Enterocytes in the anterior intestine of Oncorhynchus mykiss: Cytological characteristics related to osmoregulation

In an ultrastructural study of the pyloric ceca region of the anterior segment of the intestine of rainbow trout, we observed enterocytes with features suggestive of a role in osmoregulation. Earlier studies of the anterior portion of the intestine in fresh-water teleosts have considered this region as the site of amino acid and fat absorption. Lipoprotein synthesis is believed to take place in the enterocytes of this segment, and subsequently be released into the blood stream. At the level of the openings of the pyloric ceca, two morphological types of enterocytes could be identified on the basis of the electron density of the cytoplasm. Both light and dark enterocytes displayed ultrastructural features similar to those of cells for which physiological and ultrastructural studies have documented an osmoregulatory function, such as columnar epithelial cells in the esophagus and anterior portion of the intestine in marine and euryhaline teleosts.