N-Methyl-N-nitrosourea and saccharin: effects on epithelium of normal human urinary bladder in vitro.

The effects of N-methyl-N-nitrosourea (MNU) and saccharin on the histology of normal human bladder "urothelium" (i.e., the epithelium of the urinary bladder) were studied in long-term explant cultures. In MNU-treated cultures, a dose response was observed. Single doses of 1-100 micrograms MNU/ml induced atypical focal hyperplasia, which reverted to a single or a double cell layer as seen in controls. Exophytic, papillary-like hyperplastic structures were noted after a single dose of 10 or 100 micrograms MNU/ml. In contrast to single doses, multiple doses (given every 2 wk) of MNU at 5 or 10 micrograms/ml resulted in striking focal proliferation of dysplastic spindle cells in as little as 6 weeks (three doses of MNU). At 0.5% saccharin, urothelium on explant surfaces resembled that of controls, except in one instance in which mild focal hyperplasia persisted. In the presence of saccharin, hyperplasia induced by a single dose of MNU persisted. Following three multiple doses of MNU in the presence of saccharin, spindle cell hyperplasia was induced similar to that seen with multiple doses of MNU alone, although nuclei appeared more pleomorphic and hyperchromatic in the presence of saccharin.