Essential Thrombin Residues for Inhibition by Plasminogen Activator Inhibitor-1 in the Absence and Presence of Heparin and Vitronectin.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3986-3986
Author(s):  
Yolanda M. Fortenberry ◽  
Jill C. Rau ◽  
Lauren C. Cranford ◽  
Timothy Myles ◽  
Lawerence L. Leung ◽  
...  
Keyword(s):  
Plasminogen Activator ◽  
Slow Rate ◽  
Plasminogen Activator Inhibitor ◽  
Anion Binding ◽  
Wild Type ◽  
Plasminogen Activator Inhibitor 1 ◽  
Thrombin Inhibition ◽  
Heparin Interaction ◽  
Activator Inhibitor ◽  
Pai 1

Abstract The serine protease inhibitor (serpin), plasminogen activator inhibitor-1 (PAI-1) rapidly inactivates tissue plasminogen activator (tPA) and urokinase plasminogen activator to prevent plasminogen activation to plasmin. Although PAI-1 is a major regulator of fibrinolysis, PAI-1 also has a role in regulating coagulation due to its ability to inhibit thrombin. Previous studies have shown that replacing the 39-loop of thrombin with the 39-loop of tPA increases the rate of thrombin inhibition by PAI-1 suggesting that the 39-loop of thrombin is responsible for the relatively slow rate of inhibition by PAI-1 compared to tPA. Nevertheless, the role of other thrombin residues in the thrombin-PAI interaction [in the absence and presence of heparin and vitronectin (VN)] has not been fully investigated. We used 55 recombinant thrombin mutants in which solvent accessible residues are replaced with alanine to determine their effect on thrombin-PAI-1, thrombin-PAI-1-heparin and thrombin-PAI-1-VN interactions. Results from this study identified thrombin residues that either increased or decreased thrombin inhibition by PAI-1 relative to wild-type thrombin. First, we confirmed that Glu25 (E25A, located in the 39-loop) had an enhanced rate of inhibition by PAI-1 in the presence and absence of heparin and vitronectin. Also, thrombin residues, Asn216/Asn217 (N216A/N217A, located in the 203–206 loop) and Lys145/Thr147/Trp148 (K145A/T147A/W148A, located in the autolysis loop), showed increased rates of thrombin inhibition by PAI-1. These results suggest that these three thrombin regions contribute to the slow rate of thrombin inhibition by PAI-1. Second, we identified two anion-binding exosite-1 thrombin mutants, R68A and to a lesser extent Y71A, that showed decreased rates of inhibition by PAI-1 compared to wild-type thrombin. Consistent with this finding, there is a decrease in inhibition of γ-thrombin (α-thrombin proteolyzed in exosite-1) by PAI-1. These results suggest that Arg68 and Tyr71 of thrombin exosite-1 are potential PAI-1 interacting residues since there is a decrease in inhibition in the absence and presence of heparin and VN. Third, we identified four anion-binding exosite-2 thrombin mutants (R89A/R93A/E94A, R98, R178A/R180A/D183A, R245A/K248A/Q251) that are resistant to PAI-1-heparin accelerated inhibition compared to wild-type thrombin, which implies that the thrombin residues important for antithrombin-heparin inhibition are also involved in the PAI-1-heparin inhibition reaction. By contrast, these exosite-2 thrombin mutants are not as resistant to VN-accelerated PAI-1 inhibition, which indicates that exosite-2 is more important for heparin interaction than for VN interaction. Lastly, active site thrombin mutants (W50A, D51A, E202A) and the sodium binding site thrombin mutants (E233A, R233A) were very resistant to PAI-1 inhibition in the absence and presence of heparin and VN. Considering that thrombin, PAI-1 and VN are localized in atherosclerotic arterial vessel wall, our results illustrate the importance of various thrombin domains for PAI-1 inhibition with and without heparin and VN.

scholarly journals Low-affinity heparin stimulates the inactivation of plasminogen activator inhibitor-1 by thrombin

Blood ◽  
1994 ◽  
Vol 84 (4) ◽  
pp. 1164-1172 ◽  
Author(s):  
PA Patston ◽  
M Schapira
Keyword(s):  
Plasminogen Activator ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Plasminogen Activator Inhibitor ◽  
Initial Increase ◽  
Plasminogen Activator Inhibitor 1 ◽  
Thrombin Inhibition ◽  
Zymographic Analysis ◽  
Activator Inhibitor ◽  
Pai 1

