Effects of Short-Term, Single and Combined Exposure of Rats to NO2and O3on Lung Tissue Enzyme Activities

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Abstract
Three-month-old male Sprague-Dawley rats, free of specific pathogens, were exposed to filtered room air (control) or to 7.8 ppm (3384 μg/m3) NO2, 0.45 ppm (882 μg/m3) O3, or a combination of the two oxidants continuously for 3 d. The effects were studied in the lung by using a series of parameters, including lung weight and sulfhydryl-metabolizing and NADPH-generating enzyme activities. The results show that, relative to control, exposure to NO2 caused small changes that were nonsignificant, except the increases in isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, disulfide reductase, and NADPH-cytochrome c reductase activities, which were significant. Exposure to O3, caused significant increases in all the parameters. Exposure to 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. A statistical analysis shows that the effects of combined exposure were synergistic for glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione disulfide transhydrogenase activities, and additive for other enzyme activities, but indifferent from those of O3 exposure for lung weight and 6-phosphogluconate dehydrogenase activity.