Fibrinolytic response during exercise and epinephrine infusion in the same subjects

Exercise testing unmasks exaggerated blood pressure independent of fibrinolytic response in Black but not White postmenopausal females

Exercise testing unmasks more exaggerated systolic blood pressure responses (SBP) in Black compared with White male adults. Such responses, if translatable to females, may detect racial disparities particularly relevant during menopause. Given the endothelial involvement in BP regulation and as a source of fibrinolytic markers, it follows that fibrinolytic and BP response to exercise could be linked. Thus, we examined BP and fibrinolytic responses to exercise testing in Black and White postmenopausal females. Postmenopausal females (Black = 40; White = 41; 51-70 yr) performed maximal treadmill exercise. BP and blood draws were conducted before and immediately after exercise. Plasma samples, using minimal stasis, were analyzed for tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1) activity and antigen, respectively. Resting SBP and fibrinolytic potential were similar between races. Black females exhibited greater increases in SBP during exercise [change (d)=75, 95% CI: 64-86 mmHg, P < 0.001] than White females (d = 60, 95% CI: 48-71 mmHg, P < 0.001). Black compared with White females had smaller changes in tPA (d = 3.27, 95% CI: 2.28-4.27 IU/mL, P < 0.001 vs. d = 5.55, 95% CI: 4.58-6.53, P < 0.001) and PAI-1 (d = -2.89, 95% CI: -4.39 to -1.40 IU/mL, P < 0.001 vs. d = -5.08, 95% CI: -6.59 to -3.61, P < 0.001) activities after exercise. SBP exercise-induced changes were not associated with tPA (r = -0.10, P = 0.42) or PAI-1 (r = 0.13, P = 0.30), without any influence of race (P > 0.05). Our findings show that maximal exercise unmasks risk factors for cardiovascular disease in Black postmenopausal females.NEW & NOTEWORTHY Exaggerated SBP responses to exercise testing are more frequent in Black than in White male adults. Such responses, if translatable to females, may detect early racial disparities arriving during menopause. Because the endothelium regulates BP and fibrinolytic responses, these could be linked during exercise. At peak exercise, Black but not White postmenopausal females had more exaggerated SPB responses regardless of reduced fibrinolytic potential. Maximal exercise unmasked risk factors for cardiovascular disease in Black postmenopausal females.

Tranexamic acid for the prevention of postpartum bleeding in women with anaemia: Statistical analysis plan for the WOMAN-2 trial: an international, randomised, placebo-controlled trial

Background: Postpartum haemorrhage (PPH) is responsible for over 50,000 maternal deaths every year. Most of these deaths are in low- and middle-income countries. Tranexamic acid (TXA) reduces bleeding by inhibiting the enzymatic breakdown of fibrin blood clots. TXA decreases surgical bleeding and reduces deaths from bleeding after traumatic injury. When given within three hours of birth, TXA reduces deaths from bleeding in women with PPH. However, for many women, treatment of PPH is too late to prevent death. World-wide, over one-third of pregnant women are anaemic and many are severely anaemic. These women have an increased risk of PPH and are more likely to die if PPH occurs. There is an urgent need to identify ways to prevent severe postpartum bleeding in anaemic women. The WOMAN-2 trial will quantify the effects of TXA on postpartum bleeding in women with anaemia. Results: This statistical analysis plan (version 1.0; dated 22 February 2023) has been written based on information in the WOMAN-2 Trial protocol version 2.0, dated 30 June 2022. The primary outcome of the WOMAN-2 trial is the proportion of women with a clinical diagnosis of primary PPH. Secondary outcomes are maternal blood loss and its consequences (estimated blood loss, haemoglobin, haemodynamic instability, blood transfusion, signs of shock, use of interventions to control bleeding); maternal health and wellbeing (fatigue, headache, dizziness, palpitations, breathlessness, exercise tolerance, ability to care for her baby, health related quality of life, breastfeeding); and other health outcomes (deaths, vascular occlusive events, organ dysfunction, sepsis, side effects, time spent in higher level facility, length of hospital stay, and status of the baby). Conclusions: WOMAN-2 will provide reliable evidence about the effects of TXA in women with anaemia. Registration: WOMAN-2 was prospectively registered at the International Standard Randomised Controlled Trials registry ( ISRCTN62396133) on 07/12/2017 and ClinicalTrials.gov on 23/03/2018 ( NCT03475342).

Adrenaline May Contribute to Prothrombotic Condition via Augmentation of Platelet Procoagulant Response, Enhancement of Fibrin Formation, and Attenuation of Fibrinolysis

Background: Adrenaline is believed to play a role in thrombosis and hemostasis. The complex effect of its clinically relevant concentrations on thrombus formation, coagulation and fibrinolysis in human blood has never been specifically studied. Methods: Confocal microscopy was used to study thrombus formation under flow, exposure of phosphatidylserine (PS) in adhered platelets, to evaluate clots density, and to measure kinetics of fibrin formation and external fibrinolysis under flow. Flow cytometry was utilized to assess PS exposure in non-adhered platelets. Kinetics of clot formation and internal fibrinolysis was evaluated by thromboelastometry. Platelet aggregation was measured by optical aggremometry. Kinetics of clot retraction was assessed by using digital camera. Results: We found that adrenaline (1-10 nM) is able to enhance platelet activation evoked by subthreshold collagen (150 ng/ml), resulting in augmentation of platelet aggregation, thrombus formation under arterial flow conditions, platelet PS exposure, and formation of platelet-fibrin clots. The development of platelet procoagulant response evoked by adrenaline + low collagen was associated with the formation of denser platelet-fibrin clots and the decrease in rate of fibrinolysis despite whether lysis was initiated inside (internal fibrinolysis) or outside the clot (external fibrinolysis). The above phenomena were abolished by the α₂-adrenergic receptor antagonist, rauwolscine. Adrenaline-collagen synergism, expressed as PS exposure, was significantly reduced by cyclooxygenase inhibitor (acetylsalicic acid), GPIIb/IIIa receptor blocker (tirofiban), and P2Y₁₂ receptor antagonist (PSB 0739). Conclusion: Clinically relevant concentrations of adrenaline may significantly augment responses of human platelets in the presence of subthreshold concentrations of collagen, which should be considered during therapies involving adrenaline infusion. Routinely used antiplatelet drugs may reduce the prothrombotic state evoked by adrenaline-collagen synergism.

