Arginine-vasopressin immunoreactive material in the gastrointestinal tract

Summary Like many other neuropeptides, vasopressin is not confined to the hypothalamic neurohypophysial system. Furthermore, vasopressin was found to be a potent vasoconstrictor in the rat jejunum, reducing myenteric artery flow. These associations were the basis of this investigation on the presence of vasopressin in the gastrointestinal (GI) tract by both RIA and immunohistochemistry.Portions of the gastrointestinal tract and pancreatic islets of the rat were extracted with 0.1N HCl for RIA measurements of AVP content. Similar portions from the male cat GI tract were used for immunohistochemistry studies.Acid extracts of the GI tract were found to contain immunoreactive AVP with the highest concentration (pg/mg protein) in the fundus portion of the stomach (15.0±1.6) and slightly lower values down along the antrum-pylorus portion (6.7±0.6), proximal jejunum (8.6±0.2), distal ileum (9.7±0.3) and colon (11.9±0.5). In the pancreatic islets the concentration was much higher (72.0 pg/mg protein). The extract inhibition curves showed parallelism with the appropriate standard preparation of AVP in the specific RIA.Immunohistochemical localization showed IR-AVP in the nerve fibers around the myenteric plexus of the second portion of the duodenum. It was also found in fibers starting from where the myenteric plexus goes through the layer of muscle fibers, penetrating the submucosa and duodenal mucosa, ending near the capillaries situated along the basal side of the villous epithelium cells. Similar IR-AVP activity was found in cells located in the mucosal epithelium of the duodenum, jejunum, ileum, colon and rectum.These results show that the gastrointestinal tract of different species and pancreatic islets of the rat are a rich source of immunoreactive neurohypophysial AVP. Because of its distribution, this peptide might have some physiological significance in intestinal circulatory regulation.