The gastro-entero-pancreatic system of the turtle, Chrysemys picta.

Pancreatic endocrine cells were stained immunocytochemically for insulin, glucagon, somatostatin and pancreatic polypeptide by the PAP technique or sequentially for two hormones by the PAP followed by an indirect immunogold procedure. Pancreatic endocrine cells of Chrysemys are found scattered as single cells or small aggregates throughout the exocrine parenchyma; only the splenic region shows islets consisting of a B cell core surrounded by a loose mantle of A cells and occasional D cells. PP cells were not found in this splenic portion but were found scattered throughout the remainder of the pancreas. In contrast to the typical vertebrate islet, Chrysemys pancreatic endocrine cells are characterized by a lack of preferential association of one cell type with another and suggests that paracrine regulatory mechanisms may not be operable in this species. Insulin secretion from pieces of Chrysemys pancreas has been measured in incubation and perifusion systems employing a heterologous radioimmunoassay. Insulin release by Chrysemys B cells is enhanced by elevated levels of glucose (300 mg/dl), however, response appears to be somewhat slower compared to other vertebrate B cells. Gastrin, secretin, neurotensin, motilin, serotonin, PYY, glucagon, gastric inhibitory polypeptide, somatostatin and insulin were demonstrated immunocytochemically in open-type GEP cells of the mucosal epithelium of the Chrysemys intestine. Of these cells, gastrin, neurotensin and insulin cells appear to be the most numerous while the other types appear less frequently. Cells containing PP, bombesin, cholecystokinin and substance P could not be demonstrated. The localization of insulin to GEP cells of the turtle intestine is an unusual finding but has been confirmed by radioimmunoassay of extracts of the intestinal mucosa.