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BBNは尿中に排泄され, 膀胱の移行上皮に対しては腫瘍を発生させる発癌性物質であるが, 同じ条件で尿と接する移植した小腸上皮に対しては発癌性が非常に低い, The effect of N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) on the small intestine in rat, in which augmentation cystoplasty was performed, was examined. Seventeen rats were divided into 3 groups: 1) jejunum-transplanted group (5 cases), 2) ileum-transplanted group (6 cases) and 3) control group without operation (6 cases). A part of the small intestine was transplanted to the urinary bladder, then 0.05% BBN was given for 12 weeks. The rats were killed 30 weeks after the beginning of the administration for histopathological evaluation. Bladder tumors in various grades were confirmed in all the cases. In two cases in the jejunum-transplanted group, transitional cell carcinoma was found in the urinary bladder, one of which had an invasion to the adjacent part of the jejunum to the bladder mucosa. These findings suggest that the metabolic products of carcinogens, excreted into urine, had no effect on the transplanted small intestine.