Ischemia/Reperfusion-Induced Injury of Forebrain Mitochondria and Protection by Ascorbate

Complete, reversible forebrain ischemia was induced with a seven-vessel occlusion rat model. Previous studies of isehemic (M. A. Sciamanna, J. Zinkel, A. Y. Fabi, and C. P. Lee, 1992, Biochim. Biophys. Acta 1134, 223-232) rat brain mitochondria (RBM) showed that isehemia of 30 min caused an ∼60% decrease in State 3 respiratory rates with both succinate and NAD-linked substrates and also in energy-linked Ca2+ transport. No significant change was seen in the State 4 rates. The inhibition of respiration could be prevented by EGTA or ruthenium red. In this paper it is shown that reperfusion (5 h) following isehemia (30 min) further impaired RBM respiratory activities (succinate and NAD-linked substrates). The presence of EGTA or ruthenium red in the assay medium did not protect against ischemia/reperfusion-induced injury. The effects of ascorbate, an oxygen radical scavenger, were studied. RBM isolated from ascorbate-treated animals (0.8 mg ascorbate/kg body weight) after ischemia (30 min) alone showed only a slight increase in State 3 (∼25%) and a decrease in State 4 (∼20%) activities with succinate, when compared to untreated 30-min isehemic animals, whereas, with glutamate + malate little or no effect was seen. The respiratory activities of RBM from ascorbate-treated, ischemic/reperfused (30 min/S h) rats were restored to ∼65% of controls levels. Ascorbate protection was dose-dependent with maximum protection at 0.8 mg ascorbate/kg body weight of rat. The k of succinate oxidase-supported Ca2+ uptake also returned to 62% of control values. Protection by ascorbate was most effective when administered prior to the onset of ischemia and provided partial protection when administered after the onset of reperfusion. These results suggest that isehemia-induced injury is primarily mediated by disruption of cellular Ca2+ homeostasis, and reperfusion-induced injury by peroxidative events.