PDE3 selective inhibitors restrict thrombin-induced PDE activity. Washed platelets (2 × 10⁸/mL) were incubated with 20 μmol/L EHNA or Bay 60-7550, or 10 μmol/L milrinone, cilostazol, IBMX, or vehicle at 37°C for 30 minutes. After addition of thrombin (0.5 nmol/L) in each group at 37°C for 3 minutes, the reactions were stopped by addition of 0.5% of Triton X-100. The platelet samples, which were treated with vehicle or the inhibitors but not with thrombin, served as control basal line for each inhibitor. The hydrolysis of cAMP in each sample was determined. The control basal level of hydrolysis of cAMP was subtracted from each test sample. Data are from 4 individual experiments using different donor platelets and are means plus or minus SEM. *Significant compared with control (thrombin alone) (P > .05).