A Single Session of Aerobic Exercise Mediates Plasticity-Related Phosphorylation in both the Rat Motor Cortex and Hippocampus

A single session of aerobic exercise may offer one means to "prime" motor regions to be more receptive to the acquisition of a motor skill; however, the mechanisms whereby this priming may occur are not clear. One possible explanation may be related to the post-translational modification of plasticity-related receptors and their associated intracellular signaling molecules, given that these proteins are integral to the development of synaptic plasticity. In particular, phosphorylation governs the biophysical properties (e.g., Ca²⁺ conductance) and the migratory patterns (i.e., trafficking) of plasticity-related receptors by altering the relative density of specific receptor subunits at synapses. We hypothesized that a single session of exercise would alter the subunit phosphorylation of plasticity-related receptors (AMPA receptors, NMDA receptors) and signaling molecules (PKA, CaMKII) in a manner that would serve to prime motor cortex. Young, male Sprague-Dawley rats (n = 24) were assigned to either exercise (Moderate, Exhaustion), or non-exercising (Sedentary) groups. Immediately following a single session of treadmill exercise, whole tissue homogenates were prepared from both the motor cortex and hippocampus. We observed a robust (1.2-2.0× greater than sedentary) increase in tyrosine phosphorylation of AMPA (GluA1,2) and NMDA (GluN2A,B) receptor subunits, and a clear indication that exercise preferentially affects pPKA over pCaMKII. The changes were found, specifically, following moderate, but not maximal, acute aerobic exercise in both motor cortex and hippocampus. Given the requirement for these proteins during the early phases of plasticity induction, the possibility exists that exercise-induced priming may occur by altering the phosphorylation of plasticity-related proteins.

The effects of whole body vibration and exercise on fibrinolysis in men

Whole body vibration (WBV) is a novel modality that has been demonstrated to enhance muscular and cardiovascular functions reported to increase fibrinolytic activity. The purpose of this study was to examine the fibrinolytic response to WBV and exercise in men. Twenty healthy males (23.8 ± 0.9 years, 25.6 ± 0.2 kg m(-2)) participated in the study. Each subject performed three trials in randomized order separated by 1 week: exercise (X), vibration (V) and vibration + exercise (VX). Exercise sessions consisted of 15 min of unloaded squatting at a rate of 20 per minute. Vibration sessions were conducted on a WBV platform vibrating for 15 min. Tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) were assessed at baseline and immediately after each condition. The increase in tPA activity was significantly greater in VX (0.87 ± 0.35 to 3.21 ± 1.06 IU ml(-1)) compared to X (0.71 ± 0.36 to 2.4 ± 1.13 IU ml(-1)) or V (0.83 ± 0.25 to 1.00 ± 0.37 IU ml(-1)) conditions, and greater in the X condition compared to the V condition. PAI-1 activity decreased significantly more in the VX (6.54 ± 5.53 to 4.89 ± 4.13 IU ml(-1)) and X (9.76 ± 8.19 to 7.48 ± 7.11 IU ml(-1)) conditions compared to the V (5.68 ± 3.53 to 5.84 ± 3.52 IU ml(-1)) condition. WBV does not augment fibrinolytic activity in healthy men. However, WBV combined with squatting exercise increases fibrinolytic activity more than exercise alone.

Salmeterol enhances pulmonary fibrinolysis in healthy volunteers

OBJECTIVE

Various lung diseases are associated with local activation of coagulation and concurrent inhibition of fibrinolysis. Although salmeterol, a beta2-adrenoceptor agonist with profound bronchodilatory properties, has been studied extensively, the effects of this compound on the pulmonary hemostatic balance are not elucidated.

DESIGN

A single-blinded, placebo-controlled study.

SETTING

University hospital and laboratory.

SUBJECTS

A total of 32 human volunteers.

INTERVENTIONS

Subjects inhaled 100 microg of salmeterol or placebo (t = -30 mins) followed by 100 microg of lipopolysaccharide (LPS) or normal saline (t = 0 mins; n = 8 per group).

MEASUREMENTS AND MAIN RESULTS

Measurements were performed in bronchoalveolar lavage fluid obtained 6 hrs postchallenge. Inhalation of LPS enhanced pulmonary coagulation as determined by an increase in the concentrations of thrombin-antithrombin complexes, factor VIIa, and soluble tissue factor in bronchoalveolar lavage fluid (all p < .05 vs. saline). LPS concurrently inhibited pulmonary fibrinolysis, as reflected by a decrease in bronchoalveolar lavage fluid plasminogen activator activity together with an increase in plasminogen activator inhibitor type 1 (both p < .05 vs. saline). Moreover, LPS inhalation was associated with a suppression of the anticoagulant protein C pathway, as indicated by an increase in soluble thrombomodulin and decreases in protein C and activated protein C levels in bronchoalveolar lavage fluid (all p < .05 vs. saline). Salmeterol, either with or without LPS inhalation, enhanced fibrinolysis (plasminogen activator activity and tissue-type and urokinase-type plasminogen activator levels) but did not influence LPS-induced changes in coagulation or the protein C pathway.

CONCLUSIONS

Salmeterol has profibrinolytic properties in the normal lung and when applied in a model of sterile pulmonary inflammation.

Exercise training enhances endogenous fibrinolysis in peripheral arterial disease

PURPOSE

Acute clinical events resulting from atherosclerosis (myocardial infarction, stroke) are associated with impaired endogenous fibrinolysis, the system by which the body lyses inappropriately formed thrombus. Endurance exercise training improves fibrinolysis in normal subjects and those with coronary artery disease. The hypothesis of this study was that exercise training would improve fibrinolysis in subjects with peripheral arterial disease (PAD).

METHODS AND RESULTS

Twenty-one men with intermittent claudication (IC-EX) underwent treadmill exercise training for 6 months. Twenty age-matched male subjects with IC were followed for the same period (IC-NONEX). Fibrinolytic activity was measured prior to entry into exercise or "usual care," and at the completion of the study period. Fibrinolysis was quantified by measurement of the activity levels of tissue plasminogen activator (tPA, the activator of fibrinolysis) and its inhibitor plasminogen activator inhibitor-1 (PAI-1), using an amidolytic method. Fibrinolysis, quantified as increased PAI-1 activity, was reduced in both claudicant groups relative to healthy controls at baseline. After 6 months of exercise, subjects in the IC-EX group experienced significant improvements in fibrinolytic activity, manifested as a 23% decrease in PAI-1 activity and a 28% increase in tPA activity. No changes occurred in the IC-NONEX group. In the IC-EX group, subjects with the highest initial PAI-1 values experienced the greatest decreases in PAI-1 activity and thus the greatest benefit from exercise.

CONCLUSIONS

Patients with PAD have impaired fibrinolytic activity, manifested primarily as increases in the inhibitor of fibrinolysis, PAI-1. Six months of exercise training reduced these impairments, and may serve as an intervention to reduce cardiovascular mortality and morbidity in these patients.

Comparison of t-PA and u-PA levels in maximal treadmill and deep-water running

BACKGROUND

The differences of urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA) between maximal treadmill and deep-water running have not been reported. The purpose of this investigation was to compare u-PA and t-PA levels during maximal treadmill and deep-water running.

METHODS

Six male subjects carried out two maximal exercises, one on a treadmill and the other running in deep water using a vest. The u-PA, t-PA, total plasminogen activator inhibitor (PAI-1), epinephrine, and norepinephrine in plasma and lactate and ammonia in blood concentrations were measured after maximal exercise.

RESULTS

The blood lactate and ammonia concentrations were significantly higher in treadmill running than in deep-water running during recovery following exercise (P < 0.05). At 1 min after exercise, the plasma epinephrine, norepinephrine levels, and the u-PA and t-PA levels were higher in treadmill running compared with that in deep-water running (P < 0.05). No significant difference between the two runs was found in PAI-1 level.

