Mitotic activity of airway epithelium after short exposure to tobacco smoke and the effect of the anti-inflammatory agent phenylmethyloxadiazole.

Mitotic activity of extra- and intra-pulmonary airway epithelium has been studied in male rats exposed to tobacco smoke for 1, 2, 3, 7 or 14 days, with and without addition of the anti-inflammatory agent phenylmethyloxadiazole (PMO) to the tobacco. In both control and exposed animals the mitotic index is greater in extrapulmonary regions than intrapulmonary ones. A single exposure to tobacco smoke significantly increases mitotic activity in both airway regions. This initial level of mitotic response is not maintained but is rapidly restored by 1 day free from tobacco exposure: the second peak is as high as the first. Exposure to tobacco + PMO modifies timing and amplitude of the mitotic response. The effect of PMO is somewhat paradoxical since the first peak occurs later, i.e. after 2 days of exposure, but the increase is almost twice that seen after tobacco alone. The timing of the second peak is the same as after tobacco alone, but its amplitude is only half. In each experimental group the mitogenic effect is exerted on an intact epithelium. In animals exposed to tobacco alone, or tobacco + PMO, in extrapulmonary airways mitoses are located mainly in the basal region of the epithelium, whereas in intrapulmonary airways they are located mainly at the mid or superficial level.