Pulmonary alterations in rats exposed to 0.2 and 0.1 ppm ozone: a correlated morphological and biochemical study.

Weanling male Sprague-Dawley rats were fed either a synthetic diet supplemented with 11 mg vitamin E/kg body weight (to approximate average U.S. human dietary intake) or a commercial rat chow for 5 wk. At 2 months of age, rats were exposed to either 0.0, 0.1, or 0.2 ppm ozone continuously for 7 days. Morphological lesions were consistently present in centriacinar regions of lungs of both groups of rats at the 0.2 ppm level. At 0.1 ppm ozone, two of six rats fed the synthetic diet and two of five fed lab chow had minimal centriacinar lesions. Biochemical assays showeed that the activities of glutathione (GSH) peroxidase, GSH reductase, and G-6-P dehydrogenase and level of nonprotein sulfhydryls in the lungs of rats fed the synthetic diet and exposed to 0.1 ppm were elevated to about one-half the level that was produced by 0.2 ppm. The authors conclude that the level whereby there are no observable morphologic effects for short-term exposure to ozone in 2-month-old rats is less than, but close to, 0.1 ppm.