Endothelin as a clinical target in the treatment of systemic hypertension

Endothelin is a potent vasoconstrictor substance that also can exert proliferative, inflammatory, and fibrotic changes in blood vessels and other organs. It acts on tissues in a paracrine and autocrine fashion, with local production and regulation occurring in both endothelial and nonendothelial cells. Endothelin stimulation of ETA and ETB receptors results in different and often opposing effects, which under physiologic conditions, establishes a balance that contributes to the regulation of vascular tone and blood pressure. Dysregulation of the endothelin system can induce or mediate endothelial dysfunction and organ damage in systemic hypertension (HTN), effects which may be ameliorated by endothelin antagonists. Endothelin receptor antagonists are currently being used in the treatment of pulmonary HTN. Both selective and dual-acting endothelin receptor blockers can also reduce systemic blood pressure in animal models and in hypertensive patients. Clinical trials evaluating the efficacy and safety of these agents are underway, and show potential as a new class of antihypertensives. Studies are also in progress with a single moiety dual angiotensin-endothelin A receptor antagonist, which is being evaluated in HTN. Issues that need to be addressed include the net contribution of endothelin in the pathophysiology of HTN, its interaction with other neurohormonal systems such as the renin-angiotensin-aldosterone system, and the clinical demonstration of the effect of endothelin receptor antagonism on end-organ damage in hypertensive patients.