Immunohistochemical and histochemical investigations on in vivo thrombolysis with urokinase in rabbits

Abstract

Using human urokinase in vivo thrombolysis was studied in autologous artificial thrombi in the pulmonary circulation of rabbits by immunofluorescence and Todd's fibrinolysis autography techniques. As compared to the control thrombi of the untreated rabbits, a small increase of thrombolysis was found in the rabbits treated with urokinase. Urokinase fluorescence was observed in the leukocytes, but not along the fibrin fibrils in the thrombi of the rabbits treated with urokinase. By Todd's fibrinolysis autography, lytic areas were observed around aggregated leukocytes in the thrombi of the rabbits treated with urokinase. The small lysis of autologous artificial thrombi of rabbits by human urokinase may be caused by (1) low affinity of human urokinase for rabbit plasminogen, (2) weak adsorption of human urokinase to rabbit fibrin, (3) phagocytosis of human urokinase by leukocytes and (4) high level of antifibrinolytic activity of rabbit plasma.