CONCLUSION

The maximal treadmill running induced a greater increase in u-PA and t-PA levels than maximal deep-water running.

The effect of submaximal exercise on fibrinolysis

We studied the relationship between sustained submaximal exercise, increased tissue plasminogen activator (t-PA) levels and decreased hepatic clearance of t-PA. Six healthy male volunteers exercised for 35 min while receiving constant rate infusions of either saline or two different doses of recombinant t-PA for 90 min (40 min before, 35 min during and 15 min after exercise). Liver blood flow was estimated simultaneously by constant rate indocyanine green infusion. Since t-PA is cleared rapidly by the liver in direct proportion to liver blood flow, it was expected that a significant decrease in liver blood flow during sustained submaximal exercise would be associated with a proportional increase in plasma t-PA. During submaximal exercise with a saline (placebo) infusion, steady-state t-PA antigen increased from a resting baseline of 6.3 +/- 3.1 to 15.1 +/- 5.1 ng/ml; with a 20 microg/min t-PA infusion, t-PA antigen increased from 33 +/- 12 to 84 +/- 25 ng/ml during exercise; and with a 40 microg/min t-PA infusion, t-PA antigen increased from 77 +/- 38 to 166 +/- 42 ng/ml during exercise. During submaximal exercise, liver blood flow fell on average 71, 68 and 70%, respectively, during the three procedures, while calculated t-PA clearance decreased on average 59, 59 and 53%. t-PA concentration versus time curves, displayed in proportional units, were similar. The comparable relative increases in endogenous and exogenous t-PA with simultaneous proportional decreases in liver blood flow suggests that diminished hepatic t-PA clearance is the major cause of increased t-PA concentration and blood fibrinolytic activity enhancement during sustained submaximal exercise.

A single bout of walking exercise enhances endogenous fibrinolysis in stroke patients

PURPOSE

Impaired endogenous fibrinolysis is an important predictor for increased risk of stroke and myocardial infarction. Acute exercise can enhance fibrinolysis, primarily by stimulating short-term increases in plasma tissue plasminogen activator (tPA), which is postulated to protect against atherothrombotic events. No prior studies have examined the fibrinolytic response to exercise in stroke survivors despite their high risk for recurrent stroke and myocardial infarction. The purpose of this study was to assess the fibrinolytic response to acute submaximal exercise in chronic hemiparetic stroke patients.

METHODS

Eighteen (16 men, 2 women) untrained stroke patients with chronic hemiparetic gait deficits volunteered for participation in this single session exercise study. Fasting blood samples for determination of tPA and plasminogen activator inhibitor (PAI-1) enzyme activities were obtained before, immediately after, and 60 min after submaximal treadmill walking. Patients walked at 60% maximal heart rate reserve (low-moderate intensity) for a cumulative total of 20 min.

RESULTS

The exercise bout increased tPA activity by 79% (P < 0.01) and decreased PAI-1 activity by 18% (P < 0.01). At 1 h after completing the walking exercise, plasma tPA activity levels were still significantly elevated (43%,P < 0.01), and PAI-1 activity levels were 25% lower (P < 0.01) than baseline.

CONCLUSIONS

These findings demonstrate that a single bout of aerobic walking exercise can improve fibrinolysis profiles in chronic stroke patients. Significant increases in endogenous tPA and reductions in PAI-1 activity persist for at least 1 h after exercise cessation. The implications are that alterations in physical activity during the day may modify clot lysing potential, thereby affecting atherothrombotic risk.

Secretion of tissue plasminogen activator and plasminogen activator inhibitor 1 during cardiopulmonary bypass

INTRODUCTION

Cardiopulmonary bypass (CPB) is associated with elevated tissue plasminogen activator (t-PA) levels during CPB and increased plasminogen activator inhibitor 1 (PAI-1) levels post-operatively. The goal of this study was to estimate the rate of t-PA and PAI-1 secretion in vivo, before, during and after CPB.

MATERIALS AND METHODS

Estimated rates of t-PA and PAI-1 secretion were based on measured levels of active and total t-PA, and active and total PAI-1, obtained before, during and after CPB from nine males, combined with a computer model of each patient's vascular system that continuously accounted for secretion, clearance, hemodilution, blood loss and transfusion.

RESULTS AND CONCLUSIONS

At baseline, the average t-PA and PAI-1 secretion rates were 0.74+/-0.33 and 1.28+/-0.74 pmol/s, respectively. Within 5 min of CPB initiation, t-PA secretion increased six-fold to 4.41+/-2.58 pmol/s, while PAI-1 secretion was unchanged, resulting in a six-fold increase in active t-PA levels. t-PA secretion remained elevated throughout CPB and into the early post-operative period. Average PAI-1 secretion did not start to increase until the end of CPB. By 2 h after surgery, average PAI-1 secretion had increased 15-fold to 19.60+/-17.10 pmol/s, resulting in reduced levels of active t-PA even though t-PA secretion was still elevated. We conclude that CPB induces an immediate sustained increase in t-PA secretion followed by a delayed progressive increase in PAI-1 production. Variations in the level of active t-PA are a function of the relative rates of t-PA versus PAI-1 secretion at different times during and after surgery.

Association between physical activity and endogenous fibrinolysis in peripheral arterial disease: a cross-sectional study

The purpose of this study was to determine whether daily physical activity was independently related to endogenous fibrinolysis in subjects with peripheral arterial disease (PAD). One hundred and six subjects with peripheral arterial disease (PAD) and intermittent claudication were characterized on the activity level of tissue plasminogen activator (tPA, the activator of fibrinolysis), the activity level of plasminogen activator inhibitor (PAI-1, the inhibitor of fibrinolysis), daily physical activity, ambulatory function, and demographic information. Subjects were separated into low (n = 36), moderate (n = 34), and high (n = 36) physical activity tertiles based on a 48-hour monitoring period with use of an accelerometer. The tPA activity of the low physical activity group (1.30 +/- 0.16 IU/mL) was 21% and 19% lower (p<0.05) than that of the moderate (1.65 +/- 0.18 IU/mL) and the high (1.61 +/- 0.15 IU/mL) physical activity groups, respectively. The PAI-1 activity of the low physical activity group (21.41 +/- 1.14 AU/mL) was 15% and 23% higher than that of the moderate (18.61 +/- 1.34 AU/mL) and the high (17.47 +/- 1.14 AU/mL) physical activity groups, respectively. Group differences in tPA activity and PAI-1 activity persisted after our controlling for group differences in measured and self-reported ambulatory measures. Daily physical activity is related to a more favorable endogenous fibrinolytic profile in PAD subjects with intermittent claudication. Subjects who expend fewer than 175 kcal/day in physical activities (approximately 35 minutes) are particularly susceptible to having a prothrombotic state. Subjects should be encouraged to participate in at least 35 minutes of physical activity each day to enhance fibrinolysis.

