Glucocorticoid-induced changes in insulin secretion related to the metabolism and ultrastructure of pancreatic islets.

The effect of adrenalectomy and dexamethasone-treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake, cAMP and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that adrenalectomy was followed by a decreased glucose-induced insulin secretion, glucose oxidation, calcium uptake, cAMP and insulin content without any remarkable change observed at the ultrastructural level. Conversely, adrenalectomized-rats supplemented with dexamethasone showed an increased glucose-induced insulin secretion, glucose oxidation, calcium uptake and cAMP content but a diminished islet insulin content. At the ultrastructural level, a clear picture of increased secretory activity was found, with diminished number of mature B granules and greater number of pale granules, while rough endoplasmic reticulum and Golgi complex frequently appeared hypertrophic. These changes were only observed in the B cells. On account of our results, we might suggest that insulin secretion is partially controlled by glucocorticoid circulating levels throughout their effect on pancreatic islet metabolism.