II - Low Molecular Weight Urokinase (UK) and Different Molecular Weight Heparin (Hp) Fractions in Fibrinolysis.

We have studied the effect of HMW and LMW Hp on the rat blood LMW-UK activated. Inhibitors of fibrinolysis were evaluated by our method on fibrin activated plate (Throrab. Haem. 38, 283, 1977) and the chromogenic substrate S-2251 and fibrinolytic activity by eugLobulins. The studied dosages were of 100 - 300 P1.U/ml for LMW-UK and from 0.001 to 1,000 I.U/ml for both heparins. The reduction of Inhibitory activity brought about by LMW-UK was not altered by low HMW-Hp dosages, but hihg ones suppressed the diminishing effectinduced by LMW-UK. The activation produced by LMW-UK in euglobulins was increased with low dosages of HMW and LMW Hp whereas high dosages produced a marked Inhibition (highly significant). The inhibitory effect of Hp at high dosages was not related to the molecular variations of UK or Hp. Fundamen tal differences attributed to Hp were not found, but HMW-UK produced greater activity in euglobulins and greater decrease in inhibitors levels than LMW-UK. These results show that Hp at high levels (above 10 I.U/ml) potentiate the UK inhibitors.