Abstract: Objective To establish the bladder tumor model induced by N-methyl-N-nitrosourea in rats and to observe the dynamic histopathological changes of the bladder mucosa. Methods A bi-weekly doses of 2 mg MNU each time for 8 weeks intravesicular administration were given. The changes of the bladder mucosa were pathologically examinated at 3rd, 5th, 7th, 9th, 12th and 14th week. Results Untypical hyperplasia could be observed after 3 weeks of administration, the carcinoma in situ occurred at 7 weeks, distinctive tumor was found at 9 weeks, bladder papilloma or invasive carcinoma was observed at 12-14 weeks. The rate of carcinogenicity was 100%(6/6) after 9 weeks. The histological changes and the pathologic characters were very similar with human bladder tumor. Conclusion The method to induce bladder tumor by intravesicular administration of MNU is convenient and reliable. The carcinogenic process includes epithelial hyperplasia, papilloma and carcinomatous changes. It is an ideal animal model.

Key words: N-methyl-N-nitrosourea, Bladder neoplasms, Transitional cell carcinoma, Animal model