Anti-inflammatory drugs and experimental bronchitis.

Chronic bronchitis (chronic hypersecretion) and chronic bronchiolitis (small airways disease) are two conditions associated with cigarette smoking: both contribute to airflow obstruction in man, the latter associated with progressive deterioration in lung function. Mucous metaplasia and hyperplasia are characteristic histological changes. Experimentally, cigarette smoke given daily for two weeks, induces similar histological changes in the airways of specific pathogen-free rats, providing a suitable animal model for study: an early proliferation of basal cells, accompanied by mucous metaplasia of surface epithelial serous cells is followed by proliferation of newly formed mucous cells. There is also a significant increase in epithelial thickness due to cell hypertrophy without stratification or prior ulceration. Experimentally, secretory cell hyperplasia is inhibited completely or to varying degrees by prophylactic administration (intraperitoneal injection) of either indomethacin, flurbiprofen, dexamethasone, prednisolone, hydrocortisone (each at 2 or 4 mg/kg body weight) or a mucolytic drug, N-acetylcysteine(Nac), given orally as a 1% solution of the drinking water. Nac also inhibits the associated mucus-hypersecretion. It takes between 21 and 84 days, depending on airway level, for the increase in secretory cell number to return to control values (ie recover). Indomethacin and flurbiprofen (4 mg/kg, by ip injection) shorten recovery to between 4 and 9 days in intrapulmonary airways but have no effect on recovery time in the rat trachea. Nac is effective in 6 of 7 airway levels which showed cigarette smoke-induced mucous cell hyperplasia. In conclusion, in the rat, the response to cigarette smoke is one of mucous cell metaplasia and both basal and mucous cell proliferation. Cigarette smoke-induced mucous cell hyperplasia can be inhibited when selected drugs are given concurrently with the cigarette smoke: indomethacin, fluriprofen and Nac are also therapeutic.