Cell renewal response to nitrogen dioxide gas effects in repeated intermittent exposures in hamsters

The effect of nitrogen dioxide gas on cell renewal in the respiratory tracts of hamsters was investigated after single and repeated exposures. Single exposure to 10 ppm NO₂ for a period of five hours increased the number of cells labelled with tritiated thymidine in differing parts of the respiratory passage. The greatest increase was seen in animals killed 24h after exposure. The number of labelled cells had declined in animals killed at 42h and approached control level in animals killed at 72 h. Exposures for 5h once a week at two, six, eight and nine weeks particularly affected the bronchiolar-alveolar region, although the responses in the trachea and alveolar cells had returned to normal. The reparative response decreases as NO₂ exposure continues. Twice a week exposure at one, nine and 15 weeks showed a further reduction, although peaks still occurred in animals killed 24h after exposure in the bronchiolar-alveolar region. Attempts were made to correlate these exposures with the total number of cells involved in a given hyperplastic area in different parts of the respiratory tract.Characteristic histophatological changes occurring in the various parts of the respiratory tract as a result of intermittent NO₂ exposures are described.The effects of NO₂ on ciliated mucus epithelium in the trachea and bronchial tree were investigated and more visible NO₂ effects were found in ciliated epithelial cells in the bronchi and terminal bronchioles than in the alveolar lining cells.