Hypofibrinolysis in patients with a history of idiopathic deep vein thrombosis and/or pulmonary embolism.

An impaired fibrinolytic activity after a venous occlusion test is the most common abnormality associated with thomboembolic disease. To better characterize the causes of abnormal responses we have measured different fibrinolytic parameters, before and after 10 and 20 min of venous occlusion, in 77 patients with a history of idiopathic deep vein thrombosis and/or pulmonary embolism and in 38 healthy volunteers. The patients had a lower mean fibrinolytic response to venous occlusion than the controls and higher antigen levels of tissue-type plasminogen activator (t-PA:Ag) and plasminogen activator inhibitor type 1 (PAI-1:Ag). Before venous occlusion, PAI-1 levels were at a molar excess over those of t-PA in all patients and controls. After 20 min of venous occlusion, the release of t-PA from the vascular endothelium resulted in a molar excess of t-PA over PAI-1 in the majority of controls (72%) but only in a minority of patients (39%). To identify patients with fibrinolytic abnormalities, reference intervals (RI) for fibrinolytic activity, t-PA:Ag and PAI-1:Ag were established in healthy controls. None of the patients had low levels of t-PA:Ag, but 17 (22%) had elevated PAI-1:Ag levels before venous occlusion and 12 (16%) exhibited low fibrinolytic activity after 20 min of venous occlusion. Ten of these were among the 17 subjects with high PAI-1:Ag levels before venous occlusion. Thus, the measurement of PAI-1:Ag levels before venous occlusion (i.e. in samples taken without any stimulation) is a sensitive (83%) and specific (89%) assay for the detection of patients with an impaired fibrinolytic response to venous occlusion.     

Effect of the lupus anticoagulant on endothelial fibrinolytic activity in vitro

We investigated the effect of plasma and serum from 10 subjects with the lupus anticoagulant and thrombosis and 9 normal subjects on the secretion of tissue-type plasminogen activator (t-PA) and its rapid inhibitor (type 1 plasminogen activator inhibitor, or PAI-1) by cultured human endothelial cells. Confluent monolayers of human umbilical vein endothelial cells were incubated for 48 hours with plasma or serum diluted ten-fold in serum-free endothelial cell growth medium, and the secretion of t-PA and PAI-1 measured by enzyme-linked immunosorbent assay. No consistent differences in mean t-PA and PAI-1 release were found between cells exposed to normal plasma or serum and plasma or serum from subjects with the lupus anticoagulant and thrombosis. No plasma or serum sample produced consistent inhibition of t-PA release or stimulation of PAI-1 release (defined as t-PA levels less than the mean minus two standard deviations for normal subjects, and PAI-1 levels greater than the mean plus two standard deviations for normal subjects, respectively). These findings do not support a role for altered endothelial fibrinolytic activity in the pathogenesis of thrombosis in subjects with the lupus anticoagulant, and are consistent with previous observations that these subjects have normal fibrinolytic activity in vivo.     

Impaired fibrinolysis and postoperative thromboembolism in orthopedic patients.

The incidence of deep vein thrombosis (DVT) and pulmonary embolism was studied prospectively in patients undergoing elective total hip replacement. 96 patients were randomly allocated to receive either low molecular weight heparin (LMWH) or unfractionated heparin (UFH). All patients had bilateral phlebography and pulmonary perfusion/ventilation scintigraphy 10-12 days after surgery. The following fibrinolytic variables were analysed in plasma and related to thromboembolism: tissue plasminogen activator (t-PA) activity, t-PA antigen (t-PA Ag), plasminogen activator inhibitor (PAI-1) activity and PAI-1 antigen (PAI-1 Ag). No significant difference was found, regarding the fibrinolytic response to surgery, between patients treated with LMWH and UFH. The level of PAI-1 activity was significantly increased before operation in patients developing DVT as compared to non-DVT patients (p less than 0.03). Immediately after surgery and in the morning the first postoperative day the levels of PAI-1 activity, PAI-1 Ag and t-PA Ag were positively correlated to thromboembolism. PAI-1 activity was the only preoperative fibrinolytic variable correlated to thromboembolism.     

