Cardioprotective role of endogenous hydrogen peroxide during ischemia-reperfusion injury in canine coronary microcirculation in vivo

We have recently demonstrated that endogenous H2O2 plays an important role in coronary autoregulation in vivo. However, the role of H2O2 during coronary ischemia-reperfusion (I/R) injury remains to be examined. In this study, we examined whether endogenous-H2O2 also plays a protective role in coronary I/R injury in dogs in vivo. Canine subepicardial small coronary arteries (>= 100 mu m) and arterioles (>= 100 mu m) were continuously observed by an intravital microscope during coronary I/R (90/60 min) under cyclooxygenase blockade (n = 50). Coronary vascular responses to endothelium-dependent vasodilators (ACh) were examined before and after I/R under the following seven conditions: control, nitric oxide (NO) synthase (NOS) inhibitor N-G-monomethyl-L-arginine (LNMMA), catalase (a decomposer of H2O2), 8-sulfophenyltheophylline (8SPT, an adenosine receptor blocker), L-NMMA + catalase, L-NMMA + tetraethylammonium (TEA, an inhibitor of large-conductance Ca2+-sensitive potassium channels), and L-NMMA + catalase + 8-SPT. Coronary I/R significantly impaired the coronary vasodilatation to ACh in both sized arteries (both P < 0.01); L-NMMA reduced the small arterial vasodilatation (both P < 0.01), whereas it increased (P < 0.05) the ACh-induced coronary arteriolar vasodilatation associated with fluorescent H2O2 production after I/R. Catalase increased the small arterial vasodilatation (P < 0.01) associated with fluorescent NO production and increased endothelial NOS expression, whereas it decreased the arteriolar response after I/R (P < 0.01). L-NMMA + catalase, L-NMMA + TEA, or L-NMMA + catalase + 8-SPT further decreased the coronary vasodilatation in both sized arteries (both, P < 0.01). L-NMMA + catalase, L-NMMA + TEA, and L-NMMA + catalase + 8-SPT significantly increased myocardial infarct area compared with the other four groups (control, L-NMMA, catalase, and 8-SPT; all, P < 0.01). These results indicate that endogenous H2O2, in cooperation with NO, plays an important cardioprotective role in coronary I/R injury in vivo.