Production of urothelial tumors in the heterotopic bladder of rat by benzidine derivatives.

Male Fischer rats which had been implanted with a heterotopic bladder were randomly divided into five groups and their heterotopic bladders were instilled once a week for 20 weeks with 0.5 ml phosphate-buffered saline:dimethyl sulfoxide solution (4:1) or this solution containing 1 mumol benzidine (BZ), N'-hydroxy-N-acetylbenzidine, the N'-glucuronide of N'-hydroxy-N-acetylbenzidine, or the N-glucuronide of N-hydroxy-2-aminofluorene. These bladders were then instilled once a week for an additional 30 weeks with the phosphate-buffered saline without dimethyl sulfoxide. The experiment was terminated at the end of 50 weeks. Transitional cell carcinomas were observed in 1 of 39 (control), 1 of 29 (BZ), 18 of 30 (N'-hydroxy-N-acetylbenzidine), 28 of 28 (N'-hydroxy-N-acetylbenzidine N'-glucuronide), and 24 of 29 (N-hydroxy-2-aminofluorene N-glucuronide) rats. No histological alterations were observed in their natural bladders. These results demonstrate the urothelial carcinogenicity of the N-hydroxy metabolites of BZ and suggest that N'-hydroxy-N-acetylbenzidine N'-glucuronide may play a major role in the initiation of urothelial carcinogenesis by BZ in humans.