title: Inhibition of platelet prostaglandin synthetase by oral aspirin.
abstract: Aspirin inhibits platelet function by permanently acetylating the cyclooxygenase that forms prostaglandins. We determined the sensitivity of platelets to aspirin in normal subjects by measuring [3H-acetyl]aspirin-susceptible cyclooxygenase in washed platelets obtained at various times after aspirin ingestion. A single 325-mg aspirin dose inactivated 89% of platelet cyclooxygenase. The inhibition persisted for 2 days suggesting that oral aspirin also inactivated megakaryocyte cyclooxygenase. Thereafter, active enzyme returned with a time-course reflecting platelet turnover (life-span 8.2+/-2 days). Single doses of 20-650 mg aspirin resulted in 34- greater than 95% inhibition after 24 h. Daily doses of 20-325 mg aspirin for brief periods produced 61- greater than 95% inactivation when measured 24 h after cessation of the drug. Platelet cyclooxygenase is more sensitive to inactivation by aspirin than enzyme in sheep seminal vesicles.
mesh_terms: D000107:Acetylation; D000328:Adult; D000818:Animals; D001241:Aspirin / Q000494:pharmacology*; D001792:Blood Platelets / Q000201:enzymology*; D016861:Cyclooxygenase Inhibitors; D006801:Humans; D008297:Male; D008875:Middle Aged; D011451:Prostaglandin-Endoperoxide Synthases / Q000097:blood; D012669:Seminal Vesicles / Q000201:enzymology; D012756:Sheep
chemical_list: D016861:Cyclooxygenase Inhibitors; D011451:Prostaglandin-Endoperoxide Synthases; D001241:Aspirin