Effect of Single-Dose Aspirin on TXA 2 and PGI 2 Cyclooxygenases in vivo

The present study investigated the sensitivities of the thromboxane A2 (TXA2) cyclooxygenase and the prostacyclin (PGI2) cyclooxygenase to aspirin using an in vivo animal model. In this model, arachidonic acid (AA) was administered to mice via cardiac puncture, and plasma levels of thromboxane B2 (TXB2) and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) were determined. Infusion of AA (5, 10, 25 and 50 mg/kg) resulted in a dose-dependent increase in both TXB2 and 6-keto PGF1 alpha. Pretreatment with aspirin resulted in a dose-dependent and parallel decrease in TXB2 and 6-keto PGF1 alpha production. This nonselective inhibition occurred at all doses of aspirin (1, 10 and 50 mg/kg) and at all levels of cyclooxygenase activity (5-50 mg/kg AA). These results indicate that the TXA2 and PGI2 cyclooxygenase enzymes are equally sensitive to inhibition by a single dose of aspirin.