On the role of glucocorticoid in glucose-induced insulin secretion

To explore the role of endogenous glucocorticoid in insulin secretion, the plasma concentrations of insulin in the fasting state and in response to intravenous administration of glucose were determined in adrenalectomized and sham-adrenalectomized rats. Adrenalectomy produced a decrease in the fasting plasma insulin two days after the operation when there was found no change in the blood glucose levels. Likewise, plasma insulin response to glucose was clearly reduced in adrenalectomized rats, although there was no difference among the two groups in increment of the blood glucose after the glucose load. At this moment, a stimulatory action of insulin on glucose metabolism was rather decreased in the adipose tissue from the adrenalectomized rats when compared with that from the control rats. The pancreatic tissue from the adrenalectomized rats secreted much less amount of insulin in response to perifused glucose not only in the early phase but also in the second phase of release pattern. The pancreas from the adrenalectomized rats treated with dexamethasone showed the opposite changes. These findings support the hypothesis that the endogenous glucocorticoid may play a role in maintaining sensitivity of the B cell to insulinogenic stimuli.