Rat urinary bladder carcinomas induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine and N-methyl-N-nitrosourea.

The present investigation was conducted to examine the combination effect of N-butyl-N-(4-hydroxy-butyl)nitrosamine(BBN) and N-methyl-N-nitrosourea(MNU) in rat urinary bladder carcinogenesis. Experiment 1 was performed in the groups treated by oral BBN administration in combination with MNU intravesical instillation and their control groups. In the groups given both BBN and MNU, the ratio of rats with the nonpapillary type to carcinoma-bearing rats was significantly higher than in the controls. Since most of the carcinomas were non-invasive, the observation period was prolonged in the groups given both BBN and MNU in experiment 2. However, even after a longer observation period, no invasive carcinoma was observed. These results suggest that high-grade and invasive carcinomas similar to those induced by BBN and MNU in the heterotopically transplanted rat bladder cannot be induced in the natural bladder of the rat.