THE INCREASED SUSCEPTIBILITY TO HYDROGEN-PEROXIDE OF THE (POST-)ISCHEMIC RAT-HEART IS ASSOCIATED WITH THE MAGNITUDE OF THE LOW-MOLECULAR-WEIGHT IRON POOL

Recently we have shown that intracellular low molecular weight (LMW) iron increases during ischemia. It is hypothesized that this increase in LMW iron during ischemia underlies the reported hydrogen peroxide toxicity toward ischemic hearts. To investigate this hypothesis, rat hearts were subjected to 15 min of no-flow ischemia and reperfused with buffer saturated against 95% N-2 and 5% CO2 (anoxic reperfusion) for 7 min. Hearts were then switched to buffer saturated against 95% O-2 and 5% CO2 (reoxygenation) to assess functional recovery. The cardiac function recovered to 80 +/- 7% of the preischemic value. When the anoxic reperfusion was applied in the presence of 10 mu M hydrogen peroxide, functional recovery after reoxygenation was 47 +/- 7%. Hearts that were perfused with deferoxamine before ischemia and then subjected to ischaemia and anoxic reperfusion in the presence of 10 mu M hydrogen peroxide recovered to 78 +/- 8%. Immediate reoxygenation after ischemia led to only 45 +/- 6% recovery of function. During ischemia, LMW iron increased from 49 +/- 45 to 183 +/- 45 pmol/mg protein (p < .05) and decreased to 58 +/- 38 pmol/mg protein (p < .05) during the subsequent anoxic perfusion. Rat hearts preloaded with deferoxamine showed a slightly higher LMW iron content than normal (85 +/- 23 and 49 +/- 45 pmol/mg protein, respectively; n.s.), which showed a small, nonsignificant increase up to 136 +/- 42 pmol/mg protein after 15 min of ischemia. No significant changes ware found in reduced and oxidized glutathione content and glutathione peroxidase or catalase activities under those conditions. Our results indicate that hydrogen peroxide toxicity is determined by the mount of catalytic iron in the LMW pool and not by a decrease in antioxidant defense capacity to hydrogen peroxide.