Interference of the thromboxane antagonist SK&F 88046 with platelet activation and subsequent desensitization by arachidonic acid and the thromboxane mimetics U46619 and EP171.

We have investigated the effects of the thromboxane antagonist SK&F 88046 on human platelet activation and desensitization by arachidonic acid (AA) and by the thromboxane A2 mimetics U46619 or EP171. SK&F 88046 inhibited platelet aggregation and secretion induced by AA, U46619, EP171 and thrombin at low (0.05 U/ml) but not at a high (1 U/ml) concentrations. Platelet inhibition was reversed by washing the cells. Platelets pre-exposed to AA, U46619 or EP171 and then disaggregated with prostacyclin, washed and resuspended, failed to respond with aggregation or secretion to a second challenge by either agonist. In the presence of the endoperoxide/thromboxane receptor antagonist L636499 or of SK&F 88046, pre-exposure to AA, U46619 or EP171 failed to prevent subsequent responses to the related agonists. Our results suggest that SK&F 88046 is a selective antagonist of platelet activation and desensitization induced by TxA2 or prostaglandin endoperoxides and that it may have utility as an anti-platelet drug.