Low-dose chronic inhalation of diesel exhaust and/or coal dust by rats: effect of age and exposure on lung and liver cytochrome P-450.

Rats were exposed by inhalation to low levels of diesel exhaust and/or coal dust, seven hours/day, five days/week for 24 months. 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 months. When data were analysed across all time intervals and adjusted for age, lower benzo[a]pyrene hydroxylase activity was observed in lung microsomes from rats exposed to diesel exhaust plus coal dust than in those exposed to coal dust alone. Data are discussed in terms of interaction between diesel exhaust and coal dust and effect of infectious agents.