The effect of protamine sulfate on platelet function.

The adverse effects of protamine sulfate, used to neutralize the anticoagulant action of heparin, include systemic hypotension, pulmonary artery hypertension, thrombocytopenia and leukopenia. For further evaluation of protamine's mechanism of action, a three-part investigation was performed. In part I platelet-rich plasma (PRP) was prepared from canine blood samples (n = 6) taken before and 2 minutes after injection of protamine. In part II human PRP (n = 5) was preincubated with protamine or distilled water. Adenosine diphosphate-induced aggregation of protamine-treated platelets was unchanged, but thrombin-induced aggregation was inhibited in both canine and human preparations (p less than 0.05). In part III thrombocytopenia was produced in splenectomized dogs (n = 5), using microporous filters, to 4.5-8.4% of the initial platelet count. Protamine reversal of the heparinization caused hypotension (maximally -29 mmHg 90 s after protamine), but not pulmonary arterial hypertension. Leukopenia developed before additional thrombocytopenia appeared. Protamine-platelet interaction inhibits thrombin-induced platelet aggregation. Platelets may play an important role in the pulmonary pressure rise during protamine reversal, but do not mediate the systemic hypotension.