Diurnal variation of tissue-type plasminogen activator and its rapid inhibitor (PAI-1)

Previous studies have shown that overall fibrinolytic activity in blood follows a diurnal rhythm with a peak in the morning and a trough in the evening. The purpose of this study was to determine which fibrinolytic factor(s) was responsible for this diurnal rhythm. Resting and postvenous occlusion tissue-type plasminogen activator (t-PA) activity, resting t-PA antigen, and resting plasminogen activator inhibitor 1 (PAI-1) activity were measured in the morning and evening in 33 healthy men (mean age, 31 years) and in 15 patients (mean age, 57 years) with previous myocardial infarction or unstable angina. PAI-1 activity and t-PA antigen were significantly higher (p less than 0.01) in the morning compared with the evening in controls and patients. In contrast, resting t-PA activity was significantly lower in the morning (p less than 0.01) in both groups and was inversely correlated with PAI-1 activity (r = -0.57, p less than 0.0001). Postvenous occlusion t-PA activity and t-PA capacity were not significantly different between morning and evening in either group. Because t-PA antigen levels and PAI-1 activity were highest in the morning, the variation in t-PA activity was probably not due to decreased secretion of t-PA but instead to changes in the secretion of PAI-1. Our findings indicate that diurnal variations in PAI-1 activity may reduce fibrinolytic activity in the morning in healthy individuals and in patients with coronary artery disease.     

Effect of propranolol (long-acting) on the circadian fluctuation of tissue-plasminogen activator and plasminogen activator inhibitor-1

The incidence of myocardial infarction and sudden cardiac death is highest in the morning. Inhibition of fibrinolytic activity in blood also peaks in the morning and this inhibition may favor the development of arterial thrombosis. It has been reported that patients treated with beta blockers do not show the typical circadian pattern of onset of myocardial infarction and sudden cardiac death. This study was undertaken to investigate whether beta blockade alters the circadian rhythm of 2 major fibrinolytic factors, tissue-plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1). Repeated blood samples were taken over a 24-hour period in 13 healthy volunteers: 7 taking 160 mg/day of long-acting propranolol orally for 14 days, and the other 6 taking no medications. Blood samples were analyzed for the plasma levels of t-PA activity, t-PA antigen, PAI activity and PAI-1 antigen. A significant circadian variation of all 4 parameters was present in both groups. No significant differences in peak and nadir values, 24-hour mean, amplitude of fluctuation, and time of peak and nadir were found between the treated and untreated subjects. The data therefore suggest that propranolol treatment does not affect the plasma concentrations at rest or the endogenous circadian rhythm of t-PA and PAI-1 in healthy volunteers. The reported alteration in the circadian pattern of onset of myocardial infarction and sudden cardiac death by beta blockers does not appear to be mediated by effects on the fibrinolytic system.     

Circadian fluctuations of tissue plasminogen activator antigen and plasminogen activator inhibitor-1 antigens in vasospastic angina.

To elucidate the circadian variation of fibrinolytic components in vasospastic angina, plasma levels of tissue plasminogen activator antigen (t-PA), free plasminogen activator inhibitor antigen (free PAI-1), t-PA/PAI-1 complex, and total PAI-1 were measured in venous plasma samples. Samples were taken every 6 hours (6:00 AM, noon, 6:00 PM, and midnight) for 24 hours in 14 patients with vasospastic angina, in 9 patients with exertional angina, and in 19 normal subjects. Twenty-four-hour Holter monitoring (Holter monitor, Del Mar Avionics, Irvine, Calif.) was also carried out in all subjects. All of the fibrinolytic components showed circadian variation, with a peak level at 6:00 AM in every study group except for the t-PA/PAI-1 complex in the group of patients with exertional angina. The values for all or the fibrinolytic components at each sampling time were higher in patients with coronary artery disease than in normal subjects. In particular, the mean value of free PAI-1 at 6:00 AM in patients with vasospastic angina was significantly higher than that in normal subjects and that in patients with exertional angina. This value of free PAI-1 in patients with vasospastic angina was closely associated with the duration of ischemic attacks. These results suggested that the circadian fluctuation of fibrinolytic components may be an important factor that leads to coronary thrombosis at the time of coronary spasm, especially in the early morning.     

