Plasma . as AssessE ! d by · a Spectrophotometric S ( ) lid-Pbase Fibrin-tPA Activity Assay 1

VaScular or tissue-type plasminogen activatbr(plasma t,PA).is tb.e circulating. physiological. fibrinolytk enzyme of. endothelial cell origin which ft,mction is regulated by fibrin an~fa specific inhibitor (PAI). To • study the pattern of release of t-PA and the behavior of t-PA -PAI complexes in plasma. we determined tePA activity in 44 healthy subjects before and after TO ·min offorearm venous ?cdusion using a new spectrophotmnetrio solid-phase fibrin-tPA activity assay. The assay is based on 1) the high affinity binding of t-PA tofibrin, and 2} thedetectionof fibrin-bound t-PAby J11easuring the releaseof pNA from a chromogenic substrate. in the presence of plasminogeu. Values at.rest were rather undetectable in plasma(0:05 ± 0.03 IU/ml,in 23out of 44 samples)butwere positively detected in all the euglobulins: 0.88 ± 0.68 IU/ml. After venous occlusion the majority ofplasmas (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 preand postocclusion samples. However, when diluted plasmas were tested the inhibitory effect disappeared ~ndt-PA activity increased indicating that although t-PA s;irc1.1lates in a neutralized state it can be available for fibrinolysis. Since J) no. binding of azantiplasmin to fibrin in solid-phase could be demonstrate(\, 2) there was no correlation between arantiplasmin and t"PA activity, and 3) a PAI~depleted plasma with a normal content of ar antiplasmin did not suppress the activity of t-PA, the inhibitory effect was attributed to PAL Our findings suggest that both t-PA and PAl are released. by venous occlusion and circulates in plasma as a t-PA-PAI complex.