Combined effect of nitrogen dioxide and cold stress on the activity of the hepatic cytochrome P-450 system in rats.

The combined effects of nitrogen dioxide (NO2) and cold stress were assessed on the cytochrome P-450 system by measuring microsomal protein content, cytochrome P-450 content, aminopyrine N-demethylase activity, and aniline hydroxylase activity in the liver of male Wistar rats exposed to 4 ppm NO2 and/or cold environment (4 degrees C) for 24 h, 14 days, and 30 days. Exposure to cold alone changed the activity of the cytochrome P-450 system during the exposure up to 30 days, and exposure to NO2 alone also influenced it after 14 days and 30 days of exposure. Interactions were observed in the effect on the cytochrome P-450 system when rats were exposed to NO2 and cold simultaneously. There was a tendency that NO2 suppressed the increases in activities of the cytochrome P-450 system caused by cold of 24-h and 30-day exposure.