Effect of calcium on rat gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine

The effect of calcium carbonate (CaCO3) on the initiation of gastroduodenal carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was examined under the conditions with and without sodium chloride. Male Wistar rats were given drinking water containing MNNG (100 mg/liter) and one of the following diets during the first 20 weeks ad libitum. Group 1 was given basal diet; group 2, diet with 10% NaCl; group 3, diet with 10% NaCl and 2.5% CaCO3; group 4, diet with 10% NaCl and 7.5% CaCO3; group 5, diet with 7.5% CaCO3. During the next 20 weeks, all groups were fed with the basal diet and tap water. The carcinogenic incidences of glandular stomach between the nonsalted diet groups, 1 and 5 (15% and 16% respectively), were not significantly different at the 40th week. The incidences in the salted diet groups 2, 3, and 4 were 59, 63, and 43%, respectively, indicating no statistical difference among them. Thus, CaCO3 showed no anticarcinogenic effect on gastroduodenal carcinogenesis. In the groups 3 and 4, however, increased incidence of duodenal cancer was observed.