Abstract The influence of heparin on the reaction between thrombin and plasminogen activator inhibitor-1 (PAI-1) has been examined. With a 50- fold excess of PAI-1, the rate constant for the inhibition of thrombin was 458 mol/L-1s-1, which increased to 5,000 mol/L-1s-1 in the presence of 25 micrograms/mL unfractionated heparin or heparin with low affinity for antithrombin. The effect of low affinity heparin was then examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using close to equimolar concentrations of reactants. Thrombin and PAI-1 formed a stable stoichiometric complex in the absence of heparin, which did not dissociate after the addition of 25 micrograms/mL low-affinity heparin. In contrast, when low-affinity heparin was added at the beginning of the reaction, there was an initial increase in PAI-1- thrombin complex formation, but this was rapidly followed by substantial proteolytic cleavage of unreacted PAI-1 and of the thrombin- PAI-1 complex. The idea that the relative concentrations of thrombin and PAI-1, and the presence of low affinity heparin, could influence the products of the reaction was examined in detail. Quantitative zymographic analysis of tissue plasminogen activator and PAI-1 activities and chromogenic substrate assay of thrombin activity showed that low-affinity heparin stimulated the inactivation of PAI-1 by an equimolar amount of thrombin, but caused only a minimal stimulation of thrombin inhibition. It is concluded that low-affinity heparin stimulates thrombin inhibition when PAI-1 is in excess, but, unexpectedly, that low-affinity heparin enhances PAI-1 inactivation when thrombin is equimolar to PAI-1.

Effect of Stabilizing versus Destabilizing Interactions on Plasminogen Activator Inhibitor-1

2000 ◽  
Vol 84 (11) ◽  
pp. 871-875 ◽  
Author(s):  
Nele Vleugels ◽  
John Leys ◽  
Isabelle Knockaert ◽  
Paul Declerck
Keyword(s):  
Plasminogen Activator ◽  
Half Life ◽  
Plasminogen Activator Inhibitor ◽  
Reactive Site ◽  
Wild Type ◽  
Plasminogen Activator Inhibitor 1 ◽  
The Stability ◽  
Gate Region ◽  
Activator Inhibitor ◽  
Pai 1

SummaryPlasminogen activator inhibitor-1 (PAI-1) is a unique member of the serpin family, as it spontaneously converts into a latent conformation. However, the exact mechanism of this conversion is not known. Previous studies reported that neutralizing monoclonal antibodies as well as reversal or removal of charges on the s3C-s4C turn results in a destabilization of PAI-1 leading to an accelerated conversion to its latent form.In this study the effect of the reversal or removal of charges in this “gate region” (R186E/R187E, H190E/K191E, H190L/K191L and R356E) on a stable PAI-1-variant (PAI-1-stab) was investigated. Whereas PAI-1-stab has a half-life of 150 ± 66 h, PAI-1-stab-R186ER187E, PAI-1-stab-H190E-K191E, PAI-1-stab-H190L-K191L and PAI-1-stab-R356E have a strongly decreased half-life (p< 0.005 versus PAI-1-stab) of 175 ± 48 min, 75 ± 34 min, 68 ± 38 min and 79 ± 16 min, respectively. Wild-type PAI-1 (wtPAI-1) had a half-life of 55 ± 19 min. These data indicate that the stabilization induced by the mutated residues in PAI-1-stab is counteracted by the additional mutations, resulting in half-lives similar to that of wtPAI-1, thereby suggesting that the stabilizing and destabilizing forces act mainly independently in these mutants. Extrapolation of these data to other (stable) serpins leads to the hypothesis that the s3C-s4C turn and the distal hinge region of the reactive site loop plays a role for the stability of serpins in general.

