Effect of sulfur dioxide on the morphology and mucin biosynthesis by the rat trachea

Specific-pathogen-free rats were exposed to 400 ppm sulfur dioxide daily for up to 7 weeks. At intervals during exposure, tracheas were removed and incubated in vitro in culture medium containing radioactive glycoprotein precursors. The most prominent histological changes due to SO2 were progressive hypertrophy and hyperplasia of the submucosal mucous glands accompanied by a flattening of the epithelium with eventual recovery. Uptake of radioactive precursors into a highly purified mucin fraction correlated with these histological changes in the submucosal mucous glands, increasing progressively up to 4 times that of control. Uptake of precursors into specific mucins purified by DEAE-Sephacel showed that uptake into the 0.2 and 0.3 M NaCl fractions was stimulated several fold by SO2, and uptake into more highly acidic fractions, which was nearly absent in the control, was also greatly increased. Two weeks following the last exposure of the tracheas to SO2, their morphological and mucus-secreting properties showed signs of returning to that of the control.