Immunohistochemical localization of tryptophan hydroxylase in the human and rat gastrointestinal tracts.

Because few previous studies have shown the immunohistochemical localization of tryptophan 5-hydroxylase (TPH) in the gastrointestinal tract, we developed a specific antibody against TPH purified from mouse mastocytoma P-815 and stained human and rat gastrointestinal tracts. The specificity of the antibody was examined by Western blotting and by immunohistochemistry in brain sections. Human ileum and colon specimens, rat stomach, duodenum, jejunum, ileum and colon specimens, with and without colchicine treatment were prepared for immunohistochemistry. Immunoelectron microscopic double staining of TPH and serotonin/chromogranin A and immunofluorescence double staining of TPH and serotonin were performed to identify the cell types. Epithelial enterochromaffin (EC) cells, mast cells in the lamina propria and submucosa, and varicose fibers in the submucosa and muscle layer showed positive immunoreactivity in all segments examined from human and normal rat specimens. In colchicine-treated rat specimens, nerve cell bodies in the myenteric plexus were stained. Because the antibody does not cross react with tyrosine hydroxylase as defined in Western blotting or brain sections, these positive structures may contain TPH. The present results show evidence that EC cells, mast cells, and nerve cell bodies and fibers in the gastrointestinal tracts of both the human and the rat contain TPH and therefore may have the ability to synthesize serotonin from tryptophan. Copyright 1999 Wiley-Liss, Inc.