Mutagenic activation of dialkylnitrosamines by intact urothelial cells.

Intact urothelial cells isolated from bladders of untreated inbred NZO/BIGd or NZC/BIGd mice and NZR/Gd rats activated dimethyl, diethyl, dipropyl, and dibutyl nitrosamines in a liquid culture mutagenesis fluctuation assay using Salmonella typhimurium TA100 as target organism. Rat and mouse urothelial cells were highly effective at 1.5 X 10(5) cells/ml, in O2 gas phase, and no cofactors were required. Relative mutagenic activities were estimated at equitoxic (LD50) concentrations of the 4 nitrosamines. Nitrosamines with odd-carbon chain substitutents were more active than the C-even compounds. Although dibutylnitrosamine is a powerful bladder carcinogen in both rats and mice while the other 3 compounds very rarely cause bladder tumours, the most active promutagens were dipropyl and dimethyl, followed by diethyl and dibutyl nitrosamines. None were active in absence of urothelial cells. Mouse bladder cells were more active than those from NZR rats. There were sex differences in the mice with NZC males and NZO females predominating, but in NZR rats urothelial cells from male and female animals were equally active. These dialkylnitrosamines are widely distributed in the environment, and our results indicate that direct mutagenic activation in the urothelium could be one factor contributing to the incidence of bladder cancer.