Effects of sulphinpyrazone and aspirin on prostaglandin I2 (prostacyclin) synthesis by endothelial cells.

Synthesis of prostaglandin I2, (PGI2, prostacyclin) by vascular endothelium (assayed by the ability of cultured endothelial cells to inhibit platelet aggregation) was inhibited by aspirin. At 100 mumol/l aspirin completely blocked measurable PGI2 production, but endothelial cells had substantially recovered their ability to synthesize PGI2 24 h after removal of the drug. In contrast, the effect of 1 mmol/l aspirin was still evident 24 h after drug withdrawal. Sulphinpyrazone also inhibited PGI2 synthesis, but was about 100 fold less potent than aspirin, and the effect of the drug was lost within 24 h of its addition, even when endothelial cells were left in contact with the drug during this period.