The upstream stimulatory factor-2a inhibits plasminogen activator inhibitor-1 gene expression by binding to a promoter element adjacent to the hypoxia-inducible factor-1 binding site

Blood ◽  
2001 ◽  
Vol 97 (9) ◽  
pp. 2657-2666 ◽  
Author(s):  
Anatoly Samoylenko ◽  
Ulrike Roth ◽  
Kurt Jungermann ◽  
Thomas Kietzmann
Keyword(s):  
Plasminogen Activator ◽  
Hypoxia Inducible Factor ◽  
Plasminogen Activator Inhibitor ◽  
Wild Type ◽  
Upstream Stimulatory Factor ◽  
Plasminogen Activator Inhibitor 1 ◽  
Hypoxia Inducible Factor 1 ◽  
Stimulatory Factor ◽  
Activator Inhibitor ◽  
Pai 1

Abstract Plasminogen activator inhibitor-1 (PAI-1) expression is induced by hypoxia (8% O2) via the PAI-1 promoter region −175/−159 containing a hypoxia response element (HRE-2) binding the hypoxia-inducible factor-1 (HIF-1) and an adjacent response element (HRE-1) binding a so far unknown factor. The aim of the present study was to identify this factor and to investigate its role in the regulation of PAI-1 expression. It was found by supershift assays that the upstream stimulatory factor-2a (USF-2a) bound mainly to the HRE-1 of the PAI-1 promoter and to a lesser extent to HRE-2. Overexpression of USF-2a inhibited PAI-1 messenger RNA and protein expression and activated L-type pyruvate kinase expression in primary rat hepatocytes under normoxia and hypoxia. Luciferase (Luc) gene constructs driven by 766 and 276 base pairs of the 5′-flanking region of the PAI-1 gene were transfected into primary hepatocytes together with expression vectors encoding wild-type USF-2a and a USF-2a mutant lacking DNA binding and dimerization activity (ΔHU2a). Cotransfection of the wild-type USF-2a vector reduced Luc activity by about 8-fold, whereas cotransfection of ΔHU2a did not influence Luc activity. Mutation of the HRE-1 (−175/−168) in the PAI-1 promoter Luc constructs decreased USF-dependent inhibition of Luc activity. Mutation of the HRE-2 (−165/−158) was less effective. Cotransfection of a HIF-1α vector could compete for the binding of USF at HRE-2. These results indicated that the balance between 2 transcriptional factors, HIF-1 and USF-2a, which can bind adjacent HRE sites, appears to be involved in the regulation of PAI-1 expression in many clinical conditions.

Food deprivation induces adipose plasminogen activator inhibitor-1 (PAI-1) expression without accumulation of plasma PAI-1 in genetically obese and diabetic db/db mice

2007 ◽  
Vol 98 (10) ◽  
pp. 864-870 ◽  
Author(s):  
Katsutaka Oishi ◽  
Naoki Ohkura ◽  
Juzo Matsuda ◽  
Norio Ishida
Keyword(s):  
Plasminogen Activator ◽  
Food Deprivation ◽  
Fibrinolytic Activity ◽  
Plasminogen Activator Inhibitor ◽  
Mrna Levels ◽  
Wild Type ◽  
Plasminogen Activator Inhibitor 1 ◽  
Adipose Tissues ◽  
Activator Inhibitor ◽  
Pai 1

SummaryRelationships between energy intake and fibrinolytic functions have been documented in detail. We evaluated food deprivation (FD) as a means of modulating fibrinolytic activity in genetically obese and diabetic db/db mice and in their lean counterparts. Twelve hours of FD induced considerable gene expression of plasminogen activator inhibitor-1 (PAI-1) in both epididymal (3.8-fold, p<0.05) and intestinal (2.4-fold, p<0.05) adipose tissues without affecting plasma PAI-1 levels in db/db mice, whereas the FD did not affect these parameters in wild-type mice. Importantly, 24 hours of FD increased the plasma PAI-1 content in wild-type (1.9-fold, p<0.01) but not in db/db mice, although adipose PAI-1 mRNA levels were significantly increased in db/db mice. The plasma PAI-1 content significantly correlated with hepatic PAI-1 mRNA levels in wild-type (r=0.84, p<0.01) and in db/db (r=0.63, p<0.01) mice. However, plasma PAI-1 did not correlate with adipose PAI-1 expression in db/db mice, although adipose tissue in general is thought to be the principal site of PAI-1 production in obesity. Hepatic PAI-1 expression was closely correlated with serum levels of free fatty acids in wild-type (r=0.72, p<0.01), but not in db/db mice. Adipose PAI-1 expression significantly correlated with serum corticosterone levels in both genotypes (wild-type, r=0.52, p<0.05; db/db, r=0.51, p<0.01), suggesting that adipose PAI-1 expression is up-regulated by fastinginduced glucocorticoids. The present findings suggested that fasting differentially affects fibrinolytic activity in obese and lean subjects and that PAI-1 expression in the liver as well as in adipose tissues comprises an important determinant of increased risk for cardiovascular disease in obesity.

