Endogenous APJ receptor agonist that is secreted by adipocytes. Binds with high affinity to APJ receptors (IC50 = 5.4 nM) and potently inhibits cAMP production in vitro (EC50 = 0.52 nM). Involved in regulation of cardiovascular function, fluid homeostasis and feeding. Blocks entry of some HIV-1 and HIV-2 strains into NP-2/CD4 cells expressing APJ. MW (observed): 4200.93.