Morphologic changes in the gastric mucosa of rats after administration of N-methyl-N'-nitro-N-nitrosoguanidine. Electronmicroscopic study.

Electron microscopic findings of the effects of exposure to the cancerogenic substance N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) upon the gastric mucosa of rats are presented. MNNG was administered in drinking water at a concentration of 83 mg/l over a period of eight weeks. The resulting findings included occurrence of myelin figures in membrane structures of epithelial cells, occasional disappearance of nuclear membrane, numerous intranuclear cytoplasmic pseudoinclusions, and increased number of perichromatin and interchromatin granules and of nuclear corpuscles. Narrowing of the layer of peripheral condensed chromatin and broadening of the layer of dispersed chromatin were frequently observed. In the cytoplasm of epithelial cells, production of autophagous vacuoles was detected in differentiated types of cells, the presence of great amount of polysomes and profiles of rough endoplasmic reticulum diversely deformed was seen in the undifferentiated neck cells. These cells presented a marked proliferative activity. Some of the changes described in the nuclei of epithelial cells were also observed in different mesenchymal elements in the lamina propria mucosae. The demonstrated changes are indicative of both regressive and progressive effects of the cancerogen used in our experiment.