The discovery of endothelin two decades ago has now evolved into an intricate vascular endothelin (ET) system. Several ET isoforms, receptors, signaling pathways, agonists, antagonists, and clinical applications have been identified and documented in first-rate patents. The role of ET as one of the most potent endothelium-derived vasoconstricting factors is now complemented by a newly discovered role in vascular relaxation. ET synthesis is initiated by the transcription of ET genes in endothelial cells and the generation of the gene products preproET and big ET, which are further cleaved by specific ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ETA and ETB2 receptors in vascular smooth muscle, and stimulate [Ca2+]i, protein kinase C, mitogen-activated protein kinase and other signaling mechanisms of smooth muscle contraction, growth and proliferation. ET also binds to endothelial ETB1 receptors, which mediate the release of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. Endothelial ETB1 receptors may also function in ET re-uptake and clearance. Although the effects of ET on vascular function and growth are well-recognized, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension is not clearly established. Salt-dependent hypertension in experimental animals and some forms of moderate to severe hypertension in human may show elevated levels of plasma or vascular ET; however, other forms of hypertension show normal ET levels. The currently available ET receptor antagonists reduce blood pressure in some forms of experimental hypertension. Careful examination of recent patents may identify more effective and specific modulators of the vascular ET system for clinical use in human hypertension.
Endothelium, smooth muscle, calcium, hypertension
Harvard Medical School,Brigham and Women's Hospital, Division of Vascular Surgery, NRB 435,77 Avenue Louis Pasteur, Boston, MA 02115;