Activities of lung NADPH-cytochrome C-reductase and of cytochrome P-450 peroxidase during the protection of rat from hyperoxic injury by polyriboinosinic acid-polyribocytidilic acid.

Rats exposed to normobaric oxygen received a single i.p. injection of 2.5 mg/kg of poly I: poly C at various times (-120 to +36 h) before and after the beginning of oxygen exposure. Hyperoxic lung damage and modifications in cytochrome P-450 system components were evaluated. Our results confirmed the protective effect of poly I: poly C on rats exposed to oxygen, reducing the lung edema and the mortality. This effect was only observed when poly I: poly C was injected 48 or 36 h before the beginning of oxygen exposure. Although oxygen exposure per se decreased the total level of lung cytochrome P-450, poly I: poly C per se induced a deeper decrease to levels similar in air- or oxygen-exposed rats. Poly I: poly C did not modify the NADPH-cytochrome c reductase level nor the cytochrome P-450 peroxidase activity in air-exposed rats. The oxygen exposure induced a decrease of these two enzymes, either in the absence or in the presence of poly I: poly C, except when poly I: poly C was injected 48 or 36 h before the beginning of oxygen exposure, times at which poly I: poly C restored the enzymatic values measured in rats exposed to air. Because the times of injection of poly I: poly C were those at which the protective effect was observed, it suggested that the protective effect of poly I: poly C against oxygen toxicity was associated with a lack of oxygen-induced decrease of both the lung NADPH-cytochrome c reductase level and the lung cytochrome P-450 peroxidase activity.