RESUMEN
The distribution and morphology of 5-HT immunoreactive endocrine cells in the gastrointestinal tract of 5 adult rats were studied by the immunohistochemicael PAP method with nickel-intensified DAB on paraffin sections of intestine rolls. The density of 5-HT immunoreactive endocrine cells in the gastrointestinal tract of the rat is highest in the pylorus, duodenum and colon and moderate in the jejunum, ileum, caecum and rectum and lowest in the body of the stomach. The 5-HT immunoreactive endocrine cells are various in shape. Some of them have several processes extending between other epithelial cells. The basal portion of some endocrine cells have processes with 5-HT positive substance accumulating in their ends. The processes of the basal portion of some endocrine cells extend into lamina propria through the basal membrane. The 5-HT positive substance of many endocrine cells can be found to extend to luminal surface of the crypt or intestinal tract. These results indicate that the 5-HT immunoreactive endocrine cells can release 5-HT by both endocrine and exocrine ways.