Endogenous ligand for the apelin receptor (APLNR) (PubMed:10525157).Drives internalization of the apelin receptor (By similarity).Apelin-36 dissociates more hardly than (pyroglu)apelin-13 from APLNR (By similarity).Hormone involved in the regulation of cardiac precursor cell movements during gastrulation and heart morphogenesis (By similarity).Has an inhibitory effect on cytokine production in response to T-cell receptor/CD3 cross-linking; the oral intake of apelin in the colostrum and the milk might therefore modulate immune responses in neonates (By similarity).Plays a role in early coronary blood vessels formation (By similarity).Mediates myocardial contractility in an ERK1/2-dependent manner (By similarity).May also have a role in the central control of body fluid homeostasis by influencing vasopressin release and drinking behavior (By similarity).