Ghrelin

Ghrelin, a polypeptide in the central nervous-digestive organ axis system, was first isolated from the stomach tissue of rats Ghrelin. It was later used as an endogenous ligand with a very high affinity for the growth hormone secretagogue receptor (GHS-R). It has long been thought that pituitary growth hormone (GH) is regulated only by two endogenous polypeptides: growth hormone releasing hormone (GHRH) and inhibitor of somatostatin (SRIF). However, in 1984, a synthetic hexapeptide was found to be effective in stimulating the release of hypothalamic growth hormone by binding to the corresponding receptor. Subsequent studies have shown that some synthetic non-peptide substances such as MK-0677 and natural peptides can effectively promote the release of GH through pathways other than GHRH. Ghrelin is a 28 amino acid peptide chain, and the third serine at the amino terminus is acylated with octanoic acid to give ghrelin the ability to release growth hormone. After acylation, ghrelin becomes hydrophobic and is able to enter the central nervous system, where it regulates the release of growth hormone by binding to the corresponding receptors located in the hypothalamus and pituitary. When ghrelin specifically binds to its receptor, the third serine group at the amino terminus modified by acylation guides the recognition between the ligand and the acceptor molecule, and the hydrophobic group determines the maximum antagonistic activity of the molecule.