Strain Differences in N‐Butyl‐N‐(4‐hydroxybutyl)nitrosamine Bladder Carcinogenesis in Rats

Differences in susceptibility of the urinary bladder epithelium to N‐butyl‐N‐(4‐hydroxybutyl)‐nitrosamine (BBN) in various strains were examined. In experiment 1, 5 strains of male rats were given 0.025% BBN in the drinking water for 8 weeks followed by drinking water without BBN for 32 weeks. Analbuminemic rats (NAR) and ACI rats had high incidences of urinary bladder lesions (papillary or nodular hyperplasia, papilloma and carcinoma), F344 and Wistar rats had low incidences, and Sprague‐Dawley (SD) rats showed an intermediate incidence. Carcinoma area was largest in NAR rats followed in decreasing order by SD, ACI and F344 rats. The extent of tumor invasion was higher in NAR and ACI rats than in SD rats. In experiment 2, the 5 strains of male rats were administered 0.025% BBN in the drinking water. Some rats from each group were killed after each of weeks 4 and 8. The urinary bladder of ACI and NAR rats given BBN had the most marked lesions observed by scanning electron microscopy, with less marked changes in SD rats. F344 and Wistar rats showed the weakest response. Cytochrome P‐450 content of the liver in ACI rats treated with BBN for 4 weeks was significantly higher than those of the controls. Cytochrome P‐450 and Cytochrome b(5) contents of the control and BBN‐treated rats were significantly higher in ACI and SD rats than in Wistar, F344 or NAR rats. These results indicate that there are strain differences in the urinary bladder response to BBN.