GASTRIC CARCINOGENESIS IN RATS GIVEN HYPERTONIC SALT AT DIFFERENT TIMES BEFORE A SINGLE-DOSE OF N-METHYL-N'-NITRO-N-NITROSOGUANIDINE

A 1-ml dose of 4.5 M NaCl was given intragastrically to male Wistar rats at 10 min, 1 h, 4 h, 12 h, 24 h or 48 h before a single intragastric dose of 250 mg/kg N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). After 52 weeks the incidence of forestomach squamous cell carcinoma was 21 % in control animals receiving MNNG alone. The cancer incidence in the forestomach varied with the time elapsed between application of NaCl MNNG, and was significantly increased in animals pretreated with NaCl 4 h (43%),12 h (54%) and 24 h (41%) before MNNG. These results show that salt has a cocarcinogenic effect on initiation of forestomach carcinogenesis in rats, and that this effect depends on the time interval between pretreatment with NaCl and application of MNNG. Gastric adenocarcinomas occurred more frequently in the antrum (78%) than in the corpus (22%). The incidence of gastric adenocarcinoma in animals pretreated with salt before application of MNNG (11%-22%) was not significantly influenced by the time elapsed between pretreatment with salt and application of MNNG, and did not differ from animals receiving MNNG alone (18%). The lack of a cocarcinogenic effect of NaCl on glandular gastric carcinogenesis might be due to the use of dimethyl/sulfoxide as solvent for MNNG.