Endothelin ETA and ETB receptors mediate vascular smooth muscle contraction

1 We have investigated the receptors mediating endothelin‐induced contraction of rabbit isolated jugular vein (RJV) and rat isolated thoracic aorta (RTA). 2 Endothelin‐1 (ET‐1) and endothelin‐3 (ET‐3) contracted RJV preparations with similar potency (EC50 values ∼ 1 nm), whereas, ET‐1 (EC50:4.5 nm) was ∼ 80 fold more potent than ET‐3 in contracting RTA. In addition, the ETB receptor‐selective agonist [Ala1,3,11,15]ET‐l contracted RJV (EC50:2.1 nm) but not RTA. 3 The ETA receptor antagonist, BQ123, competitively antagonized (pA2 6.93) the contraction of RTA produced by ET‐1, but had no effect (at 10 μm) on the contractile effects of either ET‐1, ET‐3 or [Ala1,3,11,15]ET‐1 in RJV. 4 These data suggest that both ETA and ETB receptors can mediate vascular smooth muscle contraction.