. These plants would therefore be used for expression and functional studies in the future. The evolutionary studies also revealed that PNP-B had a relationship with expansins and the endoglucanase family 45. Other PNP-B related molecules were also obtained from other plant genomes and therefore used in the construction of a phylogenetic tree. The phylogenetic tree revealed that AtPNP-B clustered in the same group as CjBAp12 while AtPNP-A had its own cluster group. There were also other PNP-B like molecules that clustered in the same group as expansins (α- and β-). Thus, we postulate that, like PNP-A, PNP-B also has a possible function in water and salt homeostasis. However, due to the clustering iii of AtPNP-B into the same group as CjBAp12, a possible role of PNP-B in pathogenesis-related response is also postulated.

In this study, both physiological and cellular effects are elicited by natriuretic peptides (NPs), a novel type of plant hormone. It was found that rat ANP (rANP) influenced stomatal opening movement in Tradescantia sp., where a significant increase in stomatal opening was observed in the presence of 1 µM rANP. Furthermore, this effect is mediated by cGMP, a (putative) second messenger of NPs. Two inhibitors of guanylyl cyclase, LY 83583 and methylene blue, inhibited rANP-induced stomatal opening. In contrast, stomatal opening is induced in a concentration dependent manner by the cell permeant cGMP analogue 8-Br-cGMP. In addition it was found, that like in animals, the secondary structure of rANP is essential for rANP responses. Linearised rANP is biologically inactive. Since ANP elicit plant responses, an attempt was made to isolate NP analogues from plants. A protocol for partially purifying NP from plants was developed. It was found that two fractions eluted from an immunoaffinity chromatography column (0.5 M KCI eluted fraction and 0.75 M KCI eluted fraction) were biologically active. The level of cGMP in response to NPs was also tested. It is suggested that the receptor of NP is specific since only 0.75 M KCI eluted fractions increased cGMP levels in Zea mays root stele tissue. rANP did not elicit an effect on cGMP levels in this tissue and LY 83583 did not affect this response. It is therefore argued that a plant specific biologically active NP system is present in the stele and it is predicted that NPs modulate solute movement in this tissue. NPs also influence K⁺, Na⁺ and H⁺ fluxes in Zea mays root stele. Increase in both K⁺ and Na+ uptake were observed after 30 min., while H⁺ flux shifted immediately toward influx in the presence of both 0.5 and 0.75 KCI eluted fractions. Finally, a model is proposed for the effect of NPs on solute movement and its signalling system in plants.

Philosophiae Doctor - PhD
Plant natriuretic peptides (PNPs) are a novel class of extracellular, systemically mobile molecules that elicit a number of plant responses important in homeostasis and growth. Natriuretic peptides were first identified in vertebrates where they play a role in the regulation of salt and water balance. Subsequent experimental investigations have identified the presence of a natriuretic peptide hormone system in plants. While PNPs have been implicated in various physiological responses such as stomatal guard cell movements and regulation of net water uptake, its biological role has remained elusive. Here we have used co-expression and promoter content analysis tools to understand the biological role of the Arabidopsis thaliana PNP (AtPNP-A). The analysis of AtPNP-A and its co-expressed genes revealed that genes annotated as part of the systemic acquired resistance (SAR) pathway were over-represented, thus suggesting that AtPNP-A may function as a component of plant defense responses and specifically, SAR. The results further show that AtPNP-A shares many characteristics with pathogenesis related (PR) proteins in that its transcription is strongly induced in response to pathogen challenges, thus implying a newly described role for AtPNP-A in pathogen attack. Additional tissue expression analysis also indicated distinct localization of PNP activity in sepals and transcriptional meta-analysis showed that AtPNP-A may play a role in starch breakdown. Therefore, together with the finding that AtPNP-A plays a role in regulating phloem transport, we also hypothesize that AtPNP-A may play a role in phloem unloading in sepals to assist processes such as seed formation in plants. In plants, the second messenger, guanosine 3’,5’-cyclic monophosphate (cGMP) mediates a whole range of important processes including salinity tolerance, disease resistance, drought tolerance and responses to light. Since PNPs regulate water and salt homeostasis via a cGMP-dependent signaling pathways, it is thus important to analyse the transcriptome induced by the second messenger (cGMP) in Arabidopsis thaliana to give a better understanding of its mechanism of action. This study was also supplemented by the analysis of the gibberellic acid (GA) dependent transcriptome, since cGMP also plays a role its transcription pathway. This data analysis, together with promoter content investigation, revealed that genes upregulated after cGMP treatment and down-regulated in the GA insensitive mutant (ga1-3) were enriched with a GA response element (GARE), while no GARE enrichment were observed in genes up-regulated in the ga1-3 mutant. These findings suggest that GARE is indicative of GA-induced and cGMP-dependent transcriptional up-regulation. Gene ontology analysis confirmed previous reports that cGMP is involved in ion homeostasis and indicated that the transcriptional cGMP response is bi-polar in the sense that both genes up- and down-regulated in response to cGMP is involved in cation transport. Additionally, ab initio analysis of genes transcriptionally dependent on cGMP identified CHX8 as a hub gene and promoter content of CHX8 co-expressed genes show enrichment of the GARE motif. The fact that CHX8 has its highest expression levels during male gametogenesis and pollen tube growth, together with our findings, suggest that GA-induced and cGMP- dependent genes may play a key role in ion and water homeostasis in the male gametophyte. Finally, we propose that the type of analysis undertaken here can yield new insights into gene regulation networks and inform experimental strategies to unravel complex transcription regulatory systems under different developmental and stimulus specific conditions.
South Africa