Effect of thrombin on the production of plasminogen activators and PA inhibitor-1 by human foreskin microvascular endothelial cells

Human foreskin microvascular endothelial cells synthesize and release tissue-type plasminogen activator (t-PA) in similar amounts as do endothelial cells from umbilical cord artery and vein. Human thrombin increases the production of t-PA by these cells, which could be visualized from 8 h after addition of 0.1-5 units/ml thrombin by fibrin autography after SDS polyacrylamide gel electrophoresis of the endothelial cell conditioned media. Thrombin also increased the secretion of t-PA antigen. Together with t-PA, human microvascular cells release urokinase-type plasminogen activator (u-PA) antigen and endothelial cell-type PA inhibitor, PA inhibitor-1, which were both demonstrated by specific immunoprecipitation from radiolabeled endothelial cell conditioned medium. Thrombin increases the release of u-PA antigen, but no u-PA activity could be demonstrated. Thrombin induced a two-fold stimulation of the synthesis and secretion of PA inhibitor-1 antigen. At 0.1 unit/ml thrombin also an increase in PA inhibitor activity was found. At high concentrations of thrombin a decrease of PA inhibitor activity was found, due to the conversion of the active 46 kD PA inhibitor-1 into a 42 kD product without PA inhibitor activity. Our data indicate that interaction of thrombin with microvascular endothelial cells will shift the balance between t-PA, u-PA and PA inhibitor-1, and thus affects the regulation of fibrinolysis.     

L-158,809 and (D-Ala(7))-angiotensin I/II (1-7) decrease PAI-1 release from human umbilical vein endothelial cells

The endothelium is a major source of plasminogen activator inhibitor-1 (PAI-1), which plays a critical role in the regulation of fibrinolysis. There are many reports on the increase in the expression of PAI-1 by angiotensin II (Ang II). In the present study, we investigated the effects of angiotensin-related substances on the release of PAI-1 from human umbilical vein endothelial cells (HUVECs). Ang II increased PAI-1 and tissue plasminogen activator (t-PA) release, while its metabolite angiotensin-(1-7) (Ang-(1-7)) amino acid fragment decreased them. Angiotensin Type 1 (AT1) receptor antagonist, L-158,809 (L-1), and Ang-(1-7) receptor antagonist, (D-Ala(7))-angiotensin I/II (1-7) (D-Ala), decreased PAI-1 and t-PA release; angiotensin Type 2 (AT2) antagonist, PD123,319 (PD), however, did not have any effects on the release of PAI-1 and t-PA. The addition of the equal concentration or 10-times-higher concentration of L-1 to Ang II did not change PAI-1 release compared to that by Ang II. Although Ang-(1-7) and L-1 decreased PAI-1 release, there were no additional effects on the decrease of the amounts of PAI-1 by the mixture of Ang-(1-7) and the equal concentration or 10-times-higher concentration of L-1 compared to those by Ang-(1-7). The equal concentration of D-Ala to Ang II did not change the amounts of PAI-1, but the addition of the 10-times-higher concentration of D-Ala to Ang II resulted in significant decrease of the amounts of PAI-1 compared to those by Ang II. The addition of equal concentration or 10-times-higher concentration of D-Ala to Ang-(1-7) showed the significant decrease of the amounts of PAI-1 compared to those by Ang-(1-7). In conclusion, L-158,809 and (D-Ala(7))-angiotensin I/III (1-7) may be used as profibrinolytic drugs.     

Induction of synthesis of plasminogen activator inhibitor type-1 by tissue-type plasminogen activator in human hepatic and endothelial cells

Plasminogen activator inhibitor type-1 (PAI-1) can modify fibrinolytic activity in vitro and in vivo. The present study was performed to determine whether pharmacologic concentrations of tissue-type plasminogen activator (t-PA) can initiate negative feedback by stimulating PAI-1 synthesis. In both human hepatoma cells (Hep G2) and human umbilical vein endothelial cells (HUVEC), t-PA increased the total concentrations and appearance of newly synthesized protein in conditioned media of free PAI-1 and PAI-1 complexed with t-PA in a dose and time dependent fashion judging from results after immunoprecipitation of metabolically labeled PAI-1. The t-PA effect was not attributable simply to release of stored or matrix-bound PAI-1. In HUVEC, Northern blot analyses indicated that t-PA increased steady-state levels of PAI-1 mRNA two-fold. In contrast PAI-1 mRNA expression was not increased in Hep G2 cells. Thus, mechanisms of stimulation appeared to differ in the two cell lines. The results obtained are consistent with the hypothesis that increased PAI-1 synthesis and secretion in response to t-PA may limit or attenuate fibrinolysis locally or systemically in vivo.     

