Endocrine Cells of the Dog Gastrointestinal Mucosa

Endocrine cells in the gastrointestinal tract of the dog have been studied by electron microscopy.Seven types of endocrine cells were found in the gastric mucosa: the gastrinproducing G cells, serotonin-producing enterochromaffin cells, enterochromaffinlike cells, A-like cells, D cells, D, cells, and X cells.The enterochromaffin cells may be subdivided into two cell types according to the shape and structure of the secretory granules. Contrary to previous reports, the enterochromaffin-like cells were found to reach the gland lumen. Implications resulting from this observation are discussed. The X cells and D cells have so far been described as one single cell type. According to the present findings, the two cells differ distinctly in several respects and should be regarded as two separate cell types.The intestinal mucosa was found to contain the enterochromaffin cells, S cells, I cells and L cells. In addition, we observed an heretofore undescribed cell type, the secretory granules of which show a granular structure and a highly osmiophilic core. Since we were unable to find any transitory forms between these cells and established cell types, this cell type may represent a new element in the population of endocrine cells of the gastrointestinal mucosa.