Amylin-like immunoreactivity in pancreatic X cells of the black-spotted frog Rana (Pelophylax) nigromaculata

• Amylin-immunoreactivity was examined in frog pancreas.
• Amylin-immunoreactive cell does not contain insulin, glucagon, or somatostatin.
• Characteristics of amylin-containing cell accord with those of X cell.
• Amylin may regulate hormone secretion from A/PP cell and/or B cell.

In this study, we investigated the presence of ovoid or ellipsoidal amylin-immunoreactive cells of the pancreatic islets of the black-spotted frog Rana (Pelophylax) nigromaculata. Using double immunofluorescent staining, all amylin-immunoreactive cells were shown to be immuno-negative for insulin, glucagon, and somatostatin, and they were often observed in peripheral regions of clusters of insulin-immunoreactive cells. Under immunoelectron microscopy, amylin-immunoreactive signals were detected on the secretory granules in a specific type of endocrine cells. From our results, we conclude that the amylin-immunoreactive cells correspond to X cells among the 4 distinct types of endocrine cells (B, A/PP, D, and X) previously identified in the frog. Amylin secreted from X cells may regulate the hormone secretion from A/PP cells and/or B cells through a paracrine mechanism.