Apelin

Apelin is an endogenous peptide ligand for the apelin receptor (APLNR, also known as APJ), a G protein-coupled receptor. It acts as a balanced agonist at APLNR, activating both G-protein and β-arrestin pathways. Apelin plays key roles in cardiovascular physiology, including regulation of blood pressure, stimulation of cardiac contractility, and promotion of angiogenesis. Its cardioprotective effects are attributed to Gi signaling through APLNR, while β-arrestin pathway activation may contribute to detrimental cardiac hypertrophy[1][6]. Apelin administration has been shown to improve recovery after myocardial infarction by enhancing contractile function and reducing cellular injury markers[2]. It induces vasodilation primarily via nitric oxide release from endothelial cells but can also cause vasoconstriction depending on vascular bed and conditions[5][8]. Synthetic analogs and biased agonists targeting the apelin-APLNR axis are under investigation for heart failure and other cardiovascular diseases[1][3].