Serotonin Immunoreactive Cells in Extrahepatic Bile Ducts, Major Duodenal Papilla and Gallbladder in the Domestic Pig

The main part of serotonin in the body is synthesized and released by a certain type of enteroendocrine cells in the intestinal mucosa called enterochromaffin cells. The scarce qualitative and quantitative data on enterochromaffin and serotonin-positive mast cells in porcine extrahepatic bile ducts and gallbladder, motivated us to undertake the present study. The aim of this study was to determine the localization and density of serotonin-positive cells in the wall of the extrahepatic bile ducts and gallbladder in pigs. An immunohistochemical method was used to identify enterochromaffin cells and determine their percentage relative to the total number of endocrine cells labeled with chromogranin A. Serotonin-positive mast cells were identified after tryptase staining of serial sections. The endocrine function of mast cells was demonstrated by chromogranin A immunolabeling. The highest number of enterochromaffin cells were found in the intramural part of the ductus choledochus, followed by the papilla duodeni major, extramural part of the ductus choledochus, ductus hepaticus comunis, ductus cysticus, and gallbladder. In all parts of the extrahepatic bile ducts, the highest number of mast cells was found in the muscle layer, followed by the serosal layer and the propria. The expression of serotonin in the enterochromaffin cells of the biliary glands and in the mast cells of the analyzed organs suggests a possible synthesis of serotonin, which probably regulates physiological and pathological processes.