Purification and biological property of heparin cofactor II: Activation of heparin cofactor II and antithrombin III by dextran sulfate and various glycosaminoglycans

Heparin cofactor II (HC II) has been purified from human plasma by a mocification of the method described by Tollefsen $\text{et al}$.(J. Biol. Chem., $\text{257}$, 2162, 1982) and abilities of dextran sulfate and various glycosaminoglycans to activate the antithrombin activities of HC II and antithrombin III (AT III) were studied. By the purification method described here, highly purified HC II with the same specific activity as reported by Tollefsen $\text{et al}$. was obtained with a higher yield and in a shorter purification time. Heparin, dextran sulfate and chondroitin polysulfates 1 and 5 activated both HC II and AT III, while dermatan sulfate activated only HC II. Dextran sulfate was almost as active as heparin in the activation of HC II and AT III, indicating that in the interactions of heparin with HC II and AT III, sulfate groups of heparin are more important than carboxyl groups. When mixed with thrombin in the presence of dermatan sulfate, normal human plasma showed antithrombin activity which was not due to AT III but to HC II only. HC II did not inhibit factor Xa or plasmin in the presence of any glycosaminoglycans or dextran sulfate, suggesting that HC II would be a specific inhibitor of thrombin.     

Decrease of fibrinolytic activity in human endothelial cells by arsenite

Blackfoot disease (BFD) is an endemic peripheral vascular occlusive disease that occurred in the southwest coast of Taiwan. It is believed that arsenic in the drinking water from artesian wells plays an important role in the development of the disease. We have previously shown that BFD patients had significant lower tissue-type plasminogen activator (t-PA) antigen level and higher plasminogen activator inhibitor, Type 1 (PAI-1) antigen level than normal controls. The purpose of this study was to investigate the effects of arsenite on the fibrinolytic and anticoagulant activities of cultured macrovascular and microvascular endothelial cells. Incubation of human microvascular endothelial cells (HMEC-1), but not human umbilical vein endothelial cells (HUVECs), with arsenite caused a decrease of t-PA mRNA level, a rise of both PAI-1 mRNA level and PAI activity. Arsenite could also inhibit the thrombomodulin (TM) mRNA expression and reduce the TM antigen level in HMEC-1. In conclusion, arsenite had a greater effect on HMEC-1 as compared to HUVECs in lowering the fibrinolytic activity and may be responsible for the reduced capacity of fibrinolysis associated with BFD.     

Stimulation of tissue-type plasminogen activator synthesis by retinoids in cultured human endothelial cells and rat tissues in vivo

Tissue-type plasminogen activator (t-PA) and its inhibitor, plasminogen activator inhibitor 1 (PAI-1), play an important role in regulating the fibrinolytic capacity of plasma. Both t-PA and PAI-1 are synthesized by the endothelium. We report that retinoic acid (vitamin A acid) and other retinoids rather specifically stimulate the production of t-PA by cultured human umbilical vein endothelial cells. Effective retinoids induced a dose-dependent (range: 0.01-50 microM) increase in the production of t-PA of maximally about six-fold, while simultaneously causing no or only a small increase (less than two-fold) of PAI-1. The effects on t-PA synthesis were apparent by 4-8 h, and reached maximal values after about 24-48 h of incubation with retinoid. The retinoid effect on t-PA production was accompanied by increased t-PA mRNA levels, without any parallel change in PAI-1 or GAPDH mRNA concentrations. The study also shows that modifications at the carboxyl group of retinoic acid are associated with a decrease in stimulatory potency. The stimulatory pathway appears to be identical for all retinoids but distinct from a pathway by which another strong inducer, sodium butyrate, induces t-PA synthesis in endothelial cells. The induction of t-PA by retinoids might involve protein kinase C (PKC) as judged by an experiment using a specific PKC inhibitor. The effect of retinoids on the fibrinolytic system in vivo was assessed by feeding rats with a vitamin A deficient diet or a diet with excess of vitamin A or other retinoids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antithrombin III modulates the effect of thrombin on the metabolism of glycosaminoglycans in cultured endothelial cells

We previously reported that a treatment of cultures of endothelial cells from bovine aorta with thrombin resulted in a less accumulation of glycosaminoglycans (GAG) in the cell layer. In the present study, we found that thrombin-induced decrease in the accumulation of [³⁵s]sulfate-labeled GAG (³⁵S-GAG) such as heparan sulfate was prevented by antithrombin III (AT III) but not by heparin cofactor II (HC II). However, AT III did not show a significant effect on the ³⁵S-GAG accumulation individually. Pretreatment of the cell layer with neither AT III not HC II showed any preventive effect. When GAG in the cell layer was labeled with both [³⁵s]sulfate and [³⁵h] glucosamine, neither thrombin nor a combination of thrombin with AT III changed the ratio of the radioactivity of ³⁵S to that of ³H. Although thrombin stimulated the release of ³⁵S-GAG from the cell layer, AT III completely prevented the stimulatory effect. In conclusion, it was suggested that AT III may inhibit the thrombin action on GAG metabolism of endothelial cells to prevent thrombosis in vivo.     

