An immunohistochemical study of endocrine cells in the pancreas of the Red-bellied frog (Bombina orientalis)

The regional distribution and frequency of pancreatic endocrine cells in the red-bellied frog, Bombina orientalis, were studied by the immunohistochemical peroxidase antiperoxidase (PAP) method using five types of specific mammalian antisera to insulin, glucagon, somatostatin, bovine pancreatic polypeptide (PP) and secretin. The frequency was calculated as the mean number of each endocrine cell type/1,000 total cells (including exocrine and endocrine cells) using an automated image analysis process. The percentage of each immunoreactive (IR) cell species to the total IR cell population was also calculated. In the pancreas of the red-bellied frog, all five endocrine cell types were demonstrated. Insulin IR cells were located in the pancreas as single cells or islet-like clusters. The latter were localized in central regions. The insulin-IR cells showed a frequency of 65.40±14.56/1,000 cells. Glucagon IR cells were also detected as single cells or as clusters but in the case of clusters, two distributional patterns were detected — a central core type and a marginally distributed type. They showed an abundance of 32.70±7.32/1,000 cells. Somatostatin-IR cells were dispersed throughout the pancreatic parenchyma as single cells, three to four cells, or clusters. The clusters were located in the marginal regions. The somatostatin-IR cell frequency was 19.40±6.52/1000 cells. PP-IR cells were randomly distributed throughout the pancreatic parenchyma as single cells with a frequency of 14.70±4.92/1,000 cells. Secretin-IR cells were demonstrated as clusters or as single cells, and as clusters they occupied the central regions. They showed a frequency of 39.60±10.36/1,000 cells. This is the first report of the presence of secretin-IR cells in amphibian pancreatic endocrine cells. Overall, there were 37.20±6.84% insulin-, 21.90±5.55% glucagon-, 11.60±4.33% somatostatin-, 8.60±2.72% PP- and 23.40±4.45% secretin-IR cells.