Platelet suspensions obtained at different time intervals following a single dose of oral aspirin were incubated with [1-(14)C]-arachidonic acid and the amount of [1-(14)C]thromboxane B2 formed was determined by a double isotope technique. Since aspirin is an irreversible inhibitor of platelet cyclooxygenase and since circulating platelets do not synthesize cyclooxygenase the rate of reappearance of active cyclooxygenase determined in this way was a measure of the rate of regeneration of functioning platelets. In two subjects the regeneration half-times were 4.2 and 4.8 days.
Aspirin Blood Platelets