Summary
The activity of factor VIII in mixtures of native plasma or blood with fibrinogen
derivatives at concentrations high enough to inhibit prothrombin consumption, is greatly
reduced. On the other hand the activity of factor VIII was found normal in similar
mixtures of adsorbed native plasma with fibrinogen derivatives, where no generation
of thrombin could have taken place. The fibrinogen derivatives increased significantly
the inactivating effect of low concentrations of thrombin on the activity of factor
VIII of mixtures of adsorbed oxalated plasma with the derivatives. The same inactivating
effect was exerted by fibrinogen derivatives heated at 60° C for 15 minutes and by
plasmin lysed fibrin. In contradistinction addition of intact fibrinogen or fibrinogen
derivatives to heat-defibrinated plasma protected factor VIII from inactivation by
thrombin. When both, intact fibrinogen and its derivatives, were added simultaneously
at the same concentrations at which they were added singly, the protective effect
was intermediate between that exerted by intact fibrinogen and fibrinogen derivatives
alone. Under these conditions the fibrinogen derivatives appeared as if they potentiated
the inactivating effect of thrombin. Probably by inhibiting the formation of structural
fibrin they increased the amount of thrombin, which remained unadsorbed and free to
inactivate factor VIII.
