Functional and ultrastructural changes induced by short term ovariectomy on pancreatic islets.

The effect of short term ovariectomy and combined estrogen-progesterone treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that ovariectomy was followed by an enhanced glucose-induced insulin secretion, glucose oxidation, calcium uptake and insulin content together with striking changes at the ultrastructural level located only in the B cell population. They were represented by the appearance of broad cytoplasmic areas containing an homogeneous fine granular material, enclosing sometimes organelles, B secretory granules with their clear halo significantly enlarged and marked dilation of the rough endoplasmic reticulum. Conversely, in ovariectomized-rats supplemented with estrogen-progesterone, the insulin response as well as the above mentioned metabolic parameters return to normal control values. Although not completely, ultrastructural changes also showed a clear amelioration. On account of our results, we might suggest that insulin secretion is controlled, at least in part, by the circulating levels of estrogen and progesterone throughout their effect on pancreatic islet metabolism. The absence of this control over a short term period produces a reversible increment in B cell function and the appearance of important changes at the ultrastructural level.