Ultrastructural localization of pancreatic polypeptide in human pancreas.

Human pancreatic polypeptide (HPP) was localized in surgically obtained human pancreas by immunocytochemical electron microscopy. HPP was localized to the secretory granules of cells distinct from the alpha, beta, or delta cells of endocrine islets. The PP cells in 10 patients surveyed were most frequently located in the periphery of the islets. Immunolocalization distinguishes a fifth endocrine cell type in human islets which distinct ultrastructurally by its smaller granule diameter and lack of PP immunoreactivity.