Endothelins are a family of vasoactive peptides that includes ET-1, ET-2 and ET-3. To date, two subtypes of endothelin receptors have been identified from mammalian cells, EDNRA (ETA) and EDNRB (ETB). The EDNRA receptors have a much greater affinity for ET-1 over ET-3 and are expressed abundantly in vascular smooth muscles and stromal tissues. The EDNRB receptors bind ET-1, ET-2 and ET-3 with nearly equal affinity and are expressed abundantly in endothelial cells and epithelial tissues. Although the vasoconstrictor and proliferative effects of ET-1 are primarily mediated by EDNRA receptors, EDNRB receptors can also mediate the vasoconstrictor response through ET-1-induced nitric oxide release from endothelial cells.