Morphologic correlation of physiologic changes caused by SO2-induced bronchitis in dogs. The role of inflammation.

Chronic bronchitis was induced in 6 mongrel dogs by exposure to SO2 gas for 6 to 18 months. All of the dogs developed cough and mucus hypersecretion. Chronic airway obstruction and decreased airway responsiveness to inhaled histamine developed in 5 of the dogs. Histologic changes in dogs evaluated after SO2 exposure included significant mucous gland hypertrophy and hyperplasia, epithelial thickening, and a decrease in the number of luminal cells containing undischarged secretory granules. Acute and chronic inflammation were found in the dogs with airway obstruction and decreased responsiveness to histamine, but such inflammation was absent in the one dog that failed to develop physiologic changes. After a period of recovery from SO2 exposure of 9 to 21 months, inflammation regressed dramatically and the other histologic changes returned toward normal. Physiologic changes regressed somewhat in those dogs that had had changes. These findings suggest that inflammation may be an important factor influencing the development of airway obstruction and altered airway responsiveness in the setting of chronic bronchitis.