Localization of human pancreatic polypeptide in an argyrophilic fourth cell type in islets of the rat pancreas.

An argyrophilic fourth cell type in the rat pancreatic islet can be differentiated from other silver-staining cells by using a modification of the Grimelius aqueous silver nitrate technique. Restaining of the tissues using fluorescent techniques with anti-HPP (Human Pancreatic Polypeptide) serum results in bright fluorescence in the fourth cell type.