scholarly journals Targeting plasminogen activator inhibitor-1 in tetracycline-induced pleural injury in rabbits

2018 ◽  
Vol 314 (1) ◽  
pp. L54-L68 ◽  
Author(s):  
Galina Florova ◽  
Ali O. Azghani ◽  
Sophia Karandashova ◽  
Chris Schaefer ◽  
Serge V. Yarovoi ◽  
...  
Keyword(s):  
Plasminogen Activator ◽  
Plasminogen Activator Inhibitor ◽  
Fibrinolytic Therapy ◽  
Wild Type ◽  
Plasminogen Activator Inhibitor 1 ◽  
Sandwich Type ◽  
Pleural Injury ◽  
Activator Inhibitor ◽  
Pai 1 ◽  
Selection Of

Elevated active plasminogen activator inhibitor-1 (PAI-1) has an adverse effect on the outcomes of intrapleural fibrinolytic therapy (IPFT) in tetracycline-induced pleural injury in rabbits. To enhance IPFT with prourokinase (scuPA), two mechanistically distinct approaches to targeting PAI-1 were tested: slowing its reaction with urokinase (uPA) and monoclonal antibody (mAb)-mediated PAI-1 inactivation. Removing positively charged residues at the “PAI-1 docking site” (179RHRGGS184→179AAAAAA184) of uPA results in a 60-fold decrease in the rate of inhibition by PAI-1. Mutant prourokinase (0.0625–0.5 mg/kg; n = 12) showed efficacy comparable to wild-type scuPA and did not change IPFT outcomes ( P > 0.05). Notably, the rate of PAI-1-independent intrapleural inactivation of mutant uPA was 2 times higher ( P < 0.05) than that of the wild-type enzyme. Trapping PAI-1 in a “molecular sandwich”-type complex with catalytically inactive two-chain urokinase with Ser195Ala substitution (S195A-tcuPA; 0.1 and 0.5 mg/kg) did not improve the efficacy of IPFT with scuPA (0.0625–0.5 mg/kg; n = 11). IPFT failed in the presence of MA-56A7C10 (0.5 mg/kg; n = 2), which forms a stable intrapleural molecular sandwich complex, allowing active PAI-1 to accumulate by blocking its transition to a latent form. In contrast, inactivation of PAI-1 by accelerating the active-to-latent transition mediated by mAb MA-33B8 (0.5 mg/kg; n = 2) improved the efficacy of IPFT with scuPA (0.25 mg/kg). Thus, under conditions of slow (4–8 h) fibrinolysis in tetracycline-induced pleural injury in rabbits, only the inactivation of PAI-1, but not a decrease in the rate of its reaction with uPA, enhances IPFT. Therefore the rate of fibrinolysis, which varies in different pathologic states, could affect the selection of PAI-1 inhibitors to enhance fibrinolytic therapy.

Mice deficient in plasminogen activator inhibitor-1 have improved skeletal muscle regeneration

2005 ◽  
Vol 289 (1) ◽  
pp. C217-C223 ◽  
Author(s):  
Timothy J. Koh ◽  
Scott C. Bryer ◽  
Augustina M. Pucci ◽  
Thomas H. Sisson
Keyword(s):  
Skeletal Muscle ◽  
Plasminogen Activator ◽  
Muscle Regeneration ◽  
Plasminogen Activator Inhibitor ◽  
Skeletal Muscle Regeneration ◽  
Wild Type ◽  
Plasminogen Activator Inhibitor 1 ◽  
Activator Inhibitor ◽  
Pai 1 ◽  
Macrophage Accumulation

