A peptide hormone that is secreted chiefly by cells in the stomach lining when the stomach is empty, and increases hunger by stimulating the release of neuropeptide Y, a potent stimulant of appetite, from the arcuate nucleus in the hypothalamus. It also stimulates release of growth hormone by binding to receptors (called growth hormone secretagogue receptors) in the anterior pituitary. Ghrelin thus opposes the appetite-suppressive effects of the hormones insulin, leptin, and peptide YY. It is synthesized as a prohormone and processed to yield a 28-amino-acid peptide modified by the addition of n-octanoic acid. The concentration of ghrelin in blood rises during the fasting period before a meal, thereby promoting appetite. Paradoxically, it also appears to suppress the mobilization of fat reserves in adipose tissue. Its role in regulating the body’s energy balance has prompted interest in ghrelin as a potential target for anti-obesity treatments.