The metabolic hormones ghrelin, growth hormone, and insulin-like growth factor I are influenced by developmental age, sex, and nutritional status in domestic and free-ranging species. However the role these hormones play has not previously been explored in sub-tropical/ tropical mammals. Furthermore, the seasonality of species with less dynamic environmental cues, such as the West Indian manatee, have not been studied. The West Indian manatee is and endangered species distributed in the southeastern United States and throughout the Caribbean basin, and its nutritional physiology is influenced by environmental factors. Understanding the hormone response to nutritional status in this species and its seasonality will enhance our knowledge of the links between season, nutrition, and life history. The purpose of this research is to understand the biology and seasonal patterns of metabolic hormones in free-ranging manatees which will allow us to assess the nutritional status of wild populations. The research objectives include validation assays to accurately quantify hormone concentrations in manatees. Hormones were quantified in manatee serum using heterologous radioimmunoassay. Hormones were then evaluated between summer, fall, and winter and compared to body composition. Developmental patterns were also assessed. Lastly, hormones were examined between Florida and Antillean manatee populations. Manatees exhibited differences in GH, IGF-I, and body composition demonstrating seasonality similar to other species. Manatees exhibited differences between age classes suggesting decreased growth rate as the animals age. Differences were detected between populations. This research suggests that ghrelin, GH, and IGF-I can be used to indicate nutritional status and detect seasonality and developmental age in the manatee. This could prove to be a valuable tool in rehabilitation facilities and during captures and health assessments to provide better veterinary care and further improve overall health and body condition to better manage the survival of the species.

Title: Acipimox during Short-Term Exercise Exerts A Negative Feedback of Growth Hormone on Ghrelin Secretion in Patients with Bulimia Nervosa and in Healthy Women: The Role of Lipolysis Objective: Eating disorders, such as bulimia nervosa (BN) and anorexia nervosa (AN), are characterized by abnormal eating behavior. The main features of BN are binge-eating and inappropriate compensatory methods to prevent weight gain. The appetite-modulating peptide ghrelin is secreted by the stomach and shows a strong release of growth hormone (GH). A potential GH-ghrelin feedback loop between stomach and the pituitary has been recently reported. Acipimox (Aci), an analogue of nicotinic acid, inhibits lipolysis in adipose tissue (AT) and reduces plasma glycerol and free fatty acids (FFA) levels. Exercise and Aci are stimulators of GH secretion. We suppose that a negative feedback from increased GH levels during exercise may play a role in reducing plasma ghrelin levels. We surmised that altered baseline activity and exercise-induced activation of the sympathetic nervous system (SNS) results in excessive stimulation of lipolysis associated with negative energy balance and may lead to abnormal AT metabolism in patients with BN. Disruption of the gut-brain-AT axis might be involved in the pathogenesis of BN. The...

La première cause de maigreur chez les femmes dans les pays occidentaux est l’anorexie mentale (AM). La maigreur constitutionnelle (MC) regroupe des femmes d’Indice de masse corporelle identique aux AM mais sans les anomalies psychologiques, biologiques ou hormonales (pas d’aménorrhée) rencontrées dans l’AM. Les troubles du comportement alimentaire (TCA) comprennent l’AM restrictive pure (AM-R), l’AM avec crises boulimiques (AM-BP) et la boulimie nerveuse (BN). Notre travail explore ces troubles à la lumière de la régulation de l’appétit dont le centre organique (noyau arqué) reçoit des afférences de peptides périphériques tels que la leptine, le PYY, le GLP1 , la ghréline et l’obéstatine. Nous montrons un profil orexigène dans l’AM-R, témoignant d’une intégrité du système de régulation de la prise alimentaire et adaptatif, luttant contre la restriction alimentaire. Nous avançons le concept de ghrélino-résistance dans l’AM-R dont le substratum biologique est peut-être l’obéstatine. Nous montrons une ghréline basse chez les AM-BP comme chez les BN permettant un diagnostic différentiel précis et rapide. A l’inverse, nous montrons un profil anorexigène constitutif chez les MC participant au maintien du poids bas, proposant la MC comme un modèle humain de résistance à la prise de poids. Ces hormones peuvent agir comme arbitre organique objectif entre des entités cliniques parfois