EXPRESSION OF ISLET AMYLOID POLYPEPTIDE IN FETAL AND ADULT PORCINE AND HUMAN PANCREATIC-ISLET CELLS

The synthesis and intracellular localization of the putative hormone i slet amyloid polypeptide (IAPP) and its relation to insulin and glucag on during ontogenesis was investigated in fetal and adult porcine and human pancreatic islets. By means of ultrastructural immunogold immuno cytochemistry, it was revealed that IAPP is produced by the hormonally pluripotent endocrine stem cells from the earliest time point studied . IAPP was colocalized with insulin and glucagon in the immature and n ondifferentiated cell granules in both species. In adult man, highly i ntense IAPP immunoreactivity was found in beta-cell granules and, at l ower intensity, in delta-cell granules. Some alpha-cells also containe d a small amount of IAPP in their granules, and among these occasional granules displayed an intense immunoreactivity. In adult pig, IAPP wa s stored in quantity in beta-cell granules and in small amounts in gra nules of alpha- and delta-cells. It was difficult to determine the pre sence of IAPP in pancreatic polypeptide cells, because they were so se ldom seen in this material. It is concluded that, in both man and pig, fetal pancreatic islet stem cells synthesize and store IAPP together with insulin and glucagon. The storage in different types of cells and granules was not as predictable as that of the classical islet hormon es. The substance is more widely distributed within the pancreatic isl et cell types than are any of the other islet hormones, which presumab ly has functional implications.