Skeletal muscle possesses a remarkable capacity for regeneration. Although the regulation of this process at the molecular level remains largely undefined, the plasminogen system appears to play a critical role. Specifically, mice deficient in either urokinase-type plasminogen activator (uPA−/− mice) or plasminogen demonstrate markedly impaired muscle regeneration after injury. In the present study, we tested the hypothesis that loss of the primary inhibitor of uPA, plasminogen activator inhibitor-1 (PAI-1), would improve muscle regeneration. Repair of the extensor digitorum longus muscle was assessed after cardiotoxin injury in wild-type, uPA−/−, and PAI-1-deficient (PAI-1−/−) mice. As expected, there was no uPA activity in the injured muscles of uPA−/− mice, and muscles from these transgenic animals demonstrated impaired regeneration. On the other hand, uPA activity was increased in injured muscle from PAI-1−/− mice to a greater extent than in wild-type controls. Furthermore, PAI-1−/− mice demonstrated increased expression of MyoD and developmental myosin after injury as well as accelerated recovery of muscle morphology, protein levels, and muscle force compared with wild-type animals. The injured muscles of PAI-1-null mice also demonstrated increased macrophage accumulation, contrasting with impaired macrophage accumulation in uPA-deficient mice. The extent of macrophage accumulation correlated with both the clearance of protein after injury and the efficiency of regeneration. Taken together, these results indicate that PAI-1 deficiency promotes muscle regeneration, and this protease inhibitor represents a therapeutic target for enhancing muscle regeneration.

scholarly journals Low-affinity heparin stimulates the inactivation of plasminogen activator inhibitor-1 by thrombin

Blood ◽  
1994 ◽  
Vol 84 (4) ◽  
pp. 1164-1172
Author(s):  
PA Patston ◽  
M Schapira
Keyword(s):  
Plasminogen Activator ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Plasminogen Activator Inhibitor ◽  
Initial Increase ◽  
Plasminogen Activator Inhibitor 1 ◽  
Thrombin Inhibition ◽  
Zymographic Analysis ◽  
Activator Inhibitor ◽  
Pai 1

The influence of heparin on the reaction between thrombin and plasminogen activator inhibitor-1 (PAI-1) has been examined. With a 50- fold excess of PAI-1, the rate constant for the inhibition of thrombin was 458 mol/L-1s-1, which increased to 5,000 mol/L-1s-1 in the presence of 25 micrograms/mL unfractionated heparin or heparin with low affinity for antithrombin. The effect of low affinity heparin was then examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using close to equimolar concentrations of reactants. Thrombin and PAI-1 formed a stable stoichiometric complex in the absence of heparin, which did not dissociate after the addition of 25 micrograms/mL low-affinity heparin. In contrast, when low-affinity heparin was added at the beginning of the reaction, there was an initial increase in PAI-1- thrombin complex formation, but this was rapidly followed by substantial proteolytic cleavage of unreacted PAI-1 and of the thrombin- PAI-1 complex. The idea that the relative concentrations of thrombin and PAI-1, and the presence of low affinity heparin, could influence the products of the reaction was examined in detail. Quantitative zymographic analysis of tissue plasminogen activator and PAI-1 activities and chromogenic substrate assay of thrombin activity showed that low-affinity heparin stimulated the inactivation of PAI-1 by an equimolar amount of thrombin, but caused only a minimal stimulation of thrombin inhibition. It is concluded that low-affinity heparin stimulates thrombin inhibition when PAI-1 is in excess, but, unexpectedly, that low-affinity heparin enhances PAI-1 inactivation when thrombin is equimolar to PAI-1.

943: Plasminogen Activator Inhibitor 1 (PAI-1) is Increased in Human Peyronie's Disease

2005 ◽  
Vol 173 (4S) ◽  
pp. 255-255 ◽  
Author(s):  
Hugo H. Davila ◽  
Thomas R. Magee ◽  
Freddy Zuniga ◽  
Jacob Rajfer ◽  
Nestor F. GonzalezCadavid
Keyword(s):  
Plasminogen Activator ◽  
Plasminogen Activator Inhibitor ◽  
Peyronie’S Disease ◽  
Plasminogen Activator Inhibitor 1 ◽  
Peyronie's Disease ◽  
Activator Inhibitor ◽  
Pai 1

Relationship of Plasminogen Activator Inhibitor-1 Levels following Thrombolytic Therapy with rt-PA as Compared to Streptokinase and Patency of Infarct Related Coronary Artery

