Prostacyclin Is a More Potent Stimulator of Thrombolysis than Inhibitor of Haemostasis

The effects of prostacyclin (PGI2) on haemostasis and thrombolysis in human blood were investigated in vitro using the ‘Haemostatometer’. In freshly drawn native blood samples, 5 ng/ml PGI2 greatly inhibited haemostasis but did not influence clotting time. The effect was potentiated in heparinised blood: 1 ng/ml PGI2 effect on haemostasis was still detectable, and the duration of the effect was prolonged. Thrombolytic activity was tested in heparinised blood by first allowing haemostasis and then measuring the time until rebleeding occurred through the consolidated haemostatic plugs. PGI2 at 0.5 ng/ml had no significant effect on haemostasis, but significantly decreased the time for spontaneous thrombolysis (p < 0.001). Comparable effects were demonstrated in blood samples containing 50 U/ml strepto-kinase. Increased thrombolysis also occurred when haemostatic plugs formed from control blood were perfused with blood containing 5 ng/ml PGI2. The results suggest that PGI2 has a thrombolytic effect independent of any contribution from the vessel wall and that it is a more potent stimulator of thrombolysis than inhibitor of haemostasis.