Enterochromaffin (Argentaffin) cells of the rat gastrointestinal tract. An ultrastructural study.

Argentaffin cells from different parts of the gastro-intestinal tract were examined electron microscopically by the semi-thin/ultra-thin sectioning technique. All these cells contained round or pleomorphic secretory granules, which were mainly concentrated in the infranuclear zone, except in the antrum, where they occurred with a similar frequency in all the peri-nuclear areas. The highest frequency of granules was found in the colon. The largest granules were seen in the duodenum and the smallest in the large intestine. Argentaffin cells with processes oriented towards the glandular and villous surface were most frequent in the small intestine. No secretory granules were seen in the most apical part of these processes, where in an earlier study serotonin immunoreactivity was observed. This may indicate that serotonin can be stores in a non-granular form. No close topographic relationship was found between the argentaffin cells and other endocrine cell types or the nervous system.