Inhibition of CD40 ligand (CD154) in the treatment of factor VIII inhibitors.

The development of persistent, high titer inhibitors represents a serious complication of the treatment of patients with severe hemophilia A. Elimination of these inhibitory antibodies is usually attempted through repeated administration of high doses of factor VIII. Such regimens are costly, time-consuming and often fail when the inhibitor is of very high titer or of longstanding duration. A potential alternative approach to inhibit the production of antifactor VIII antibodies is blockade of the T-cell/B-cell collaboration that is required to generate humoral responses. One cognate receptor pair that is required for T-cell-dependent B-cell activation consists of CD40, which is expressed on B-lymphocytes and other antigen presenting cells, and CD40 ligand (CD40L, CD154), which is transiently expressed on activated T-cells. To determine whether blockade of the CD40-CD40L pathway can inhibit the production of anti-factor VIII antibodies, a clinical study has been designed in which patients with hemophilia A and a high titer inhibitor (> 10 BU) receive monthly exposures to factor VIII in the presence of a humanized mouse monoclonal antibody to human CD40L (hu5c8*). Subjects must be between the ages of 5 and 60 years old and be HIV seronegative. To date, three subjects have received at least three doses of hu5c8 at the initial protocol dose of 10 mg/kg. Preliminary results suggest that anti-CD40L inhibition may be effective in blocking anamnestic responses to factor VIII in some patients. It remains to be determined whether this effect will persist and whether patients may eventually become tolerant to factor VIII in the absence of hu5c8 co-administration.

Effect of transient abrupt vessel closure during otherwise successful angioplasty for unstable angina on clinical outcome at six months. Hirulog Angioplasty Study Investigators.

OBJECTIVES: The objective of this study was to identify predictors of major adverse cardiac events after successful coronary angioplasty. BACKGROUND: The acute complications of angioplasty are related to baseline clinical and angiographic variables, and early complications adversely affect long-term outcome. However, the predictors of enduring success after uncomplicated angioplasty are less well defined. METHODS: Of 4,098 patients undergoing angioplasty in the Hirulog Angioplasty Study, 3,899 (95%) had a successful procedure without in-hospital death, emergent bypass surgery or clinical evidence of myocardial infarction. Baseline and procedural variables for these 3,899 patients were examined. RESULTS: Major adverse cardiac events occurred in 22% of the patients with initially successful procedures at 6 months: death in 1%, myocardial infarction in 2% and repeat revascularization in 21%. Univariable predictors of increased events included successful salvage from abrupt vessel closure (p < 0.001), emergency stenting (p < 0.001), multilesion angioplasty (p < 0.001), diabetes (p=0.02), target lesion in the left anterior descending artery (p=0.02), unstable angina (p=0.03) and smaller final luminal diameter (p=0.04). There was a trend toward increased events among patients with prior angioplasty (p=0.08), but asymptomatic elevation of the creatine kinase was not predictive (p=0.5). In a multivariable model, abrupt vessel closure was the strongest independent predictor of major adverse cardiac events at 6 months (p < 0.001; odds ratio [95% confidence interval]=3.6 [2.5 to 5.1]), while multivessel angioplasty, target lesion in the left anterior descending artery and diabetes also remained independent predictors (all p < or = 0.02). CONCLUSIONS: This analysis suggests that "uncomplicated" abrupt vessel closure is a powerful predictor of adverse clinical outcome following successful angioplasty. Improved techniques to reduce abrupt closure during angioplasty are thus urgently needed, and patients who experience "uncomplicated" closure require closer surveillance during follow-up.

Effect of direct thrombin inhibition with Bivalirudin (Hirulog) on restenosis after coronary angioplasty.

The direct antithrombin, bivalirudin, did not reduce angiographic restenosis measured either as the dichotomous restenosis rate of 62% for bivalirudin and 58% for heparin (p = 0.70), or as the late loss in lumen diameter of 0.44 +/- 0.47 mm for bivalirudin and 0.39 +/- 0.53 mm for heparin (p = 0.62). Direct thrombin inhibition with bivalirudin neither reduces angiographic restenosis nor alters the impact of several established risk factors for restenosis.

Randomized, double-blind comparison of hirulog versus heparin in patients receiving streptokinase and aspirin for acute myocardial infarction (HERO). Hirulog Early Reperfusion/Occlusion (HERO) Trial Investigators.

