The mucosa of the pyloric antrum was taken by biopsy from seven patients under a direct inspection with a fiber-gastroscope and studied by electron microscopy. At least four types of basal-granulated cells were found in the deeper layer of the antral mucosa:
1. Enterochromaffin cells were fewer than in the human duodenum. A possible subtype with vacuolated granules was found.
2. G cells with rounded cell body and partly vacuolated basal granules were the most numerous and were considered to be the source of gastrin.
3. Endocrine cells of a third type were characterized by spotted distribution of basal granules of dense and small type and abundant cytoplasmic filaments.
4. Cells tentatively called gastric D-like cells because of their morphologic resemblance to the pancreatic D cells and duodenal D-like cells were found though less frequently than in the duodenum. A possible secretion of secretin from D type cells was discussed.
5. In all the types of basal-granulated cells, a narrowed apical cytoplasm was extended to the epithelial surface and provided with microvilli projecting into the lumen. A hypothesis of unicellular feedback mechanism in the secretion of gastrin and other antral hormones was proposed on the basis of this fine structure of basal-granulated cells.