Rats were exposed to amounts of ozone ranging from 0.5 to 2.0 ppm for intervals of 1, 2, or 3 weeks. Collagen synthesis rates in their lungs were quantitated by biochemical analyses performed with lung minces. Correlative histological observations were made in different lung lobes from the same rats. At all levels of ozone tested, collagen synthesis rates of the lungs were significantly elevated and histologically discernible fibrosis of the alveolar duct walls was observed. Within the range of ozone concentrations studied, the elevation of collagen synthesis rate in exposed rats was a linear function of the level of ozone to which the animals were exposed. We conclude that exposure of rats to near-ambient levels of ozone causes biochemically and histologically discernible fibrotic changes in their lungs, suggesting that such effects may occur at levels of ozone at or near the current ambient air quality standard for this pollutant.
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