Morphological effects of nitrogen dioxide on the rat lung.

Morphological studies of the rat lung exposed to 20 ppm NO2 for 20 hr (experiment 1), to 0.5 ppm for 19 months (experiment 2), and to 10 ppm for 14 days (experiment 3) were conducted. Changes in the mast cells of the tracheas and main bronchi of rats exposed to 0.5 ppm (experiment 4) were also observed. In the alveolus, cytoplasmic blebbing occurred in a small number of type I cells immediately after exposure to 20 ppm NO2 for 20 hr, and remarkable vacuolar change was observed 3 days after 10 ppm exposure. Exposure to 0.5 ppm did not cause degeneration. Swelling and hyperplasia of type II cells were observed. The cells gradually became flat and began a transition from type II to type I cells. These intermediate-type cells were noticed in experiments 1 and 2, but no intermediate-type cells were found in experiment 3. In each experiment, pinocytotic vesicles of endothelial cells in capillaries, followed by interstitial edema in the alveolar walls, were observed. In addition to these changes, desquamation of endothelium and widening of the endothelial junction of endothelial cells occurred in experiment 3. The early changes observed in the animals exposed to 0.5 ppm NO2 were the numerical and histochemical changes of mast cells in the trachea and main bronchus.