The Role Of Factor VIII: C In Fibrinogen - Fibrin Conversion

The cascade mechanism for the coagulation pathway has prevailed since its original proposal, and subsequent observations have supported the role of thrombin on coagulation reactions other than in Fibrinogen - Fibrin conversion. In very small quantities, thrombin has been reported as increasing the activity of Factor VIII: C. We report here, observations which support a reverse proposal, namely that Factor VIII: C increases activity of thrombin in Fibrinogen - Fibrin conversion. Thrombin clotting times were performed employing human Fibrinogen solutions, fresh citrated normal platelet - poor human plasma and fresh citrated platelet - poor plasma from severely affected Hemophilia A patients, in whom Factor VIII : C assays were less than 1% in a one stage, activated partial thromboplastin time assay. A platelet aggregometer was used to assess the thrombin time, and the rate of clot formation (fibrin polymerization) was indicated by optical density change in the form of a curve, the tangent of the maximal slope of curve being equated with this clot formation rate. Results indicate that with very small concentrations of thrombin, Factor VIII: C enhances the rate of fibrin clot formation and that Factor VIII: C restores the abnormal rate of clot formation observed in severe Hemophilia A; the test system was known to be calcium-free, which ensured that activation of Factor X did not ensue. The concentration of Fibrinogen remained constant in all experiments. The observed phenomena are confirmed when employing purified fibrinogen solutions, using decreasing amounts of Factor VIII: C.