Endothelins (ET-1, ET-2 and ET-3) are 21-amino acid vasoactive peptides that bind to G-protein-linked transmembrane receptors, ET-RA and ET-RB. As well as modulating vasoconstriction, endothelins regulate growth in several cell types and may also affect differentiation, inflammation and angiogenesis. Both macrophages and endothelins are found in areas of hypoxia in solid tumors and ET-2 expression may be modulated by hypoxia in some tumors. Endothelin-1 (ET-1) is both a potent vasoconstrictor and mitogenic factor that has been implicated as a cause of the micro- and macrovascular complications of diabetes mellitus. The pathway by which the high-glucose environment of diabetes mediates increased levels of endothelins has not been completely elucidated but appears to involve endothelin-converting enzyme (ECE-1), which converts inactive big ET-1 to active ET-1 peptide. Endothelin-2 (ET-2) is a 21 residue vasoactive peptide which is biosynthesized from big ET-2 (1-38) by a specific cleavage at Trp21-Val22 with an ET converting enzyme (ECE).

In a healthy individual, a delicate balance between vasoconstriction and vasodilation is maintained by endothelin, calcitonin and other vasoconstrictors on the one hand and nitric oxide, prostacyclin and other vasodilators on the other.  Overproduction of endothelin in the lungs may cause pulmonary hypertension, which can sometimes be treated by the use of an endothelin receptor antagonist, such as bosentan or sitaxsentan. The latter drug selectively blocks endothelin A receptors, decreasing the vasoconstrictive actions and allowing for increased beneficial effects of endothelin B stimulation, such as nitric oxide production. The precise effects of endothelin B receptor activation depends on the type of cells involved.