The grandular stomach of animals, especially that of rats and mice, has been found to be highly resistant to the action of known carcinogenetic substances without yielding the development of carcinoma.
Considering the fact that there are a large number of gastric cancer originated from gastric ulcer in Japan, The author thought that it might be possible to expect some change in the susceptibility of the mucous membrane of the glandular stomach of mice or rats if chronic ulcer had previously been produced.
In this connection, the method of producing chronic ulcer was studied. Mice were found to be inadequate for this purpose and the best method found with rats was to inject 0.1 ml of 20 % caustic silver solution into the submucous layer of the stomach by laparotomy. This method gave the best survival rate with the highest rate of ulcer formation.
Rats thus treated to produce ulcer were administered with a daily dose of 2 mg of 20-methylcholanthrenene dissolved in drinking water. This substance was first. dissolved in polyethylenglycol to be rendered water-soluble and then tap water was added. Only the rats fed on this water more than 20 days were subjected to the present study.
A total of 52 rats became available and marked heterotopic metaplasia of the mucous membrane was seen in 6 cases, atypical metaplasia in 6 cases and intestinal epithelial metaplasia in 6 cases. All of these lesions are commonly observed on the stomach of human gastric cancer. Development of gastric cancer, however, was not recognized. Control animals, moreover, showed no such lesions.
This experiment was not successful in developing gastric cancer, but all lesions mentioned above were detected only on the lesions or scars of experimentally produced ulcer suggesting that the mucous membrane of those parts have shown a considerable reaction against the influence of carcinogenetic substances.
In order to facilitate the development of gastric cancer, therefore, this method should be tried when undertaking similar experiments employing other kinds of laboratory animals, carcinogenetic substances or the solvents.
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