Effect of dose on the induction of urothelial proliferation by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide and its relationship to bladder carcinogenesis in the rat.

The effect on urothelial proliferation of a urinary bladder carcinogen, N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT), fed to male F344 rats at doses of 0.2, 0.1, 0.05, 0.01, 0.005 and 0.001% of diet for 4 or 10 weeks was evaluated by autoradiography, using [3H-methyl]thymidine, and by histopathology. At week 4, hyperplasia was induced in 10/11 and 6/11 rats given 0.2% and 0.1% FANFT, respectively. The dose-related increase of labeling index in the bladder epithelium was significant for the groups given 0.01% or higher doses of FANFT. At week 10, histopathologic lesions were observed in groups given 0.05% or higher doses of FANFT. This was accompanied by a significant increase in labeling index for these groups. The results are consistent with the long-term carcinogenicity studies conducted with the same dose levels of FANFT. The interrelationships between numbers of cells (hyperplasia), cell proliferation (labeling index) and cancer induction are discussed utilizing a computerized model of bladder carcinogenesis.