Pharmacological actions of ICI 180080, a novel thromboxane receptor antagonist

ICI 180080 (5(Z)-7-[2,2-dimethyl-4-(2-hydroxyphenyl)-1,3-dioxan-cis-5-yl] heptenoic acid) potently inhibited contractions of rat and rabbit aortae and guinea-pig trachea elicited by 11,9-epoxymethano PGH2 (U-46619). This antagonism was selective because contractions of aortae to noradrenaline and 5-hydroxytryptamine and trachea to histamine were not antagonized by ICI 180080. Schild analysis of data obtained from experiments on rabbit aortae indicated that this thromboxane receptor antagonism was competitive (pA2 = 7.50, slope = 1.07). Addition of ICI 180080 to human platelet-rich plasma caused dose-related inhibition of U-46619-induced platelet aggregation. This modification of platelet aggregation was not associated with inhibition of thromboxane synthetase, cyclo-oxygenase or lipoxygenase. ICI 180080 did not modify the primary phase of ADP-induced aggregation of human platelets neither did it affect the platelet inhibitory activity of prostacyclin. When dosed orally to anaesthetized guinea-pigs, ICI 180080 (5-50 mg kg-1) caused dose-related inhibition of U-46619-evoked bronchoconstriction. We conclude that ICI 180080 is a potent, selective, competitive, orally active thromboxane antagonist.