External pneumatic compression and fibrinolysis in abdominal surgery

INTRODUCTION

External pneumatic compression (EPC) devices prevent lower extremity deep venous thrombosis by increasing venous flow and thereby reducing stasis. Early studies suggested that they also enhance systemic fibrinolytic activity and thus prevent thrombus formation; more recent studies have been conflicting. The hypothesis of this study was that EPC devices enhance systemic fibrinolysis or reduce postoperative fibrinolytic impairment in patients undergoing abdominal surgical procedures.

METHODS

Each of 48 patients (98% male; mean age, 67 years) undergoing major intra-abdominal surgical procedures (36 bowel procedures, 12 aortic reconstructions) was prospectively randomized to one of three treatments for deep venous thrombosis prophylaxis: subcutaneous heparin injections (HEP group), use of a thigh-length sequential EPC device (EPC group), or both (HEP + EPC group). Antecubital venous samples were collected for measurement of systemic fibrinolytic activity on the day before surgery, after induction of anesthesia but before prophylaxis was initiated, and on postoperative days 1, 3, and 5. Fibrinolysis was assessed through measurement of the activities of the rate limiting fibrinolytic activator, tissue plasminogen activator, and its inhibitor plasminogen activator inhibitor-1 with amidolytic methods.

RESULTS

On the day before surgery, plasminogen activator inhibitor-1 activity was elevated in all groups in comparison with that in age-matched and sex-matched controls (20.3 +/- 0.6 AU/mL). In the HEP group, plasminogen activator inhibitor-1 activity was further elevated above the value for the day before surgery on postoperative day 1 (28.5 +/- 4.3 AU/mL; P =.04) and postoperative day 3 (25.1 +/- 1.9 AU/mL; P =.07). No significant decrease in plasminogen activator inhibitor-1 activity occurred in either group treated with EPC devices in comparison with the HEP group at any time. There were no changes in tissue plasminogen activator activity postoperatively in the HEP group and no significant increases in either EPC group at any point.

CONCLUSIONS

Reduced systemic fibrinolytic activity ("fibrinolytic shutdown") occurred in these patients after abdominal surgery; it was manifested as increased plasminogen activator inhibitor-1 activity. EPC devices did not enhance systemic fibrinolysis or prevent postoperative shutdown either by decreasing plasminogen activator inhibitor-1 activity or by increasing tissue plasminogen activator activity. These data suggest that EPC devices do not prevent deep venous thrombosis by fibrinolytic enhancement; effective prophylaxis is achieved only when the devices are used in a manner that reduces lower extremity venous stasis.

Synergistic effect of adrenal steroids and angiotensin II on plasminogen activator inhibitor-1 production

Recent data suggest an interaction between the renin-angiotensin-aldosterone system and fibrinolysis. Although previous work has focused on the effect of angiotensin II (Ang II) on plasminogen activator inhibitor (PAI-1) expression, the present study tests the hypothesis that aldosterone contributes to the regulation of PAI-1 expression. To test this hypothesis in vitro, luciferase reporter constructs containing the human PAI-1 promoter were transfected into rat aortic smooth muscle cells. Exposure of the cells to 100 nmol/L Ang II resulted in a 3-fold increase in luciferase activity. Neither 1 micromol/L dexamethasone nor 1 micromol/L aldosterone alone increased PAI-1 expression. However, both dexamethasone and aldosterone enhanced the effect of Ang II in a dose-dependent manner. This effect was abolished by mutation in the region of a putative glucocorticoid-responsive element. A similar interactive effect of Ang II and aldosterone was observed in cultured human umbilical vein endothelial cells. The time course of the effect of aldosterone on Ang II-induced PAI-1 expression was consistent with a classical mineralocorticoid receptor mechanism, and the effect of aldosterone on PAI-1 synthesis was attenuated by spironolactone. To determine whether aldosterone affected PAI-1 expression in vivo, we measured local venous PAI-1 antigen concentrations in six patients with primary hyperaldosteronism undergoing selective adrenal vein sampling. PAI-1 antigen, but not tissue plasminogen activator antigen, concentrations were significantly higher in adrenal venous blood than in peripheral venous blood. Taken together, these data support the hypothesis that aldosterone modulates the effect of Ang II on PAI-1 expression in vitro and in vivo in humans.

Potential Antithrombotic and Fibrinolytic Properties of the Angiotensin Converting Enzyme Inhibitors

As a class of therapeutic agents, the ACE inhibitors have proven to have long-term mortality benefit when used after myocardial infarction and among patients with symptomatic congestive heart failure. Clinical trial data also indicate that the use of ACE inhibitors is associated with reduced rates of recurrent coronary thrombosis, an observation that raises the possibility that the renin-angiotensin system may be directly involved in the thrombotic process and that the ACE inhibitors may have valuable fibrinolytic and/or antithrombotic effects. Recent in vitro and in vivo studies of angiotensin II and its interactions with the fibrinolytic system, particularly with the primary inhibitor of intravascular fibrinolysis, plasminogen activator inhibitor type 1 (PAI-1), provide substantial support for this hypothesis. In addition, a series of cross-sectional studies have described a genetic linkage between a common ACE gene polymorphism (DD) and the prevalence of clinical cardiovascular events, an intriguing finding as this polymorphism may account for much of the population variability in plasma ACE levels. Taken together, the totality of available clinical and experimental findings support the possibility of a direct linkage between the ACE system and vascular thrombosis that merits further prospective evaluation.

Comparative effect of angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor antagonism on plasma fibrinolytic balance in humans

Angiotensin-converting enzyme (ACE) inhibition significantly decreases plasminogen activator inhibitor-1 (PAI-1) without altering tissue plasminogen activator (tPA) during activation of the renin-angiotensin-aldosterone system in humans. Because ACE inhibitors and angiotensin II type 1 (AT(1)) receptor antagonists differ in their effects on angiotensin II formation and bradykinin degradation, the present study compared the effect of equivalent hypotensive doses of an ACE inhibitor and AT(1) antagonist on fibrinolytic balance. Plasma PAI-1 antigen, tPA antigen, plasma renin activity, and aldosterone were measured in 25 normotensive subjects (19 white, 6 black; 14 men, 11 women; mean age 38.5+/-1.8 years; mean body mass index 25.3+/-0.7 kg/m(2)) during low salt intake alone (10 mmol Na/d), low salt intake + quinapril (40 mg PO bid), and low salt intake + losartan (50 mg PO bid). Compared with low salt alone (systolic blood pressure [BP] 118.8+/-2.2 mm Hg), both quinapril (106.3+/-2.5 mm Hg, P<0.001) and losartan (105.4+/-2. 8 mm Hg, P<0.001) reduced BP. No statistical difference was found between quinapril and losartan in their BP lowering effect. Losartan (P=0.009), but not quinapril, lowered heart rate. Both drugs significantly lowered aldosterone (P<0.001 versus low salt alone for each); however, this effect was significantly greater for quinapril than for losartan (P<0.001 for quinapril versus losartan). Treatment with quinapril, but not with losartan, was associated with a decrease in both PAI-1 antigen (P=0.03) and activity (P=0.018). PAI-1 activity was lower during treatment with quinapril than with losartan (P=0.015). The average PAI-1 antigen concentration was 13. 0+/-2.0 ng/mL during low salt alone, 10.5+/-1.6 ng/mL during quinapril treatment, and 12.3+/-2.1 ng/mL during losartan treatment. In contrast, plasma tPA antigen concentrations were reduced during treatment with losartan (P=0.03) but not with quinapril. This study provides the first evidence that ACE inhibitors and AT(1) antagonists differ in their effects on fibrinolytic balance under conditions of activation of the renin-angiotensin-aldosterone system. Further studies are needed to address the mechanism for the contrasting effects of these 2 classes of drugs on fibrinolysis and to define the clinical significance of these differences.

