Differences in pulmonary biochemical and inflammatory responses of rats and guinea pigs resulting from daytime or nighttime, single and repeated exposure to ozone

Abstract

Rats and guinea pigs were exposed to 0.8mg ozone (O 3)/m 3 (∼0.4 ppm) for 12 hr during the daytime, 12 hr during the nightime, or continuously to investigate circadian variation in O 3-induced pulmonary toxicity during single and repeated O 3 exposures. Biomarkers in bronchoalveolar lavage (BAL) fluid and lung tissue were measured as indicators of biochemical and inflammatory responses. Nighttime O 3 exposure of rats resulted in larger increases of protein, albumin, and inflammatory cells in BAL fluid compared to those after daytime O 3 exposure and this daytime-nighttime difference was statistically significant ( p < 0.05). Single daytime or nighttime O 3 exposure of guinea pigs resulted in comparable increases of BAL fluid proteins and inflammatory cells without a daytime-nighttime difference. Nighttime and continuous O 3 exposure of rats for 3 days resulted in comparable increases in lung antioxidant enzyme activities, both of which differed statistically from effects from daytime O 3 exposures ( p < 0.05). Continuous O 3 exposure of guinea pigs for 3 days caused, in general, statistically larger increases in lung tissue parameters compared to nighttime O 3 exposures ( p < 0.05). These results suggest that the extent of O 3-induced acute pulmonary biochemical and inflammatory responses is directly related to the level of physical and respiratory activity. For rats, effects from continuous O 3 exposure appear to be controlled by the nighttime, physically active period. In guinea pigs, the comparable responses following daytime or nighttime O 3 exposure seem in accordance with their random behavioral daily activity pattern. This study supports the view that physical activity-related increases in inhaled dose significantly enhance the pulmonary O 3 responses.