Low-dose aspirin inhibits platelet and venous cyclo-oxygenase in man.

In a group of normal subjects we have compared rates of recovery of venous prostacyclin (PGI2) and platelet thromboxane B2 (TXB2) production after a single 300 mg dose of aspirin. Marked inhibition of both venous PGI2 synthesis and platelet TXB2 synthesis persisted for the 72 hours duration of the study. We also examined the effect of four daily doses of 40 mg aspirin on platelet and vessel wall prostaglandin biosynthesis. This produced a cumulative inhibitory effect on TXB2 production with 98.6 per cent mean inhibition at 72 hours. At this time 81-100 per cent inhibition of PGI2 was demonstrated in the four subjects studied. We conclude that the cyclo-oxygenase enzyme in human vein is sensitive to inhibition by very low doses of aspirin. No evidence was found to substantiate the view that rapid recovery of vessel wall cyclo-oxygenase activity occurs after inhibition by a single dose of aspirin.