RELEASE PATTERN OF THE VASCULAR PLASMINOGEN-ACTIVATOR AND ITS INHIBITOR IN HUMAN POSTVENOUS OCCLUSION PLASMA AS ASSESSED BY A SPECTROPHOTOMETRIC SOLID-PHASE FIBRIN-TPA ACTIVITY ASSAY

  • 28 October 1987
    • journal article
    • research article
    • Vol. 58  (3) , 843-849
Abstract
Vascular or tissue-type plasminogen activator (plasma t-PA) is the circulating physiological fibrinolytic enzyme of endothelial cell origin which function is regulated by fibrin and a specific inhibitor (PAI). To study the pattern of release of t-PA and the behavior of t-PA-PAI complexes in plasma we determined t-PA activity in 44 healthy subjects before and after 10 min of forearm venous occlusion using a new spectrophotometric solid-phase fibrin-tPA activity assay. The assay is based on (1) the high affinity binding of t-PA to fibrin, and (2) the detection of fibrin-bound t-PA by measuring the release of pNA from a chromogenic substrate in the presence of plasminogen. Values at rest were rather undetectable in plasma (0.05 .+-. 0.03 IU/ml, in 23 out of 44 samples) but were positively detected in all the euglobulins: 0.88 .+-. 0.68 IU/ml. After venous occlusion the majority of plasmas (36 out of 44) showed a slight increase in t-PA activity (0.65 .+-. 0.63 IU/ml) as compared to the important level observed in all the euglobulins (9.78 .+-. 9.58 IU/ml). So the ratio plasma/euglobulin t-PA activity was very low (0.06) and remained identical in both pre- and postocclusion samples. However, when diluted plasmas were tested the inhibitory effect disappeared and t-PA activity increased indicating that although t-PA circulates in a neutralized state it can be available for fibrinolysis. Since (1) no binding of .alpha.2-antiplasmin to fibrin in solid-phase could be demonstrated, (2) there was no correlation between .alpha.2-antiplasmin and t-PA activity, and (3) a PAI-depleted plasma with a normal content of .alpha.2-antiplasmin did not suppress the activity of t-PA, the inhibitory effect was attributed to PAI. Our findings suggest that both t-PA and PAI are released by venous occlusion and circulates in plasma as a t-PA-PAI complex.