Studies on biochemical effects of nitrogen dioxide. II. Changes of the protective systems in rat lungs and of lipid peroxidation by acute exposure.

This work was done to clarify the relation between the change of lipid peroxidation and the protective systems in lungs after NO2 exposures. JCL:Wistar 8-wk-old male rats were exposed continuously to 10 ppm NO2 for 2 wk. Lipid peroxidation, measured by ethane exhalation in the breath of the rats and by the reaction of thiobarbituric acid with lung homogenates, increased to a maximum at 3 d after a decline at 1 d, and then returned to the initial level (of d 0). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), disulfide reductase (DSR), and superoxide dismutase (SOD) in the 105,000 X g supernatant of lung homogenates were depressed slightly at 1 d. Thereafter, they increased significantly to their maximum levels from 5 to 10 d, and these maximum levels were maintained until d 14. The pattern of change of these protective enzymes was symmetric to that of lipid peroxidation after 3 d. The order of the ratio of the increased value to the initial value was G6PD greater than DSR greater than 6PGD greater than GR greater than GPx greater than SOD. The time course of nonprotein sulfhydryls was similar to that of the protective enzymes. In contrast, the amounts of vitamin E increased to a maximum at 2 d and then returned to the initial level. The periodic change of vitamin E was similar to that of lipid peroxidation rather than that of the protective enzymes. These results suggest that the ability of the enzyme systems in lungs to protect against NO2 fluctuated in a complex manner and the activities of the protective enzymes varied inversely with lipid peroxidation.