Granule release from endocrine cells in acidified human duodenal bulb: an electron microscope study of biopsy materials.

The endocrine cells of the human duodenal bulb were observed under the electron microscope in biopsy tissues taken by normal procedure and after luminal acidification. 1. The endocrine cells in this portion were found more frequently than in the lower part of the duodenum previously examined by our research group. 2. At least 9 types of endocrine cells were distinguished by their fine structures, i.e., EC, EC-like, D, D1, G, L. M, S and A-like cells. 3. Emiocytotic granule release was recognized in 4 types, i.e., D, D1, L and M cells, 5 min after the infusion of 40ml of 0.1N HCl (pH 1.5) into the duodenal lumen. 4. The hormones produced by these 4 cell types were proposed to be anti-acidic agents such as secretin, enterogastrone or GIP, CCK-PZ and enteroglucagon. 5. The possible significance of the other 5 types of endocrine cells were also discussed.