Factor V Inhibits Fibrinolysis In Vivo

Background—Factor V (fV) predisposes to thrombosis by enhancing thrombin formation. This study tested the hypothesis that fV inhibits fibrinolysis in vivo. Methods and Results—Radiolabeled clots were injected into the jugular veins of wild-type mice and mice heterozygous (fV ) or homozygous (fV) for fV. Mean percent clot lysis 5 hours later was significantly reduced in fV mice (14.3 3.6%, n 13) compared with wild-type mice (40.2 7.0%, n 17; P 0.01) and intermediate in fV /Q mice (29.4 8.7%, n 9; P 0.03 versus fV, P 0.36 versus wild type). The rate of in vitro lysis of plasma clots prepared from fV /Q or fV mice was significantly slower than that of wild-type plasma clots, whereas in vitro clot lysis did not differ significantly between groups after inhibiting thrombin-activatable fibrinolysis inhibitor. Conclusions—fV inhibits fibrinolysis in vivo, suggesting an additional pathway by which this mutation promotes thrombosis. (Circulation. 2004;110:3594-3598.)