APJ is a seven-transmembrane G protein coupled receptor. Apelin is an endogenous ligand of APJ [1]. It is well known that Apelin and APJ receptor are widely distributed in a variety of organs including the heart, brain, kidney, stomach, lung, adipose tissues, endothelium, vascular smooth muscle cells, testis, ovary, and gland, particularly in the cardiovascular system. The Apelin/APJ system plays multiple important roles in various physiological and pathological processes such as regulation of blood pressure, cardiac contractility, water homeostasis, immunity, glucose metabolism, fat metabolis...
