ELECTRONMICROSCOPIC IDENTIFICATION OF DIFFERENT TYPES OF ISLET-CELLS IN PANCREAS OF NORMAL ALBINO RATS

1. A light microscopic comparison of silver-stained sections has permitted to identify in the electron microscope an argyrophilic A1 cell of the islets in albino-rats. The small secretory granules are very dense. They are located in bulging areas of the cisternae. 2. In the A2 cells numerous dense secretory granules are packed at the vascular pole. Granulolysis and granulopoiesis may be found at the same time in one cell. 3. At the stage of granulopoiesis, the B cells have a darker aspect. They contain many ribosomes and show numerous mitochondria but only very few dense granules. At the stage of secretory maturity, the B cells are clear. They contain scarce mitochondria but many dense granules. At the stage of granulolysis, the B cells are clear but there is a progressive disappearance of the granules. 4. The D cells are resting B cells and contain many ghost-like granular inclusions. Some isolated D-cells show a particularly well-developed Golgi complex with presecretory granules. 5. Transitional forms between A1 and A2 cells, as well as between B and D cells were observed. The question of the existence of transitional forms between A2 and B cells remains unsolved. 6. Acinar-islet-cells may lead to A1 cells, or more generally, to A2 cells. No transitional forms leading to B cells have been observed. © 1969 Springer-Verlag.