Early ultrastructural changes of epithelial cells of the glandular stomach in rat induced by N-methyl-N'-nitro-N-nitrosoguanidine

The early ultrastructural events that occur In the gastric epithelial cells of the glandular stomach of rat from 12 hours to 3 weeks after oral administration of N-methyl-N'-nitro-N-nitrosoguanidine were examined and compared with the X-irradiation effects on mouse gastric mucosa. The mucoid cells of the pyloric mucosa, particularly the surface and pit mucous cells exhibited the greatest ultrastructural alterations among the 6 types of gastric epithelial cells. The earliest changes of the mucoid cells were observed in the nuclei, and were characterized by the sequential development of first nucleolar enlargement, which consisted of the increase of both the fibrillar and granular components, followed by the occurrence of nucleolar segregation, reduction and clumping of the chromatin, and irregularity of the nuclear membrane. Significant degenerative changes of the cytoplasm in the mucoid cells could be observed after these nuclear alterations. Later, giant cell formation in the mucoid cells and mesenchymal cells, and the development of epithelial cells containing two cell specificity were found. These ultrastructural alterations of the mucoid cells seem to represent the morphologic manifestations of biochemical interaction between N-methyl-N'-nitro-N-nitrosoguanidine and biological materials.