1999 ◽  
Vol 82 (07) ◽  
pp. 104-108 ◽  
Author(s):  
Franck Paganelli ◽  
Marie Christine Alessi ◽  
Pierre Morange ◽  
Jean Michel Maixent ◽  
Samuel Lévy ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Acute Myocardial Infarction ◽  
Thrombolytic Therapy ◽  
Plasminogen Activator ◽  
Plasminogen Activator Inhibitor ◽  
Control Group ◽  
Plasminogen Activator Inhibitor 1 ◽  
Vessel Patency ◽  
Activator Inhibitor ◽  
Pai 1

Summary Background: Type 1 plasminogen activator inhibitor (PAI-1) is considered to be risk factor for acute myocardial infarction (AMI). A rebound of circulating PAI-1 has been reported after rt-PA administration. We investigated the relationships between PAI-1 levels before and after thrombolytic therapy with streptokinase (SK) as compared to rt-PA and the patency of infarct-related arteries. Methods and Results: Fifty five consecutive patients with acute MI were randomized to strep-tokinase or rt-PA. The plasma PAI-1 levels were studied before and serially within 24 h after thrombolytic administration. Vessel patency was assessed by an angiogram at 5 ± 1days. The PAI-1 levels increased significantly with both rt-PA and SK as shown by the levels obtained from a control group of 10 patients treated with coronary angioplasty alone. However, the area under the PAI-1 curve was significantly higher with SK than with rt-PA (p <0.01) and the plasma PAI-1 levels peaked later with SK than with rt-PA (18 h versus 3 h respectively). Conversely to PAI-1 levels on admission, the PAI-1 levels after thrombolysis were related to vessel patency. Plasma PAI-1 levels 6 and 18 h after SK therapy and the area under the PAI-1 curve were significantly higher in patients with occluded arteries (p <0.002, p <0.04 and p <0.05 respectively).The same tendency was observed in the t-PA group without reaching significance. Conclusions: This study showed that the PAI-1 level increase is more pronounced after SK treatment than after t-PA treatment. There is a relationship between increased PAI-1 levels after thrombolytic therapy and poor patency. Therapeutic approaches aimed at quenching PAI-1 activity after thrombolysis might be of interest to improve the efficacy of thrombolytic therapy for acute myocardial infarction.

Fibrinolysis in Normal Subjects - Comparison Between Plasminogen Activator Inhibitor and Other Components of the Fibrinolytic System

1988 ◽  
Vol 59 (02) ◽  
pp. 299-303 ◽  
Author(s):  
Grazia Nicoloso ◽  
Jacques Hauert ◽  
Egbert K O Kruithof ◽  
Guy Van Melle ◽  
Fedor Bachmann
Keyword(s):  
Plasminogen Activator ◽  
Fibrinolytic Activity ◽  
Plasminogen Activator Inhibitor ◽  
Venous Occlusion ◽  
Venous Stasis ◽  
Plasminogen Activator Inhibitor 1 ◽  
Plate Assay ◽  
Fibrin Plate ◽  
Activator Inhibitor ◽  
Pai 1

SummaryWe analyzed fibrinolytic parameters in 20 healthy men and 20 healthy women, aged from 25 to 59, before and after 10 and 20 min venous occlusion. The 10 min post-occlusion fibrinolytic activity measured directly in diluted unfractionated plasma by a highly sensitive 125I-fibrin plate assay correlated well with the activity of euglobulins determined by the classical fibrin plate assay (r = 0.729), but pre-stasis activities determined with these two methods did not correlate (r = 0.084). The enhancement of fibrinolytic activity after venous occlusion was mainly due to an increase of t-PA in the occluded vessels (4-fold increase t-PA antigen after 10 min and 8-fold after 20 min venous occlusion). Plasminogen activator inhibitor (PAI) activity and plasminogen activator inhibitor 1 (PAI-1)1 antigen levels at rest showed considerable dispersion ranging from 1.9 to 12.4 U/ml, respectively 6.9 to 77 ng/ml. A significant increase of PAI-1 antigen levels was observed after 10 and 20 min venous occlusion. At rest no correlation was found between PAI activity or PAI-1 antigen levels and the fibrinolytic activity measured by 125I-FPA. However, a high level of PAI-1 at rest was associated with a high prestasis antigen level of t-PA and a low fibrinolytic response after 10 min of venous stasis. Since the fibrinolytic response inversely correlated with PAI activity at rest, we conclude that its degree depends mainly on the presence of free PAI.

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