Recent identification of novel appetite-regulating hormones has revealed the complex interactions between these humoral factors in the regulation of feeding behavior in mammals. One such hormone is ghrelin, which is a natural ligand of the orphan growth hormone secretagogue receptor. Ghrelin was first purified from rat stomach and is able to stimulate growth hormone release from pituitary cells. Ghrelin is a peptide of 28 amino acids, in which Ser3 is modified by an n-octanoic acid. This modification is essential for the activity of ghrelin. The peptide regulates food intake by acting on the hypothalamic arcuate nucleus, which is a region known to control food intake. Thus, gastric ghrelin is an endogenous regulator of feeding behavior that is found in both peripheral tissues and the central nervous system.