Role of Ghrelin in Regulation of Growth Hormone Secretion by Ghrelin-pituitary-gh Axis Linkage

Background: Ghrelin is the endogenous ligand of the growth hormone (GH) secretagogue receptor and is the first hormone linking gastrointestinal-pituitary axis. Actions of ghrelin on GH secretion provide a strong force for envisioning that one of the major role of ghrelin could be the regulation of secretion of GH. Aims & Objective: To explore the intriguing dimensions on the possible physiological role of the Ghrelin /GHRP system. Materials and Methods: The search was performed in electronic databases (Medline, Embase, Cochrane, Google scholar) and by hand searching by 2 reviewers. Clinical trials (Randomised and non-randomised trials), review articles, systematic reviews, conference proceedings and meta-analysis were included in the study. Results: Ghrelin stimulates strong increase in circulating GH levels both in vitro and in vivo in a dose-dependent manner. Human or animal ghrelin was found to be significantly more potent than a synthetic GHS, hexarelin. The regulation of GH by Ghrelin is influenced by various other factors like autonomic nervous system, GHRH, IGF-1, anterior pituitary hormones, obesity, etc. Conclusion: Ghrelin is a specific endogenous ligand for the GHS receptor and suggests the existence of a GHS–GHS receptor signaling system in the regulation of GH secretion. Stomach-ghrelin pituitary-GH axis links nutritional intake to regulation of GH secretion. However, the mechanism underlying the feedback actions of GH on the regulation of ghrelin remains unanswered. Under physiological conditions, ghrelin administered either centrally or peripherally, exerts a potent, time-dependent stimulation of pulsatile secretion of GH by ghrelin-pituitary-GH axis.