Abstract
Among the several mechanisms proposed for ischemic preconditioning (IPC), generation of reactive oxygen species (ROS) is reported to be involved in the cardioprotective effects of IPC. The present study was designed to investigate whether repetitive exposure to hydrogen peroxide (H2O2) can protect the myocardium against subsequent ischemia/reperfusion injury, and whether the H2O2-induced cardioprotection is related to the preservation of energy metabolism. Langendorff-perfused rat hearts were exposed to two, 5 min episodes of IPC or to various concentrations of H2O2 twice and then to 35 min global ischemia and 40 min reperfusion. Using 31P nuclear magnetic resonance (31P-NMR) spectroscopy, cardiac phosphocreatine (PCr) and ATP and intracellular pH (pHi) were monitored. IPC and the treatment with 2 μmol/L H2O2 significantly improved the post-ischemic recovery of left ventricular developed pressure (LVDP) and the PCr and ATP compared with those of the control ischemia/reperfusion (LVDP: 36.9 ±7.4% of baseline in control hearts, 84.0±3.5% in IPC, 65.4±3.8% in H2O2; PCr: 51.1±5.3% in control hearts, 81.4±5.5% in IPC, 81.7±5.2% in H2O2; ATP: 12.3±1.6% in control hearts; 30.0±2.8% in IPC, 28.6±2.3% in H2O2, mean ± SE, p<0.05). However, lower (0.5 μmol/L) or higher (10 μmol/L) concentration of H2O 2 had no effect. There were significant linear correlations between mean LVDP and high-energy metabolites after 40 min reperfusion in H2O2-treated hearts. In IPC-treated hearts, the mean LVDP was greater than that in the 2 μmol/L H2O2-treated hearts under similar levels of high-energy metabolites. IPC also ameliorated intracellular acidification (6.38±0.03 in control hearts, 6.65±0.04 in IPC, p<0.05), but treatment with H2O2 did not affect pHi during ischemia (6.40±0.05 in H2O2). In conclusion, H2O2 had protective effects against ischemia/reperfusion injury and the effects were related to the preservation of energy metabolism. IPC could have additional protective mechanisms that are associated with the amelioration of intracelluar acidosis during ischemia. (Circ J 2003; 67: 253 - 258)
