Background: It has been previously demonstrated that endothelial Cu, Zn-SOD and caveolin-1 play crucial roles of hydrogen peroxide (H₂O₂) production as an endothelium-derived hyperpolarizing factor (EDHF) in mouse mesenteric arteries. We thus examined whether this mechanism is involved in the EDHF-mediated responses in diabetes mellitus (DM) during acute coronary occlusion.

Methods: Canine subepicardial coronary collateral small arteries (CSA>100µm) and arterioles (CA <100µm) were visually traced by an intravital microscope between left anterior descending artery (LAD) and left circumflex coronary artery (LCX) with an injection of indocyanine green. We examined bradykinin-induced vasodilatation of native coronary collaterals before and after myocardial ischemia by proximal LAD occlusion (90min) under the following conditions (n=6 each); (i) control and (ii) DM (alloxan, 1 week prior to study, IV) with cyclooxygenase blockade (ibuprofen, 12.5 mg/kg, IV) before the onset of the ischemia. Myocardial levels of Cu,Zn-SOD, caveolin-1 and H₂O₂ (Amplex Red) and plasma levels of 8-OHdG, as a marker of oxidative stress and tetrahydrobiopterin in the coronary sinus were measured by ELISA and high-performance liquid chromatography.

Results: Although the levels of Cu, Zn-SOD, tetrahydrobiopterin and caveolin-1 in the LAD area were comparable between the control and DM groups, caveolin-1 levels were greater in coronary microvessels than in coronary conduit arteries in the control group. Nitric oxide (NO)-mediated coronary vasodilatation of CSA by bradykinin significantly decreased in DM compared with control, and was restored by compensation of EDHF/H₂O₂ in CA with H₂O₂ production for the loss of NO. Oxidative stress (8-OHdG) was significantly increased in DM compared with control.

Conclusions: NO-mediated, endothelium-dependent vasodilatations of CSA during acute coronary occlusion are impaired in DM and are compensated by EDHF/H₂O₂ in dogs in vivo.