à tort confondues. Une leptine basse chez une jeune fille maigre signe une AM, une ghréline basse chez une AM signe la présence de crises boulimiques. Ces éléments forts nous poussent à continuer notre travail de précision et de phénotypage de ces entités pour mieux en comprendre la physiopathologie / The commonest group of underweight young women in the developed world is restrictive anorexia nervosa (AN). However, constitutional thinness (CT) is a condition described in the same low weight range as AN. CT women display normal menstruation an do not present with psychological or hormonal features of AN. Eating disorders (EA) displays Anorexia Nervosa with restrictive food behaviour (AN-R), Anorexia Nervosa with binge purge associated (AN-BP) and bulimia Nervosa (BN ). Food intake is controlled by the arcuate nucleus through integration of peripheral hormonal signals such as leptin, ghrelin, peptide YY (PYY) and glucagon like peptide 1 (GLP-1). Our objective was to understand thinness and EA through those hormonal signals. AN-R presents an orexigenic adaptative profile contrasting with the anorexigenic constitutive one in CT, proving the integrity of the appetite regulation system. We propose the ghrelin resistance concept with the putative obestatin. AN-BP presents a very different profile of appetite regulatory peptides when compared with AN-R, with low ghrelin levels. The hormones appear to be valuable biomarkers to distinguish AN and CT in severe underweight patients and to diagnose binge purge in AN. The assessment of ghrelin (and eventually obestatin) could be of particular interest for differential diagnosis between AN-R and AN-BP. The assessment of leptin could also be useful for differential diagnosis between AN and CT

La ghréline acylée, une hormone produite par l’estomac, favorise la prise de poids corporel, majoritairement sous forme de masse grasse, par le biais de divers mécanismes centraux et périphériques via le récepteur sécrétagogue de l’hormone de croissance (GHSR). Le GHSR est un récepteur couplé aux protéines G qui, en plus de répondre à la ghréline acylée, possède une signalisation indépendante de la ghréline par le biais de son activité constitutive ou par une modulation de réponses dopaminergiques via oligomérisation du GHSR avec des récepteurs dopaminergiques. Malgré les puissantes réponses pharmacologiques à la ghréline acylée, des modèles animaux capables d’appréhender la complexité du système ghréline acylée-GHSR in vivo manquent, ce qui a considérablement ralenti l’élucidation des rôles physiologiques de cette hormone et de son récepteur. En effet, les modèles génétiques murins générés jusqu’à présent manquent de spécificité au niveau de l’hormone (incapacité à discriminer la ghréline acylée de la ghréline désacylée), et/ou au niveau du GHSR (incapacité à discriminer les différents modes de signalisation du GHSR). Dans ce contexte, de nouveaux modèles qui impacteraient de façon différentielle les voies de signalisation du GHSR seraient des outils pertinents pour contribuer au déchiffrage du système ghréline acylée-GHSR in vivo. Nous nous sommes ainsi attachés à caractériser un modèle de rats porteur d’une mutation ponctuelle dans le Ghsr qui prédit la délétion d’un domaine régulateur dans l’extrémité C-terminale du GHSR (GhsrQ343X). Dans des modèles cellulaires, nous avons montré que cette mutation découple le GHSR des processus d’internalisation du récepteur et de recrutement de la β-arrestine induits par la ghréline acylée, tout en augmentant la réponse aux agonistes du GHSR dans la voie des protéines G. Conformément à ce mécanisme, les rats mutants homozygotes GhsrM/M ont une réponse accrue à l’administration d’agonistes du GHSR sur le plan de la libération d’hormone de croissance, de la prise alimentaire ou de l’activité locomotrice. L’exploration physiologique et comportementale des rats GhsrM/M indique que la mutation GhsrQ343X est associée à une augmentation du poids et de l’adiposité indépendamment de la prise alimentaire, une diminution de l’oxydation globale des acides gras, de la flexibilité métabolique et de la tolérance au glucose, sans impact critique sur la prise alimentaire homéostatique. En outre, étant donné que la mutation GhsrQ343X n’augmente pas les niveaux circulants de ghréline, le phénotype métabolique général des rats GhsrM/M est en accord avec une sensibilité augmentée du GHSR en réponse au tonus endogène de ghréline acylée. Enfin, des résultats préliminaires suggèrent que la mutation GhsrQ343X pourrait être associée à des altérations relatives aux fonctions de récompense et de mémoire dont les mécanismes sous-jacents restent à décrypter. En résumé, nous proposons le modèle de rat mutant GhsrQ343X comme un nouvel outil, plus spécifique que les modèles