蛛网膜下腔出血后知浆t—PA、PAI—1变化的临床意义

对28例蛛网膜下腔出血（SAH）后患者的血浆组织型纤溶酶原激活物（t-PA）、纤溶酶原激活物抑制物（PAI-1）变化进行了观察,并与30例健康者进行对照。结果显示,与对照组比较,SAH后1～14天患者血浆纤溶性明显增高;其中伴发脑血管痉挛（CVS）者出血第7天、14天血浆PAI-1活性均明显高于无CVS者;出血量多者血浆t-PA、PAI-1活性较高。提示血浆t-PA、PAI-1活性在SAH后呈动态变化,二者可能均参与SAH的发生、发展、其活性测定可望成为监测SAH、CVS及出血量的有效指标。     

培哚普利对慢性心力衰竭患者血浆t-PA和PAI-1水平的影响

目的评价培哚普利对慢性心力衰竭(CHF)患者血浆组织型纤溶酶原激活物(t-PA)和纤溶酶原激活物抑制物-1(PAI-1)水平的影响。方法采用酶联免疫吸附法测定60例CHF患者(CHF组)及20例健康人(正常对照组)血浆t-PA、PAI-1水平。CHF组患者又随机均分为常规治疗亚组和培哚普利亚组。培哚普利亚组在常规治疗基础上加用培哚普利2~4mg,每日1次。所有CHF患者治疗2周后复测血浆t-PA、PAI-1水平。结果CHF患者血浆t-PA、PAI-1水平比正常对照组明显增高(P<0.01)。治疗后,培哚普利亚组血浆PAI-1水平比常规治疗亚组明显降低(P<0.01),血浆t-PA水平比常规治疗亚组明显升高(P<0.01)。结论培哚普利不仅可降低PAI-1水平,而且可升高t-PA水平,改善内源性纤溶功能。     

脑血栓形成病人血浆及脑脊液t-PA及其PAI-1含量的观察

目的：研究动脉粥样硬化性脑血栓形成病人血浆及脑脊液组织型纤溶酶原激活物（t-PA)及其抑制物（PAI-1）含量的变化及其临床意义。方法：采用双抗体夹心固相酶联免疫吸附法（ELISA）检测35例脑血栓形成病人血浆和其中31例病人脑脊液t-PA及PAI-1抗原含量，与35例正常对照组血浆和其中20例对照组脑脊液进行比较。结果；脑血栓形成组血浆t-PA含量高于对照组，PAI-1含量显著高于对照组；其脑脊液t-PA,PAI-1含量均显著高于对照组，脑脊液中t-PA,PAI-1的含量分别与血浆中t-PA,PAI-1的含量，分别与血浆中t-PA,PAI-1的含量呈正相关；脑血栓形成组病人神经功能缺损评分与血浆及脑脊液t-PA,PAI-1抗原含量呈正相关。结论：脑血栓形成病人纤溶活性明显下降，t-PA及PAI-1参与了脑血栓形成之病理过程；t-PA及PAI-1抗原含量是反映体内纤溶活性的两个重要指标；可用血浆或脑脊液t-PA,PAI-1的含量作为判断病情的参考指标之一。     

Evidence for an active fibrinolytic system in normal human bone marrow

Normal human bone marrow from patients undergoing heart surgery was analysed quantitatively for components of the fibrinolytic system, using functional and immunological assays. Marrow was found to contain considerable fibrinolytic activity, reflecting high levels of t-PA (tissue-type plasminogen activator). The t-PA was in an active form, despite the presence of the inhibitors PAI-1 and PAI-2. Plasminogen and α₂-antiplasmin (α₂-AP) were also present in marrow. The balance of proteases and inhibitors differed dramatically from that observed in plasma, with higher levels of t-PA, PAI-1 and PAI-2, and lower levels of u-PA (urokinase), plasminogen, α₂-AP and t-PA-PAI-1 complex in bone marrow, and resulted in favourable conditions for fibrinolysis. The presence of plasmin–α₂-AP complex at concentrations of the same order of magnitude as total plasminogen and α₂-AP demonstrated that active generation of plasmin was indeed occurring. A role for the active fibrinolytic system in normal human bone marrow may be the removal of unnecessary fibrin deposits formed in the cavities of the marrow, in order to maintain flow through this tissue.     

