I - High Molecular Weight Urokinase (UK) and Different Molecular Weight Heparin (HP) Fractions in Fibrinolysis

Following our previous works on the interaction of UK and Hp (Thromb. Haem, 38, 105, 1977), we have carried out research to clarify the possible influence of the specific molecular weights characteristics in that interaction, We have studied the relationship of HMW-UK (54,000) to HMW and LMW Hp in rat blood. Inhibitors were evaluated by chromogenic substrate 5-2251 and by our method on an activated fibrin plate, and fibrinolysis by euglobulins. The HMW-UK was tested in a dosage range of 100 to 300 PI.U/ml and Hp ones were: from 0.001 to 1,000 I.U/ml. Hp did not alter the basal inhibitor levels measured on fibrin substrate but we obtained on synthetic substrate an inhibition of 12% on the basal value for all Hp dosages. HMW-Hp produced an increase in the fall of the inhibitory activity induced by HMW-UK for low dosages of Hp, whilst high dosages produced an increase of inhibition, suppressing the UK indeed reduction of inhibitor levels. For LMW-Hp the low dosages did not alter the UK effect while high ones imppreased it. Euglobulins activity HMW-UK induced were not modified by low dosages but high ones induced a highly significant inhibition (for both Hp fractions).