Quantitative Method for the In Vivo Testing of Fibrinolytic Agents: Effect of Intravenous Trypsin on Radioactive Thrombi and Emboli

Quantitative methods for testing fibrinolytic agents in vivo are described. Methods based on the incorporation into the clot of P32 labeled blood cells or Cr51 labeled erythrocytes were found to be unsatisfactory. Clots were produced with I131 labeled fibrinogen. Dissolution of a clot resulted in decrease of radioactivity. This was recorded by placing segments of blood vessels in a special lead shield containing a scintillation detector head, connected to a radiation rate meter and an Esterline recorder. Pulmonary, peripheral and coronary emboli were produced by injecting radioactive clots produced and ground, in vitro. Using these methods it was found that maximal tolerated doses of trypsin showed no significant fibrinolytic effect.