Bradykinin stimulates tissue plasminogen activator release in human vasculature

Bradykinin stimulates tissue plasminogen activator (tPA) release in isolated perfused animal tissues. The present study tests the hypothesis that bradykinin increases tPA release in humans through local effects on the vasculature. Graded doses of sodium nitroprusside (0.8 to 3.2 micrograms/min), acetylcholine (ACh) (7.5 to 60 micrograms/min), and bradykinin (100 to 400 ng/min) were administered intra-arterially in random order in 10 salt-depleted (10 mmol/d of Na) normotensive volunteers. None of the drugs altered mean arterial pressure or heart rate. Forearm blood flow (FBF) was measured by strain-gauge plethysmography. All 3 drugs caused a dose-dependent increase in FBF, although ACh was less potent than either nitroprusside or bradykinin (maximum FBF 7.5+/-2.4 versus 10.0+/-1.5 and 11.9+/-2.1 mL. 100 mL-1. min-1, respectively). Bradykinin caused a significant, dose-dependent increase in venous (effect of dose F=9. 9, P=0.028 by ANOVA), but not arterial (F=0.154, P=0.92) tPA antigen in the infused arm. Thus, net tPA release increased significantly in response to bradykinin (50.6+/-13.3 at the highest dose versus 0. 9+/-0.4 ng. 100 mL-1. min -1 at baseline, P=0.014). In contrast, bradykinin did not affect plasminogen activator inhibitor antigen. Neither nitroprusside nor ACh altered plasma levels of tPA or plasminogen activator inhibitor antigen. Bradykinin increased tPA release across the forearm in the absence of systemic effects. This effect could not be attributed to changes in blood flow because doses of equivalent potency of the vasodilator nitroprusside did not increase tPA. These data demonstrate that bradykinin stimulates tPA release in the human vasculature.

Progressive intermittent claudication is associated with impaired fibrinolysis

PURPOSE

Acute complications of atherosclerosis such as stroke and myocardial infarction are caused by thrombosis and may be associated with impaired fibrinolytic activity. The current study was performed to determine whether peripheral arterial disease (PAD) and its progression are also associated with impaired fibrinolysis, by measurement of tissue plasminogen activator (tPA, the activator of fibrinolysis) and its inhibitor plasminogen activator inhibitor-1 (PAI-1).

METHODS

The study group consisted of 80 men with a mean age of 69 years. This included 18 patients with mild intermittent claudication (MC, pain-free walking distance > or = 200 meters) and 51 patients with severe claudication (SC, walking distance <200 meters). Eleven age- and sex-matched patients without PAD served as controls. All patients had measurements of serum tPA antigen using an enzyme-linked immunoadsorbent assay. Serum levels of tPA and PAI-1 activity were assayed with an amidolytic method. Mean +/- SEM levels of the enzyme levels in patients with progressively more severe PAD were compared with normal controls.

RESULTS

Serum PAI-1 activity levels were significantly elevated in both PAD groups compared with normal controls (p < 0.02). There were no significant differences in the PAI-1 activity levels in groups with worsening degrees of PAD. There was a significant decrease in tPA activity levels in patients with SC (p = 0.01) relative to those with MC and the normal subjects. There was also a significant increase in tPA antigen level in the patients with SC compared with those with MC and the control subjects, as well as a significant inverse correlation between tPA antigen levels and pain-free walking time in patients with claudication (p = 0.001).

CONCLUSIONS

All patients with PAD in this study had significant reductions in endogenous fibrinolytic activity. Patients with SC had more impaired fibrinolytic activity than those with MC and the control subjects, suggesting that the progression to more severe levels of PAD may be associated with worsening endogenous fibrinolysis.

Physical activity status and adverse age-related differences in coagulation and fibrinolytic factors in women

Adverse changes in coagulation and fibrinolytic factors are thought to contribute to the increased risk of cardiovascular disease and atherothrombosis with age. We tested the hypothesis that such age-related changes in specific coagulation and fibrinolytic factors are absent in physically active women. Resting levels of plasma fibrinogen, tissue-type plasminogen activator (t-PA) antigen and activity, plasminogen activator inhibitor-1 (PAI-1) antigen and activity, and fibrin D-dimer were measured in 24 healthy premenopausal women: 11 sedentary (aged 28+/-1 years; Pre-S) and 13 physically active (aged 30+/-1 years; Pre-PA) and in 27 healthy postmenopausal women: 14 sedentary (aged 61+/-1 years; Post-S) and 13 physically active (aged 58+/-1 years; Post-PA). Post-S had higher (P<.05) fibrinogen, t-PA antigen, PAI-1 antigen, PAI-1 activity, and fibrin D-dimer levels and lower t-PA activity than Pre-S. Post-PA demonstrated lower (P<.01) plasma fibrinogen, t-PA antigen, PAI-1 antigen, and PAI-1 activity and higher (P<.01) t-PA activity levels than Post-S. In addition, plasma fibrin D-dimer levels tended (P=.06) to be lower in Post-PA than in Post-S. Although plasma levels of fibrinogen and fibrin D-dimer in Post-PA were lower than in Post-S, they were higher (P<.05) than in Pre-PA. Importantly, however, the fibrinolytic profile of Post-PA did not differ from that of Pre-PA. The results of the present study demonstrate that the adverse age-associated differences in plasma fibrinogen concentrations and the endogenous fibrinolytic system in sedentary healthy women are either attenuated or absent in highly physically active women. The smaller or absent age-related differences in coagulation and fibrinolytic factors in women who habitually exercise may represent an important mechanism contributing to their lower age-related increase in both cardiovascular disease and atherothrombotic events. Future studies need to determine whether women who are moderately active would demonstrate the same favorable hemostatic profile.

Regression of proximal deep venous thrombosis is associated with fibrinolytic enhancement

PURPOSE

Recanalization after acute lower limb deep venous thrombosis (DVT) is well documented, but the precise mechanism and timing of these events has not been well characterized. Regression of DVT has been presumed to result from activation of the endogenous fibrinolytic system. This study was performed to compare measurements of the enzymatic components of the intrinsic fibrinolytic system (tissue plasminogen activator [tPA], plasminogen activator inhibitor [PAI-1]) with the observed morphologic changes in thrombosed venous segments using venous duplex ultrasound scanning (VDUS) at intervals after diagnosis of acute DVT.

