METABOLIC ACTIONS OF GHRELIN.

Ghrelin, a peptide predominantly produced by the stomach, has been discovered as natural ligand of the GH Secretagogue (GHS) receptor type 1a and supposed to play a major role in the control of somatotroph function. Instead ghrelin turned out to exert pleiotropic actions on several endocrine and non-endocrine target tissues consistently with its widespread expression distribution and that of its receptors. Among its actions, particular attention has been focused on its central orexigenic effect, and more recently on its peripheral metabolic influence on glucose and lipid metabolism. Interestingly, some metabolic ghrelin actions are independent of its acylation supporting the hypothesis of the existence of ghrelin receptors subtypes, distinct from the GHS-R1a. Consistently with its remarkable metabolic impact, ghrelin secretion itself (70% in its non-acylated form) is mostly under metabolic control being modulated by glucose, insulin and feeding. Recent studies suggest the hypothesis that ghrelin system would play a role in type 2 diabetes, metabolic syndrome and atherogenesis.