MONOCYTES MODULATE THE FIBRINOLYTIC BALANCE OF ENDOTHELIAL CELLS

Cultured endothelial cells (ECs) produced a constitutive plasminogen activator inhibitor-1 (PAI-1), whereas primary culture of monocytes from blood did not produce a detectable amount of PAI-1. Addition of monocytes to ECs caused the accumulation of a large amount of PAI-1 in the supernatant in a dose- and time-dependent manner. Having almost no effect on the production of tissue-type plasminogen activator (t-PA), monocytes decreased the potential fibrinolytic activity of ECs. The 6 hours conditioned medium obtained from the coculture system between monocytes and either ECs or paraformaldehyde-fixed ECs had almost the same effect on the other ECs to produce PAI-1 and t-PA as monocytes that were direct contact with ECs. In addition, this effect was specifically inhibited by using two antibodies against interleukin-1β and tumor necrosis factor-α. These results indicate that interleukin-1β and tumor necrosis factor-α induced by the coculture are mostly responsible for decreasing the fibrinolytic activity of ECs.© 1997 Elsevier Science Ltd     

Tissue-type plasminogen activator, type 1 plasminogen activator inhibitor and their complex in plasma with disseminated intravascular coagulation.

The levels of tissue-type plasminogen activator (t-PA), type 1 plasminogen activator inhibitor (PAI-1), and t-PA/PAI-1 complex antigens were analyzed in the plasma of disseminated intravascular coagulation (DIC) patients and healthy controls. Other fibrinolytic parameters such as the levels of plasminogen, alpha 2-antiplasmin (alpha 2-AP), plasmin/alpha 2-AP (PAP), and D-dimer were also estimated to clarify the fibrinolytic states in these plasmas. The antigens of t-PA, PAI-1, and t-PA/PAI-1 complex were found to increase from 8.5 +/- 4.3, 54.4 +/- 21.2, and 8.6 +/- 3.5 ng/ml in normal plasma to 36.4 +/- 25.1, 106.8 +/- 54.7, and 46.6 +/- 34.5 ng/ml in DIC plasma, respectively. The molar ratio of total t-PA to total PAI-1 was 1:6 and 1:3 in normal plasma and DIC plasma, respectively, indicating an enhanced fibrinolytic state in the DIC plasma. The DIC plasma revealed a significant consumption of plasminogen (62.1 +/- 27.8%), and alpha 2-AP (63.7 +/- 25.3%) and an increase in PAP (2.6 +/- 2.7 micrograms/ml) and D-dimer (3.9 +/- 10.7 micrograms/ml). These results suggest that the production and secretion of t-PA and PAI-1 from endothelial cells were enhanced in DIC, resulting in an increased t-PA/PAI-1 complex with dominant fibrinolytic activity.     

Determinants of induction of increased synthesis of plasminogen activator inhibitor type-1 in human endothelial cells by t-PA.

Tissue-type plasminogen activator (t-PA) induces synthesis of a rapidly acting inhibitor, plasminogen activator inhibitor type-1 (PAI-1) in human umbilical vein endothelial cells (HUVEC) in culture. In vivo, an analogous process may induce negative feedback on the fibrinolytic system. To define specific determinants in the t-PA molecule contributing to the induction, PAI-1 synthesis was characterized in 35S-methionine labeled HUVEC in response to several molecular variants of t-PA. Catalytically active variants devoid of several specific structural domains in the A-chain retained the capacity to form complexes with PAI-1 and to induce increased concentrations of total PAI-1 (free and complexed) in conditioned media without depleting PAI-1 from the extracellular matrix. Surprisingly, a mutant t-PA with markedly reduced catalytic activity reflecting replacement of the active site serine with threonine (S478T) formed complexes with PAI-1 and induced increased PAI-1 synthesis as well. However, in contrast to wild-type t-PA and A-chain variants, it did not release 35S-methionine labeled PAI-1 from the extracellular matrix. Thus, its effects appeared to reflect increased secretion exclusively. Our results suggest that induction of PAI-1 synthesis in HUVEC by t-PA depends on its protease domain but that an active site serine is not a requirement.     

