Stimulation of DNA synthesis in lungs of hamsters tolerant to nitrogen dioxide

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Abstract
Nitrogen dioxide (NO 2 ) is both edematogenic and cytotoxic to the lung. Preexposure to NO 2 protects against mortality from formation of excessive pulmonary edema (tolerance) and, depending on the preexposure schedule, may or may not protect against the cytotoxic effects of NO 2 in the lung. Measurement of DNA synthesis in hamster lung was used to study the question of whether the more subtle cytoiogical injury induced by NO 2 is mediated by a system that also exhibits tolerance. It was found that when hamsters are preexposed daily to 10 ppm NO 2 , they develop tolerance for normally lethal concentrations of NO 2 , are protected against further cytoiogical injury from 10 ppm NO 2 , but are not protected from the cytotoxic effects of NO 2 at concentrations greater than 10 ppm. Animals exposed weekly to 10 ppm NO 2 are not protected from further cytoiogical injury induced by weekly exposures to 10ppm NO 2 , but do develop tolerance for lethal concentrations of NO 2 . Thus, the data indicate that induction of tolerance to NO 2 does not necessarily protect the cell populations of the lung from the cytotoxic effects of NO 2 .

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