Alterations in islet cell ultrastructure following streptozotocin-induced diabetes in the rat

The response of islet cells to streptozotocin-induced diabetes was investigated by transmission electron microscopy. Rats were given streptozotocin i.p. (100 mg/kg followed by another dose of 25 mg/kg 24 h later) and sacrificed after 10 days. Pancreata from rats with high serum glucose values (381-553 mg/100 ml) were selected for ultrastructural examination. Islets in these animals were smaller and much less frequent than those of control animals. Cell types were not always easily identifiable in diabetic animals: distinction between A and B cells was often difficult. Cells of some islets displayed diminished electron density and less structured cytoplasm, yet nuclei were not pyknotic. Such cells were usually deficient in secretion granules. A cells were least affected. Cells in the centers of some islets possessed multivesicular bodies, prominent dilated Golgi cisternae and secretory granules which were often pleomorphic. Nuclear envelopes of some peripheral islet cells were swollen and distended; mitochondria were enlarged and the rough endoplasmic reticulum prominent. Some islet cells retained features of B cells in spite of marked ultrastructural alterations. This diversity of morphological findings contrasts with the homogeneity of the population of streptozotocin-diabetic rats with respect to metabolic responses.