Dose-response studies on early lesions and carcinogenesis of urinary bladder were carried out in male rats treated with N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). In experiment 1, BBN was given in 6 different concentrations as solutions in drinking water to examine early lesions of the urinary bladder to F344, 6-week-old rats for up to 12 weeks. Doses of more than 0.01% BBN induced histologically simple hyperplasia and papillary or nodular hyperplasia, and scanning electron microscopically pleomorphic microvilli, short, uniform microvilli, and ropy or leafy microridges. 0.005% BBN treatment also induced ropy or leafy microridges. In experiment 2, BBN was given in 3 different doses to Wistar, 8-week-old rats for up to 82 weeks. The highest dose, 0.005% induced urinary bladder carcinoma and the lowest dose, 0.0005% did not develop any changes of the urinary bladder.