METHODS

Nineteen patients with acute DVT underwent serial VDUS to assess regression of thrombus at intervals of 1 to 2 weeks, 3 to 6 weeks, 8 to 12 weeks, and 24 to 36 weeks. The extent of thrombus in each limb was quantitated at each interval by VDUS of the residual thrombus present in each of five major axial venous segments: the common femoral, superficial femoral, profunda femoris, popliteal, and tibial veins. Thrombus scores for the group at each interval were compared with baseline scores at diagnosis to calculate the percent residual thrombus. Endogenous fibrinolytic activity was determined at the same intervals by serologic assay of the biologic activities of tPA and its inhibitor PAI-1.

RESULTS

Thrombus regression was evident by VDUS at 1 to 2 weeks and progressed such that only 26% of residual thrombus remained at 24 to 36 weeks. Complete resolution of thrombus occurred in 10 of 18 patients (56%) who completed the 9-month study. Baseline mean tPA activity was 0.60 +/- 0.07 IU/ml and increased to 1.31 +/- 0.26 IU/ml at 1 to 2 weeks (p = 0.014). tPA activity remained significantly elevated through the 8 to 12 week interval and returned to baseline at 24 to 36 weeks. PAI-1 activity was elevated relative to an age-matched population at baseline (23.1 +/- 1.8 AU/ml) but remained unchanged throughout the study period. Progression of thrombus was observed in three patients (15.8%). Patients who experienced propagation of thrombus did not have the increased tPA activity that appeared to mark activation of intrinsic fibrinolysis.

CONCLUSIONS

Regression of acute DVT begins early and continues for at least 9 months. It is accompanied by significant enhancement of the endogenous fibrinolysis, which appears to be primarily mediated by increased tPA activity. Patients who have thrombus propagation in spite of standard antithrombotic therapy may have failure of activation of endogenous fibrinolysis.

Fibrinolytic responses to acute physical activity in older hypertensive men

We tested the hypothesis that the fibrinolytic response to acute physical activity is impaired in sedentary older hypertensive men, which may contribute to the risk of exertion-triggered acute myocardial infarction in this population. Tissue-type plasminogen activator (t-PA) antigen and activity and plasminogen activator inhibitor-1 (PAI-1) antigen and activity were measured in 12 hypertensive (69 +/- 1 yr) and 11 normotensive (64 +/- 1 yr) men before and after an acute bout of submaximal exercise. Contrary to our hypothesis, there were no differences between the two groups in the fibrinolytic response to exercise. t-PA antigen and activity were significantly elevated in both the hypertensive (38 and 172%, respectively) and normotensive (45 and 130%, respectively) groups immediately after exercise but they returned to resting levels within 30 min. There was no change in PAI-1 antigen levels immediately after exercise in either group; however, PAI-1 antigen was significantly lower at 30 and 60 min postexercise in both the hypertensive (31 and 16%, respectively) and normotensive (35 and 20%, respectively) groups. PAI-1 activity was significantly lower immediately after exercise in both the hypertensive (25%) and normotensive (22%) groups and remained lower than preexercise levels at 30 min (23 and 26%, respectively) and 60 min (16 and 12%, respectively) postexercise in both groups. The results of this study demonstrate that the fibrinolytic response to an acute bout of moderate physical activity is not impaired in sedentary older hypertensive men.

Defective fibrinolysis occurs after infrainguinal reconstruction

PURPOSE

Early thrombosis of infrainguinal bypass grafts may occur as a result of hypercoagulable states. Major surgical procedures are known to induce a procoagulant state that is manifested in part by reduced endogenous fibrinolytic activity or fibrinolytic shutdown. This study was performed to assess the timing and biologic mechanism of fibrinolytic shutdown after infrainguinal bypass procedures by direct assay of the serologic markers of in vivo fibrinolytic activity.

METHODS

Twenty patients underwent infrainguinal bypass procedures under epidural anesthesia. Endogenous fibrinolytic activity was assessed by measurement of tissue plasminogen activator (tPA) and its naturally occurring inhibitor, plasminogen activator inhibitor (PAI-1). The tPA and PAI-1 antigen (total protein) levels were determined using enzyme-linked immunosorbent assays, and measurements of in vivo biologic activity were performed using an amidolytic method. Measurements of tPA and PAI-1 were made before surgery, after surgery, and on postoperative days 1, 2, 7, and 30.

RESULTS

The mean preoperative PAI-1 activity was 20.6 +/- 1.4 arbitrary units (AU)/ml, which was higher than that of an age-matched population without severe atherosclerosis. PAI-1 activity rose significantly after surgery (29.6 +/- 2.2 AU/ml; p = 0.002) and remained elevated through the second day after surgery. Preoperative tPA activity level was 2.04 +/- 0.59 IU/ml and fell to 0.79 +/- 0.23 IU/ml (p = 0.046) immediately after the bypass procedure. All serologic indicators of fibrinolytic shutdown returned to baseline levels by 72 hours after surgery. No early graft thrombosis or other atherothrombotic complications occurred in these study patients.

CONCLUSIONS

Defective endogenous fibrinolytic activity occurs in the early postoperative period after infrainguinal bypass grafting procedures. Diminished endogenous fibrinolytic activity in these patients appears to be mediated by a combination of reduced tPA activity and significantly increased PAI-1 activity. No practical method is available to directly treat postoperative fibrinolytic shutdown, but postoperative antithrombotic therapy may be useful during this period to prevent early graft occlusion related to a relative hypercoagulable state.

Lifestyle, fibrinolysis and lipids

Lifestyle including eating habits, physical training, smoking, drinking alcoholic beverages etc. can to a certain extent maintain or spoil our health. The physiological mechanisms of haemostasis and of lipoprotein metabolism play a role in acute cardiovascular diseases but also in a great number of chronic diseases in which vascular pathology is prominent. Imparied fibrinolysis and increased lipid levels are often incriminated in vascular disease. Lifestyle can modify fibrinolysis as well as lipid levels. Physical training, moderate eating habits, no smoking, moderate alcohol intake will be a beneficial influence on both fibrinolysis and lipid levels. The possibility that long-term pharmacological intervention may adversely affect fibrinolysis and lipid levels should always be considered.

Epinephrine exerts anticoagulant effects during human endotoxemia

To determine the effect of a physiologically relevant elevation in the plasma concentrations of epinephrine on the activation of the hemostatic mechanism during endotoxemia, 17 healthy men were studied after intravenous injection of lipopolysaccharide (LPS, 2 ng/kg), while receiving a continuous infusion of epinephrine (30 ng/kg/min) started either 3 h (n = 5) or 24 h (n = 6) before LPS injection, or an infusion of normal saline (n = 6). Activation of the coagulation system (plasma concentrations of thrombin-antithrombin III complexes and prothrombin fragment F1+2) was significantly attenuated in the groups treated with epinephrine when compared with subjects injected with LPS only (P <0.05). Epinephrine enhanced LPS-induced activation of fibrinolysis (plasma levels of tissue-type plasminogen activator and plasmin-alpha2-antiplasmin complexes; P <0.05), but did not influence inhibition of fibrinolysis (plasminogen activator inhibitor type I). In subjects infused with epinephrine, the ratio of maximal activation of coagulation and maximal activation of fibrinolysis was reduced by >50%. Hence, epinephrine exerts antithrombotic effects during endotoxemia by concurrent inhibition of coagulation, and stimulation of fibrinolysis. Epinephrine, whether endogenously produced or administered as a component of treatment, may limit the development of disseminated intravascular coagulation during systemic infection.

