Endogenous APJ receptor agonist (EC50 = 20 nM) that is secreted by adipocytes. Binds with high affinity to human APJ receptors expressed in HEK-293 cells (pIC50= 8.61). 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.