Effect of 2-chloro-4-methylthiobutanoic acid in a rapid bioassay for gastric carcinogens.

2-Chloro-4-methylthiobutanoic acid (CMBA, a mutagen from Japanese salted fish) at 15-500 mg/kg body weight induced several-fold increase in replicative DNA synthesis (RDS) (P < 0.05) after 80 min and 17 h, equivocal unscheduled DNA synthesis (UDS) after 80 min and necrosis 80 min after its administration in the stomach pyloric mucosa of F344 and ACI male rats. A positive control, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 50 mg/kg body weight), induced RDS, UDS and erosion. However, the negative control L-methionine (500 mg/kg body weight) did not display any effect. The results suggest possible tumor-initiating and -promoting activity of CMBA but at a lower potency than that of MNNG.