Tissue plasminogen activator (t-PA) is targeted to the regulated secretory pathway. Catecholamine storage vesicles as a reservoir for the rapid release of t-PA

Tissue-type plasminogen activator (t-PA) is a serine protease that plays a central role in the regulation of intravascular thrombolysis. The acute release of t-PA in vivo is induced by a variety of stimuli including exercise, trauma, and neural stimulation. These types of stimuli also result in sympathoadrenal activation and exocytotic release of amines and proteins from catecholamine storage vesicles of the adrenal medulla and sympathetic neurons. Therefore, we tested the hypothesis that t-PA is packaged in and released directly from catecholamine storage vesicles, using several chromaffin cell sources including the rat pheochromocytoma PC-12 chromaffin cell line, primary cultures of bovine adrenal chromaffin cells, and human pheochromocytoma. t-PA was expressed in chromaffin cells as detected by Northern blotting, immunoprecipitation of [35S]Met-labeled t-PA, and specific t-PA enzyme-linked immunosorbent assay of cell homogenates. In addition, chromaffin cell t-PA was enzymatically active by fibrin zymography. To explore the subcellular localization of the expressed t-PA, PC-12 cells were labeled with [3H]norepinephrine, homogenized, and subjected to sucrose density fractionation. [3H]Norepinephrine and t-PA antigen were co-localized to the same subcellular fraction with a major peak at 1.4 M sucrose, consistent with the buoyant density of catecholamine storage vesicles. In addition, catecholamine storage vesicle lysates isolated from human pheochromocytoma tumors were enriched approximately 30-fold in t-PA antigen, compared with tumor homogenate. Furthermore, exposure of PC-12 cells or primary bovine adrenal chromaffin cells to chromaffin cell secretagogues (60 microM nicotine, 55 mM KCl, or 2 mM BaCl2) resulted in co-release of t-PA in parallel with catecholamines. These data demonstrate that t-PA is expressed in chromaffin cells, is sorted into the regulated pathway of secretion, and is co-released with catecholamines by chromaffin cell stimulation. Catecholamine storage vesicles may be an important reservoir and sympathoadrenal activation an important physiologic mechanism for the rapid release of t-PA. In addition, expression of t-PA by chromaffin cells suggests a role for this protease in the proteolytic processing of chromaffin cell proteins.

Effect of angiotensin II receptor blockade on fibrinolysis during acute hyperinsulinemia in patients with essential hypertension

We performed the present study to investigate indirectly the in vivo effects of angiotensin II on fibrinolysis and catecholamines by treatment with losartan, a selective angiotensin II type 1 receptor antagonist. The effects were evaluated in basal conditions as well as in two different models of acute hyperinsulinemia physiologically induced by oral glucose ingestion and by a euglycemic glucose clamp technique. Twenty subjects with moderate hypertension were included in a randomized, double-blind, placebo-controlled crossover study of 4-week treatment periods. Plasma levels of catecholamines, tissue plasminogen activator activity and antigen, and plasminogen activator inhibitor type 1 activity and antigen were unchanged in the basal state after 4 weeks of treatment. During both models of hyperinsulinemia, plasminogen activator inhibitor activity and antigen decreased significantly (both P<.001), and tissue plasminogen activator activity increased significantly (P<.Ol). Norepinephrine did not change during any of the procedures, whereas epinephrine increased significantly after 3 hours of the oral glucose tolerance test. Changes from baseline did not differ between the treatment and placebo regimens during the hyperinsulinemic procedures with regard to either of the fibrinolytic variables or the catecholamines. In conclusion, we could not demonstrate any effects of 4 weeks of treatment with losartan on plasma levels of fibrinolytic variables or catecholamines either in basal conditions or during acute hyperinsulinemia. However, the present findings do not preclude more direct effects of angiotensin II or involvement of other receptor subtypes on fibrinolysis.

The fibrinolytic system is not impaired in older men with hypertension

The fibrinolytic system is thought to be impaired in older hypertensive adults, thus contributing to the elevated risk of atherothrombosis, stroke, and acute myocardial infarction in this population. However, studies that have examined the fibrinolytic system in hypertensive individuals have failed to control for the confounding effects of other metabolic risk factors, making it difficult for one to determine the independent effect of hypertension on the fibrinolytic system. The purpose of the present study was to test the hypothesis that the fibrinolytic system is not impaired in older sedentary hypertensive men when the confounding effects of cardiovascular disease, diabetes, and dyslipidemia are controlled. Plasma concentrations of tissue-type plasminogen activator antigen and activity as well as plasminogen activator inhibitor-1 antigen and activity were measured under resting conditions in 12 hypertensive (69.4 +/- 1.4 years) and 11 normotensive 65.2 +/- 1.3 years) older men. The hypertensive and normotensive subjects had similar anthropometric and metabolic characteristics. There were no significant differences between the hypertensive and normotensive men in tissue-type plasminogen antigen (7.3 +/- 0.5 versus 6.1 +/- 0.6 ng/mL) and activity (1.8 +/- 0.3 versus 1.7 +/- 0.2 IU/mL) or plasminogen activator inhibitor-1 antigen (14.1 +/- 2.3 versus 10.8 +/- 2.2 ng/mL) and activity (17.4 +/- 1.2 versus 17.5 +/- 1.8 arbitrary units [AU]/mL) levels. In addition, the molar concentration ratio of active tissue type plasminogen activator to active plasminogen activator inhibitor-1 did not differ between the hypertensive (1:9.7 +/- 2.3) mmol/L) and normotensive (1:10.5 +/- 2.2 mmol/L) subjects, indicative of no impairment in fibrinolytic potential in either group. These results support the hypothesis that hypertension does not directly result in impaired fibrinolytic function in older adults. Furthermore, our findings suggest that abnormalities in fibrinolytic function in older hypertensive men are likely due to the primary effects of other metabolic disorders that usually accompany hypertension, such as hyperinsulinemia and dyslipidemia.

The circulatory regulation of TPA and UPA secretion, clearance, and inhibition during exercise and during the infusion of isoproterenol and phenylephrine

BACKGROUND

Exercise to exhaustion and infusions of isoproterenol and phenylephrine were used to study interactions between plasminogen activator regulation and the control of regional blood flow in 10 healthy males.

