Endothelin-A receptor antagonist-mediated vasodilatation is attenuated by inhibition of nitric oxide synthesis and by endothelin-B receptor blockade.

BACKGROUND: The role of endothelin (ET)-1 in maintenance of basal vascular tone has been demonstrated by local and systemic vasodilatation to endothelin receptor antagonists in humans. Although the constrictor effects mediated by the vascular smooth muscle ET(A) receptors are clear, the contribution from endothelial and vascular smooth muscle ET(B) receptors remains to be defined. The present study, in human forearm resistance vessels in vivo, was designed to further investigate the physiological function of ET(A) and ET(B) receptor subtypes in human blood vessels and determine the mechanism underlying the vasodilatation to the ET(A)-selective receptor antagonist BQ-123. METHODS AND RESULTS: Two studies were performed, each in groups of eight healthy subjects. Brachial artery infusion of BQ-123 caused significant forearm vasodilatation in both studies. This vasodilatation was reduced by 95% (P=.006) with inhibition of the endogenous generation of nitric oxide and by 38% (P