The antithrombotic effect of desethyl KBT-3022, which is the main active metabolite of the new antiplatelet agent, KBT-3022 (ethyl 2-[4,5-bis(4-methoxyphenyl)thiazol-2-yl] pyrrol-1-ylacetate; a cyclooxygenase inhibitor), was determined using a photochemically induced arterial thrombosis model in the rat femoral artery. Pretreatment with desethyl KBT-3022 (0.1, 0.3 and 1 mg/kg, i.v.) prolonged the time required to achieve thrombotic occlusion in the femoral artery and inhibited collagen-induced platelet aggregation in whole blood ex vivo, each in a dose-dependent manner. In all 6 rats used, particularly at the highest dose (1 mg/kg, i.v.) tested, cyclic variations in blood flow were hardly ever observed and complete cessation of blood flow did not occur during the 30-min observation time. BM-13505 (1, 3 and 10 mg/kg, i.v.), a thromboxane A2 receptor antagonist, also prolonged the time to occlusion, but cyclic variations in blood flow did occur. On the other hand, aspirin (10 and 30 mg/kg, i.v.) had little effect in terms of preventing thrombosis, although it inhibited collagen-induced platelet aggregation to the same extent as did desethyl KBT-3022. Desethyl KBT-3022 inhibited the thrombin-induced aggregation of washed platelets in a concentration-dependent manner (1-40 μM), whereas aspirin and BM-13505 did not. These findings suggest that the potent antithrombotic effect of desethyl KBT-3022 may be attributable in part to its additional ability to inhibit thrombin-induced platelet aggregation. Accordingly, thromboxane A2 and thrombin may be important thrombotic mediators in this rat model.
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