Growth hormone-regulatory peptides (GHRH and somatostatin) and feeding: a model for the integration of central and...

The present paper provides an overview of findings that implicate growth hormone-releasing hormone (GHRH) and somatostatin (SS), the two peptides that regulate growth hormone secretion, in the central regulation of feeding. Evidence is presented that GHRH and SS increase food intake, in the rat, via a common centrally mediated mechanism involving the suprachiasmatic nucleus. Food intake is increased by increasing motivation to eat as evidenced by facilitation of operant behavior. Macronutrient-choice studies indicate that GHRH (and possibly SS) selectively facilitate protein consumption. Time of day is also important, with evidence that endogenous GHRH and SS-induced feeding is most strong in the early nocturnal period. GHRH and SS, together with other nutrient-specific signals, such as neuropeptide Y, noradrenaline and galanin, may determine the circadian expression of food intake in animals. Other behavioral and physiological effects of these peptides, both central and peripheral, are reviewed in the context of a possible mechanism by which these peptides integrate diverse, but complimentary, central and peripheral functions related to nutrition, metabolism and growth.