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

Because few previous studies have shown the immunohistochemical localizatio n of tryptophan 5-hydroxylase (TPH) in the gastrointestinal tract, we devel oped a specific antibody against TPH purified from mouse mastocytoma P-815 and stained human and rat gastrointestinal tracts. The specificity of the a ntibody was examined by Western blotting and by immunohistochemistry in bra in sections. Human ileum and colon specimens, rat stomach, duodenum, jejunu m, ileum and colon specimens, with and without colchicine treatment were pr epared 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 submucos a, and varicose fibers in the submucosa and muscle layer showed positive im munoreactivity in all segments examined from human and normal rat specimens . In colchicine-treated rat specimens, nerve cell bodies in the myenteric p lexus were stained. Because the antibody does not cross react with tyrosine hydroxylase as defined in Western blotting or brain sections, these positi ve structures may contain TPH. The present results show evidence that EC ce lls, mast cells, and nerve cell bodies and fibers in the gastrointestinal t racts of both the human and the rat contain TPH and therefore may have the ability to synthesize serotonin from tryptophan, (C) 1999 Wiley-Liss, Inc.