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Figure 2 EndothelinA (ETA) receptors in the human forearm vasculature cause vasoconstriction, whereas ETB receptors mediate vasodilation via release of nitric oxide (NO). (A) When BQ-123 (10 nmol/min), a selective ETA-receptor antagonist, is infused intra-arterially in healthy subjects, a progressive increase in forearm blood flow is noted. In contrast, intra-arterial infusion of BQ-788 (1 nmol/min), a selective ETB-receptor antagonist, decreases forearm blood flow. (B) Vasodilation induced by infusion of BQ-123 (100 nmol/min; intra-arterially) in healthy subjects is attenuated by inhibition of NO synthesis with L-NMMA (200 µg/100 ml forearm volume) and concomitant sodium nitroprusside (12 to 30 ng/min, adjusted to restore basal blood flow) infusion ("NO clamp"). Acetylsalicylic acid (600 mg orally) had no effect on BQ-123-induced vasodilation. (Modified from [63]).
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