Data was collected in two main phases; 1. A field study undertaken in the Cordillera Real Region of Bolivia. 2. Laboratory investigation of terrestrial, hypobaric and normobaric hypoxia. Phase 1 The aim of phase one of the studies was to investigate the endocrine changes (specifically brain natriuretic peptide (BNP), arginine vasopressin (AVP), cortisol, catecholamine and copeptin) with ascent to high altitude. These changes were investigated during a “real world” trekking expedition to Bolivia. Other potential markers for AMS namely high-sensitivity C reactive protein (hs-CRP), high-sensitivity cardiac troponin T (hs-cTnT) and neutrophil gelatinase associated lipocalin (NGAL) were also studied. The overarching hypothesis was that Acute Mountain Sickness (AMS) would be associated with fluid retention and elevated BNP and that changes in other hormones involved in fluid balance such as AVP, copeptin and cortisol may also reflect AMS. The hypotheses investigated included;  That BNP would rise with high altitude (HA) illness and be associated with both AMS and a high pulmonary artery systolic pressure (PASP).  That copeptin would accurately reflect changes in AVP at altitude and therefore have utility in future field studies as a surrogate for AVP.  That AMS would be associated with either elevated copeptin/AVP or with failure to suppress the copeptin/AVP response to exercise.  Inflammation and/or rises in PASP occur with the development of high altitude illness and would lead to a detectable rise in hs-cTnT, NGAL or hs-CRP.  The dynamic changes in stress hormones associated with exercise are key in the pathogenesis of altitude illness.  The physiological stress of HA would lead to a rise in cortisol. This would contribute to fluid retention and be linked to the development of AMS.  There would be no difference between total body water (TBW) measured by single or multifrequency bioimpedance analysis. v Methods: This was an observational study with data collection at sea-level and then subsequently over a 10 day ascent from 3800m to 5129m. Daily physiological data was collected with more detailed investigation performed at 3833m, 4450m and 5129m. At these altitudes, data was collected post exercise (after the ascent) and at rest (the following day). Venous blood samples were collected for hormonal assays. BNP and NGAL were analysed in situ using point of care testing technology. Assessment of TBW was performed using bioimpedance devices and pulmonary artery systolic pressure (PASP) was estimated using transthoracic echocardiography. Results and implications: 50 subjects were recruited to the study, 48 of whom were studied at 3833m and 4450m with 47 subjects studied at 5129m. Results presented as mean (range, SD) unless otherwise stated. Significant findings were: Oxygen saturations fell with ascent to altitude to a nadir of 79% (SD 4.4., range 68-88) at 5129m. Fluid balance showed no significant change with altitude or relation to AMS. Plasma osmolality did not change with ascent. AVP and copeptin did not increase until extreme altitude (5129m) and both increased by a greater degree in those recording higher levels of perceived exertion. This was despite no change in osmolality which suggests a non-osmotic stimulus to their secretion. Cortisol secretion increased at 5129m and may support the possibility that the rise in copeptin and AVP was related to physiological stress at extreme altitude. Plasma normetanephrine increased with increasing altitude reaching a maximum of 1423.72 (786.0, 355–4159 pmol/L) at 5129m. Thirst proved difficult to quantify and the visual analogue scale used showed no correlation with total body water, osmolality or AVP. BNP (and NT-proBNP) increased with increasing severity of AMS as assessed by Lake Louise Score (LLS). vi BNP (and NT-proBNP) were higher in those with a high PASP. Hs-cTnT showed an increase with PASP and but no association with AMS. Hs-CRP showed an increase with altitude but no association with AMS. NGAL showed no association with change in altitude. A consistent finding was an evident separation between subjects recording a low Borg score and those recording a Borg rating consistent with “hard work”. Subjects recording a Borg score > 15 (“hard work”) had higher cortisol, AVP, copeptin and an increased LLS. This led to investigation of an additional hypothesis that a higher rating of perceived exertion will lead to an increase in reported AMS symptoms. This was found to be the case with significantly lower SpO2 at rest, higher heart rates and higher LLS in those reporting a Borg RPE > 15.

Several lines of cellular and physiological evidence have suggested the presence of a novel class of systemically mobile plant molecules that are recognized by antibodies generated against vertebrate atrial natriuretic peptides (ANPs). Functional characterization of these immunoanalogues, referred to as immunoreactive plant natriuretic peptides (irPNPs) or plant natriuretic peptides (PNPs), has shown that they play important roles in a number of cellular processes crucial for plant growth and maintenance of cellular homeostasis. Although the various biological roles of PNPs in plants are known, their exact mode of action remains elusive. To elucidate the mechanisms of action for these immunoanalogues, we have prepared a biologically active recombinant PNP from Arabidopsis thaliana (AtPNP-A) and the biological activity was demonstrated by showing its ability to induce water uptake into Arabidopsis thaliana protoplasts. In addition, the molecule was shown to downregulate photosynthesis while at the same time up-regulating respiration, transpiration as well as net water uptake and retention capacities in the sage Plectranthus ecklonii. Further analysis of the recombinant AtPNP-A indicated that the peptide can induce systemic response signalling though the phloem. A recombinant Arabidopsis wall associated kinase-like protein (AtWAKL10) that has a domain organization resembling that of vertebrate natriuretic peptide (NP) receptors was also partially characterized as a possible receptor for the recombinant AtPNP-A. Vertebrate NP receptors contain an extracellular ligand-binding domain and an intracellular guanylate cyclase (GC)/kinase domain and signal through the activity of their GC domain that is capable of generating intracellular cGMP from GTP. The structural resemblance of AtWAKL10 to vertebrate NP receptors could suggest a functional homology with receptor molecules and it is conceivable that such a receptor may recognize PNPs as ligands. The characterization of the recombinant AtWAKL10 showed that the molecule functions as both a GC and a kinase in vitro. This strengthened the suggestion that AtWAKL10 could be a possible AtPNP-A receptor especially considering the fact that AtPNP-A applications to plant cells also
trigger cGMP transients. Furthermore, a bioinformatic analysis of the functions of AtPNP-A and AtWAKL10 has inferred both molecules in plant pathogen responses and defense mechanisms, thus indirectly functionally linking the two proteins.

