Early lesions in experimental bladder cancer in rats by N-butyl-N-(4-hydroxybutyl) nitrosamine

Papillomas of urinary bladder were induced in female Wistar rats by gastric intubation of Nbutyl-N-（4-hydroxybutyl）nitrosamine（BBN）with the use of a quantitative dosing schedule.The lesions of the urinary bladder progressed from mild hyperplasia at 2 week after the first intubation to moderate hyperplasia at 4 week,and papillary hyperplasia at 8 week as observed by light microscopy,and at 12 week we could see the papillomas by naked eyes.On scanning electron microscopy,the flat and smooth mucosas of the bladders became irregular and rough,gave a“cobblestones or hills”appearance.The flat polygonal surfaces of the superficial transitional cells were changed to mild pleomorphism,moderate swelling,presented a round or semidome semblance,protruding into the lumen.More and more normal microridges on the surfaces of these cells became leafy or rounded,and were gradually replaced by the uniform microvilli.