Effects of ethanol, potassium metabisulfite, formaldehyde and hydrogen peroxide on gastric carcinogenesis in rats after initiation with N-methyl-N'-nitro-N-nitrosoguanidine.

Ethanol, potassium metabisulfite, formaldehyde and hydrogen peroxide were tested for tumor-promoting activity in a two-stage stomach carcinogenesis experiment. Male outbred Wistar rats were given N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the drinking water (100 mg/liter) and a diet supplemented with 10% sodium chloride for 8 weeks. Thereafter, they were maintained on drinking water containing either 10% ethanol, 1% potassium metabisulfite, 0.5% formalin (formaldehyde) or 1% hydrogen peroxide for 32 weeks and then sacrificed for necropsy and histological examination. In the pylorus of the glandular stomach, potassium metabisulfite and formaldehyde significantly increased the incidence of adenocarcinoma after initiation with MNNG and sodium chloride. Hydrogen peroxide did not enhance the tumor yield, and ethanol showed a tendency to decrease neoplastic development. In the forestomach the incidence of squamous cell papilloma was significantly increased in the groups given hydrogen peroxide or formaldehyde, irrespective of prior initiation. Duodenal adenocarcinoma was induced by the initiation alone (10%) and the incidence was not affected by the subsequent treatments. The results indicate that potassium metabisulfite and formaldehyde both exert tumor-promoting activity in the rat glandular stomach.