Salvianolic acid B modulates hemostasis properties of human umbilical vein endothelial cells

Salviae miltiorrhizae (SM), a clinical, commonly used herb, can activate blood circulation and resolve stasis. We have investigated the effects of salvianolic acid B (Sal B), a pure compound extracted from the dried SM roots, on fibrinolytic (tissue-type plasminogen activator and plasminogen activator inhibitor, t-PA and PAI) and anticoagulant (thrombomodulin,TM) properties of cultured human umbilical vein endothelial cells (HUVECs). When HUVECs were treated with Sal B, a dose- (0.0125–0.5 mg/ml) and a time-dependent decrease in PAI activity were observed. PAI type 1 (PAI-1) antigen and PAI-1 mRNA expression significantly decreased compared to control values in the conditioned media of HUVECs pretreated with Sal B for 12 h. Moreover, TM activity reached a maximum stimulation of 1.25-fold over control levels in the pretreatment of Sal B for 12 h and t-PA and TM specific mRNA expression also increased (1.7- and 1.8-fold, respectively). In conclusion, Sal B increased the fibrinolytic and anticoagulant potential of cultured HUVECs by up-regulating the expression of t-PA and TM and by down-regulating the expression of PAI-1. These data suggest that Sal B is clinically effective because of its ability to change the gene expression profile of endothelial cells thereby preventing vascular events.     

Hyperfibrinolysis in alcoholic cirrhosis: relative plasminogen activator inhibitor type 1 deficiency

BACKGROUND: Over activity of the fibrinolytic system (hyperfibrinolysis) occurs in cirrhosis and has been shown to correlate with the risk of variceal hemorrhage. We have developed a model for assessing acute tissue plasminogen activator (t-PA) release in vivo in man. The aims of the study were to assess the contribution of basal and stimulated t-PA release to hyperfibrinolysis in patients with alcoholic cirrhosis. METHODS: Bilateral forearm blood flow and plasma fibrinolytic variables were measured in 8 patients with biopsy proven alcohol induced cirrhosis, ascites and portal hypertension, and 8 age and sex matched healthy controls during infusion of bradykinin (100-900 pmol/min; endothelium-dependent vasodilator that releases t-PA) followed by sodium nitroprusside (SNP 2-8 microg/min; a control endothelium-independent vasodilator). RESULTS: Baseline plasma t-PA antigen concentrations were higher in patients (14+/-2 vs 9+/-1 ng/mL; p<0.05) whereas plasma plasminogen activator inhibitor type-1 (PAI-1) antigen concentrations were similar (59+/-16 vs 55+/-11 ng/mL; p=NS). This resulted in an increased t-PA activity (3+/-1 vs 0+/-0 IU/mL; p<0.05) and reduced PAI-1 activity (9+/-2 vs 21+/-2 AU/mL; p<0.05) indicating a relative deficiency of PAI-1 in patients with cirrhosis. Bradykinin and SNP caused dose-dependent vasodilatation (p<0.001 for both) that did not differ between the two groups. Bradykinin caused a similar release of t-PA antigen (p<0.05 for both) in both patients and controls (24+/-17 vs 23+/-7 ng/100 mL/min; p=ns) without affecting PAI-1 concentrations. Local t-PA activity was increased in patients following acute stimulated t-PA release (5+/-1 vs 3+/-1 IU/mL; p<0.05). SNP caused no significant change in fibrinolytic parameters. CONCLUSION: Patients with alcoholic cirrhosis have a higher basal plasma t-PA activity because of a failure to increase plasma concentrations of its inhibitor, PAI-1. Furthermore, despite releasing normal amounts of t-PA acutely, higher t-PA activity remained due to the relative deficiency of PAI-1. This suggests that the pathogenesis of hyperfibrinolysis in alcoholic cirrhosis is the result of a relative PAI-1 deficiency and enhanced basal t-PA release.     

