Effects of acetylsalicylic acid (ASA; 1 to 100 μM), potassium 2,5-dihydroxyphenyl sulfonate (DHPS; 1 to 100 μM) and potassium 2,5-diacetoxyphenyl sulfonate (DAPS; 1 to 100 μM) on cyclooxygenase (COX)-1 (A) and COX-2 (B) activity. Data are expressed as the percentage of the total COX activity obtained in the absence of inhibitors and the results are the mean ± SEM of two independent experiments performed in duplicate. Panel C shows the effects of intravenously administered ASA (10 mg/kg; eq. to 0.05 mmol/kg), DHPS (10 mg/kg; eq. to 0.04 mmol/kg) and DAPS (10 mg/kg; eq. to 0.03 mmol/kg) on bleeding time (BT) in anesthetized rats. The data are expressed as the mean ± SEM of the percentage of increase in BT with respect to the basal determination for each animal. The numbers of rats used for the measurements are indicated in parentheses: *p < 0.05 vs. ASA; † p < 0.05 vs. DHPS, by one-factor ANOVA followed by Student-Newmann-Keuls test.