Hyperoxia increases oxygen radical production in rat lungs and lung mitochondria.

Abstract

An increased production of oxygen radicals has been postulated to be a major factor in the etiology of lung damage during hyperoxia.Mitochondrial electron transport was inhibited with CN-or with antimycin A in both rat lung slices and isolated mitochondria.CN" or antimycin A-insensitive O2 uptake was measured polarographically, as a function of PO,, and served as an approximate index of intracellular 02and Hz02 production.In lung slices, CN--resistant respiration increased as a function of Po,, accounting for 9% of total respiration in air and becoming 18% of total respiration when the tissue was incubated in 85% 02.CN--resistant respiration in isolated mitochondria also increased as a function of Po2 rising from 0 at 15% O2 t o 1.34 nmol of O2 consumed/min*mg of mitochondrial protein at 85% 02.Mitochondria accounted for 15 f: 3% of the CN" resistant respiration in rat lungs under hyperoxic conditions and released H202 extramitochondrially at a rate of 50 nmol/min/l.5g of rat lung.The HzO2 generation is dependent on Po, and substrate and most, if not all, Hz02 arises from dismutation of 02produced by autooxidation of respiratory chain components.2,4-Dinitrophenol increased respiratory chain 02production in a dose-dependent fashion.This phenomenon occurred when mitochondria were treated with nitroaromatic compounds which can be reduced to nitroanion free radicals capable of reducing O2 t o 02-.Nonreducible uncouplers such as salicylate did not increase mitochondrial 0 2 -generation, suggesting that uncoupling, per se, does not necessarily favor increased rates of mitochondrial 02production.These data suggest that hyperoxia increases the pulmonary production of oxygen radicals and that mitochondria contribute significantly to this phenomenon.This report describes efforts to characterize the effect of oxygen concentration on the production of partially reduced species of oxygen in rat lungs, and estimates the contribution of lung mitochondria.Gerschman (1) f i t proposed that oxygen toxicity may be caused by the formation of free radicals which could then lead to destructive oxidations.She further noted that oxygen at 20% is potentially toxic, and speculated that its gradual accumulation in the atmosphere had provoked the evolution of cellular defenses (1).These suppositions are supported by the observation that anaerobic bacteria, which are deficient in