THE EFFECTS OF CHRONIC SMOKING ON THE FIBRINOLYTIC POTENTIAL OF PLASMA AND PLATELETS

We studied tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) in healthy individuals divided by smoking habit into current smokers, former smokers and non-smokers (who had never smoked). Plasma PAI-1 antigen was significantly higher in smokers than in non-smokers with intermediate levels in former smokers. A similar trend was observed for plasma PAI activity but this did not reach statistical significance. Platelet PAI-1 and plasma t-PA were not significantly different when comparing the three groups. After venous occlusion t-PA rose significantly in all groups; no significant change in plasma PAI-1 was observed. The ratio of t-PA to PAI-1 in plasma was similar in non-smokers and former smokers but lower in smokers, suggesting that there is at least partial restoration of plasma fibrinolytic potential after smoking cessation. Plasma PAI-1 antigen and PAI activity correlated with estimated pack-years of cigarettes smoked among smokers and former smokers. When all subjects were studied collectively, plasma PAI-1 correlated strongly with plasma t-PA and triglycerides; plasma t-PA also correlated strongly with triglycerdes.
We conclude that chronic smoking is associated with impaired fibrinolysis in plasma and that this largely reflects elevated plasma PAI-1 in smokers. Smoking does not appear to affect the response to venous occlusion. The postulated effect of chronic smoking on plasma PAI-1 may be mediated by the influence of smoking on triglycerides and insulin resistance. Stopping smoking appears to return impaired fibrinolysis towards normal. Smoking does not quantitatively affect the platelet pool of PAI-1. Smoking habit should be controlled for in clinical analyses of PAI-1 and t-PA.     

组织型纤溶酶原激活剂及其抑制剂与肺血栓栓塞症

肺血栓栓塞症（PTE）的发病与机体的纤溶和凝血系统功能密切相关。组织型纤溶酶原激活物（t-PA）及其抑制物（PAI-1）因调节机体的纤溶系统而在静脉血栓形成及栓塞性疾病的发病机制中发挥重要作用,因此,本文对t—PA和PAI-1与PTE的关系作如下综述。     

Abnormal fibrinolysis in healthy male cigarette smokers: role of plasminogen activator inhibitors

The extrinsic fibrinolytic system and its response to cigarette smoking was studied in five healthy male smokers 35-45 years old. Tissue plasminogen activator (t-PA) release in response to venous occlusion was intact both at 8:00 A.M. and 3:00 P.M. Acutely smoking two cigarettes neither stimulated fibrinolysis nor changed levels of t-PA or plasminogen activator inhibitors. Functional plasminogen activator inhibitor (PA-I) levels and euglobulin lysis times were higher in the smoking group than in a control group matched for age, sex, and body mass. Antigenic levels of PA-I 1, the PA-I derived from vascular endothelial cells and platelets, were similar in both groups. While smoking did not acutely alter fibrinolysis in chronic smokers, these individuals had a high frequency of abnormal fibrinolysis characterized by high levels of PA-I activity. This abnormality is due to either high specific activity of PA-I 1 or to the presence of other antigenically distinct plasminogen activator inhibitors. Abnormal fibrinolysis may be one mechanism contributing to the thrombotic diathesis of cigarette smokers.     

Possible Involvement of Tissue-Type Plasminogen Activator in Gastric Ulcer Formation —Biochemical Evaluation Using Biopsy Specimens From Gastric Mucosa—

Abstract: Microvascular endothelial changes are thought to be a crucial step in the development of hemorrhagic changes in various pathological states. Tissue-type plasminogen activator (t-PA) is an endothelium-derived fibrinolytic mediator which regulates microvascular permeability. In this study, we determined the activity and amount of t-PA in the biopsy specimens taken from gastric mucosa of patients with gastric ulcers to evaluate endothelial alterations and vascular permeable changes in situ. In addition, to elucidate the relationship between local fibrinolytic disturbance and systemic blood coagulation, several factors such as plasminogen activator inhibitor were also assayed. The results of this investigation revealed that the mucosal t-PA amount in the active ulcer proved to be 2–3 folds higher than that in healthy controls, however, t-PA levels in plasma samples showed no remarkable differences among the groups. Increased t-PA activity appeared to well correlate to the degree of inflammation of gastric mucosa in contrast to t-PA amount which was still increased in healed ulcer lesion. PAI-1 in plasma samples from gastric ulcer patients showed a significantly high level as compared with healthy subjects. The present study indicates that t-PA activation may play an important role in the pathogenesis of gastric ulcer formation and that t-PA determination in gastric biopsy specimens may be useful for the evaluation of clinical activity of gastric ulcers in terms of the mucosal microvascular endothelial changes.     

