The endocrine cells in the gastroenteropancreatic system of the bowfin, Amia calva L.: An immunohistochemical, ultrastructural, and immunocytochemical analysis

The gastroenteropancreatic (GEP) endocrine system of bowfin (Amia calva) wa s described using light and electron microscopy and immunological methods. The islet organ (endocrine pancreas) consists of diffusely scattered, mostl y small islets and isolated patches of cells among and within the exocrine acini. The islets are composed of abundant, centrally located B cells immun oreactive to bovine and lamprey insulin antisera and D cells showing a wide spread distribution and specificity to somatostatin antibodies. A and F cel ls are present at the very periphery of the islets and are immunoreactive w ith antisera against glucagon (and glucagon-like peptide) and several pepti des of the pancreatic polypeptide (PP)-family, respectively. The peptides o f the two families usually collocates within the same peripheral islet cell s and are the most common immunoreactive peptides present in the extra-isle t tissue. Immunocytochemistry and fine structural observations characterise d the granule morphology for B and D cells and identified two cell types wi th granules immunoreactive to glucagon antisera. These two putative A cells had similar granules, which were distinct from either B or D cells, but on e of the cells had rod-shaped cytoplasmic inclusions within cisternae of wh at appeared to be rough endoplasmic reticulum. The inclusions were not immu noreactive to either insulin or glucagon antisera. Only small numbers of ce lls in the stomach and intestine immunoreacted to antisera against somatost atin, glucagon, and PP-family peptides. The paucity of these cells was refl ected in the low concentrations of these peptides in intestinal extracts. T he GEP system of bowfin is not unlike that of other actinopterygian fishes, but there are some marked differences that may reflect the antiquity of th is system and/or may be a consequence of the ontogeny of this system in thi s species. (C) 2001 Wiley-Liss, Inc.