It was recently established that oral administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in solution as drinking water produced adenocarcinoma in the glandularstomach of rats and hamsters. In some animals metastases were observed to the perigastriclymph node and liver.
The present paper descibes the histopathological findings of stomach carcinoma in doginduced by MNNG. MNNG solution was administered to 8 dogs as drinking water. Fourdogs of experimental group I, 3 month old and weighing about 4.7kg were given at a concentrationof 167 μg/ml for 1 month and of 83 μg/ml for following 14 months. And 4 dogs ofexperimental group II, 4 month old and weighing about 7 kg were given at a concentrationof 83 μg/ml for 2 weeks, 6 months, 9 months and 12 months, respectively.
Adenocarcinomas of the stomach developed in 7 dogs. Metastases were not found. Thesecarcinomas were most frequently found in the cardiac portion along the greater curvatureand in the antrum and corpus along the lesser curvature. And carcinomas developed wheremucosal atrophy was pronounced.
In the cardiac portion, 5 dogs developed well differentiated papillary or tubular adenocarcinomas, which were infiltrating the serosa in 1 dog, infiltrating the submucosa in 2dogs and intramucosal in 2 dogs. Other 3 dogs developed atypical glands of various degrees.
And in the gastric antrum, 7 dogs developed well defferentiated papillary or tubularadenocarcinomas or adenocarcinomas with or without signet ring cells. These papillaryand tubular adenocarcinomas were infiltrating into the muscularis propria in 2 dogs andinfiltrating the submucosa 1 dog and intramucosal in 4 dogs. And signet ring cell type adenocarcinomaswere found in 3 dogs. The differences of the histological type of the tumorsin the site may be due to the difference in the site of tumor cells proliferation or in sensitivityof the tissues to MNNG.
In the histological findings, atypical cells with vesicular nuclei and prominent nucleoli, similar to those of adenocarcinoma involving the serosa, were occasionally found at or near thegastric pit and neck region. The development of these carcinomas arising from the gastricmucosa appeared unrelated to prior erosions or ulcers of the mucosa, since the muscularismucosae was frequently intact although hypertrophied. Therefore, carcinomas might originate from the gastric pit or neck region so far as gastric carcinoma of dogs by MNNG, is concerned, although the possibility of carcinoma originating in repeated erosions orshallow ulcers not involving the muscularis mucosae still remained.
It is necessary to study neoplastic changes at earlier stages to evaluate the relationshipsbetween carcinomas and erosions or shallow ulcers.
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