The apelin gene encodes a pre-proprotein that is processed to generate bioactive peptides consisting of 36, 17, or 13 amino acids: apelin-36 , apelin-17, and apelin-13 , respectively. Apelin-13 is an endogenous ligand of the APJ receptor, activating this G protein-coupled receptor with an EC50 value of 0.37 nM. (Glp1)-Apelin-13 is a pyroglutamylated form of apelin-13, in that the N-terminal glutamine residue is cyclized to pyroglutamic acid. Like apelin-13, this compound is a potent APJ receptor agonist (EC50 = 0.30 nM). (Glp1)-Apelin-13 is the major apelin isoform in the plasma of healthy human subjects. It can have vasoconstrictor and antipyretic effects in vitro and in vivo.
