Abstract 5516: Cardioprotective Effects of Hydrogen Peroxide and Erythropoietin During Acute Coronary Occlusion in Canine Coronary Native Collateral Microvessels in vivo

Abstract

Background: We have previously demonstrated that endothelium-derived hydrogen peroxide (H 2 O 2 ) is an endothelium-derived hyperpolarizing factor (EDHF) in canine coronary autoregulation in vivo. The aim of this study was to examine the role of H 2 O 2 during acute coronary occlusion with recombinant human erythropoietin (EPO) in the collateral vasodilatation of coronary microcirculation in vivo. Methods and Results: Canine subepicardial native collateral coronary small arteries (CSA, ≥100 μ m) and arterioles (CA, <100 μ m) were observed by an intravital microscope under cyclooxygenase blockade. Experiments were performed after LAD occlusion (90 min) under the following 8 conditions (n=5, each); control, low-dose EPO (100 IU/kg, L-EPO), high-dose EPO (1000 IU/kg, H-EPO), H-EPO+catalase (a H 2 O 2 decomposer), H-EPO+NO synthase inhibitor (L-NMMA), H-EPO+L-NMMA+catalase, H-EPO+L-NMMA+tetraethylammonium (TEA, a K Ca channels blocker) and H-EPO+ wortmannin (PI3K inhibitor). Ischemia caused a significant collateral arteriolar vasodilatation of control, which was significantly inhibited by catalase. After H-EPO, the vasodilatation was significantly increased in both-sized arteries (CSA 6±1%, CA 22±4%) compared with control (CSA 1±1%, CA 16±3%) or L-EPO (CSA 2±1%, CA 18±3%) associated with increase in collateral blood flow (microsphere technique). H-EPO+catalase significantly decreased the vasodilatation in CA (12±2%). The vasodilatation was markedly attenuated after H-EPO+L-NMMA+catalase (CSA −4±1%, CA 6±1%), H-EPO+L-NMMA+TEA (CSA −5±1%, CA 6±1%) and H-EPO+ wortmannin (CSA −5±1%, CA 6±1%). In the control group, expression of Akt phosphorylation in the ischemic LAD area was significantly decreased compared with the H-EPO group. In H-EPO+L-NMMA+catalase or H-EPO+wortmannin group, expression of Akt phosphorylation was further decreased compared with H-EPO or L-NMMA+H-EPO group. Plasma 8-hydroxydeoxyguanosine from coronary sinus as a myocardial oxidative stress marker (HPLC-ECD method) significantly decreased in H-EPO compared with control. Conclusions: H 2 O 2 and EPO play an important collaborative role in native collateral vasodilatation in response to acute coronary occlusion in canine coronary microcirculation in vivo.