The ultrastructural basis for the identification of cell types in the pancreatic islets. II. Rabbit, dog and opossum.

Abstract

The pancreatic islets of rabbit, dog and opossum have been studied by light and electron microscopy. Silver-positive cells in the rabbit are predominantly sandwiched between the peripheral A and central B cells, and by electron microscopy are identified as D cells. Pancreatic islets in the tail of the dog pancreas have A, B, and D (silver-positive) cells, but the islets in the uncinate process of the dog pancreas lack phosphotungstic acid hematoxylin-positive A cells. By electron microscopy the characteristic D cells are found in both tail and uncinate process, but A cells are confined to the tail islets, confirming the identification of cell types. A unique cell type termed the F cell is found in the dog uncinate islets and it is characterized by secretory granules of angular profiles. In the opossum, the A cells contain considerable amounts of glycogen demonstrable by both light and electron microscopy. A unique cell type is also present in the opossum islets termed an E cell (Thomas, 1937), which has large secretory granules (400–500 mμ). The physiological implications of a multiplicity of cell types in pancreatic islets is discussed.