METHODS AND RESULTS

Experimental measurements of cardiac output, heart rate, tissue plasminogen activator (TPA), urokinase plasminogen activator (UPA), plasminogen activator inhibitor (PAI-1), C1-inhibitor, and TPA/C1-inhibitor complex during the infusions and exercise were used to develop a comprehensive fluid-phase model of the circulatory regulation of fibrinolysis. alpha- and beta-adrenergic agonists increased TPA and UPA in plasma by different mechanisms: Phenylephrine decreased hepatic blood flow and thus clearance while isoproterenol stimulated increased secretion of TPA and UPA. Exercise to exhaustion increased TPA and UPA through a combination of increased secretion and decreased clearance. The time course of UPA and TPA release were similar, but the magnitude of their secretion responses differed. In vivo, C1-inhibitor bound to TPA at a rate of 553 mol-1.s-1. C1-inhibitor contributed equally with PAI-1 to TPA inhibition when active PAI-1 levels were low (20 to 50 pmol/L) but was less important when active PAI-1 levels were high.

CONCLUSIONS

We conclude that secretion, inhibition, clearance, and regional blood flow effects must all be taken into account when evaluating changes in plasminogen activator levels.

A comparative study of captopril and enalapril on endothelial cell function in congestive heart failure patients

Angiotensin-converting enzyme (ACE) inhibitors have been shown to reduce the incidence of future coronary artery thromboses in postmyocardial infarction patients. A possible prothrombotic role for the angiotensin system has been postulated, and support for this has been provided by a recent study that demonstrated that an infusion of angiotensin increases levels of the prothrombotic plasminogen activator inhibitor (PAI). In the current study the authors have investigated the effect of two ACE inhibitors, captopril and enalapril, on tissue plasminogen activator (tPA) and PAI in 33 congestive heart failure (CHF) patients. Blood samples were obtained pretreatment and then at weeks 1, 12, and 24 after initiation of ACE inhibitor therapy for measurement of tPA antigen and PAI activity levels. The results of the study indicated that the initiation of ACE inhibitors had no significant effects on tPA antigen or PAI activity levels at the time points studied, and no significant differences were demonstrated between captopril and enalapril. The results suggest, therefore, that ACE inhibitors do not affect tPA antigen or PAI activity in CHF patients, and thus another mechanism is probably responsible for the observed decrease in coronary artery thromboses in post-MI patients treated with ACE inhibitors.

New concepts regarding events that lead to myocardial infarction

In addition to new knowledge concerning the mechanisms whereby conventional risk factors act, other risk factors have been newly described, such as dietary antioxidants, lack of exercise, insulin resistance, excess iron stores, increased plasma angiotensin-converting enzyme, and left ventricular hypertrophy. An intact endothelium protects both by the formation of nitric oxide, which is a vasodilator and also an inhibitor of platelet aggregation and neutrophil adhesion, and by manufacturing tissue plasminogen activator. The acute thrombotic event occurs with a diurnal variation but may be precipitated by acute exertion, especially in untrained individuals, and reflects a balance between vasoconstrictory and vasodilatory stimuli from the vascular endothelium, as well as procoagulant versus anticoagulant effects of complex balancing systems. Increased risk of sudden cardiac death in the morning is thought to be a reflection of transient risk factors, such as a blood pressure increase, heart rate increase, and changes in coagulation factors, as well as changes in platelet aggregation. There is an apparent paradox between the acute effect of exercise in promoting sudden cardiac death and the chronic effect of exercise training in decreasing the risk of myocardial infarction. The explanation may be that chronic exercise training has an inhibitory effect on adrenergic discharge.

Fibrinolytic responses to moderate intensity exercise. Comparison of physically active and inactive men

The purposes of this study were to compare fibrinolytic responses to moderate intensity exercise in physically active and inactive men and during morning and evening exercise. Fourteen physically inactive men (mean age, 34.7 +/- 4.0 years) and 12 regularly active men (34.8 +/- 4.0 years) performed two exercise sessions, morning and evening, at 50% of maximal oxygen consumption. Tissue plasminogen activator (TPA) and plasminogen activator inhibitor-1 (PAI-1) activity were measured before and after exercise. Data were analyzed using a three-way ANOVA with repeated measures. TPA activity increased with exercise in both groups, although the active group demonstrated greater increases than the inactive group. Postexercise TPA activity was greater with evening than morning exercise. The inactive group exhibited greater PAI-1 activity than the active group. PAI-1 activity was higher during the morning than evening but did not change with exercise for either group. We conclude that moderate intensity exercise increases TPA activity in physically active and inactive men, with greater increases seen in active men, particularly during evening exercise. Moderate intensity exercise does not appear to affect PAI-1 activity. The lower PAI-1 activity in active men may be one mechanism whereby regular physical activity lowers the risk for coronary artery disease.

Physical exercise and hemostasis

A number of hemostatic changes involving platelets, coagulation and fibrinolysis have been reported after acute physical exercise. Results have sometimes been controversial, due to differences in subjects investigated, type of exercise and methods used for hemostatic evaluation. On the whole, physical exercise has been shown to induce: (1) increases in platelet number and activity, (2) activation of coagulation leading to a slight but significant thrombin generation and (3) activation of fibrinolysis. These changes are short lasting. Less known are hemostatic changes induced by exercise training programs: a few data are available on the effects on platelets and coagulation, whereas studies performed on fibrinolysis show a decrease in plasminogen activator inhibitor-1 levels at rest and an increase in fibrinolytic capacity after training.

Stimulation of plasminogen activator inhibitor in vivo by infusion of angiotensin II. Evidence of a potential interaction between the renin-angiotensin system and fibrinolytic function

BACKGROUND

Recent clinical trial data indicate that the use of angiotensin converting enzyme (ACE) inhibitors among patients with left ventricular dysfunction results in reduced rates of coronary thrombosis, a provocative finding that suggests a potential interaction between the renin-angiotensin system and fibrinolytic function.

METHODS AND RESULTS

In four normotensive subjects and six hypertensive patients, we investigated whether infusion of angiotensin II (Ang II) affected circulating levels of plasminogen activator inhibitor-1 (PAI-1), the most important physiological inhibitor of tissue-type plasminogen activator (t-PA). Overall, mean levels of PAI-1 antigen increased significantly from 20.1 ng/mL before Ang II infusion to 36.0 ng/mL at the end of Ang II infusion (p = 0.008), whereas no change in PAI-1 was observed for control subjects infused with 5% dextrose (p = 0.46). Among the normotensive subjects for whom graded doses of Ang II were infused at 0, 1, 3, and 10 ng.kg-1.min-1, mean PAI-1 levels increased sequentially from 14.7 ng/mL to 23.0, 26.8, and 33.5 ng/mL, a dose-response relation that, compared with controls, was highly significant (p < 0.001). Among the hypertensive patients for whom a single 45-minute infusion of Ang II was given at a dose of 3 ng.kg-1.min-1, PAI-1 levels increased from 23.7 to 37.7 ng/mL, whereas PAI-1 levels among control subjects infused with 5% dextrose decreased from 16.9 to 10.8 ng/mL (p = 0.04). Finally, when compared with infusion of 5% dextrose solution, infusion of Ang II appeared to have little effect on circulating levels of t-PA antigen.

CONCLUSIONS

These in vivo data suggest that infusion of Ang II results in a rapid increase in circulating levels of PAI-1, a finding that may help to explain clinical observations linking the renin-angiotensin system and thrombotic risk.