Apelin, the endogenous peptide ligand of the APJ receptor, is expressed in brain regions implicated in food and water intake. The APJ receptor belongs to a family of 7-transmembrane G-protein coupled receptors.The ligand was named “apelin” after APJ endogenous ligand.

Apelin and APJ are widely expressed in homogenates from animal organs in a pattern shared with angiotensinogen and the angiotensin receptor. Apelin is widely distributed in the CNS and periphery, especially in the heart, kidney, lung and mammary glands.present study investigated basal plasma levels of apelin, orexin-A, and leptin in morbid obese patients.

Apelin-12, one of the most potent apelin peptides, lowers blood pressure via a nitric oxide-dependent mechanism. It is also involved in the central control of feeding by stimulating cholecystokinin (CCK) secretion. Apelin-12 levels also were inversely correlated with levels of nt-proBNP.