Any of several related peptides, all comprising 21 amino acids and first identified in cultured endothelial cells. Endothelin 1 (ET-1) is released by the endothelium of blood vessels and is a potent vasopressor, causing constriction of vessels and raising blood pressure. The other endothelins resemble ET-1 structurally but are synthesized in other tissues. The endothelins bind to either of two classes of G-protein-coupled receptors, ET_A and ET_B, and antagonists of these receptors are used to treat pulmonary arterial hypertension.