hexarelin and Anorexia-Nervosa

The identification and cloning of the receptor for synthetic growth hormone (GH) secretagogues, even before the endogenous ligand has been identified or its precise physiological role established, suggests that there is a novel target of action for this class of drug. In an attempt to select patients who will benefit from GH treatment, GH secretagogues are being evaluated for their usefulness in diagnosing GH deficiency. The effects of GH-releasing peptides (GHRPs) on GH release as a function of age and metabolic status, and in different neuroendocrine pathologies, are described, as are the different mechanisms of action, potency and reproducibility of the response to GHRPs compared with GH-releasing hormone (GHRH). GHRPs offer the advantage over GHRH in natural models of deranged GH secretion in that, in various metabolic states (e.g. obesity, anorexia nervosa and non-insulin-dependent diabetes mellitus), the GH response to GHRH is more impaired than it is to GHRPs. However, in some neuroendocrine pathologies, the reverse is true. Thus, both secretagogues provide separate information on the physiological status of somatotrophs.

Topics: Anorexia Nervosa; Endocrine System Diseases; Growth Hormone-Releasing Hormone; Human Growth Hormone; Humans; Oligopeptides

Anorexia nervosa (AN) is a chronic disease in which an enhanced GH response to GHRH, a paradoxic increase after TRH and LHRH, and low IGF1 levels may be present according to the patient's clinical state. It is well known that the GH hypersecretory state commonly found in the "acute phase" of AN is restored with weight gain. The new synthetic hexapeptide, Hexarelin (HEX), which is chemically similar to GH-releasing peptide 6, has recently been shown to possess a stronger GH-releasing activity than GHRH in humans and to share a synergistic effect with GHRH when administered intravenously. Indeed, HEX shows a slight cortisol and PRL-releasing activity. The aim of the study was to evaluate the effect of i.v. administration of old (GHRH) and new (HEX) GH-releasing peptides on GH, PRL and cortisol secretion in 9 AN patients in the "recovery phase" of the disease, after partial but significant weight gain. For controls we studied 7 normal cycling women. No significant difference in GH secretion after GHRH was found between AN and controls. GHRH was not able to release cortisol or PRL either in AN or controls. HEX produced a significantly (p < 0.05) higher GH peak in controls than in AN, while GH AUC was slightly but not significantly higher. Indeed, only in controls, HEX was a stronger GH-releasing peptide than GHRH. These findings could be explained by the fact that, in AN, GH secretion is already stimulated both by reduced IGF1 levels and by increased GHRH/somatostatin ratio. As reported in the literature, the action of HEX action is only slightly influenced by variations in somatostatin tone. It therefore appears likely that the absolute or relative GHRH increase present in AN could partially mimic the unknown hypothalamic factor necessary for HEX action on the hypophisis and that, following a structural modification of pituitary HEX receptors, GHRH would become able to bind to HEX receptors on somatotropic cells. Consequently, the pituitary cells would already be over-activated and so unable to respond maximally to HEX stimulation. Indeed, in AN, GHRH might play a role of negative modulation in the control of HEX action. Finally, in our study HEX was able to produce a persistent PRL release in controls but not in AN, thus suggesting that its action could be partially dependent on the estrogen milieu, while it stimulated cortisol secretion only transiently in the patients studied.

Topics: Adolescent; Adult; Anorexia Nervosa; Area Under Curve; Female; Gonadotropin-Releasing Hormone; Growth Substances; Human Growth Hormone; Humans; Hydrocortisone; Infusions, Intravenous; Oligopeptides; Prolactin

Both the basal levels and the neuroregulation of GH secretion are perturbed in patients with anorexia nervosa. It is unknown if these alterations are due to severe undernutrition or if they reflect basic neurotransmitter alterations of the patient's neural pathways. On the other hand, prior administration of the GH secretagogue hexarelin in normal subjects blocks the GH-releasing capability of GH releasing hormone (GHRH) administered 2 hours later. In the present work a sequential test was performed using the administration of hexarelin as first stimulus followed 120 minutes later by GHRH. The two aims of the study were: (a) to evaluate the interaction of GHRH and hexarelin, and (b) to further understand the alterations in GH neuroregulation in patients with anorexia nervosa.. The GH stimuli used were hexarelin (1 micrograms/kg i.v.), a GH stimulus whose main action is hypothalamic, followed 120 minutes later by GHRH (1 micrograms/kg i.v.) as a pituitary stimulus. Each woman was tested once.. Thirty-two woman matched for age participated in the study: six normal-weight women as controls, 14 women with anorexia nervosa, seven women with secondary amenorrhoea due to voluntary weight loss for aesthetic reasons, and five normal-weight women after 72 hours of a controlled hypocaloric diet (800 cal/day).. Plasma GH levels were measured by time-resolved fluoroimmunosasay, each value shown is the mean +/- SE in mU/l.. The administration of hexarelin to the normal-weight women induced a clear-cut GH secretion (expressed as mean +/- SE of GH peak in mU/l of 77.5 +/- 21.8, but blocked the GH-releasing capability of GHRH administered 120 minutes later (6.6 +/- 2.8, P < 0.05). In contrast, the women with anorexia nervosa showed a normal GH response after the two stimuli: hexarelin 64.8 +/- 9.2. GHRH 71.1 +/- 14.2. The absence of heterologous desensitization was specific to anorexia nervosa, because the women with amenorrhoea due to voluntary weight loss but with a normal energy intake showed a pattern similar to the controls (GH after hexarelin 60.3 +/- 9.5 and to GHRH 120 minutes later 6.2 +/- 1.0 (P < 0.05)). Similarly, the women after the short-term hypocaloric diet showed a hexarelin-mediated GH secretion of 99.6 +/- 17.8, which blunted the subsequent administration of GHRH (GH mean peak of 9.9 +/- 2.9, P < 0.05 vs hexarelin).. In the normal subjects, the administration of hexarelin induced clear-cut GH secretion, but inhibited the action of GHRH when administered 120 min later, while this heterologous desensitization was not observed in the patients with anorexia nervosa. This sequentially delayed test may be of some value in the clinical setting for assessing the status of patients with anorexia nervosa.

Topics: Adult; Amenorrhea; Anorexia Nervosa; Female; Growth Hormone; Growth Hormone-Releasing Hormone; Growth Substances; Humans; Hypothalamus; Oligopeptides; Pituitary Gland; Stimulation, Chemical; Time Factors