A comparison of biochemical effects of nitrogen dioxide, ozone, and their combination in mouse lung: I. Intermittent exposures

Swiss Webster mice were exposed to either 4.8 ppm (9024 μg/m 3) nitrogen dioxide (NO 2), 0.45 ppm (882 μg/m 3) ozone (O 3), or their combination intermittently (8 hr daily) for 7 days, and the effects were studied in the lung by a series of physical and biochemical parameters, including lung weight, DNA and protein contents, oxygen consumption, sulfhydryl metabolism, and activities of NADPH generating enzymes. The results show that exposure to NO 2 caused relatively smaller changes than O 3, and that the effect of each gas alone under the conditions of exposure was not significant for most of the parameters tested. However, when the two gases were combined, the exposure caused changes that were greater and significant. Statistical analysis of the data shows that the effects of combined exposure were more than additive, i.e., they might be synergistic. The observations suggest that intermittent exposure to NO 2 or O 3 alone at the concentration used may not cause significant alterations in lung metabolism, but when the two gases are combined the alterations may become significant.