Demonstration of carboxyl-terminal PP-like peptides in endocrine cells and nerves

Pancreatic polypeptide (PP) has been isolated from the pancreas of several species, and has been localized by immunohistochemistry to a distinct population of pancreatic endocrine cells. Recently, PP-like immunoreactivity has been demonstrated outside the pancreas, in gut endocrine cells and central and peripheral nerves, in studies using antisera raised to natural PPs. The antigenic determinants recognised by these antisera are not known in any detail, and, therefore, the identity of the molecules in these extrapancreatic localizations is also unknown. We have raised an antiserum to the synthetic COOH-terminus of PP (PP6), which, therefore, is directed exclusively towards the biologically active, invariant region of mammalian PPs. PP6-like immunoreactivity was localized in pancreatic cells which were revealed also by antiserum to human PP (hPP). Outside the pancreas, no localizations were obtained with anti-hPP antiserum, whereas antiserum to PP6 demonstrated immunoreactivity in a variety of tissues including gut glucagon cells, adrenal chromaffin cells, and nerve fibres in the gastrointestinal tract and adrenal gland. We would suggest that the wide distribution in nerves and endocrine cells of PP6-immunoreactive material, which may be biologically active, should be taken into account in the search for a physiological role for PP.