Effect of L-Tryptophan and Sodium Saccharin on Urinary Tract Carcinogenesis Initiated by N-[4-(5-Nitro-2-furyl)-2-thiazolyl]formamide

The effect of sodium saccharin (SAC) or L-tryptophan (LT) on urinary bladder carcinogenesis initiated by feeding N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) for 4 weeks as 0.2% of the diet to male F344 weanling rats was evaluated. SAC was fed as 5% of the diet, and LT was 2% of the diet. FANFT fed for 4 weeks followed by 100 weeks of control diet did not produce any carcinomas; one of 25 rats developed a bladder papilloma. Of 26 rats fed SAC for 100 weeks after FANFT, two developed papillomas, and five developed carcinomas (p > 0.03). Of 26 rats fed LT for 100 weeks after FANFT, three developed papillomas, and two developed carcinomas (p > 0.1). Eight rats fed FANFT for 72 weeks all developed bladder carcinomas, but rats fed control diet alone, control diet with SAC, or control diet with LT did not develop any bladder tumors. Scanning electron microscopic examination at Week 104 of the experiment showed the presence of pleomorphic microvilli on the bladder surface of some rats fed SAC or LT whether following 4 weeks of control diet alone or 4 weeks of FANFT. Four weeks of FANFT feeding, a lower dose than used previously in our studies, appears to be a subcarcinogenic level. Under these experimental conditions, the promoting activity of SAC is demonstrated with statistical significance. The results with LT were not statistically significant.