Activation of endothelial cells, coagulation and fibrinolysis in children with Dengue virus infection

Dengue virus causes a febrile illness: Dengue fever (DF), and less frequently a life-threatening illness: Dengue hemorrhagic fever (DHF). Although severe bleeding remains a major cause of death in DHF, the pathogenesis of bleeding is poorly understood. This prospective cohort study was designed to determine the extent of activation of endothelial cells and the hemostatic system in correlation with clinical severity, and also to detect the best prognostic factor(s) for DHF. Endothelial cell activation, coagulation, anticoagulant and fibrinolysis parameters were measured in 42 children with Dengue infections (20 with DF and 22 with DHF) during three phases of illness. In DHF patients, during the febrile phase, von Willebrand factor antigen (vWF:Ag), tissue factor (TF) and plasminogen activator inhibitor (PAI-1) were significantly elevated, while platelet counts and ADAMTS 13 (a disintegrin and metalloprotease with thrombospondin repeats) were significantly low compared to DF patients. During the toxic phase, soluble thrombomodulin (sTM), tissue plasminogen activator (t-PA) and PAI-1 were also significantly increased, while ADAMTS 13 and thrombin activatable fibrinolysis inhibitor (TAFIa) were significantly low compared to DF patients. Abnormal vWF multimers were seen only in DHF patients. For endothelial cell injury and release of procoagulant components, activation of the coagulation cascade with thrombin generation, increased antifibrinolytic factors and consumption of natural anticoagulants, each appeared to play an important role in the development of hemorrhage in Dengue patients. Using logistic regression analysis, we found plasma VWF:Ag to be the best indicator of progression to DHF.     

Plasminogen activators and plasminogen activator inhibitor 1 before and after venous occlusion of the upper limb in thromboangiitis obliterans (Buerger's disease).

Plasma levels of plasminogen activators (t-PA, u-PA) and their inhibitor (PAI-1) were studied in patients suffering from Buerger's disease and healthy volunteers before and after 15 minutes of venous occlusion test. The baseline levels of t-PA in group of patients did not differ from those of controls. On the contrary patients with Burger's disease showed a marked increase in u-PA antigen concentrations with concomitant decrease in PAI-1 antigen levels. During venous stasis t-PA antigen concentrations increased in all subjects, however it was much pronounced in controls. Venous occlusion resulted in significant decrease in free PAI-1 levels in the group of patients only. In conclusion, Buerger's disease is associated with the endothelial derangement with increased u-PA release and decreased PAI-1 release, which does not influence the function of fibrinolytic system. The fact that the reduced response of the endothelium to release t-PA after venous stasis goes in parallel with marked decrease in PAI-1 antigen levels seems to suggest that patients suffering from Buerger's disease are not at high risk of intravascular fibrin deposition.     

Regional fibrinolysis following total hip replacement

The local effect of operative trauma on the fibrinolytic system was studied in ten patients undergoing total hip replacement. Catheters were inserted in the femoral veins on both sides and blood was sampled from these catheters perioperatively. The following fibrinolytic variables were analysed in plasma and related to the different steps of surgery: tissue plasminogen activator (t-PA) activity, t-PA antigen and plasminogen activator inhibitor (PAI-1) activity. During surgery PAI-1 activity and t-PA antigen in the operated limb were significantly increased compared with preoperative values. There was a significant difference in PAI-1 activity and t-PA antigen between the operated and the non-operated limbs during surgery and within one hour postoperatively. During fixation of the femoral implant there was a significant difference between the operated and the non-operated limbs in t-PA activity. Thus the regional fibrinolytic response to trauma was dissociated from the response in the non-operated limb. The clinical relevance of the observed alterations in regional fibrinolysis, as related to thrombogenic mechanisms after hip surgery, remains to be elucidated.     

Aspirin, indomethacin and dazoxiben do not affect the fibrinolytic activation induced by venous occlusion

A cause-effect relation between the synthesis and release of prostaglandins and fibrinolytic activation has been suggested. We have reinvestigated this relation in a double-blind, placebo-controlled, cross-over study with cyclooxygenase inhibitors (aspirin and indomethacin) and a thromboxane synthase inhibitor (dazoxiben) in nine healthy volunteers. Euglobulin fibrinolytic activity (EFA) and tissue-type plasminogen activator antigen level (t-PA:Ag) were studied before and after 10 min of venous occlusion. Despite effective suppression of prostaglandin synthesis by aspirin and indomethacin and enhanced prostacyclin formation by dazoxiben, baseline EFA and t-PA:Ag levels did not significantly change within 2 hours after ingestion of the different drugs. The release of t-PA by venous occlusion was not altered by any of the drugs. Thus, our study does not support the hypothesis that prostaglandins play a significant role in the modulation of the synthesis or release of t-PA.