Inhibitory Effect of Protamine on Action of Intravenous Thromboplastin in Dogs.

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Abstract
Intravenous administration of protamine (7-10 mg/kg) markedly increased the amount of slowly infused homologous brain thromboplastin required for defibrination of dogs. Protamine (25 mg/kg) given during infusion of thromboplastin to a dog already partially depleted of fibrinogen, arrested further decrease in plasma fibrinogen level. Intravenous administration of protamine (7-10 mg/kg) protected dogs from the lethal effect of subsequent rapid injection of thromboplastin. Inactivation of thromboplastin by protamine probably resulted from a salt-like interaction between its terminal, basic arginine groups and the acidic phospholipid components of the thromboplastic protein. Possible clinical utilization of the antithromboplastic properties of protamine was considered.