Regulation of PAR-1 in patients undergoing percutaneous coronary intervention: effects of unfractionated heparin and bivalirudin.

Aims We examined the specific effects of unfractionated heparin and bivalirudin on thrombin-inducible platelet PAR-1 in patients undergoing percutaneous coronary intervention (PCI). Methods and results To simulate in vivo conditions that may precipitate a bleeding event, we added thrombin in vitro to blood samples from 89 patients who had been randomly assigned to receive heparin or bivalirudin for elective PCI and examined thrombin-inducible PAR-1 expression. Thrombin-inducible cleavage of PAR-1 was inhibited by heparin, but not affected by bivalirudin (P = 0.0001). Further, PAR-1 internalization was more effectively inhibited by heparin than bivalirudin (P = 0.002). Conclusion Heparin has stronger inhibitory effects on thrombin-dependent PAR-1 cleavage and internalization, thus providing a biological explanation for lower clinical bleeding rates with bivalirudin.