Atrial natriuretic peptide (ANP) of atrial myocyte origin, has been shown to play a role in the diuresis, natriuresis, and antagonism of angiotensin and vasopressin. However, it is now apparent that in addition to the production of the peptide in the heart and in its role in fluid and electrolyte homeostasis, it is also produced in the central nervous system participating in the regulation of pituitary hormone secretion. Administration of ANP through both central and peripheral routes has been shown to inhibit secretion of luteinizing hormone (LH) in the gonadectomized rat model. A better understanding of the modulatory role of ANP on LH secretion and its possible mechanisms will add to our knowledge of the effects of neuropeptides on reproductive function. Brain natriuretic peptide (BNP) is a bioactive peptide of 26 amino acid residues recently identified in porcine brain. The peptide exerts potent diuretic-natriuretic and vasorelaxant effects, in a manner similar to that of ANP. BNP has a remarkable high sequence homology to ANP, especially in the 17 amino acid ring formed by an intramolecular disulfide linkage which is required for biological activity. The presence of BNP with ANP in the mammalian brain and remarkable resemblance in their molecular structures and physiological functions implies that BNP may also exert an inhibitory effect on LH secretion like ANP. This research focused on the effects of centrally administered ANP and BNP on pulsatile LH secretion and their possible mechanisms of action in ovariectomized rats. After third ventricle infusion of ANP or BNP, inhibition of mean plasma LH level, LH pulse amplitude and pulse frequency was observed. In searching for the possible mechanisms of inhibitory effect of ANP or BNP on pulsatile LH secretion, the effect of inhibiting the endogenous opiate system with naloxone on the action of centrally administered ANP or BNP was tested. Application of naloxone reversed the inhibitory effect of ANP and BNP on mean plasma LH level and LH pulse amplitude, but in terms of pulse frequency, naloxone treatment failed to reverse the inhibitory effect of ANP or BNP. In separate experiments, pretreatment with pimozide, a dopaminergic receptor blocker, prevented the inhibitory action of ANP and BNP on LH secretion. After infusion of ANP or BNP, there were no significant decrease in mean plasma LH level, pulse amplitude and pulse frequency in the pimozide-pretreated rats. In summary, the present study shows that both ANP and BNP inhibit pulsatile LH secretion, suggesting that the inhibitory effects on LH secretion once thought to be mediated by ANP alone may be regulated through a dual mechanism involving both ANP and BNP. Furthermore, the inhibitory mechanisms may involve the interactions of ANP and BNP with central opiate system and dopaminergic system on LH secretion.
Medicine, Faculty of
Obstetrics and Gynaecology, Department of
Graduate

Abstract Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are cardiac hormones, which are involved in the regulation of blood pressure and fluid homeostasis. The major determinant for ANP and BNP release are atrial and ventricular wall stretch, but also some vasoactive factors such as endothelin-1 (ET-1) can enhance cardiac hormone secretion. The mechanical stretch rapidly activates multiple signal transduction pathways in cardiac cells, but the cellular mechanisms mediating stretch-induced ANP secretion are still unknown. The aim of the present study was to examine the cellular mechanisms of autocrine/paracrine factors and stretch-induced ANP secretion. Genistein, a potent protein tyrosine kinase (PTK) inhibitor, rapidly increased cardiac contractile force and ANP secretion in perfused rat heart. This effect of genistein may be unrelated to the inhibition of PTKs since this stimulation was blocked by a L-type calcium channel antagonist and Ca2+/calmodulin-dependent protein kinase II inhibitor. Pregnancy hormone relaxin increased heart rate and ANP secretion in perfused spontaneously beating heart, suggesting that relaxin may have a role in modulating cardiac function. Cellular mechanisms of atrial wall stretch-induced ANP secretion were also studied. This enhanced secretion was blocked by sarcoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin and PTK inhibitor lavendustin A, indicating that thapsigargin sensitive Ca2+ pools and activation of PTK orPTK cascade have an important role in the regulation of stretch-secretion coupling. In addition, protein phosphatase inhibitor okadaic acid accelerated stretch-induced ANP secretion, suggesting that precise balance of protein kinase and phosphatase activity plays a role in mechanical stretch-induced ANP secretion. Finally interactions of endothelial factors regulating ANP exocytosis were studied. The potent nitric oxide synthase inhibitor L-NAME increased basal and atrial wall stretch-induced ANP secretion in the presence of ET-1, suggesting that nitric oxide may tonically inhibit ANP secretion.

Addenda and corrigenda are tipped-in & numbered leaves 281-282. Copies of author's previously published articles are inserted back end paper. Bibliography: leaves 222-279. Studies were performed in the Langendorff-perfused isolated rat heart, using a paradigm in which atrial distension was prevented. The release of natriuretic peptides and endothelin-1, along with cardiac function was monitored during periods of transient ischaemia or hypoxia. Additional studies were performed in patients undergoing cardiac catheterization.

Abstract Ischemic stroke is associated with cardiovascular autonomic nervous system (ANS) disturbances, including reduced heart rate (HR) variability and acute phase neurohumoral activation with elevated stress hormone levels. The impact of HR variability and neurohumoral factors such as natriuretic peptides on the long-term survival of patients with ischemic stroke has not been studied previously. This study was designed to evaluate cardiovascular autonomic regulation in ischemic stroke patients by assessing HR dynamics and various neurohumoral factors. The values of the assessed variables in predicting mortality were evaluated. HR variability assessments were performed in the acute phase of ischemic stroke and for a general elderly population. Various neurohumoral factors were also assessed in the acute phase of stroke. After follow-up, the survival of the subjects was assessed and the prognostic values of the measured factors were evaluated. Stroke patients were found to have cardiovascular autonomic and hormonal disturbances manifested as reduced traditional time and frequency domain measures of HR variability, altered long-term HR dynamics and elevated levels of natriuretic peptides in the acute phase. Altered long-term HR dynamics in the acute phase of stroke predicted long-term mortality after stroke and cerebrovascular mortality in the general elderly population. Neuroendocrine activation involving elevated natriuretic peptide values that were associated with high cortisol and catecholamine levels was observed in the acute phase of ischemic stroke. Neurohumoral disturbance was prognostically unfavourable. The most powerful predictors of poststroke mortality were altered long-term HR dynamics and elevated levels of natriuretic peptides and cortisol, which predicted mortality independently of the conventional risk factors in multivariate analysis. Prognostically unfavourable cardiovascular autonomic dysfunction with disturbances in the long-term behaviour of HR dynamics was found to be related to ischemic stroke. Neurohormonal activation with elevated natriuretic peptide and cortisol levels in the acute phase predicts long-term mortality after ischemic stroke.

