Coexistence of pancreatic polypeptide (PP)-and glucagon-immunoreactivity in pancreatic endocrine cells of mouse.

Immunocytochemical double staining techniques were used to study PP- and glucagon-like-immunoreactivity in pancreatic endocrine cells of mouse. An antiserum against FMRFamide appeared to react with all PP-immunoreactive endocrine cells. With fluorescence microscopy most PP/FMRFamide-immunoreactive cells also showed glucagon-immunoreactivity, but cells containing only PP- or glucagon-like substances were found as well. The proportion of cells containing PP-, glucagon, and both immunoreactivities varied strongly from islet to islet in all parts of the pancreas. Using an electron microscopical immunogold double staining procedure on Lowicryl-embedded pancreas, PP/FMRFamide- and glucagon-immunoreactivity appeared to be present in the majority of endocrine A cells; both immunoreactivities were randomly distributed within the granules of these cells. Cells containing only PP/FMRFamide- or glucagon-immunoreactivity were also found. Glucagon- and a faint FMRFamide-immunoreactivity was also observed in osmicated epon-embedded tissue. Independent of their immunoreactivity all positive cells showed the same round electron dense secretory granules.