川崎病血浆组织型纤溶酶原激活物及其抑制物的变化与冠状动脉损伤的关系

目的通过对川崎病(Kawasakidisease,KD)患儿血浆组织型纤溶酶原激活物(t-PA)及其抑制物(PAI-1)的测定观察与血管损伤的关系,探讨KD合并冠状动脉病变的机制。方法采用酶联免疫吸附试验(ELISA)测定血浆t-PA、PAI-1,同时采用彩色超声心动图检测川崎病的冠状动脉并加以分析。结果KD患儿组的t-PA、PAI-1急性期和恢复期均高于对照组,差异有统计学意义(P<0.01);合并冠状动脉病变(CAL)组PAI-1、t-PA高于无冠状动脉损伤(NCAL)组,在恢复期CAL组PAI-1、t-PA持续增高,与NCAL组相比差异有统计学意义(P<0.01);CAL组的t-PA与PAl-1的比值明显低于NCAL组。两组相比差异有统计学意义(P<0.01)。结论纤溶系统与川崎病血管损伤发生、发展有着密切的关系。纤溶指标t-PA水平升高、PAI-1的大幅度升高及低t-PA/PAl-1(比值)反映了川崎病存在明显的纤溶系统功能的削弱,与冠状动脉损伤有关,为进一步探讨川崎病治疗提供了理论依据。     

Glycation amplifies lipoprotein(a)-induced alterations in the generation of fibrinolytic regulators from human vascular endothelial cells

Increased lipoprotein(a) [Lp(a)] in plasma is an independent risk factor for premature cardiovascular diseases. The levels of glycated Lp(a) are elevated in diabetic patients. The present study demonstrated that glycation enhanced Lp(a)-induced production of plasminogen activator inhibitor-1 (PAI-1), and further decreased the generation of tissue-type plasminogen activator (t-PA) from human umbilical vein endothelial cells (HUVEC) and human coronary artery EC. The levels of PAI-1 mRNA and its antigen in the media of HUVEC were significantly increased following treatments with 5 μg/ml of glycated Lp(a) compared to equal amounts of native Lp(a). The secretion and de novo synthesis of t-PA, but not its mRNA level, in EC were reduced by glycated Lp(a) compared to native Lp(a). Treatment with aminoguanidine, an inhibitor for the formation of advanced glycation end products (AGEs), during glycation normalized the generation of PAI-1 and t-PA induced by glycated Lp(a). Butylated hydroxytoluene, a potent antioxidant, inhibited native and glycated Lp(a)-induced changes in PAI-1 and t-PA generation in EC. The results indicate that glycation amplifies Lp(a)-induced changes in the generation of PAI-1 and t-PA from venous and arterial EC. This may attenuate fibrinolytic activity in blood circulation and potentially contributes to the increased incidence of cardiovascular complications in diabetic patients with hyperlipoprotein(a). EC-mediated oxidative modification and the formation of AGEs may be implicated in glycated Lp(a)-induced alterations in the generation of fibrinolytic regulators from vascular EC.     

Does chronic smoking influence fibrinolytic potential in Type 1 diabetes mellitus?

Tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1) were studied in 18 smokers and 18 closely matched non-smokers, all of whom had Type 1 diabetes mellitus (DM). None of the patients had advanced complications of diabetes. The t-PA and PAI-1 antigen levels were measured in plasma before and after venous occlusion, and were normal in Type 1 diabetes regardless of smoking status. Platelet PAI-1 levels were also measured and were found to be normal both in smokers and non-smokers. In smokers with Type 1 DM, plasma PAI-1 was significantly correlated with triglycerides. The normal fibrinolytic potential found in smokers with diabetes contrasts starkly with the significantly elevated plasma PAI-1 reported in smokers without diabetes. In smokers, triglycerides may effect low levels of PAI-1 release into plasma; this process may be significantly augmented in the presence of smoking-induced insulin resistance. The lack of endogenous insulin release in Type 1 diabetes may obviate the characteristic rise in plasma PAI-1 found in smokers who do not have diabetes. © 1998 John Wiley & Sons, Ltd.     

