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The suitability of using coloscopy as a diagnostic method is investigated with respect to colonic carcinomas induced locally by the administration of N-nitrosoacetoxymethyl-methylamine, N-methyl-N-nitrosourea, and methylnitro-nitrosoguanidine, or systemically by subcutaneous injection of 1,2-dimethylhydrazine in Sprague-Dawley rats. The endoscopic diagnostic examination proved to be clearly superior to methods of animal inspection, palpation, investigation for occult blood and exploratory laparotomy which have so far been employed in animal experiments with small rodents. The relevance of this method is discussed for the early detection of chemically induced colonic tumors, and the observation of tumor development under experimental cytostatic therapy.

Tumours of the glandular stomach and upper small intestine were induced in rats by oral administration of MNNG. In most cases the lesions were identified histologically as adenocarcinomas and their prestages, such as polypeous and downward growing adenomatous hyperplasias. Out of 48 adenomatous hyperplasias and adenocarcinomas of the stomach and 24 well differentiated adenocarcinomas of the small intestine, we observed argyrophilic cells in nearly the half of the cases. Endocrine cells were also identified by electron microscopy. The frequency of endocrine cells was reduced with decreasing degree of tissue differentiation. In poorly differentiated carcinomas, including signet ring cell carcinomas, no argyrophilic cells were found. Out of 10 adenomatous hyperplasias and tumours of the stomach investigated immunohistochemically, 5 cases showed gastrin producing cells. Most of these animals were radioimmunologically characterized by strongly elevated serum gastrin levels. Derivation and potential relevance of the endocrine cells in tumours are discussed.