Assay of urokinase activity in plasma with a chromogenic substrate

Abstract

Plasma urokinase(UK) activity was measured using synthetic substrate(S-2444, Kabi) and aprotinin. The factors which were necessary for retention of UK activity during UK administration were examined. The suitable concentration of aprotinin which did not suppress the activity of UK on S-2444 and inhibited the plasmin activity as well as the decrease in UK activity during plasminogen activation, was 10 KIU/ml. When UK was infused at a speed of 12×10 4 IU/hr for 4 hours, UK activity appeared after 2 hours and increased to 75 IU/ml after 4 hours. The activity of α 2-plasmin inhibitor decreased to 57% after 2 hours and reached 39% after 4 hours. These results suggest that the UK activity was regulated mainly by the level of α 2-PI and began to appear when the level of α 2-PI activity fell below about 50%.