PANCREATIC ISLET CELLS IN THE NORMAL AND CoCl2-TREATED GUINEA-PIG. A FINE STRUCTURAL STUDY

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Abstract
SUMMARY: 1. The islets of Langerhans were studied by light and electron microscopy in the normal and cobalt chloride (CoCl2)-treated guinea-pig. 2. Within the guinea-pig islets, the α cells occur singly or in groups. The β cells are present in large majority and the α/β-cell ratio is normally 1:5. 3. In electron micrographs the α granules are smaller, more electron dense and more homogeneous than the β granules, many of which may have an eroded 'moth-eaten' appearance. 4. Scantily granulated forms of both α and β cells are common but in normal islets the agranular 'C' cells of Bensley (1911) were not identified. 5. Following a single intravenous injection of CoCl2 (25 mg./kg. body weight): (a) No adverse changes were detected in the α cells; in fact the staining for tryptophan by the post-coupled benzylidene method was more intense 2½ hr. after treatment. (b) By 24 hr. after injection many of the β cells appeared to be adversely affected as indicated by some degree of inter-membranous mitochondrial vacuolation, partial degranulation, cytoplasmic vacuolation and the appearance of cytoplasmic lipid droplets. (c) The exocrine tissue showed dilatation of its endoplasmic reticulum and a general reduction in the clear definition of cytoplasmic membranes in electron micrographs. 6. After two CoCl2 injections a reduced number of secretory granules was observed in many of the α cells, and in some of these cells degenerative changes similar to those reported in the β cells (5b above) could be detected. 7. In all CoCl2-treated guinea-pigs, the following additional cytological features were noted: (a) A preponderance of the small-sized over the larger secretory granules in many α cells. (b) Long double membranous sheets of granular endoplasmic reticulum in the α cells. (c) Short bristle-like processes extending into intercellular spaces from the surfaces of a few α cells. (d) The presence of cells lacking any specific secretory granules. These features are discussed. 8. The fine structure of the pancreatic vasomotor nerves is described and discussed.