Inhibitory effect of staphylokinase on platelet aggregation

We investigated the effect of staphylokinase (SAK), which has specific thrombolytic properties, on human platelet aggregation. Platelet aggregation induced with collagen was observed following preincubation of platelets in platelet-rich plasma (PRP) or washed platelet suspension (WP) with SAK at 37 degrees C for 30 min. SAK inhibited platelet aggregation in PRP only at the highest examined concentration (1 x 10(-4) g/ml). Although SAK did not inhibit platelet aggregation in WP which contained fibrinogen, it did when the platelets had been preincubated with SAK and plasminogen. The most effective concentration in WP was 1 x 10(-6) g/ml. The effect could be inhibited by adding aprotinin or alpha 2-antiplasmin. The highest generation of plasmin in the same preincubation fluid was detected at 1 x 10(-6) g/ml SAK. We concluded that SAK can inhibit platelet aggregation in WP by generating plasmin and/or fibrinogen degradation products, but is only partially effective in PRP because of the existence of alpha 2-antiplasmin.