Thrombin and PAR-1 peptide agonist up-regulate cAMP-PDE activity. Washed platelets (2 × 108/mL) were treated with (A) thrombin or (B) SFLLRN peptide at 37°C for 3 minutes, and vehicle was added in the sample,which served as control basal line. Activities of cAMP-PDE in the platelet samples were determined by measurement of hydrolysis of cAMP. The changes of hydrolysis of cAMP induced by thrombin or SFLLRN peptide were calculated as that of each value minus the control base line. Data are from 4 individual experiments using different donor platelets. Error bars represent means plus or minus SEM.