BACKGROUND: Thrombolytic therapy improves survival after myocardial infarction through reperfusion of the infarct-related artery. Thrombin generated during thrombolytic administration may reduce the efficacy of thrombolysis. A direct thrombin inhibitor may improve early patency rates. METHODS AND RESULTS: Four hundred twelve patients presenting within 12 hours with ST-segment elevation were given aspirin and streptokinase and randomized in a double-blind manner to receive up to 60 hours of either heparin (5000 U bolus followed by 1000 to 1200 U/h), low-dose hirulog (0.125 mg/kg bolus followed by 0.25 mg x kg(-1) x h(-1) for 12 hours then 0.125 mg x kg(-1) x h(-1)), or high-dose hirulog (0.25 mg/kg bolus followed by 0.5 mg x kg(-1) x h(-1) for 12 hours then 0.25 mg x kg(-1) x h(-1)). The primary outcome was Thrombolysis In Myocardial Infarction trial (TIMI) grade 3 flow of the infarct-related artery at 90 to 120 minutes. TIMI 3 flow was 35% (95% CI, 28% to 44%) with heparin, 46% (95% CI, 38% to 55%) with low-dose hirulog, and 48% (95% CI, 40% to 57%) with high-dose hirulog (heparin versus hirulog, P=.023; heparin versus high-dose hirulog, P=.03). At 48 hours, reocclusion had occurred in 7% of heparin, 5% of low-dose hirulog, and 1% of high-dose hirulog patients (P=NS). By 35 days, death, cardiogenic shock, or reinfarction had occurred in 25 heparin (17.9%), 19 low-dose hirulog (14%), and 17 high-dose hirulog patients (12.5%) (P=NS). Two strokes occurred with heparin, none with low-dose hirulog, and two with high-dose hirulog. Major bleeding (40% from the groin site) occurred in 28% of heparin, 14% of low-dose hirulog, and 19% of high-dose hirulog patients (heparin versus low-dose hirulog, P<.01). CONCLUSIONS: Hirulog was more effective than heparin in producing early patency in patients treated with aspirin and streptokinase without increasing the risk of major bleeding. Direct thrombin inhibition may improve clinical outcome.

Hirulog: a direct thrombin inhibitor for management of acute coronary syndromes.

Hirulog therapy has been studied extensively in numerous settings including prevention of DVT, treatment of unstable angina, treatment of acute myocardial infarction during thrombolysis, and prevention of acute complications of PTCA. Being one of the first direct thrombin inhibitors in clinical development, it has had to 'test the waters', so to speak, of the relationship between pathophysiology and clinical trial design: what are the correct indications, patient entry criteria, endopoints, frequency and duration of dosing, and so on? Our findings validate a role for thrombin in treating arterial thromboembolism and demonstrate clinical activity and tolerability of Hirulog.

Treatment with bivalirudin (Hirulog) as compared with heparin during coronary angioplasty for unstable or postinfarction angina. Hirulog Angioplasty Study Investigators.

BACKGROUND: Heparin is often administered during and after coronary angioplasty to prevent closure of the dilated vessel. However, ischemic or hemorrhagic complications occur in 5 to 10 percent of treated patients. We studied whether these complications could be prevented when the direct thrombin inhibitor bivalirudin (Hirulog) was used in place of heparin. METHODS: We performed a double-blind, randomized trial in 4098 patients undergoing angioplasty for unstable or postinfarction angina. Patients were assigned to receive either heparin or bivalirudin immediately before angioplasty. The primary end point were death in the hospital, myocardial infarction, abrupt vessel closure, or rapid clinical deterioration of cardiac origin. RESULTS: In the total study group, bivalirudin did not significantly reduce the incidence of the primary end point (11.4 percent, vs. 12.2 percent for heparin) but did result in a lower incidence of bleeding (3.8 percent vs. 9.8 percent, P < 0.001). In the prospectively stratified subgroup of 704 patients with postinfarction angina, bivalirudin therapy resulted in a lower incidence of the primary end point (9.1 percent vs. 14.2 percent, P = 0.04) and a lower incidence of bleeding (3.0 percent vs. 11.1 percent, P < 0.001), but in a similar cumulative rate of death, myocardial infarction, and repeated revascularization in the six months after angioplasty (20.5 percent vs. 25.1 percent, P = 0.17). CONCLUSIONS: Bivalirudin was at least as effective as high-dose heparin in preventing ischemic complications in patients who underwent angioplasty for unstable angina, and it carried a lower risk of bleeding. Bivalirudin, as compared with heparin, reduced the risk of immediate ischemic complications in patients with postinfarction angina, but this difference was no longer apparent after six months.