复方丹参滴丸对冠心病患者纤溶系统t-PA、PAI-1含量与活性的调控

目的观察复方丹参滴丸对冠心病患者内源性纤溶活性及血管内皮功能的影响，探讨其作用机制。方法冠心病患者78例，随机分为对照组和复方丹参滴丸组。对照组采用常规治疗；复方丹参滴丸组在常规治疗基础上加用复方丹参滴丸每次10粒，每日3次。两组用药时间均为4周。比较治疗前后血浆组织型纤溶酶原激活剂（t-PA）、纤溶酶原激活剂抑制因子-1（PAI-1）活性及浓度。结果复方丹参滴丸治疗4周后，患者血浆PAI-1活性及浓度下降（P〈0．05），t—PA活性及浓度含量升高（P〈0．05），与治疗前比较差异有统计学意义；常规治疗组治疗前后t-PA和PAI-1活性差异无统计学意义。结论复方丹参滴丸可有效地调控改善冠心病患者内源性纤溶活性及血管内皮功能。     

Effect of PAI-1 levels on the molar concentrations of active tissue plasminogen activator (t-PA) and t-PA/PAI-1 complex in plasma

We determined the in vivo molar concentrations of active tissue plasminogen activator (t-PA), active plasminogen activator inhibitor type 1 (PAI-1), and t-PA/PAI-1 complex. t-PA activity was measured in plasma stabilized by immediate acidification. PAI-1 activity and t- PA/PAI-1 complex antigen were measured in citrated plasma; these measurements were corrected for the loss in PAI-1 activity and increase in complex that occurs in unacidified plasma samples due to the continued reaction between t-PA and PAI-1 after the sample was drawn. To convert t-PA and PAI-1 activity measurements into molar concentrations we determined the specific molar activity of t-PA and PAI-1 in vivo: 4.48 x 10(13) IU/mol. Of 72 subjects studied, 13 had less than 150 pmol/L active PAI-1; in these individuals 33% +/- 21% of their t-PA was active and the molar ratio of active t-PA to active PAI- 1 was 0.20 +/- 0.13. In the 11 subjects with greater than 500 pmol/L active PAI-1, 1.5% = 1.1% of the t-PA was active and the molar ratio of active t-PA to active PAI-1 was 0.0043 +/- 0.0036. Overall, the fraction of active t-PA declined exponentially as a function of the active PAI-1 concentration. During the day, the percentage of total t- PA that was active increased from 12% at 8:00 AM to 31% at 8:00 PM, while the molar ratio of active t-PA to active PAI-1 increased from 0.05 to 0.22 from morning to evening (n = 12).     

老年高血压患者心房颤动急性发作后血栓前状态的改变

目的观察老年高血压患者心房颤动(房颤)急性发作时及药物复律后血栓前状态的改变。方法老年高血压患者急性房颤发作29例(急性房颤组),发作48 h内成功复律,未予抗凝治疗,复律后窦性心律维持时间>1个月。分别于复律前,复律后1、7、14、30天检测血浆纤维蛋白原(Fib)、D-二聚体水平,组织型纤溶酶原激活剂(t-PA)活性和纤溶酶原激活物抑制剂-1(PAI 1)活性。另选高血压合并窦性心律患者30例(窦性心律组),高血压合并永久性房颤,且未予华法林抗凝治疗者30例(慢性房颤组),健康体检者30例(健康对照组),分别检测上述指标。结果急性房颤组和慢性房颤组患者Fib、D-二聚体水平显著高于窦性心律组和健康对照组。急性房颤组患者复律后Fib水平于第7天降至窦性心律组水平,D-二聚体浓度于第7天升至最高峰,其后逐渐下降,但直至复律后第30天仍高于窦性心律组。急性房颤组患者复律前及复律后t-PA及PAI-1活性与健康对照组和窦性心律组比较,差异均无统计学意义。结论老年高血压患者房颤急性发作时存在血栓前状态,并且在复律后仍可持续1个月。     

全蝎纯化液对实验性动脉血栓形成t-PA、PAI-1的影响

目的观察全蝎纯化液对新西兰白兔颈总动脉血栓形成组织型纤溶酶原激活物(t-PA)、纤溶酶原活化物抑制剂(PAI-1)、血小板计数(Pt)的变化。方法将50只健康新西兰白兔随机分成5组:空白组、模型组、全蝎纯化液大剂量组(20mg/kg)、全蝎纯化液中剂量组(10mg/kg)和全蝎纯化液小剂量组(5mg/kg)。耳缘静脉注射药物(空白组、模型组注射同等体积的生理盐水)后,采用H2O2损伤新西兰白兔颈总动脉制备血栓模型,造模2h后,采血并取血栓,酶联免疫吸附法(ELISA法)检测血浆t-PA、PAI-1的含量。结果与空白组比较,模型组t-PA明显降低,PAI-1明显升高,差异有统计学意义(P<0.01);与模型组相比,全蝎纯化液各剂量组能明显抑制PAI-1活性,增加t-PA活性,差异均有统计学意义(P<0.01),而各组的血小板计数差异无统计学意义(P>0.05)。结论全蝎纯化液各剂量组可明显促进血浆t-PA的分泌,抑制血浆PAI-1活性,提示全蝎纯化液抗血栓作用机制可能与其促纤溶作用有关。     

