Sensitivity of fatty acid cyclooxygenase from human aorta to acetylation by aspirin

The rate of acetylation of fatty acid cyclooxygenase (prostaglandin synthase, EC 1.14.99.1) by [acetyl-3H]-aspirin was measured in microsomes from human aortas and coronary arteries and intact and disrupted human platelets. We also measured the inhibition by aspirin of prostacyclin generation from exogenous arachidonic acid in shredded human aorta. Cyclooxygenase in human aorta and coronary artery microsomes is approximately 1/250th as sensitive to aspirin as enzyme in intact platelets, and 1/60th as sensitive to aspirin as enzyme measured in a platelet microsomal preparation. On the basis of the in vitro data presented, we predict that small oral doses of aspirin are sufficient to inhibit platelet prostaglandin production but are not sufficient to substantially affect aorta or coronary artery prostaglandin production.