Morphology and endocrine production of cells in the islets of langerhans of the Chacma baboon

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Abstract
Biopsies of the pancreas head, tail, and uncinate regions of 6 Chacma baboons (Papio ursinus) were processed for ultrastructural and immunocytochemical (ICC) studies using avidin‐biotin peroxidase label for light microscopy (LM) and immunogold for electron microscopy (EM). Survey 0.5 μm sections of Spurrs resin embedded tissue revealed areas of suitable islets. Thin 100‐nm sections were then cut and stained from the osmicated blocks for ultrastructural studies. For ICC investigations, 1 μm sections were immunolabeled for LM before areas were selected for thin sectioning for ultrastructural immunolabeling. The baboon endocrine pancreas ultrastructure was found to be similar to that of other mammals with minor differences in islet and secretory granule size and shape and in electron opacity of the secretory granule cores. Insulin glucagon, somatostatin and pancreatic polypeptide (PP) producing cells were described. A small number of cells were seen to contain both glucagon and PP and some D cells were observed to contain a few granules with both the appearance and immunoreactivity of A cell secretory granules. Statistical analysis of 100 secretory granule diameters of each of the 4 cell types in 6 baboons revealed significant differences (p < 0.001) in size between all but those of the A and D cells. The insulin precursor subunit, C‐peptide, and the glucagon precursor, glicentin, were each found together with the final hormone product in their respective secretory granules. The precursors were often located toward the periphery of the secretory granule, suggesting that the conversion of precursor to active hormone may be membrane associated. A nonrandom topographical association was observed between A and D cells, suggesting a strong functional implication.