Durante a transição menopausal e a pós-menopausa cerca de 75% das mulheres apresentam sintomas de hipoestrogenismo, tais como fogachos. O emprego de terapia hormonal (TH) para alívio dos sintomas da menopausa está bem estabelecido, mas seus efeitos cardiovasculares (CV) permanecem controversos. Dados de estudos recentes indicam a presença de duas populações distintas quanto aos efeitos CV da TH. Essa diferenciação estaria relacionada principalmente com a idade e o tempo de pós-menopausa. Evidências sugerem também que a presença de fatores de risco cardiovascular antes do início do TH, ou de uma associação de fatores de risco, podem ser determinantes dos efeitos CV do TH. Dose de medicação, via de administração e o tipo de progestogênio utilizado em associação com estrogênio para TH também vem sendo estudados como possíveis fatores relacionados ao impacto CV do TH. O presente trabalho é composto por: 1) Ensaio clínico randomizado, comparando os efeitos da via oral baixa dose e via não oral sobre variáveis relacionadas com risco CV em uma população de mulheres saudáveis na pósmenopausa recente; 2) Ensaio clínico randomizado, onde foram avaliados os efeitos da adição de progesterona natural micronizada ao estrogênio não oral durante TH em mulheres na pós-menopausa recente; e 3) Revisão sistemática e meta-análise, onde foram sistematicamente buscados todos os artigos com TH baixa dose que avaliassem os efeitos desta terapia sobre variáveis relacionadas com risco cardiovascular: peso, índice de massa corporal, pressão arterial, proteína C reativa e lipídios. Desenvolvemos ensaio clínico randomizado, cross-over, com objetivo de avaliar os efeitos de dois tipos de tratamento hormonal na menopausa: oral baixa dose, estradiol 1 mg e drospirenona 2 mg diário e não oral, estradiol 17 β gel 1.5 mg (ou nasal 300 mcg) diário e progesterona micronizada vaginal, 200 mg, 14 dias por mês, sobre peptídeo natriurético atrial, variáveis relacionadas com inflamação e função endotelial, perfil antropométrico e metabólico em mulheres na pós-menopausa recente e sem doença clínica evidente. 101 mulheres na pós-menopausa foram alocadas aleatoriamente para iniciar o TH por um dos dois grupos de tratamento: via oral baixa dose (n=50) ou via não oral (n=51). Todas as pacientes utilizaram ambos os TH de forma seqüencial. Após o primeiro período de 2 a 3 meses de TH a paciente passava para o segundo tratamento, sem período de washout. A avaliação laboratorial foi realizada antes e após cada um dos tratamentos. A amostra do estudo foi composta por mulheres com média etária de 51 ± 3 anos e tempo de amenorréia de 22 ± 10 meses. Oitenta e seis pacientes concluíram o estudo. Peso e índice de massa corporal não se modificaram, enquanto que a circunferência da cintura reduziu de forma similar em ambos os grupos de tratamento. Colesterol total e LDL-C reduziram após ambos os TH, e triglicerídeos reduziram somente após a TH não oral. Insulina e glicemia de jejum não se modificaram. Não foram observadas modificações nos níveis de fibrinogênio, fator von Willebrand (FvW) e proteína C reativa (PCR) após TH oral. Após TH não oral, observou-se redução significativa de fibrinogênio e FvW. Níveis de PCR não se modificaram. Houve redução do número de pacientes no maior tertil de PCR (alto risco CV) após TH não oral. Essas pacientes passaram a integrar os grupos de risco intermediário e baixo. Níveis de peptídeo natriurético atrial (PNA) mantiveram-se inalterados após os ambos os TH. Não houve modificações significativas na pressão arterial e esta não se correlacionou com valores de PNA. Realizamos análise adicional do TH não oral, quanto às diferenças entre a via nasal e a percutânea e quanto aos efeitos da adição de progesterona natural micronizada ao estrogênio. Não houve diferenças significativas para todas as variáveis estudadas entre a via nasal e a via percutânea. A adição de progesterona natural micronizada não modificou os efeitos metabólicos e CV do estrogênio não oral. Foi realizada busca sistemática de todos os artigos que incluíssem como TH estrogênio baixa dose e avaliassem os efeitos deste tratamento sobre as variáveis de interesse: peso, índice de massa corporal, pressão arterial, proteína C reativa e lipídeos. Foram consultadas as bases MEDLINE, Cochrane CENTRAL, EMBASE. Foram revisadas todas as referências dos artigos de interesse e revisões e metaanálises no assunto, em busca de artigos relevantes. Após exclusão dos artigos em duplicata, 8610 artigos foram revisados. Destes, 28 artigos foram selecionados para meta-análise. Desta análise foi possível concluir que pacientes em uso de TH baixa dose apresentaram em média menor peso corporal, colesterol total e LDL-C do que não usuárias. A TH baixa dose não apresentou efeitos deletérios sobre demais variáveis estudadas. Em conclusão, ambos os TH apresentaram efeitos neutros ou benéficos sobre variáveis relacionadas com risco CV em uma população de mulheres na pósmenopausa recente e sem evidência de doença CV. A adição de progesterona natural micronizada não modificou os efeitos do estrogênio não oral. Os resultados da metaanálise sobre TH baixa dose e variáveis relacionadas com risco CV também permitem concluir que a TH baixa dose não exerceu efeitos deletérios sobre lipídeos e pressão arterial, e foi observado um possível efeito benéfico deste tratamento sobre o peso corporal.
During the menopausal transition and postmenopause about 75% of women have symptoms of hypoestrogenism symptoms such as hot flushes. The use of hormone therapy (HT) for relief of menopausal symptoms is well established, but its cardiovascular effects (CV) remain controversial. Data from more recent studies suggest the presence of two distinct populations regarding the cardiovascular effects of HT. This differentiation is related mainly to age and time after menopause. Evidence also suggests that the presence of cardiovascular risk factors before the onset of HT, or a combination of risk factors may be determinants of CV effects of HT. Medication dose, route of administration and type of progestin used in combination with estrogen for HT has also been studied as possible factors related to the CV impact of HT. This work consists of: 1) Randomized clinical trial, comparing the effects of low dose oral and non-oral route of variables related to CV risk in a population of healthy women in early postmenopausal; 2) A randomized clinical trial, which we assessed the effects of the addition of natural micronized progesterone to non-oral estrogen for HT in women in early postmenopausal; and 3) systematic review and meta-analysis, which were systematically searched all items with low-dose HT to assess the effects of this therapy on variables related to cardiovascular risk: weight, body mass index, blood pressure, C-reactive protein and lipids. A cross-over, randomized clinical trial was designed in order to evaluate the effects of two types of HT: low dose oral treatment, estradiol oral 1 mg and drospirenone 2 mg, by day and non-oral treatment, estradiol 1.5 mg 17 β gel by percutaneous route (or nasal route 300 mcg) by day and vaginal micronized progesterone, 200 mg/d, 14 days by month on atrial natriuretic peptide, variables associated with inflammation and endothelial function, anthropometric and metabolic variables on early and healthy postmenopausal women. One hundred one women were randomly allocated to start with one of the treatments: low dose oral treatment (n=50) or non-oral treatment (n=51). At the end the first three months period, the patients were crossed over without washout for an additional three months. Laboratory evaluated were carried before and after oral and non-oral HT. The sample of the study included postmenopausal women with a mean age of 51 years and duration of amenorrhea of 22±10 months. Eighty-six patients completed the study. Weight and body mass index remained unchanged, while the waist circumference decreased similarly in both treatment groups. Total cholesterol and LDL-cholesterol reduced after both the HT and triglycerides reduced only after nonoral HT. Insulin and fasting glucose did not change. No changes were observed in the levels of fibrinogen, von Willebrand factor (vWF) and C-reactive protein (CRP) after oral HT. After non-oral HT, there was a significant reduction of fibrinogen and vWF. CRP levels did not change. There was a reduction in the number of patients in the highest tertile of CRP (high CV risk) after non-oral HT. These patients have joined the groups of intermediate and low risk. Levels of atrial natriuretic peptide, ANP, were unchanged after both HT. There were no significant changes on blood pressure and did not correlate with values of ANP. We performed additional analysis of nonoral HT, for the differences between nasal and percutaneous and about the effects of addition of natural micronized progesterone to estrogen. There were no significant differences for all the variables studied between the nasal and percutaneously. The addition of micronized natural progesterone did not modify the metabolic and CV effects of non-oral estrogen. Systematic search of all articles that include as TH low dose estrogen and evaluate the effects of this treatment on the variables of interest was taken: weight, body mass index, blood pressure, C-reactive protein and lipids. The MEDLINE, Cochrane CENTRAL, EMBASE databases were consulted. All references of interest and reviews and meta-analyzes on the subject, in search of relevant articles were reviewed. After removing duplicate articles, 8610 articles were reviewed. Of these, 28 articles were selected for meta-analysis. From this analysis it was concluded that patients using low-dose TH had on average lower body weight, total cholesterol and LDL-C than non-users. The TH low dose showed no deleterious effects on other variables. In conclusion, low-dose oral and non-oral treatments had neutral or beneficial effects on variables related to CV risk in a population of women in early post menopausal and without evidence of CV disease. The addition of micronized natural progesterone did not modify the effects of non-oral estrogen. The results of the metaanalysis of low dose and TH variables related CV risk also showed that the TH low dose did not exert deleterious effects on lipids and blood pressure, and a possible beneficial effect of this treatment on body weight was observed.

