ghreline

Ghrelin is a peptide hormone produced mainly by X/A-like cells in the stomach. It serves as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R1a) and plays a key role in stimulating appetite and regulating energy balance. The spelling ghreline is encountered occasionally, but ghrelin is the standard term for the hormone.

Ghrelin exists in two major forms: acylated ghrelin, which is octanoylated at serine-3 and is active at GHS-R1a, and desacyl ghrelin, which lacks the acyl group and has unclear or distinct receptor activity. The acylation is carried out by the enzyme ghrelin O-acyltransferase (GOAT). The gene GHRL encodes the ghrelin precursor, which is processed to these mature forms.

Ghrelin acts by binding to GHS-R1a in the hypothalamus and other brain regions to stimulate growth hormone release and promote hunger. It also influences gastric motility, energy expenditure, and may affect reward pathways and glucose metabolism. Circulating ghrelin levels rise during fasting and fall after meals, with a circadian pattern that includes a nocturnal peak.

Ghrelin was identified in 1999 by Kojima and colleagues as the endogenous ligand for the growth hormone secretagogue receptor. Clinically, ghrelin and its signaling pathway have been explored as targets for conditions such as cancer cachexia and anorexia, with ghrelin agonists investigated to stimulate appetite and weight gain. Ongoing research continues to clarify the distinct roles of desacyl ghrelin and potential alternative receptors.