Aurintricarboxylic acid prevents acute rethrombosis in a canine model of arterial thrombosis.

Acute rethrombosis following thrombolytic therapy occurs in 5% to 25% of patients. We evaluated the effect of aurintricarboxylic acid (ATA), a triphenyl dye that blocks von Willebrand factor (vWF) binding to platelet glycoprotein Ib, on arterial reperfusion and acute rethrombosis following fibrinolytic therapy. Primary thrombosis was induced in the femoral arteries of anesthetized dogs by application of anodal current and partial arterial constriction. Blood flow was monitored with an electromagnetic flow probe, and primary thrombosis was considered to have occurred when blood flow was reduced to and remained at zero. Reperfusion was induced by intravenous streptokinase 30 minutes after thrombosis. Streptokinase reduced plasma fibrinogen levels from an average of 144 mg/dL to < 5 mg/dL resulting in inhibition of ADP- and epinephrine-induced platelet aggregation ex vivo. Acute rethrombosis following reperfusion occurred within 37 +/- 18 (mean +/- SD) minutes in 89% (16/18) of animals receiving thrombolytic activator treatment. Histological examination of reoccluding thrombi revealed densely aggregated platelets and erythrocytes with no detectable fibrin. In the two other study groups, ATA was infused in conjunction with thrombolytic therapy (10 arteries) or at near completion of acute rethrombosis following fibrinolytic activator treatment (6 arteries). In each case ATA prevented rethrombosis. However, concomitant administration of ATA and thrombolytic therapy delayed restoration of blood flow. ATA had no direct effect on hemodynamics, thrombin time, platelet count, or platelet aggregation response to ADP, epinephrine, or collagen. These data indicate that inhibition of vWF-platelet glycoprotein Ib interaction is effective in preventing acute rethrombosis following thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

A pilot, early angiographic patency study using a direct thrombin inhibitor as adjunctive therapy to streptokinase in acute myocardial infarction.

BACKGROUND: The success of streptokinase in acute myocardial infarction is hampered by the high failure rate to achieve early reperfusion. This study evaluates the possible benefit of Hirulog (Biogen, Cambridge, Mass), a direct thrombin inhibitor, as adjunct therapy to streptokinase to enhance early patency and prevent rethrombosis. Heparin has been shown to be of very limited benefits in this setting. METHODS AND RESULTS: Forty-five patients were randomized to Hirulog or heparin (2:1 ratio). Coronary angiography documented a TIMI 2 or 3 flow after 90 minutes in 77% of the patients treated with Hirulog and streptokinase and in 47% of patients treated with heparin and streptokinase (P < .05) and after 120 minutes in 87% and 47% of patients, respectively (P < .01). TIMI 3 flow was established in 77% of patients with Hirulog compared with 40% with heparin (P < .02). The clinical outcome and the bleeding rate was also favorable to Hirulog; no reocclusion was observed at late angiography performed 4.7 days later. CONCLUSIONS: Hirulog in this pilot study significantly improved the early patency rate of the infarct-related artery with a favorable clinical profile. This new direct thrombin inhibitor exhibits promise as adjunctive therapy to thrombolysis.

Percutaneous Transluminal Coronary Angioplasty for Unstable Angina: Predictors of Outcome in a Multicenter Study.

