Inhibition of human platelet aggregation by plasmin digests of human and bovine fibrinogen preparations: role of contaminating factor VIII-related material.

Preparations of human fibrinogen, digested by plasmin, inhibited ADP-induced platelet aggregation; the inhibitory activity was confined to the small dialyzable fragments accumulating during the degradation. Purified large molecular weight fragments D and E had no effect on ADPinduced aggregation, but fragment E inhibited thrombin-induced aggregation. Extensively degraded bovine fibrinogen preparations also inhibited platelet aggregation by ADP. Both human and bovine fibrinogen preparations were contammated with factor VIlI-related material (factor VIll-related antigen and factor VIII procoagulant activity, respectively); separation of factor VIll-related material from human or bovine fibrinogen by gel chromatography and subsequent plasmin digestion of the fractions revealed that the inhibitory activity was mainly linked to digested factor VIll-related material. This inhibitory activity was dialyzable. The effect of fibrinogen digests on platelet aggregation should therefore be re. considered.