Neuropeptide Y and peptide YY immunoreactivities in the pancreas of various vertebrates.

NPY-like immunoreactivity was observed in nerve fibers and endocrine cells in pancreas of all species examined except the eel, which showed no NPY innervation. The density of NPY-positive nerve fibers was higher in mammals than in the lower vertebrates. These nerve fibers were distributed throughout the parenchyma, and were particularly associated with the pancreatic duct and vascular walls. In addition, the density of NPY-positive endocrine cells was found to be higher in lower vertebrates than mammals; in descending order: eel = turtle = chicken > bullfrog > mouse = rat = human > guinea pig = dog. These NPY-positive cells in the cel and certain mammals tended to be localized throughout the islet region, whereas in the turtle and chicken they were mainly scattered in the exocrine region. PYY-immunoreactivity was only present in the pancreatic endocrine cells of all species studied, and localized similarly to NPY. Thus these two peptides may play endocrine or paracrine roles in the regulation of islet hormone secretion in various vertebrate species.