High-Dose Heparin Impairs Nitric Oxide Pathway and Vasomotion in Rats

Abstract

Background-Platelet-activating effects have been reported with high-dose heparin in acute thrombotic disorders. Recent studies have shown that increased platelet aggregation is due to reduced nitric oxide (NO) production in endothelial cells cultured in the presence of high-dose heparin. The aim of this study was to determine whether heparin can affect the NO pathway and the regulation of the vascular tone in vivo. Methods and Results-Anesthetized and mechanically ventilated Sprague-Dawley rats were treated with high-dose heparin. After 4 hours, the endothelial constitutive NO synthase (ecNOS) protein content in the aorta decreased (36% reduction, PϽ0.05), as detected by immunoblotting, and NO-dependent vascular reactivity was impaired. In fact, the increase in mean arterial blood pressure after inhibition of ecNOS with N G -nitro-L-arginine methyl ester (30 mg/kg) was smaller in heparin-treated animals than in controls (ϩ26.9Ϯ4.8 versus ϩ48.3Ϯ9.1 mm Hg, PϽ0.05), and further infusion of the biological ecNOS substrate L-arginine (0.5 g/kg) was ineffective in reversing systemic vasoconstriction (Ϫ1% versus 28% vasodilatation, PϽ0.001 eparin is the most widely used anticoagulant in current clinical practice. However, there is growing evidence that heparin can induce platelet activation. Recent studies report that therapeutic doses of heparin increase spontaneous and stimulated platelet aggregation when administered during acute coronary syndromes or unstable angina, but also in healthy subjects. [1][2][3] This effect is associated with impaired endothelial nitric oxide (NO) synthesis in bovine aortic endothelial cells exposed to high-dose heparin. 4 Endothelial synthesis of NO plays a fundamental role both in the regulation of platelet reactivity and in the control of vascular tone. 5 However, the effects of high-dose heparin on NO-mediated vasoreactivity in vivo have never been addressed. This effect would be clinically relevant in procedures such as PTCA and cardiopulmonary bypass, in which an activated partial thromboplastin time Ͼ100 seconds is currently used.The present study investigated the effects of heparin on systemic vascular tone of anesthetized rats after either inhibition or activation of the NO pathway by N G -nitro-L-arginine methyl ester (L-NAME) or L-arginine, respectively. Endothelial constitutive NO synthase (ecNOS) protein expression after heparin administration was also measured. Methods Animal PreparationThe investigation was conducted according to the Guide for the Care and Use of Laboratory Animals (US National Institutes of Health). Twenty-one Sprague-Dawley rats, maintained on a standard diet (mean body weight, 250Ϯ50 g), were anesthetized with sodium pentobarbital (30 mg/kg IP). A tracheostomy was performed, and the animals were mechanically ventilated to ensure physiological levels of arterial blood gases (PO 2 , 70 to 80 mm Hg; PCO 2 , 27 to 35 mm Hg). A single-lumen catheter was placed in the right carotid artery for blood pressure recording, and a second catheter was placed in the ri...

Heparin Impairs Glycocalyx Barrier Properties and Attenuates Shear Dependent Vasodilation in Mice

“…4,6,34 In the present study, we hypothesized that competitive binding of heparin to glycocalyx-associated proteins would affect the mechanotransduction of shear stress to the endothelium. We found that a clinically relevant dose of heparin (Ϸ50 U/kg of body weight) was associated with an increased clearance of large dextrans from the systemic circulation and a reduction in the duration of arteriolar vasodilation during reactive hyperemia in the mouse cremaster muscle.…”

“…2 In addition, there is evidence that heparin can induce antibodyindependent platelet activation, and this effect has been associated with an impaired endothelial NO production 3 and NO-dependent vascular reactivity. 4 On the other hand, increases in endothelial NO production and associated arteriolar vasodilation by heparin have been reported as well. 5,6 Heparin exerts its anticoagulation effect primarily by catalyzing the inhibition of thrombin by the serine protease inhibitor antithrombin III, apparently as a result of a conformational change within antithrombin III.…”

Carotid compression: Investigation of cerebral autoregulative reserve in rats

“…Heparin administration has been reported to augment (Kouretas et al, 1998) or impair (Bachetti et al, 1999) endothelial function. However, according to our procedure, in which we tried to minimize the dose of heparin given to the rat, we found neither the activation-flow coupling response nor the clip responses changed during experiments.…”

Role of nitric oxide in heparin-induced attenuation of hypoxic pulmonary vascular remodeling

“…Although eNOS was increased, the expression of eNOS mRNA was not, suggesting modulation occurs at the level of translation rather than transcription (17). However, these findings are contradicted by Bachettie et al (1), who reported a decrease in aortic eNOS protein expression and impairment of NO-dependent vascular reactivity after heparin infusion in rats. It is unlikely that inducible NOS plays a significant role because our laboratory's previous studies have indicated that it is minimally present compared with eNOS in normoxic or hypoxic rats (5).…”