Endogenous production of superoxide by rabbit lungs: effects of hypoxia or metabolic inhibitors

We find spontaneous light emission from isolated Krebs-Henseleit-perfused rabbit lungs when the light-emitting super-oxide trap lucigenin is added to the perfusate. Lucigenin light emission appears to be specific for superoxide anion, because light emission from the lung caused by a superoxide-generating system is abolished by superoxide dismutase but not by catalase or dimethylthiourea. We also studied the relative sensitivity of lucigenin photoemission to superoxide and to H2O2 in vitro. Lucigenin photoemission is three to four orders of magnitude more sensitive to superoxide than to H2O2 and probably cannot detect H2O2 in concentrations thought to occur in biological systems. Basal lucigenin photoemission by the lung is oxygen dependent, because severe hypoxia completely inhibits light emission. Superoxide dismutase reduces basal photoemission by 50%, and administration of the low-molecular-weight superoxide scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid (tiron) inhibits basal photoemission by approximately 90%. These observations suggest that endogenous superoxide production is primarily intracellular and that approximately half of the superoxide reaches the extracellular space. Superoxide transport may involve anion channels, because the anion channel blocker 4,4′diisothiocyanostilbene2,2′disulfonic acid increases photoemission, suggesting intracellular accumulation of superoxide. A cytochrome P-450 inhibitor, SKF 525A, or the mitochondrial transport inhibitor antimycin decreased basal photoemission by approximately 50%, suggesting that cytochrome P-450-mediated reactions and perhaps mitochondrial function contribute to basal superoxide production in the isolated perfused lung. Endogenous superoxide production may be important in regulation of pulmonary vascular reactivity and may contribute to the pathogenesis of lung reperfusion injury.