Subacute effects of nitrogen dioxide on membrane constituents of lung, liver, and kidney of rats.

Male Wistar rats were exposed to 0.4, 1.2, and 4.0 ppm nitrogen dioxide (NO2) for up to 14 weeks to examine subacute effects of NO2 on membrane constituents of lung, liver, and kidney. In the lung, cytochrome P-450 decreased to 59% (P less than 0.01) and 57% (P less than 0.01) of the control values after 1 and 10 weeks of exposure to 4.0 ppm NO2, respectively, and remained at control levels at other exposure periods. The activity of succinate-cytochrome c reductase also decreased to 75% (P less than 0.01) of the control values after 2, 4, and 14 weeks of exposure to 4.0 ppm NO2, respectively. Exposures to 0.4 and 1.2 ppm NO2 resulted in similar patterns of alterations in these enzymes. In the liver, cytochrome P-450 decreased to 72% (P less than 0.01), 70% (P less than 0.05), and 73% (P less than 0.05) of the control values after 1, 5, and 8 weeks of exposure to 4.0 ppm NO2, respectively, and remained at control levels at other exposure periods. The activity of NADPH-cytochrome P-450 reductase also decreased in a fashion similar to cytochrome P-450. Exposures to 0.4 and 1.2 ppm NO2 resulted in similar patterns of alterations in these enzymes. In addition, cytochrome b5 showed a reduced value between 5 and 12 weeks of exposures to 1.2 and 4.0 ppm NO2 and then recovered. In the kidney, all components of the microsomal electron-transport systems increased during 12-week exposures to 1.2 and 4.0 ppm NO2. These results show that subacute exposures to 0.4-4.0 ppm NO2 caused a periodic reduction in microsomal cytochrome P-450 and mitochondrial succinate-cytochrome c reductase in the lung and in components of the microsomal electron-transport systems in the liver, whereas exposures to 1.2 and 4.0 ppm NO2 resulted in induction of the microsomal electron-transport systems in the kidney.