Comparison of pulmonary biochemical effects of low-level ozone exposure on mice and rats.

The biochemical effects of a 5-d continuous exposure to 0.45 ppm (882 microgram/m3) O3, were studied in the lungs of 2-mo-old male, specific-pathogen-free mice (Swiss Webster) and three strains of rats (Long-Evans, Wistar, and Sprague-Dawley). The results, expressed per lung, indicated a general increase in lung weight, DNA and protein contents, oxygen consumption, sulfhydryl metabolism, and the activities of several NADP+-reducing enzymes for all exposed animals relative to their controls. When the increases in the two species (mice versus three strains of rats) were compared, the mice showed significantly higher increases than the rats in several parameters. The responses among the three strains of rats were variable, but the differences were not significant. These observations suggest that Swiss Webster mice may offer a more sensitive animal model than rats for studying the pulmonary effects of a given low-level O3 exposure.