The effect of tobacco smoke, with or without phenylmethyloxadiazole (PMO), on rat bronchial epithelium: a light and electron microscopic study.

The effect of whole cigarette smoke on rat airway epithelium and of the addition of an anti-inflammatory drug, phenylmethyloxadiazole (PMO), to the tobacco, was studied in experiments extending up to 6 weeks. Two airway levels were studied, the left main extrapulmonary bronchus and a distal intrapulmonary bronchiolus. After cigarette smoke alone, the greatest change was found in the main extrapulmonary bronchus where there was an increase in epithelial thickness due to cell hypertrophy and a change in cell shape. The number of cells increased in proportion to the duration of exposure. Hyperplasia was not preceded by epithelial degeneration or necrosis. In the animals exposed to tobacco smoke alone, ciliated, mucous and basal cells increased whilst intermediate and epithelial serous cells decreased in number. The appearance of cells intermediate in structure suggests that epithelial serous cells transformed into mucous cells. The change involved an increase in secretory granule size, number and electron-lucency, the last probably reflecting a chemical alteration in the glycoprotein. In ciliated cells, mitochondria increased in length. The concentration of dividing cells increased, notably at days 1 and 7. Addition of PMO to the tobacco, 2 per cent. by weight, diminished the increase in bronchial epithelial thickness, cell size, mucous cell number and percentage of dividing cells seen after tobacco smoke alone: the shift in proportion of the various cell types was similar except that the increase in ciliated cell number was much greater than the increase seen with tobacco smoke alone.