An immunohistochemical study of various peptide-containing endocrine cells and neurones at the equine ileocaecal junction.

The ileocaecal junctions of 5 horses and 2 donkeys were examined by using antisera to the following peptides: somatostatin, glucagon, gastrin, neurotensin, vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY). Antisera to somatostatin, neurotensin and NPY demonstrated endocrine cells in the ileal- and caecal parts of the ileocaecal junction, while immunoreactivity for glucagon was demonstrated in endocrine cells of the ileal part only. Nerve cell bodies showing immunoreactivity to SP, VIP, CGRP and PHI were demonstrated in the myenteric and submucosal plexuses and were associated with small blood vessels in the submucosa of all the regions tested. Ramified nerve fibres in the submucosa immunoreactive to SP, VIP, CGRP and PHI extended to the mucosa and to small blood vessels in the submucosa. Nerve fibres showing immunoreactivity to SP, VIP and PHI extended to the circular smooth muscle layer of the ileocaecal junction.