A Histopathological Study on the Respiratory Organ of Rats Exposed to Ozone and Tobacco Smoke with Special Reference to Changes in Centriacinar Alveoli

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The histopathological changes in the respiratory organs of rats due to the combined exposure to tobacco smoke and O<SUB>3</SUB> were evaluated. Male Wistar rats were exposed to 0.5 ppm O<SUB>3</SUB> for 8 hours a day and 6 days a week and simultaneously to tobacco smoke 5 times a week for 2, 4, 8, 16, 20, 24 and 52 weeks, and killed for the histopathological study. The multi-layered epithelial hyperplasia were shown locally in the trachea, and the edema and collagen fiber hyperplasia were observed in the tracheal wall after the exposure for 4 weeks. The squamous metaplasia was noticed in the tracheal epithelium in 1 of the 7 rats, which were exposed for 24 weeks. The epithelial cell swelling and hyperplasia toward the alveoli were shown in the bronchioles by the exposure for 4 weeks or longer. The cells in the areas showing alveolar bronchiolization were composed of 2 to 3 layers, and were consisted of ciliated and non-ciliated epithelial cells. The squamous metaplasia was observed in some rats. These changes persisted until the exposure for 52 weeks. However, the number of the rats, which showed the fibrosis and the flattening of epithelial cells into a single layer, increased by the exposure for 20 weeks or longer, and no tumor generation was observed.
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