Immunocytochemical studies on the pancreatic islets of the ratfish Chimaera monstrosa

The islet cells and nerves in the pancreas of the ratfish Chimaera monstrosa were examined immunocytochemically by using antisera against mammalian brain-gut peptides. Five types of islet cells were recognized. The B and D cells reacted to anti-insulin and anti-somatostatin sera, respectively. The A and X cells exhibited glucagon-like immunoreactivities. The N-terminal anti-glucagon serum reacted both to the A and the X cells, while the C-terminal anti-glucagon serum bound specifically to the X cells. These results suggested that the X cells contained pancreatic-type glucagon, whereas the A cells, an enteroglucagon (glicentin)-like substance. A fifth type of endocrine cell was scattered in the islets and contained serotonin-like immunoreactivity. Two kinds of peptide nerves were identified. Vasoactive intestinal polypeptide (VIP)-immunoreactive neuronal somata were located in the intrapancreatic ganglia. Nerve fibers and terminals containing VIP-like immunoreactivities occurred in the pericapillary space surrounding the islets. Gastrin releasing peptide (GRP)-immunoreactive nerve somata and fibers were scattered along the margins of the islets. The pericapillary arrangement of these nerve terminals suggests a hemocrine release of the peptides.