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.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
D000328:Adult; D005337:Fibrin; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D015849:Plasminogen Inactivators; D013053:Spectrophotometry / Q000379:methods; D010959:Tissue Plasminogen Activator / Q000097:blood*; D014652:Vascular Diseases / Q000097:blood*
D006023:Glycoproteins; D015849:Plasminogen Inactivators; D005337:Fibrin; D010959:Tissue Plasminogen Activator