Immunohistochemical localization of endocrine cells in the alimentary tracts of six frog species

A peroxidase-antiperoxidase method was used to detect the cells showing immunoreactivities to six hormone antibodies in the alimentary tracts of six frog species, Rana nigromaculata, R. rugosa, R. amurensis coreana, R. catesbeiana, Bombina orientalis, and Hyla arborea japonica, inhabiting Korea. The cells immunoreactive to gastrin and cholecystokinin-8 were observed in the pylorus of the stomachs and in the small intestines of all frog species examined. In contrast, these somatostatin-immunoreactive cells were identified in the esophagus and the whole gastrointestinal tracts, but were absent from the large intestines in R. rugosa, R. catesbeiana, B. orientalis, and H. arborea japonica. The pancreatic polypeptide (PP)-immunoreactive cells represented their distribution limited to the small intestines of R. amurensis coreana and H. arborea japonica, and they were additionally identified in the pylorus of the stomachs in the other four species. Serotonin- and glucagon- immunoreactive cells revealed different regional distributions in which the former were observed throughout the whole alimentary tracts in all frog species investigated, whereas the latter were not found in these regions at all. Endocrine cells were relatively abundant in the pyloric portion of the stomach compared to other organs. The present study showed that all endocrine cells except for PP had a similar distribution in the alimentary tracts of all frog species used