HYDROGEN-PEROXIDE RELEASE BY MITOCHONDRIA FROM NORMAL AND HYPOXIC LUNGS

Ischemia/reperfusion mechanisms contribute to lung injury after transp lantation, pulmonary embolism, and resolution of atelectasis. Alveolar tissue becomes hypoxic and deprived of substrate only when both venti lation and perfusion are interrupted, a situation modeled in vivo by c omplete, unilateral lung collapse. Because previously hypoxic mitochon dria may be an important intracellular source of superoxide and hydrog en peroxide (H2O2) during reperfusion and re-oxygenation, the authors, in this study, investigated whether mitochondrial H2O2 release change d as a result of lung hypoxia/hypoperfusion resulting from collapse. M itochondria were isolated from hypoxic (previously collapsed) right or contralateral left rabbits' lungs and from control rabbits' lungs. Mi tochondrial H2O2 release, a marker of superoxide production, was measu red fluorometrically after incubation with or without 1 mmol/L cyanide and 0.1 mmoI/L nicotinamide adenine dinucleotide, Mitochondrial recov ery was determined by assaying succinate dehydrogenase activity in mit ochondrial preparations and lung homogenates. Lung succinate dehydroge nase activity and mitochondrial recovery were comparable among groups. Calculated lung mitochondrial content did not change (control subject s: left 7.9 +/- 0.5, right 13.8 +/- 1.7; hypoxic: left 10.3 +/- 1.3, r ight 10.5 +/- 2.4, all mg mitochondrial protein/lung). Mitochondria re leased hydrogen peroxide at approximately 5.6 nmol/h/mg pro in buffer alone and 14.8 nmol/h/mg pro in buffer with cyanide and nicotinamide a denine dinucleotide. However, lung collapse and resulting hypoxia caus ed no change in mitochondrial number or capacity to release H2O2 in vi tro. Based on these findings, it is suggested that other sources of re active oxygen metabolites, including xanthine oxidase and activated ne utrophils, contribute to the oxidant injury observed in this model.