Effect of sulfur dioxide inhalation on the respiratory tract of the rat.

In order to study the initial effect of SO2 exposure by electron microscopy, Wistar rats were subjected to the gas for 8 hours at a concentration of 800 ppm. A gradient of decreasing damage was observed in the tracheobronchial tree in peripheral direction. The trachea epithelium showed the most severe lesions represented by groups of detached cells, necrotic cells and disappearance of cilia and goblet cells. The entire apical surface was composed of short protrusions. A complementary ultracytochemical chromatin labelling method could demonstrate a gradient with a decreasing labelling rate of epithelial cells towards the peripheral airways. The cytochemical findings may indicate an increased mitotic and metabolic activity of epithelial cells surviving in a region of marked morphological damage as a response to high SO2 concentration. This nuclear activity seems to decrease in peripheral parts of the respiratory tract along the gradient of decreasing morphological damage.