Background. Cardiac ischemia reperfusion (I/R) injury causes coronary vascular dysfunction. Coenzyme Q10 (CoQ, which preserves cardiac mechanical function after I/R, recently has been recognized as a free radical scavenger. We hypothesized that CoQ protects coronary vascular reactivity after I/R via an antioxidant mechanism. Methods. Rats were pretreated with either CoQ (20 mg/kg intramuscular and 10 mg/kg intraperitoneal [CoQ group]) or a vehicle (Control) before the experiment. Isolated perfused rat hearts were subjected to 25 minutes of global normothermic ischemia and 40 minutes of reperfusion. The reperfusion-induced oxidative burst was directly assessed by lucigenin enhanced chemiluminescence. Coronary flow was measured at equilibration and after reperfusion with or without bradykinin, an endothelium-dependent vasodilator, and sodium nitroprusside (SNP), an endothelium-independent vasodilator. The effect of intracoronary infusion of hydrogen peroxide (H2O2 0.1 μmol/gm body weight given over 5 minutes), simulating the free radical burst after I/R, also was evaluated. Results. I/R decreased the bradykinin-induced change in coronary flow (-5% ± 4% versus 26% ± 3% at equilibration; p < 0.05) and the SNP-induced change (+20% ± 6% versus +56% ± 5% at equilibration; p < 0.05). The coronary vasculature after H2O2 infusion revealed a similar loss in vasodilatory responsiveness (+4% ± 4% in response to bradykinin, +35% ± 8% in response to SNP; p < 0.05 versus equilibration). Pretreatment with CoQ improved BK-induced vasorelaxation after I/R (+12% ± 2%; p < 0.05 versus control I/R) or H2O2 infusion (18% ± 4%; p < 0.05 versus control I/R) but failed to improve SNP-induced vasorelaxation. The CoQ pretreatment decreased the I/R-induced maximal free radical burst (9.3 ± 0.8 x 103 cpm versus 11.5 ± 1.1 x 103 cpm; p < 0.05) during the early period of reperfusion. Conclusions. Endothelium-dependent vasorelaxation is more sensitive than endothelium-independent relaxation to I/R injury. Via a direct antioxidant effect, CoQ preserved endothelium-dependent vasorelaxation by improving tolerance to I/R injury.
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