murins d’invalidation génétique, pour explorer in vivo la signalisation du GHSR dans diverses fonctions biologiques, et à plus long terme aider au design de composés pharmacologiques ciblant le GHSR efficaces dans un cadre clinique. / The stomach-derived hormone acyl ghrelin promotes body weight gain, mostly in the form of fat mass, by means of several central and peripheral mechanisms mediated by the growth hormone secretagogue receptor (GHSR). The GHSR is a G protein-coupled receptor that, in addition to respond to acyl ghrelin, displays agonist-independent signaling through high constitutive activity and possibly heteromerization with dopamine receptors. Despite the potent biological properties of exogenous acyl ghrelin, the lack of animal models able to apprehend the complexity of the acyl ghrelin-GHSR system in vivo has been hampering the elucidation of its physiological roles. Indeed, genetic mouse models generated so far lack specificity either at the level of the hormone (not able to discriminate between acyl ghrelin versus desacyl ghrelin) and/or at the level of the GHSR (not able to discriminate between GHSR signaling modes). In this context, new models differentially affecting GHSR signaling pathways would represent valuable tools to decipher the acyl ghrelin-GHSR system in vivo. We therefore aimed at characterizing a new rat model carrying a point mutation in Ghsr that predicts truncation of a regulatory domain in the C-terminus, the GhsrQ343X mutation. In cellular models, this mutation was found to uncouple the GHSR from agonist-dependent receptor internalization and β-arrestin recruitment, while enhancing GHSR responsiveness in the G protein pathway. Accordingly, homozygous mutant GhsrM/M rats show enhanced responsiveness to exogenous GHSR agonists in terms of growth hormone release, food intake and locomotor activity. Physiological and behavioral exploration of GhsrM/M rats supports that the GhsrQ343X mutation is associated with increased body weight gain and adiposity independently of calorie intake, reduced whole-body fat oxidation, metabolic flexibility and glucose tolerance, without any critical impact on homeostatic feeding behavior. Moreover, given that circulating ghrelin levels are not increased by the GhsrQ343X mutation, the overall metabolic phenotype of GhsrM/M rats is consistent with enhanced GHSR sensitivity to the endogenous tone of acyl ghrelin. Furthermore, preliminary results suggest that the GhsrQ343X mutation could be associated with behavioral alterations related to reward and memory functions, through mechanisms that remain to be elucidated. Altogether, we propose the GhsrQ343X mutant rat model as a novel tool, more specific than knockout mouse models in its mechanism-of-action, to explore GHSR signaling across biological functions in vivo, and ultimately help in the design of efficient GHSR-targeting drugs.

Bypass or resection of the stomach and oesophagus, has long been recognised to result in profound changes in the handling of ingested nutrients. This results in significant morbidity after radical surgery for oesophago-gastric cancer, in particular post-prandial hypoglycaemia, altered appetite, early satiety and noxious post-prandial symptoms. By profiling and challenging the gut hormone axis in healthy volunteers and patients who had undergone total or subtotal gastrectomy, or oesophagectomy, this thesis explores the possible causative mechanisms for the challenges faced by this patient population. In the surgical groups, an oral glucose tolerance test (OGTT) resulted in enhanced secretion of satiety and incretin gut hormones (GLP-1, GIP, PYY) and insulin, followed by hypoglycaemia in a cohort of patients. Continuous glucose monitoring of gastrectomy participants over two weeks of normal lifestyle identified an increased incidence of day and night time hypoglycaemia. RNAseq and mass spectrometry based peptidomics of human and murine enteroendocrine cells in the pre- and post-operative populations revealed no significant change in the underlying cellular pathways for nutrient sensing and gut hormone secretion, indicating that the altered hormone secretion is primarily driven by accelerated nutrient transit, rather than adaptive changes in the gut. Finally, specific blockade of the GLP-1 receptor in post-gastrectomy patients using Exendin 9-39 normalised insulin secretion and prevented reactive hypoglycaemia after an OGTT. In conclusion, profound changes in gut hormone secretion as a result of enhanced nutrient transit after foregut surgery likely underlie the early and late post-prandial symptoms seen in this group, and therapies specifically targeting the gut hormone axis, and GLP-1 in particular, could be the first targeted treatments for post-gastrectomy syndromes.