Heart failure and left ventricular dysfunction are major causes of morbidity and mortality. In this thesis, metabolic, hormonal, genetic and prognostic aspects of echocardiographically determined left ventricular function were investigated in a fairly large longitudinal population-based study of men. The participants were examined both at age 50 and 70 years and were followed for mortality using the national cause-of-death registry.

Several factors associated with the insulin resistance syndrome predicted left ventricular systolic dysfunction independent of myocardial infarction, hypertension, diabetes and the use of cardiovascular medication after twenty years follow-up. Plasma levels of N-terminal atrial natriuretic peptide (N-ANP) were significantly increased in men with left ventricular dysfunction in comparison to healthy men. However, the diagnostic accuracy was poor due to the extensive overlapping between the groups. Relations between a haplotype of the novel hUNC-93B1 gene and the E/A-ratio were found and validated in separate samples of the cohort. Myocardial performance index (a Doppler derived index of combined left ventricular systolic and diastolic function) and left ventricular ejection fraction were found to be predictors for cardiovascular mortality independent of traditional cardiovascular risk factors in a longitudinal analysis with a mean follow-up of seven years.

In conclusion, this thesis showed that left ventricular function is influenced by metabolic, hormonal and genetic factors and that echocardiographic measurements of left ventricular function, such as the myocardial performance index, are strong independent risk factors for cardiovascular mortality in elderly men.

