Effects of short-term, single and combined exposure to low-level NO2 and O3 on lung tissue enzyme activities in rats.

To examine the pulmonary effects of relatively low levels of NO2 and O3, and test for any possible interaction in their effects, we exposed 3-mo-old male Sprague-Dawley rats, free of specific pathogens, to either filtered room air (control) or 1.20 ppm (2256 micrograms/m3) NO2, 0.30 ppm (588 micrograms/m3) O3, or a combination of the two oxidants continuously for 3 d. We studied a series of parameters in the lung, including lung weight, and enzyme activities related to NADPH generation, sulfhydryl metabolism, and cellular detoxification. The results showed that relative to control, exposure to NO2 caused small but nonsignificant changes in all the parameters; O3 caused significant increases in all the parameters except for superoxide dismutase; and a combination of NO2 and O3 caused increases in all the parameters, and the increases were greater than those caused by NO2 or O3 alone. Statistical analysis of the data showed that the effects of combined exposure were synergistic for 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, glutathione reductase, and superoxide dismutase activities, and additive for glutathione peroxidase and disulfide reductase activities, but indifferent from those of O3 exposure for other enzyme activities.