Abstract

Bronchial epithelial metaplasia of the rats was experimentally studied by mean of inhalation of Nitrogen Dioxide (1,000ppm, 500ppm and 100ppm in concentration). Used animals were healthy adult rats weighing about 250gm and having no pulmonasy diseases. No₂ gas was administered according to the exposure chamber and 10 sections were taken from the definite sites of the trachea and main bronchi of lungs. The following results and conclusions were made. 1. In the group of control(0 ppm NO2) was net observed any typical squamous metaplasia of bronchial epithelium in the course of time. 2. In the group which was exposed to the NO2 gas, the incidence of epithelial metaplasia of trachea and bronchi was approximately 83 per cent. Male rat (93% positive) showed definite high positivity compared to the female rat (78% positivity). 3. In the groups which was exposed for long time (-average 74hrs-90% positive), metaplastic tendency was apparently increased compared to that of short term exposure groups(-average 6 and 7hrs-78% positive). But invasiveness of metaplasia was relatively high and especially conspicuous in the groups of high No₂ concentration (1, 000ppm and 500ppm). 4. Observation on distribution of metaplasia indicated that site prepondence was trachea, carina and right upper lobe bronchus in orders, which were proximal parts of tracheobronchial tree. But on range of metaplasia, failed to indicate any specificity. 5. In the group which was exposed to No₂ gas epithelial finidings to be consistent with atypical metaplasia or carcinoma in situ were not observed.