[Ghrelin and GH secretion]

Ghrelin is an acylated peptide recently isolated from rat and human stomach that potently stimulates GH release in vivo and in vitro in rats and humans. Ghrelin specifically activates the receptor for the growth hormone secretagogues (GHS) and it has been proposed that it may be the endogenous ligand mimicked by these synthetic compounds. Ghrelin is primarily produced in endocrine cells of the stomach, and to a lesser extent, in other peripheral tissues, including the pituitary. Although ghrelin is the most potent GH-secretagogue so far identified, its circulating levels do not correlate with those of GH either in physiological and pathological conditions. Because of these and many other observations, it may be postulated that ghrelin is not physiologically involved in the regulation of growth hormone secretion. Nonetheless, ghrelin may serve as a very useful model for the development of more potent synthetic GHS, which may be therapeutically useful for the treatment of human GH deficiency.