Mechanism of action of aspirin as antiplatelet drug is its inhibitory action on?

Ans. (C) Thromboxane A2(Ref: KDT 8/e p677)By inhibiting cyclooxygenase enzyme, aspirin initially decreases the level of both prostacyclins (in endothelium) and TXA2 (in platelets). However after some time prostacyclin synthesis resumes due to presence of nucleus in endothelium whereas TXA2 remain depressed because platelets are enucleated. Thus final effects of aspirin are due to decrease in TXA2 synthesis.