Cellular proliferation induced in the lung by cadmium aerosol

Rats were exposed to a polydispersed aerosol of 0.1 per cent cadmium chloride in physiologic saline for a single period of 2 hours, and the evolution of damage was followed for a 10-day period. Control animals were unexposed rats and rats exposed to an aerosol of physiologic saline. Wet lung weight doubled by the fourth day in animals exposed to cadmium chloride, but not in the control groups. Apart from a transient increase in fluid content at 1 day, there was no evidence that the lung weight gain was due to inflammatory edema. Uptake of [3H]thymidine markedly increased during the first four days after exposure to cadmium chloride. Light autoradiography showed that [3H]thymidine labeling occurred almost exclusively in Type II alveolar cells at 1 day: later, the label appeared in interstitial cells and cells lying free within alveoli. These changes correlated well (r=0.70) with the increase in deoxyribonucleic acid on the fourth day after exposure. Uptake of [3H]thymidine and deoxyribonucleic acid content in rats exposed to cadmium chloride showed a significant difference from the control groups (P less than 0.001). These experiments demonstrate that exposure to cadmium chloride aerosol evokes a wave of cellular proliferation in rat lung. This finding is of interest, because heavy industrial exposure to cadmium in humans is known to be associated with severe physiologic impairment and anatomic damage.