Background: Angiographic and clinical studies have demonstrated that coronary artery plaque rupture with thrombus formation, spasm, or both are frequently responsible for the syndrome of unstable angina. Percutaneous transluminal coronary angioplasty (PTCA) is commonly used in the treatment of patients with coronary artery disease and unstable angina. A number of studies have shown, however, that intracoronary thrombus increases the risk of abrupt vessel closure. The purpose of this study was to define preprocedural variables predictive of the outcome of PTCA performed on patients with unstable angina in a prospective multicenter study using a core angiographic laboratory. Methods and Results: A total of 386 patients with unstable angina underwent coronary angioplasty of 487 lesions treated with balloon PTCA at 9 medical centers. Multivessel or left main coronary artery diseasewas present in 55% and recent myocardial infarction in 22%. Clinical success was achieved in 317 of 386 patients (82.1%), as defined by <50% residual stenosis at every target lesion evaluated in the core angiographic laboratory and no major complication during hospitalization. Major complications (death, Q-wave or non-Q-wave myocardial infarction, or emergency coronary artery bypass surgery) occurred in 36 patients (9.3%), and abrupt vessel closure occurred in 50 (13.0%). Logistic regression analysis identified preprocedural variables that were predictive of outcome of angioplasty. Strong predictors of any complication (major complication or abrupt vessel closure) included age [odds ratio (OR) = 1.04; 95% confidence interval [CII 1.02. 1.071) for each additional year of age; p < 0.001), number of diseased vessels (OR = 1.58; 95% Cl = 1.16, 2.15 per additional vessel; is = 0.012), the number of le~ions treated at angioplasty (OR) = 1.04%; 95% confidence interval [CI] 1.02, 1.07]) for each additional year of age; p < 0.001), number of diseased vessels (OR = 1.58%; 95% CI = 1.16, 2.15 per additional vessel; p = 0.012), the number of lesions treated at angioplasty (OR = 1.72%; 95% CI = 1.11, 2.66;; p = 0.014), and angiographic evidence of filling defect preceding angioplasty (OR = 3.30; 95% CI = 1.11, 9.75; p < 0.001). Conclusions: The outcome of PTCA performed for unstable angina is influenced by a combination of clinical, angiographic, and procedural variables. This study suggests that PTCA performed on lesions associated with filling defects or on more than one lesion at the time of the procedure carries an increased risk of complication. The outcome of PTCA for unstable angina may be improved by identifying new strategies for the treatment of lesions associated with filling defects and by using more accurate methods to identify and treat the culprit lesion responsible for unstable angina.

Usefulness and tolerability of hirulog, a direct thrombin-inhibitor, in unstable angina pectoris.

In an open-label pilot study of 20 patients with unstable angina (Braunwald class I-IIIB), hirulog was administered as a continuous intravenous infusion for 5 days in a dose of 0.2 mg/kg/hour to produce an activated partial thromboplastin time of approximately 200% of control. The primary end points of the study were: death, development of a transmural myocardial infarction, and intractable angina needing interventions such as an intraaortic balloon pump insertion, angioplasty and surgery. The secondary end points were the presence of an intracoronary thrombus detected on angiography and hemorrhagic complications during therapy. There was no death or transmural infarction in this study cohort; however, 1 patient developed intractable angina. Intracoronary thrombus was documented in 2 patients. Infusion of hirulog resulted in a steady prolongation of the activated partial thromboplastin time without any hemorrhagic or other adverse effect. Hirulog appears to be an effective antithrombotic agent that is tolerated well and may have advantages over heparin in the management of patients with unstable angina.

Nitric oxide-mediated, endothelium-dependent vasodilation is selectively attenuated in the postischemic extremity.

BACKGROUND: Attenuation of endothelium-dependent relaxing factor (EDRF) release may contribute to adverse sequelae commonly seen after reperfusion of an acutely ischemic extremity. The purpose of this study was to identify the compound responsible for the EDRF activity in the extremity and to evaluate its modulation by ischemia and reperfusion. METHODS: Isolated rat hindlimbs were perfused at constant pressure with an albumin-enriched crystalloid buffer. Increasing log dose infusions of acetylcholine and nitroprusside were used to measure endothelium-dependent (EDRF-mediated) and endothelium-independent vasoreactivity, respectively. RESULTS: Graded reductions in total vascular resistance were seen in response to both agonists in the control group (n = 11). In the postischemic group (n = 7), 60 minutes of normothermic ischemia and 10 minutes of reperfusion reduced endothelium-dependent vasodilation to acetylcholine by approximately 40% (p < 0.01). Endothelium-independent vasodilation to nitroprusside was unaffected. NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of nitric oxide release, attenuated vasodilation to acetylcholine (p < 0.01) but not nitroprusside in both control and postischemic groups. CONCLUSIONS: Endothelium-dependent vasodilation in the rat hindlimb, mediated by nitric oxide, was selectively impaired by injury from ischemia and reperfusion. Strategies designed to minimize postischemic attenuation of nitric oxide release may be beneficial in the management of acute limb ischemia.

Analysis of shear stress and hemodynamic factors in a model of coronary artery stenosis and thrombosis.

