IMMUNOLOCALIZATION OF NEUROPEPTIDE-Y IN HUMAN PANCREATIC ENDOCRINE TUMORS

Neuropeptide Y (NPY) is a 36 amino acid peptide known to inhibit gluco se-stimulated insulin secretion. NPY has recently been shown to be syn thetized within rat islets of Langerhans and to be secreted in a diffe rentiated rat insulin-secreting cell line, and as to this date the loc alization of NPY in human endocrine pancreas has not been reported. As NPY shares high amino acid sequence homology with peptide YY (PW) and pancreatic polypeptide (PP), the polyclonal antibodies raised against these peptides often cross-react with each other. To demonstrate the presence of NPY in the human endocrine pancreas, we used a highly spec ific monoclonal antibody raised against NPY and another against its C- flanking peptide (CPON). We studied three cases of hyperplasia of Lang erhans islets and 11 cases of endocrine tumors of the pancreas. NPY an d CPON were detected in all three cases of hyperplasia. For the 11 pan creatic tumors, five and nine of the tumors were positive for the anti bodies NPY and CPON, respectively. The two negative tumors for CPON im munoreactivity were differentiated insulinomas, which showed no eviden ce of other hormonal secretion. In normal human Langerhans islet, NPY and CPON immunoreactivities were colocalized in glucagon-producing cel ls (cu-cells) and in a few insulin-secreting cell (p-cells). In conclu sion, 1) NPY-specific immunoreactivity was found to be present in huma n Langerhans islets and some tumors of the endocrine pancreas, 2) in n ormal human Langerhans islet, NPY is predominantly present in cu-cells and in a few beta-cells, 3) NPY may be used as a marker of the endocr ine pancreas, and 4) the functional role of NPY within human islets of Langerhans and plasma NPY levels in patients diagnosed with endocrine pancreatic tumors remains to be established.