Aspects of the neuroendocrine control of somatotropic function in calorically restricted dogs and patients with eating disorders: studies with cholinergic drugs

Abstract

A series of studies was devised in both an experimental model of food deprivation, i.e., beagle dogs undergoing a progressive reduction of calorie intake and adolescent females with anorexia nervosa (AN) in the acute and recovery phase, and in patients with atypical eating disorders. The studies were aimed at ascertaining whether the alleged function of the hypothalamic system inhibitory to growth hormone (GH) secretion, i.e., the somatostatinergic, may account for at least some of the abnormalities of GH secretion present in AN patients (e.g., elevated basal GH levels, paradoxical GH rise after glucose or thyrotropin releasing hormone, etc). Caloric restricted dogs or patients with eating disorders were given an intravenous injection of the physiologic GH-releasing peptide GHRH alone or preceded by pirenzepine, a muscarinic cholinergic antagonist reportedly capable of eliciting hypothalamic release of somatostatin (SS), or pyridostigmine, a muscarinic cholinergic agonist which, conversely, would restrain hypothalamic release of SS. In addition, dogs were challenged with acute administration of glucose or thyrot-ropin-releasing hormone, compounds also thought to act via somatostatinergic influences. Data obtained in dogs under caloric restriction or in AN patients in the acute phase of the disease with drugs affecting cholinergic transmission suggest that the latter is increased in both conditions (only partial suppression of the GHRH-induced GH rise with pirenzepine, failure of pyridostigmine to further enhance the GH response to GHRH). Instead, in the same AN patients in the acute phase tested during recovery, in AN patients during the recovery phase, and in patients with atypical eating disorders, pirenzepine completely suppressed the GH response to GHRH, as it did in controls. Finally, data obtained on basal and GHRH-stimulated GH release in dogs given glucose or thyrot-ropin-releasing hormone and in AN patients given arginine, another compound thought to act via inhibition of somatostatinergic influences, do not support the view that somatostatinergic function is impaired in states of food deprivation.