The apelin receptor gene, also known as APJ or angiotensin receptor-like 1, was first cloned in 1993. APJ has strong sequence homology with the angiotensin II receptor (AT1); 54% for intrans membrane domains and 31% for the entire sequence. Nevertheless, APJ does not bind with angiotensin II. In 1998, Apelin, the first endogenous ligand for APJ, was identified in bovine stomach extracts. Both apelin and APJ are widely expressed in various tissues including the heart, brain, limbs, retin...