Le diabète de type 2 (DT2) représente un enjeu de santé publique au regard de ses complications, qui sont des maladies complexes, où interagissent des déterminants génétiques et environnementaux.L'objectif de ce travail était d'étudier ces déterminants dans trois populations indépendantes de patients DT2 en couplant études transversales (DIAB2NEPHROGENE) et longitudinales (SURDIAGENE et DIABHYCAR) totalisant 7767 sujets. Via une approche gène-candidat, nous avons focalisé nos recherches sur le système des peptides natriurétiques, le gène NPR3 (codant le récepteur de clairance aux peptides natriurétiques) et les apports sodés puis la voie métabolique des hormones sexuelles, le gène CYP19A1 (codant l’aromatase) et les concentrations de stéroïdes sexuels. Nous avons montré que l'allèle G du rs2270915 du NPR3 est un allèle de risque de pression artérielle (PA) plus élevée et de moindre sensibilité pressive à la réduction sodée qui ne confère pas d'augmentation significative de risque d'évènements cardiovasculaires (ECV) contrairement au rs6889608. Enfin, la survie sans ECV est significativement modulée par les apports en sel avec un risque de morbi-mortalité réduit chez les sujets diabétiques consommant le plus de sel malgré un niveau de PA plus élevé.Nous avons confirmé que le sexe masculin est un facteur de risque pour la néphropathie diabétique (ND) mais également pour la survenue d'ECV. Nous avons montré, chez les hommes, que des concentrations plus élevés d'oestradiol s'associent à une prévalence plus importante de ND mais ne se traduisent pas par une augmentation des événements rénaux oucardiovasculaires. CYP19A1 n'est associé ni avec les niveaux d'oestradiol, ni avec la prévalence ou la sévérité de la ND. Deux SNP s'associent toutefois significativement avec la survenue d'insuffisance rénale chronique terminale.Au total, nous avons identifié dans 2 voies métaboliques distinctes des déterminants génétiques de complications du DT2 ainsi qu'une interaction gène-environnement
Type 2 diabetes (T2D) is a public health issue because of vascular and renal complications, which are complex diseases with interaction between genetic and environmental determinants.The objective of this work was to study these determinants in three independent populations of T2D patients by coupling cross-sectional (DIAB2NEPHROGENE) and longitudinal studies (SURDIAGENE and DIABHYCAR). Through a candidate-gene approach, we first focused on the natriuretic peptides system, NPR3 gene and sodium intake and then on the metabolic pathway of sex hormones, CYP19A1 gene (coding for aromatase) and sex steroid levels.Our first results showed that NPR3 rs2270915 G Allele was associated with high blood pressure (BP) and a reduced salt-sensitivity of BP. However, this SNP was not associated with any significant risk of cardio-vascular events (CVE) or death, at variance with rs6889608. Ultimately, CVE-free survival was impacted by salt intake with a reduced risk of morbi-mortality in those patients having the greatest intake, though a higher BP.In our second study, we confirmed that male gender was a risk factor for diabetic nephropathy (DN), but also for the occurrence of CVE. In men, we showed higher levels of estradiol (E2) associated with a higher prevalence of ND but without any significant increase in renal or CVE during follow-up. CYP19A1 variants were not associated with either E2 levels or the prevalence of ND. However, 2 SNPs tested, were significantly associated with the occurrence of end stage renal failure. Altogether, we have identified 2 different metabolic ways contributing to the genetic determinants of complications associated with T2D including a gene-environment interaction

Plant natriuretic peptides (PNPs) are a novel class of extracellular, systemically mobile molecules that elicit a number of plant responses important in homeostasis and growth. Natriuretic peptides were first identified in vertebrates where they play a role in the regulation of salt and water balance. Subsequent experimental investigations have identified the presence of a natriuretic peptide hormone system in plants. While PNPs have been implicated in various physiological responses such as stomatal guard cell movements and regulation of net water uptake, its biological role has remained elusive. Here we have used co-expression and promoter content analysis tools to understand the biological role of the Arabidopsis thaliana PNP (AtPNP-A). The analysis of AtPNP-A and its co-expressed genes revealed that genes annotated as part of the systemic acquired resistance (SAR) pathway were over-represented, thus suggesting that AtPNP-A may function as a component of plant defense responses and specifically, SAR. The results further show that AtPNP-A shares many characteristics with pathogenesis related (PR) proteins in that its transcription is strongly induced in response to pathogen challenges, thus implying a newly described role for AtPNP-A in pathogen attack. Additional tissue expression analysis also indicated distinct localization of PNP activity in sepals and transcriptional meta-analysis showed that AtPNP-A may play a role in starch breakdown. Therefore, together with the finding that AtPNP-A plays a role in regulating phloem transport, we also hypothesize that AtPNP-A may play a role in phloem unloading in sepals to assist processes such as seed formation in plants. In plants, the second messenger, guanosine 3&rsquo
,5&rsquo
-cyclic monophosphate (cGMP) mediates a whole range of important processes including salinity tolerance, disease resistance, drought tolerance and responses to light. Since PNPs regulate water and salt homeostasis via a cGMP-dependent signaling pathways, it is thus important to analyse the transcriptome induced by the second messenger (cGMP) in Arabidopsis thaliana to give a better understanding of its mechanism of action. This study was also supplemented by the analysis of the gibberellic acid (GA) dependent transcriptome, since cGMP also plays a role its transcription pathway. This data analysis, together with promoter content investigation, revealed that genes upregulated after cGMP treatment and down-regulated in the GA insensitive mutant (ga1-3) were enriched with a GA response element (GARE), while no GARE enrichment were observed in genes up-regulated in the ga1-3 mutant. These findings suggest that GARE is indicative of GA-induced and cGMP-dependent transcriptional up-regulation. Gene ontology analysis confirmed previous reports that cGMP is involved in ion homeostasis and indicated that the transcriptional cGMP response is bi-polar in the sense that both genes up- and down-regulated in response to cGMP is involved in cation transport. Additionally, ab initio analysis of genes transcriptionally dependent on cGMP identified CHX8 as a hub gene and promoter content of CHX8 co-expressed genes show enrichment of the GARE motif. The fact that CHX8 has its highest expression levels during male gametogenesis and pollen tube growth, together with our findings, suggest that GA-induced and cGMP- dependent genes may play a key role in ion and water homeostasis in the male gametophyte. Finally, we propose that the type of analysis undertaken here can yield new insights into gene regulation networks and inform experimental strategies to unravel complex transcription regulatory systems under different developmental and stimulus specific conditions.

