IMMUNOHISTOCHEMICAL STUDIES OF THE ENDOCRINE-CELLS WITHIN THE GASTROENTEROPANCREATIC SYSTEM OF OSTEOGLOSSOMORPHA, AN ANCIENT TELEOSTEAN GROUP

The identification and distribution of endocrine cells within the gast ro-entero-pancreatic (GEP) system of five species of the Osteoglossomo rpha (Osteoglossum bicirrhosum, Scleropages jardini, Pantodon buchholz i, Notopterus chitala and Gnathonemus petersii) were analyzed by immun ohistochemistry. Four immunoreactive cell types were identified within the pancreatic islets (A, B, D, and F cells), using antisera directed against mammalian insulin (m-INS), somatostatins (SST-14, SST-25), an d members of the pancreatic polypeptide (aPY, NPY, PYY) and glucagon ( GLU, GLP) families. The B cells were located throughout the center of the islets in the five species and, in general, D cells had a similar distribution. However, immunoreactivity to anti-somatostatins varied b etween four of the species and G. petersii which showed less intensely stained D cells in the islets, but greater SST immunoreactivity in bo th the intestinal and the stomach epithelia than in comparable epithel ia of other species. For peptides of both the pancreatic polypeptide a nd the glucagon families, the immunoreactivity was detected at the per iphery of the islets, and there was a suggestion of an interfamily col ocalization of peptides in some cells. In addition, glucagon family pe ptides showed a scattered immunoreactivity throughout the central port ion of the islets. A moderately abundant number of cells in the intest ine were immunoreactive to the PP family antisera in all five species. However, immunoreactivities to GLU, GLP, SST, and m-INS anti- sera we re variable in intestinal cells of the species. Immunoreactivity with sera raised against m-INS and PYY was also observed in the stomach of P. buchholzi. The significance of these findings is discussed in both ontogenetic and phylogenetic contexts with respect to the GEP system i n actinopterygian fishes and with respect to the possibility of variab le processing of prohormones in the different organs of these osteoglo ssomorphs. (C) 1998 Academic Press.