Purification and Distribution of Ghrelin: The Natural Endogenous Ligand for the Growth Hormone Secretagogue Receptor

Growth hormone secretagogues (GHS) are small synthetic molecules that act through a specific G-protein coupled receptor (GPCR) termed GHS-R, which is a distinct receptor from that of growth hormone releasing hormone (GHRH). This receptor was one of the orphan GPCR, i.e. a GPCR with no known natural ligand, until we purified its endogenous ligand from rat stomach and named it "ghrelin". Ghrelin is a 28-amino-acid peptide, in which the serine 3 is modified by an n-octanoic acid and this modification is essential for ghrelin's activity. The discovery of ghrelin indicates that the release of GH from the pituitary may be regulated not only by hypothalamic GHRH, but also by ghrelin from the stomach and hypothalamus.