Tissue-type plasminogen activator and streptokinase induce platelet hyperaggregability in the rabbit.

The ex vivo aggregability of rabbit platelets was assessed after rabbits were treated in vivo with thrombolytic doses of tissue plasminogen activator (t-PA) or streptokinase (SK). t-PA was evaluated at 2 doses; an effective thrombolytic dose of 10 micrograms/kg/min, i.v. and a higher dose of 30 micrograms/kg/min, i.v.. At both concentrations, ex vivo platelet hyperaggregability was observed when collagen, arachidonic acid or ADP were employed as the aggregating agonists. Significant falls in circulating platelet counts were observed after t-PA infusion. Infusion of SK also resulted in ex vivo platelet hyperaggregation. These data reveal that thrombolytic therapy may result in hyperaggregable platelets which may play a role in reocclusion of successfully recanalized blood vessels.