PYY IN DEVELOPING MURINE ISLET CELLS - COMPARISONS TO DEVELOPMENT OF ISLET HORMONES, NPY, AND BRDU INCORPORATION

Exhaustive characterizations of antisera to the structurally related p eptides pancreatic polypeptide (PP), neuropeptide Y (NPY), and peptide YY (PYY) enabled us to establish the developmental pattern of these p eptides in rat and mouse pancreas. PYY was the earliest detectable pep tide and was present in all early appearing endocrine cell types, NPY appeared later and occurred exclusively in a subpopulation of insulin cells, whereas PP cells arose latest. At the earliest stage studied, a ll endocrine cells stored PYY, Most of these cells also contained gluc agon. Subsequently, the endocrine cells comprised glucagon + PYY cells and glucagon + PYY + insulin cells, Later, cells storing either only insulin or insulin + PYY appeared. Quantitations of the relative numbe rs of these cell populations during development were consistent with a precursor role of triple-positive (insulin + glucagon + PYY) tells, M oreover, bromodeoxyuridine (BrdU) injections at E15.5 showed that a la rge percentage of triple-positive cells were in S-phase and therefore were actively dividing, whereas almost no pure insulin cells or insuli n + PYY cells synthesized DNA at this time, These results suggest that PYY-positive endocrine cells may represent precursors for mature isle t cells.