Action of the novel selective thromboxane antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazolepropan oic acid on vascular smooth muscle preparations.

Abstract

The action of the thromboxane A2-receptor-antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazo lepropanoic acid (Bay u 3405) on vascular smooth muscle preparations was investigated in vitro. In rabbit aortic rings Bay u 3405 is a potent inhibitor of vasoconstriction produced by thromboxane A2 (TXA2)/PG endoperoxides generated by stimulated human platelets (EC50 1.3 x 10(-6) mol/l), (+/-)-cTA2 (Carbocyclic thromboxane A2 [2 beta(Z),3 alpha-(1E,3R*)-3- (3-hydroxy(1-octenyl)-bicyclo[3.1.1]hept-2-yl-5-heptenoic acid]) (EC50 3.3 x 10(-7) mol/l) and U 46619 (EC50 3.8 x 10(-7) mol/l). In pig circumflex coronary arteries Bay u 3405 was 150 times more potent (EC50 2.6 x 10(-9) mol/l) than in rabbit aorta. In rabbit and rat aorta the concentration-response curves for U 46619 were shifted to the right in a parallel manner and the maximum responses were not suppressed. The Schild-plot yielded a straight line with a slope of 1.14 (rabbit) or 1.29 (rat) and pA2 values of 7.43 and 8.59, respectively. The vasoconstrictive action of other agonists such as KCl, serotonin, histamine, epinephrine, norepinephrine, acetylcholine and angiotensin were not affected. In human platelets inhibition of the TXA2-synthase was seen only at concentrations of Bay u 3405 of 2.4 x 10(-5) mol/l and above. From these findings it is concluded that Bay u 3405 is a potent, competitive TXA2/endoperoxide receptor antagonist in vascular smooth muscle.