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The effects of discontinuing administration of high levels of 2-acetylaminofluorene on the transitional epithelium of the mouse urinary bladder.

The purpose of this study was to investigate the effects of discontinuing the administration of a high level of 2-acetylaminofluorene (2-AAF) on the transitional epithelium of the urinary bladder of BALB/c mice. Mice were fed 500 ppm of 2-AAF for 6 and 13 weeks and sacrificed at periodic intervals after discontinuing the compound. Urothelial hyperplasia regressed slower in the animals receiving the 2-AAF for 13 weeks than those receiving 2-AAF for only 6 weeks. A small number of bladder carcinomas were seen in the animals fed 2-AAF for 13 weeks and sacrificed at 26 and 39 weeks. Our results suggest that exposure to a high level of a carcinogen even for a relatively brief period may result in the development of carcinomas after the cessation of exposure.