Shear stress and alterations in blood flow within a stenosed artery promote platelet-dependent thrombosis. Using the Folts model of coronary thrombosis, we evaluated morphology, histology, and the hemodynamic properties of the stenosed vessel in 18 animals. The average stenosis created was 58 +/- 8%, with stenosed vessel diameters ranging from 0.084 to 0.159 cm. Histological examination of the stenosed vessel demonstrated that thrombi were composed primarily of platelets and formation occurred 1.0 mm downstream from the apex of the constriction, propagating distally. Peak shear stress occurred just upstream from the apex of the stenosis and varied from 520 to 3,349 dyn/cm2. Only small differences in shear forces were noted when blood viscosity was calculated using Newtonian and non-Newtonian properties. In contrast, shear stress computed for Poiseuille flow with use of the stenosis diameter underestimated the apical shear stress. Blood flow remained laminar within the stenosis with a Reynolds number range of 292-534. Our data indicate that the geometry of the stenosis inflow region must be considered in the evaluation of platelet activation and thrombus formation within a stenosed artery.

Initial experience with a direct antithrombin, Hirulog, in unstable angina. Anticoagulant, antithrombotic, and clinical effects.

BACKGROUND: Currently available antithrombotic therapy for unstable angina is unwieldy and occasionally ineffective. This study was designed to investigate the potential of Hirulog, a new synthetic specific antithrombin agent, for the management of this condition. METHODS AND RESULTS: A total of 55 patients in the acute phase of unstable angina received intravenous Hirulog according to one of two protocols. In an acute dose-escalating study, 0.02, 0.05, 0.1, 0.25, and 0.5 mg.kg-1 x h-1, each for 30 minutes, were infused in 15 patients. Prolongation of activated partial thromboplastin time (aPTT) (r = .95), fibrinopeptide A inhibition (r = .96), and Hirulog plasma levels (r = .91) correlated closely with the dose infused, with significant changes compared with baseline appearing at doses of 0.25 mg.kg-1 x h-1 and higher. The purposes of the second protocol were to determine whether the anticoagulant and antithrombotic effects of the drug were sustained during a 72-hour infusion and to assess whether such treatment prevented the complications of unstable angina. Based on the initial study, we planned to give a dose of 0.25 mg.kg-1 x h-1 to each patient until 2 patients failed therapy, then successively higher doses until a 95% success rate was achieved or adverse effects intervened, increasing the dose after two failures had occurred at each level. Five patients received the 0.25-mg.kg-1 x h-1 dose and 14 the 0.5-mg.kg-1 x h-1 dose before two failures occurred. Failure was observed in only one of 21 patients at the dose of 1 mg.kg-1 x h-1. aPTT (+/- SEM) levels increased to 62 +/- 5, 76 +/- 2, and 98 +/- 3 seconds at the three doses, with minimal intraindividual variation, and Hirulog plasma levels to 1050, 2100, and 4200 mg/mL, respectively. Fibrinopeptide A plasma levels decreased at all doses but more consistently at the dose of 1 mg.kg-1 x h-1. The overall clinical success rate was 87.5%: 60% (3/5) at the low dose, 86% (12/14) at the intermediate dose, and 95% (20/21) at the high dose. No deaths, myocardial infarctions, or bleeding complications occurred. CONCLUSIONS: In unstable angina patients, Hirulog infusions quickly and reproducibly yield stable, dose-dependent anticoagulant and antithrombotic effects with a favorable clinical efficacy profile.

Anticoagulant effects of hirulog, a novel thrombin inhibitor, in patients with coronary artery disease.

