Standardized Vascular Injury and the Influence of Aspirin

women. Twenty-four hours after a single dose of 600 mg aspirin, in vitro production of thromboxane B2 in response to collagen fell by 95%, whereas in vivo production of thromboxane B2 and 6-keto-PGF,a in bleeding time blood fell by 87% and 66%, respectively. Subjects with the lowest absolute levels of thromboxane B2 24 hours after aspirin were also those with the longest postaspirin bleeding times. Recovery of 6-keto-PGFla production was faster than recovery of thromboxane B2 production, but 6-keto-PGFI, production for most subjects was still below basal 72 hours after aspirin. The influence of two different doses of long-term aspirin (80 mg every other day and 325 mg daily) on the in vivo production of thromboxane B2 and 6-keto-PGFl. was studied in normals and diabetics. After 14 days of 80 mg aspirin every other day, thromboxane B2 and 6-keto-PGFIa production were both substantially inhibited (93% and 78%, respectively). After 14 days of 325 mg aspirin daily, thromboxane B2 production was similarly substantially inhibited (93%), whereas 6-keto-PGFIa was significantly less affected (only 45% inhibition). Study of a second group of five normal subjects confirmed that 6-keto-PGFl. production was significantly inhibited 24 hours after the first dose of 325 mg aspirin but was not significantly less than basal after 14 days of 325 mg aspirin. The results suggest that 325 mg aspirin daily is more antithrombotic compared with 80 mg every other day due to the superior preservation of prostacyclin production. (Circulation 1989;79:29-38)