Light- and electron-microscopic studies on isolated bovine islets of Langerhans.

While several recent studies have focussed on the critical assessment of yield, purity and function of isolated islets, fine-structural investigations of isolated islets have been the subject of only a few studies. After intraductal injection of collagenase solution, the distended bovine pancreata were processed in a continuous digestion-filtration device, after which the purification of the islet suspension was accomplished by density gradient centrifugation. Purified islets were then prepared for light- and transmission electron-microscopic analysis. In semithin sections, no evidence of either connective tissue or exocrine tissue surrounding isolated islets was found. Endocrine cells exhibiting cytoplasmic granules were packed in clusters varying in size. In ultrathin sections, A-cells containing numerous secretory granules were distinctive; their cytoplasm contained conspicuous formations of rough endoplasmatic reticulum and juxtanuclear Golgi complexes. In the B-cells, the Golgi complexes were also prominent; these elements, however, were poor in endoplasmic reticulum and displayed characteristic B-cell granules surrounded by a halo. A few ultrastructurally heterogeneous cells were scattered among the identified cellular elements.