Effects of treatment with N-methyl-N-nitrosourea, artificial sweeteners, and cyclophosphamide on adult rat urinary bladder in vitro.

The effect of N-methyl-N-nitrosourea (MNU), sodium saccharin, sodium cyclamate and cyclophosphamide on rat bladder explants in vitro was studied. MNU administered as a single dose or in multiple treatments induced concentration-dependent changes in urothelial ultrastructure and cell surface topography. In a single treatment protocol, extensive cytotoxicity was observed in both the urothelium and stroma at concentrations of 500 to 1000 micrograms/ml, establishing a toxic threshold within this range. In a multiple treatment protocol, repeated doses of low concentrations of carcinogen (7 or 8 x 50 micrograms/ml, 6 x 100 micrograms/ml) induced hyperplastic and dysplastic changes in the urothelium with no cytotoxicity, but cytotoxic effects were observed following treatments of 4 x 200 micrograms/ml or 2 x 400 micrograms/ml. Sodium saccharin, sodium cyclamate, and cyclophosphamide induced changes in urothelial cell surface topography consistent with hyperplasia and preneoplasia. Prolonged exposure to saccharin or cyclamate followed by a single dose of MNU elicited more extensive abnormalities in the urothelium than either saccharin or cyclamate alone, suggesting that these artificial sweeteners have initiating activity in a multistage process. The ultrastructural changes induced by in vitro treatment showed a good correlation with the pathological changes observed in vivo in rats treated with MNU or fed either with saccharin or cyclamate.