The Clara cell: an electron microscopy examination of the terminal bronchioles of rats and monkeys following inhalation of hexachlorocyclopentadiene.

The effects of inhalation of hexachlorocyclopentadiene (Hex) up to 14 wk on the terminal bronchioles of rats and monkeys was examined by electronic microscopy. Exposed rats elicited a concentration-related increase in the incidence of electron-lucent inclusions in the bronchiolar Clara cells when compared to controls. The inclusions in the high-concentration (0.2 ppm) group were round and more abundant than the rod-shaped inclusions observed in the intermediate (0.05 ppm) and low-concentration (0.01 ppm) exposure group. No ultrastructural changes were observed that could be attributed to the inhalation of Hex vapor in exposed monkeys. The origin and significance of these inclusions is discussed in light of the literature.