Apelin, the endogenous ligand of APJ which is a member of G protein-coupled receptors, has been shown to be expressed in a variety of tissues in vivo and to exert significant biological effects. Studies have indicated that the apelin/APJ system is involved in the regulation of a variety of physiological functions and pathological processes, and that it is associated with cardiovascular diseases (such as atherosclerosis, hypertension, heart failure and myocardial injury), diabetes with microvascular complications, ischemia reperfusion injury, tumors, pre-eclampsia, as well as others. The occurr...