Pulmonary responses after continuous exposure of rats to concentrations of ozone (O3) ranging from 0.12 to 0.64 ppm were quantified by measuring tissue collagen synthesis rate, tissue protein and DNA content, and various constituents of bronchoalveolar lavage fluid. After 7 days of exposure to 0.64 ppm of O3, lung collagen synthesis rate and tissue content of protein and DNA were elevated. After shorter durations of exposure to 0.64 ppm of O3, significant elevations were observed in the protein content and the activities of lactate dehydrogenase, acid phosphatase, and N-acetyl-β-d-glucosaminidase from lavage fluid. After exposure of rats to 0.20 ppm of O3 for 7 days, changes could be detected in both lung collagen synthesis rate and tissue protein content. Total lavagable protein content, a sensitive indicator for O3-induced effects upon the lung, was significantly elevated in lungs of rats exposed to 0.12 or 0.20 ppm of O3. To examine whether a synergistic interaction occurred between 0.20 or 0.64 ppm of O3 and acid aerosols, rats were continuously exposed to O3 with and without concurrent exposure to 5 mg/m3 of ammonium sulfate. A synergistic interaction between 0.20 ppm of O3 and ammonium sulfate aerosol was observed by measurement of total lavagable protein and of lung collagen synthesis rate. These results demonstrate that ammonium sulfate aerosol interacts synergistically with O3 at concentrations of O3 that approach ambient levels.
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