Immediate in-vivo effect of corticosterone on glucose-induced insulin secretion in the rat

The effect of infused corticosterone (300 micrograms/h per kg body wt) on the concentrations of insulin in the plasma of the rat was examined (1) when glucose concentration was basal, (2) at standardized glucose levels attained by modulated glucose infusion and (3) in response to a standard or a modulated glucose pulse. There was no effect of corticosterone on the levels of plasma insulin when the glucose concentrations were either basal or raised in response to the standard pulse of glucose. However, when glucose was infused a significantly reduced plasma level of insulin was detected after 60 min when the glucocorticoid was present and this level remained significantly reduced after the modulated pulse of glucose. Thus the infusion of corticosterone leads to an acute depression of the concentrations of insulin in the plasma and of their response to a glucose pulse only when the hormone acts in the presence of a concentration of glucose in the plasma that is insulin-stimulatory.