When given intratracheal injections of a suspension of benzo(a)pyrene-ferric oxide, rats and hamsters showed striking species differences in the response of their respiratory tracts to the carcinogen. Hamsters produced squamous metaplasia of the trachea and large bronchi; in contrast, squamous cell nodules of bronchioloalveolar origin developed in rats within a few weeks after carcinogen application. The different sites of the early proliferative and metaplastic responses correlated in their location with the sites of later tumor development. There were no obvious differences between the two species in retention of benzo(a)pyrene in the lungs or tracheas. A species difference was observed, however, in the localization of the benzo(a)pyrene in the tracheal tissues using ultraviolet fluorescence microscopy. Carcinogen was found to be present in the epithelium of hamsters but not in the epithelium of rats, suggesting a species difference in penetration of carcinogen from the lumen into the tracheal tissues.

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Research supported jointly by the Carcinogenesis Program of the National Cancer Institute and the United States Atomic Energy Commission under contract with the Union Carbide Corporation.

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