Chronic inhalation of diesel exhaust and coal dust: effect of age and exposure on selected enzyme activities associated with microsomal cytochrome P-450 in rat lung and liver.

Male Fisher-344 rats were exposed by inhalation to low levels of diesel exhaust and coal dust, alone or in combination, or to filtered air, 7 h/d, 5 d/wk for 24 mo. Cytochrome P-450-associated benzo[a]pyrene hydroxylase and 7-ethoxycoumarin deethylase activities were assayed in lung and liver microsomes after 3, 6, and 24 mo. Age-related changes in enzyme activities were observed, but they were not altered by the exposures. When the data were adjusted for age, only one difference was observed. Lung benzo[a]pyrene hydroxylase activity in rats exposed to diesel exhaust and coal dust in combination was lower than that in animals exposed to coal dust alone (2.8 versus 4.4 pmol/min X mg protein). Neither value, however, differed significantly from the filtered-air controls, and no differences were observed in the other lung and liver activities. The data suggest exposure of the rats to diesel exhaust and/or coal dust had little or no effect on the selected lung and liver cytochrome P-450 activities under the conditions of the experiment.