博士
國立臺灣大學
醫學研究所
79
ANP 是晚近被發現的一種心臟賀爾蒙，具有強大的利尿、利鈉與血管擴張作用。 ANP 只貯存在心房特殊顆粒中，當身體需要時即釋放而；出不用時反而有愈積愈多的現象 。這在大鼠禁水的模式裡可以看出，右心房特殊顆粒禁水一週後增加了；而在人類的 標本裡，心房顆粒與鼠類略有差別，它散佈在細胞各處，不集中在細胞核周圍；它數 目少，比較小。 利用血液中具生物活性的α-ANP（1-28胺基酸）去製造單源抗體，所得到的抗體皆為 IgM 亞型，其抗原點與α ANP第 7及23胺基酸之間所形成的雙硫鍵有關。此等抗體皆 具同一抗原點，因此無法建立三明治式的免疫分析，以測定 ANP的濃度，但卻可以 用在組織免疫化學的研究上，以證實 ANP只存在於心房組織而不在心室組織。 使用放射免疫分析法，測知 ANP的濃度在心臟的冠狀靜脈竇最高，其次為右心房，因 此得知心房之 ANP大部分皆自冠狀竇分泌而出，流到右心房以至於全身。心房肌細胞 內， ANP係先以pre pro-ANP 合成，然後送到特殊顆粒貯存時，即變成 pro-ANP；當 分沁澤放到血液中，在我們的觀察，它以兩種分子形態釋出，即17KD的 pro-ANP與3kd的α-ANP，此點隱示，心房組織與血液中均存在有某種蛋白可以分解 pro-ANP 。 ANP 與心臟功能、血流動力學有極密切的關係。心臟病人左心室射出分率與血中ANP 濃度成負相關；左心功能差的， ANP濃度高；左心功能好的， ANP濃度低。自此觀點 ，血中 ANP濃度似可做為臨床上治療心衰竭病人的一個指標。此外，各種心臟病人心 臟腔室血中 ANP的濃度受到其壓力的影響。大致上，右心 ANP濃度與右心房、室壓力 有關；左心 ANP濃度則與肺動脈與左心室壓力有關。先天性心臟病病人，右心 ANP濃 度與自左至右分流量大小有關。 ANP 如同其他賀爾蒙，在正常人有晝夜濃度的差異。主要可見三種型式，第一型為晝高夜 低者，第型為晝低夜高者，第三型無晝夜差別者。其中第一、二型者，與血壓、留鹽 激素、腎素活性存在著複雜的交互調節的關係。有待進一步探討。 心房與心室組織皆同胚胎組織演化發育而來，ANP 的基因胚胎時，在兩種組織表現一 致，而到了出生後，心室即逐漸不再表現，而心房則愈來愈多。吾人從自製的cDNA基 因庫中選殖出全長的ANP cD^1A ，並利用北方墨點法證實心房與心室ANP RNA 確實有 極大的差異，此種差異的分子機轉尚不清楚，進一步研究ANP 基因分子化上的表現， 可作為研究心臟中其他基因表現受成長分化調整的一個模式。 /////// The regulation of ANP gene expression is controlled by development and pathological state. To facilitate the molecular study of ANP gene. We clone ANPcDNA, We isloate mRNA from rat atria. A cDNA library is constructed using loig-dT as primer and λ gt 10 for in-vitro packaging. The titer of the library is determined to be about 2x105 plasma forming unit. We screen thes library using an ANP oligonucleotide (5''-GCTCTCGGCTCCAATCCTGCTAATCCT-3''). Eight positive clones are harvested after secondary screening. Two of them have insert size of about 0.8 kb, which show positive signal on Southern blot. One of ghem is subcloned into plasmid vector (PGEM3Z) and sequenced by dideoxy chain termination method, which is confirmed to be the full length of ANP cDNA (813 bp). Northern blot using RNA from rat atria and ventricles, is hybridized to ANP cDNA, β-actine cDNA and F1 ATPase cDNA. We demonstrate ANP gene is specifically transcribed in atrial tissue. The molecular basis of this differential expression needs clarification.

