Abstract
Glucocorticoids and corticotropin-releasing hormone (CRH) have been proposed to inhibit counterregulatory responses to recurrent hypoglycemia. We used the CRH knockout (CRH KO) mouse to test the hypothesis that combined CRH and glucocorticoid deficiency would prevent development of counterregulatory deficits after repeated hypoglycemia. To develop a mouse model of recurrent hypoglycemia, we first tested the effects of daily lente insulin injection on counterregulatory responses to acute hypoglycemia in male C57BL/6 mice. Treatment with up to 250 U/kg per day lente insulin resulted in significantly greater decreases in plasma glucose, suggestive of impaired counterregulation, after hypoglycemia induced by acute insulin injection. Plasma catecholamine responses to hypoglycemia in repeatedly hypoglycemic C57BL/6 mice were unexpectedly higher than in naive mice, which we interpreted as a compensatory response to the greater decreases in plasma glucose. Lente insulin doses had to be reduced (50-75 U/kg per day) for CRH KO mice to survive repeated hypoglycemia. Wild-type (WT) mice treated with 50 to 75 U/kg per day lente insulin exhibited enhanced sympathetic activity after hypoglycemia, resembling the compensatory responses associated with impaired glucose homeostasis in C57BL/6 mice treated with 250 U/kg per day lente insulin. During acute hypoglycemia, CRH KO mice maintained higher plasma glucose levels that correlated with higher plasma norepinephrine and greater glycogen mobilization. Recurrent hypoglycemia did not enhance liver glycogen depletion or the markedly impaired glucocorticoid and epinephrine responses to hypoglycemia in CRH KO mice. Previously hypoglycemic CRH KO mice also did not display the further increases in sympathetic activity that in WT mice were suggestive of compensation for impaired counterregulation. Despite the apparent resistance of CRH KO mice to the counterregulatory effects of repeated hypoglycemia, their greater mortality after hypoglycemia tolerated by WT mice indicates that combined CRH and glucocorticoid deficiency does not significantly improve counterregulation after repeated hypoglycemia.