Ontogeny of rat pancreatic polypeptide (PP) cells.

Cells storing pancreatic polypeptide (PP) appear in rat pancreas at the time of parturition, much later than insulin and glucagon cells. At this stage, the pancreatic polypeptide (PP) cells occur scattered in the exocrine parenchyma and in the islets. Subsequently, 5-7 days postnatally, an abrupt increase in the number of PP cells occurs. At this stage, they are fairly numerous in the islets and comparatively rare in the exocrine parenchyma. Not until 8-10 days after birth is the number of PP cells similar to that in the adult pancreas. A few PP cells were seen in the antral mucosa during the first 10 days after birth. They were not seen elsewhere in the gut.