Grhelin is an endogenous ligand for the growth hormone secretagogue receptor from the stomach. It is a 28-aminoacid peptide of which the serine 3 residue is n-octanoylated. Ghrelin strongly stimulates GH secretion in vivo as well as in vitro. This endogenous ligand promotes the production of orexigenic neuropeptides (NPY and AgRP) in the hypothalamic arcuate nuclei and activates the neurons that produce these orexigenic peptides, resulting in an increase in feeding and body weight. Ghrelin has other significant actions, including control of acid secretion, influences on sleep and on the regulation of anxiety.