POSSIBLE ROLE OF ENDOTHELIN IN ENDOTHELIAL REGULATION OF VASCULAR TONE

In vascular beds, a potent vasoconstrictor of endothelin-1 (ET-1) is p roduced by endothelial cells and released preferentially to the basal side of endothelial cells. It acts on endothelial cells and on the und erlying smooth muscle cells, as a modulator of vascular tone, in an au tocrine and paracine manner. ET-1 induces release of relaxing factors (nitric oxide and prostacycline) from endothelial cells. Whether relax ation or constriction is predominantly elicited by endogenous ET-I may depend on the concentration of ET-1 in vascular beds, the density and mode of distribution of ET receptor subtypes on the endothelial and s mooth muscle cells, the turnover of the receptors, and the existing co nditions of each vascular beds. When ET-1 is overproduced by endotheli al cells at pathological conditions, endogenous ET-1 acts as a vasocon strictor. However, ET-1 may act as a vasodilator at physiologically lo w concentrations, depending on the existing condition.