Acute arterial thrombosis causes endothelial dysfunction: A new paradigm for thrombolytic therapy

Purpose: The goals of this study were to delineate the time course of endot helial dysfunction after arterial thrombosis, to determine the cause of end othelial dysfunction in this setting, and to determine whether modulating s tandard thrombolytic therapy would ameliorate the thrombosis-mediated endot helial dysfunction. Methods: Male adult rats underwent infrarenal aortic occlusion by means of clip ligature to induce arterial thrombosis. After 30 minutes, 1, 2, and 3 hours, ring segments from the infrarenal aorta were harvested and placed in to physiologic buffer baths. With the use of a force transducer, both endot helial dependent relaxation (EDR) and endothelial-independent relaxation (E IR) were measured. Endothelial function and presence were determined by mea ns of factor VIII immunohistochemical staining. Endothelial morphology was evaluated with scanning electron microscopy (SEM). Nitric oxide (NO) levels a,crc determined with a chemiluminescent assay of its nitrite/nitrate meta bolites (NOx). Standard thrombolytic therapy with urokinase (UK) was infuse d into thrombosed aortic ring segments and compared with UK supplemented wi th both low-dose L-arginine (2 mmol) and high-dose L-arginine (20 mmol). Results: Arterial thrombosis decreases EDR. The nadir of EDR occurs 1 hour after thrombosis (mean +/- SE, 13% +/- 6.4% vs 94% +/- 2.6% for controls, P <.005), with persistent lowering of EDR as long as 3 hours after thrombosi s. EIR is preserved, and vasoconstriction with norepinephrine or potassium buffer is unaltered. Both endothelial function and presence (n = 6 per grou p) were documented by means of factor VIII immunohistochemistry. An intact monolayer of endothelium at all time intervals after thrombosis was reveale d by means of SEM analysis. No differences between control and thrombosed s pecimens were revealed by means of the grading of SEM images. Local NO, lev els were lower after I hour of thrombosis, with an increase higher than bas eline values at 3 hours. The addition of low-dose L-arginine resulted in a minor increase in EDR. However, high-dose L-arginine resulted in a signific ant increase in EDR versus controls receiving UK alone (64% +/- 6.3% vs 38% +/- 4.4%, P <.05). Correspondingly, local NO. levels were 20-fold higher a fter the high-dose L-arginine supplementation when compared with UK thrombo lysis alone (2.8 +/- 0.52 mu mol/L vs 0.133 +/- 0.02 mu mol/L, n = 6 sample s/group, P <.005). Conclusion; Acute arterial thrombosis causes endothelial dysfunction, witho ut causing endothelial cell loss. Endothelial function reaches a nadir afte r 1 hour of thrombosis. EIR and vasoconstriction remain unaffected, indicat ing normal smooth muscle cell function. NOx levels suggest that NO levels a re decreased acutely after thrombosis. Supplementing standard thrombolytic therapy with the NO precursor, L-arginine, ameliorates the endothelial dysf unction seen after acute thrombosis by increasing local NO production.