Die kardialen Hormone Atriales (ANP) und B-Typ (BNP) Natriuretisches Peptid üben bekannte renale und kardiovaskuläre Effekte aus, welche durch ihren gemeinsamen, cGMP-bildenden Guanylatzyklase-Rezeptor A (GC-A) vermittelt werden. Diese Effekte sind entscheidend an der physiologischen Aufrechterhaltung des arteriellen Blutdrucks sowie des intravaskulären Blutvolumens beteiligt. Darüber hinaus zeigen aktuelle Studien, dass NPs die Mobilisierung von Fettsäuren aus dem Fettgewebe und deren Oxidation durch die Skelettmuskulatur steigern sowie die Thermogenese in braunem und weißem Fettgewebe aktivieren können. Dadurch können NPs den Energieverbrauch erhöhen und die Insulinsensitivität verbessern. Desweiteren ist Übergewicht mit einer gestörten NP/GC-A/cGMP-Signalübertragung verbunden, die möglicherweise zur Entwicklung von Diabetes Typ 2 und dessen kardio-metabolischen Folgeerkrankungen beiträgt. In vitro stimuliert synthetisches ANP über GC-A die Glukose-stimulierte Insulinsekretion aus kultivierten pankreatischen Inseln und die β-Zellproliferation. Die Bedeutung für die systemische Insulin/Glukosehomöostase in vivo ist jedoch unklar. Um zu untersuchen, ob die endogenen Herzhormone die sekretorische Funktion und/oder die Proliferation von β-Zellen unter (patho)physiologischen Bedingungen in vivo modulieren, haben wir ein neues genetisches Mausmodell mit selektiver Deletion des GC-A-Rezeptors in β-Zellen (ß GC-A KO) generiert. In kultivierten Inseln von β GC-A KO-Mäusen waren die insulinotropen und proliferativen Effekte von ANP aufgehoben. Übereinstimmend damit führte die Infusion von BNP bei Kontroll-Tieren in vivo zu leicht erhöhten basalen Plasma-Insulinspiegeln und verbesserter Glukose-induzierter Insulinsekretion. Dieser Effekt von exogenem BNP konnte bei β GC-A KO-Mäusen nicht beobachtet werden, was die effiziente Deletion des GC-A-Rezeptors in β-Zellen bestätigt. Interessanterweise hatte die Ablation des GC-A-Rezeptors auf ß-Zellen unter basalen Bedingungen keinen Einfluss auf physiologische und metabolische Parameter in vivo. Sowohl männliche als auch weibliche ß GC-A KO-Tiere zeigten keine Unterschiede in der basalen Insulin- und Glukosehomöostase, da sie ähnliche Nüchtern-Blutzucker- und Insulinspiegel (nach Fasten über Nacht) aufwiesen wie die Kontroll-Mäuse. Allerdings zeigten die mit HFD gefütterten β GC-A KO-Tiere frühzeitiger Glukose-Intoleranz sowie eine verminderte adaptive β-Zellproliferation. Abgesehen davon war das konsistenteste Ergebnis der in vivo-Studien der geschlechtsabhängige Unterschied in der Auswirkung der ß-Zellspezifischen GC-A-Deletion auf die Glukose-stimulierte Insulinsekretion. Weibliche, aber nicht männliche ß GC-A KO-Mäuse zeigten erhöhte Nüchtern-Insulinspiegel und eine signifikant erhöhte Glukose-stimulierte Insulinsekretion, was zu einer deutlich verbesserten Glukosetoleranz führte. Der postulierte und untersuchte Mechanismus beinhaltet eine Interaktion von Östrogenen und NPs, welche die Expression des mitochondrialen Uncoupling Protein 2 beeinflussen. Diese Arbeit erweitert das derzeitige Wissen über die metabolischen Effekte des NP/GC-A-Systems. Insbesondere zeigen die Ergebnisse, dass Natriuretische Peptide zu einer gesteigerten ß-Zellfunktion und Vitalität in frühen Stadien eines erhöhten Insulinbedarfs, d.h. bei Diabetes Typ 2, beitragen. Da die Studien eine wesentliche Rolle dieser kardialen Hormone im endokrinen Pankreas aufdecken, ist es umso wichtiger die pleiotropen Eigenschaften von NPs und ihre möglichen therapeutischen Anwendungen bei kardio-metabolischen Erkrankungen weiter zu untersuchen
The cardiac hormones atrial (ANP) and B-type (BNP) natriuretic peptide exert well-known renal and cardiovascular actions which are mediated by their shared cGMP-forming guanylyl cyclase A receptor (GC-A). These actions are critically involved in the physiological maintenance of arterial blood pressure and intravascular volume homeostasis. In addition, recent studies indicate that NPs can increase fatty acid mobilization from adipose tissue and their oxidation by skeletal muscles and activate a thermogenic program in brown and white fat. Thereby NPs increase energy expenditure and improve insulin sensitivity. Moreover, obesity is associated with impaired NP/GC-A/cGMP signaling, which possibly contributes to the development of type 2 diabetes and its cardiometabolic complications. In vitro, synthetic ANP, via GC-A, stimulates glucose-dependent insulin release from cultured pancreatic islets and β-cell proliferation. However, the relevance for systemic insulin/glucose homeostasis in vivo is not known. To dissect whether the endogenous cardiac hormones modulate the secretory function and/or proliferation of β-cells under (patho)physiological conditions in vivo, here we generated a novel genetic mouse model with selective disruption of the GC-A receptor in β-cells (ß GC-A KO). In vitro, the insulinotropic and proliferative actions of ANP were abolished in islets isolated from β GC-A KO mice. Concordantly, in vivo, infusion of BNP mildly enhanced baseline plasma insulin levels and glucose-induced insulin secretion in control mice. This effect of exogenous BNP was abolished in β GC-A KO mice, corroborating the efficient inactivation of the GC-A receptor in β-cells. Interestingly, the ablation of the GC-A receptor under basal conditions had no effect on physiological and metabolic parameters in vivo. Both male and female ß GC-A KO animals showed no differences in basal insulin and glucose homeostasis, as they have similar fasting blood glucose and insulin levels (after overnight fasting) as the control mice. However, HFD-fed β GC-A KO animals had accelerated glucose intolerance and diminished adaptative β-cell proliferation. Apart from that, the most consistent result of the in vivo studies was the gender dependent difference in the impact of ß-cell GC-A deletion on glucose-stimulated insulin secretion. Female, but not male, ß GC-A KO mice showed enhanced fasted insulin levels and a markedly enhanced glucose-stimulated insulin secretion resulting in a distinctly improved glucose tolerance. The postulated and investigated mechanism involves an interaction of estrogens and NPs affecting expression levels of mitochondrial uncoupling protein 2. This thesis extends the current knowledge of the metabolic actions of the NP/GC-A system. Specifically the results indicate that natriuretic peptides contribute to enhanced ß-cell function and vitality during early stages of increased insulin demand, i.e. in type 2 diabetes. Since the studies show an essential role of these cardiac hormones in the endocrine pancreas, it becomes even more important to further investigate the pleiotropic actions of NPs and their potential therapeutic applications in cardio-metabolic diseases