Diurnal changes of fibrinolysis in patients with liver cirrhosis and esophageal varices

Variceal bleeding, whose triggering mechanisms are largely unknown, occurs with a circadian rhythmicity, with 2 peaks, one greater, in the evening, and one smaller, in the early morning. We assessed some clotting and hemodynamic parameters, possibly involved in variceal hemorrhage, over a 24-hour period, at 4-hour intervals, in 16 patients with cirrhosis and esophageal varices and in 9 controls. At each time interval, tissue plasminogen activator (tPA) and tPA inhibitor-1 (PAI-1) antigens and activities and total euglobulin fibrinolytic activity were determined and portal-vein flow velocity, volume, and congestion index were measured by duplex-Doppler. Significant circadian rhythms were searched for by least-squares and cosinor methods. tPA activity showed a circadian rhythm in cirrhosis, with a peak of 2.85 times the trough value, calculated at 18:42, and remained over 2.5-fold until shortly after 22:00. Total fibrinolytic activity showed a similar pattern, which was statistically significant also in controls. tPA and PAI antigens also showed significant circadian rhythm both in controls and cirrhotics, with higher values in the morning. Among the portal hemodynamic parameters only the congestion index showed significant rhythmic changes and only in cirrhosis, with the highest values in the late evening, but with limited diurnal excursion (+/- 5.5%). In conclusion, we showed the existence of a circadian rhythm of fibrinolysis in cirrhosis, whose temporal distribution might suggest a role of fibrinolysis in variceal hemorrhage on the basis of the comparison to the known chronorisk of variceal bleeding.     

Different effects of lipopolysaccharide on plasminogen activator inhibitor-1 production in aortic media in vivo and in culture

Background Lipopolysaccharide (endotoxin) has been shown to increase the expression of plasminogen activator inhibitor type-1 (PAI-1) in the vessel wall. Endotoxin is known to increase PAI-1 production in endothelial cells, but its action on smooth muscle cells (SMCs) is presently not clear. In this study we determined the effect of endotoxin on PAI-1 and tissue plasminogen activator (t-PA) production by aortic SMCs in vivo in two animal species, and in culture.Methods The aortas of Sprague Dawley rats and of New Zealand White rabbits were rapidly excised after parenteral administration of endotoxin. Total RNA was extracted from the aortic media, and PAI-1 and t-PA mRNA levels were quantified after Northern blotting. In addition, cultured rat aortic SMCs were treated with endotoxin. PAI activity in the conditioned medium was determined with a spectrophotometric assay, and total RNA was extracted from the cells and analyzed.Results A rapid and strong induction in the aortic media of PAI-1 mRNA was observed by endotoxin in both rat (50 mg/kg) and rabbit (1 mg/kg). t-PA mRNA was barely detectable and was not increased by endotoxin. Studies in cultured SMCs showed low expression of PAI-1 mRNA under serum-free conditions and little PAI activity in the cell-conditioned medium. Endotoxin did not increase the levels of PAI-1 mRNA nor PAI activity under serum-free conditions. The effect of endotoxin (10 mg/ml) in the presence of 10% (v/v) newborn calf serum on PAI-1 mRNA was negligible; PAI activity, however, increased by 50.3 ± 7.3% compared with controls. mRNA levels of t-PA and low-density lipoprotein/receptor-related protein/₂-macroglobulin receptor also increased after endotoxin administration. PAI activity was identified as PAI-1 by immunoblotting. Fibrin zymography showed that t-PA was present only in complex with PAI-1.Conclusions A strong increase in PAI-1 gene expression by endotoxin was observed in aortic SMCs in vivo but not in culture. This suggests that the effect of endotoxin on SMCs is indirect. The fibrinolytic/proteolytic potential of the SMCs in the vessel wall is likely to have important implications for the migration of cells during vessel wall remodeling, such as neointima formation, during tumor cell metastasis, and for the fate of intramural thrombi.