Morphological alterations to the bronchial mucosa in high-dosage long-term exposure to sulfur dioxide.

Light- and electron-microscopic studies were carried out on chronic bronchitis in the rat, produced by high-dosage long-term exposure to sulfur dioxide. Particular attention was given to the advanced stages of the disease. Inflammatory intramural infiltration and fibrosis developed in the regions of the bronchial tree near the hilus and in the peripheral sections. The highly differentiated cells of the bronchial epithelium perish at the same time. After a loss of the goblet and ciliate cells, extensive epithelial metaplasias with dysplasias develop in the central regions of the bronchus. Bronchiolitis obliterans develops in the peripheral regions of the bronchus. In the bronchiolar epithelium, the Clara cells, which play a crucial role in the maintenance of bronchial secretion in the advanced stages of the disease, are preserved.