A modification of the sulfur dioxide (SO2)-exposed rat model proposed by Reid for the study of chronic bronchitis was employed to evaluate mucus retention and cytologic changes. Rats were exposed to from 600 to 700 ppm of SO2 for 3 hours per day, and groups were examined after 0, 9, 18, and 30 hours of cumulative exposure. Tracheal mucus retention and statistically significant increases (two- to four-fold) in the amount of solid material (cellular and mucus) recovered by bronchia lavage developed as a function of exposure time. The increase in bronchial solids was primarily due to inflammatory cells. The goblet cell population in secondary bronchi declined initially, with a significant increase after 30 hours of exposure (P less than .001). The cytologic data provide additional support to Reid's suggestion that the SO2-exposed rat may be considered as a chronic bronchitis model.

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