Selective thrombin inhibitors are a new class of antithrombotic drugs that, unlike heparin, can effectively inhibit clot-bound thrombin and escape neutralization by activated platelets. Hirulog is a 20 amino acid hirudin-based synthetic peptide that has shown promise in experimental models of thrombosis. Little information is available about the effects of hirulog in patients with coronary artery disease. Forty-five patients undergoing cardiac catheterization, who were taking aspirin, were randomized to receive either (1) hirulog, 0.05 mg/kg intravenous bolus followed by 0.2 mg/kg/hour intravenous infusion until the end of the catheterization; (2) hirulog, 0.15 mg/kg intravenous bolus followed by 0.6 mg/kg/hour intravenous infusion; or (3) heparin; 5,000 U intravenous bolus. Serial activated partial thromboplastin time (APTT), prothrombin time, activated clotting time and fibrinopeptide A were measured. Hirulog produced a dose-dependent prolongation of all coagulation parameters; the 0.6 mg/kg/hour dose prolonged the APTT to 218 +/- 50% of baseline after 2 minutes and 248 +/- 50% of baseline after 15 minutes. The half-life of the effect on APTT was 40 minutes. The hirulog blood level correlated well with the APTT, prothrombin time and activated clotting time (r = 0.77, 0.73, and 0.82 respectively, all p < 0.001). Both doses of hirulog potently suppressed the generation of fibrinopeptide A (p < 0.05). There were no major hemorrhagic, thrombotic or allergic complications in patients treated with hirulog or heparin. Thus, hirulog, a direct thrombin inhibitor, provides a predictable level of anticoagulation and appears to have a potent yet well-tolerated anticoagulant profile in patients with coronary artery disease.

Heparin-associated thrombocytopenia: a critical review and pooled analysis.

The purpose of this study is to determine the incidence of heparin-associated thrombocytopenia (HAT) for various subgroups of heparin exposed patients and the impact of study quality on the reported incidence. Articles were identified using a Medline search, a manual search of the Index Medicus, and a review of article references. Key data included heparin type, administration route, indication, treatment duration, outcome criteria, incidence, and platelet count reliability. The pooled incidence estimate in studies requiring a repeatedly abnormal platelet count was compared with estimates from studies not requiring a repeated platelet count. The results showed that there were no adequately designed studies to estimate the incidence of HAT-related thrombosis or hemorrhage. The pooled incidence of HAT in studies requiring a reproducibly lowered platelet count (< 100,000/microL) was 3/281 (1.1%) with intravenous porcine heparin and 4/140 (2.9%) with intravenous bovine heparin. This difference was not statistically significant. The incidence of HAT with intravenous bovine heparin was significantly lower in studies that required a repeated platelet count. The incidence of HAT with heparin administered subcutaneously was small (0%) and in those studies requiring a repeatedly abnormal platelet count, there was no difference between porcine and bovine heparin. The authors concluded that the incidence of HAT is < 3% with intravenous heparin and extremely low for subcutaneous heparin. Study quality may influence the reported incidence of HAT.

Heparin prevents postischemic endothelial cell dysfunction by a mechanism independent of its anticoagulant activity.

PURPOSE: Heparin may have protective effects on postischemic vascular endothelial cell function that are distinct from its anticoagulant, antiplatelet, or anticomplement activity. We tested this hypothesis in isolated rat hindlimbs. METHODS: Isolated rat hindlimbs underwent 60 minutes of normothermic ischemia and 10 minutes of reperfusion. Potential heparin interaction with plasma-based proteins or cells was eliminated by perfusion of the hindlimbs with a nonrecirculated albumin-enriched crystalloid buffer. Endothelial function was assessed by measurement of endothelium-derived relaxing factor (EDRF) activity. Limbs perfused at constant pressure were subjected to increasing log dose infusions of acetylcholine and nitroprusside to measure endothelial-dependent (EDRF-mediated) and endothelial-independent vasoreactivity, respectively. Fifty limbs were divided into seven groups: two nonischemic groups (one with heparin) and five ischemia/reperfusion groups treated with increasing doses of heparin (0 to 1.0 U/ml perfusate). RESULTS: The nontreated ischemia/reperfusion group (n = 12) had a 46.2% reduction in endothelial-dependent vasodilation of the rat hindlimb when compared with the nonischemic control (n = 7, p < 0.05). Treatment with heparin 0.5 U/ml (n = 6) nearly abolished this attenuation of endothelial-dependent vasodilation (4.3% reduction, p = not significant vs nonischemic control). The endothelial protective effect of heparin was dose-dependent: groups treated with 0.25 U/ml (n = 6) and 0.1 U/ml heparin (n = 7) showed progressive impairment in postischemic EDRF-mediated vasodilation. Endothelial-independent vasodilation induced by nitroprusside was unchanged by ischemia/reperfusion or heparin treatment, which confirmed that the postischemic damage and its protection by heparin were specific to the endothelium. CONCLUSIONS: Heparin prevented postischemic endothelial cell dysfunction by a mechanism independent of its interactions with plasma-based proteins or cells. This nonanticoagulant protective effect may contribute to the salutary effects of heparinization during acute ischemic events.