Glucocorticoid-deficient corticotropin-releasing hormone knockout mice maintain glucose requirements but not autonomic responses during repeated hypoglycemia

Abstract

Glucocorticoids have been implicated in hypoglycemia-induced autonomic failure but also contribute to normal counterregulation. To determine the influence of normal and hypoglycemia-induced levels of glucocorticoids on counterregulatory responses to acute and repeated hypoglycemia, we compared plasma catecholamines, corticosterone, glucagon, and glucose requirements in male wild-type (WT) and glucocorticoid-deficient, corticotropin-releasing hormone knockout (CRH KO) mice. Conscious, chronically cannulated, unrestrained WT and CRH KO mice underwent a euglycemic (Prior Eu) or hypoglycemic clamp (Prior Hypo) on day 1 followed by a hypoglycemic clamp on day 2 (blood glucose both days, 65 +/- 1 mg/dl). Baseline epinephrine and glucagon were similar, and norepinephrine was elevated, in CRH KO vs. WT mice. CRH KO corticosterone was almost undetectable (<1.5 microg/dl) and unresponsive to hypoglycemia. CRH KO glucose requirements were significantly higher during day 1 hypoglycemia despite epinephrine and glucagon responses that were comparable to or greater than those in WT. Hyperinsulinemic euglycemia did not increase hormones or glucose requirements above baseline. On day 2, Prior Hypo WT had significantly higher glucose requirements and significantly lower corticosterone and glucagon responses. Prior Hypo and Prior Eu CRH KO mice had similar day 2 glucose requirements. However, Prior Hypo CRH KO mice had significantly lower day 2 epinephrine and norepinephrine vs. Prior Eu CRH KO and tended to have lower glucagon than on day 1. We conclude that glucocorticoid insufficiency in CRH KO mice correlates with 1) impaired counterregulation during acute hypoglycemia and 2) complex effects after repeated hypoglycemia, neither preventing decreased hormone responses nor worsening glucose requirements.

Loss of islet sympathetic nerves and impairment of glucagon secretion in the NOD mouse: relationship to invasive insulitis

“…This impairment is unlikely to be due to the anaesthesia and surgery used in our study because both the basal glucagon levels and the response to IIH in our non-diabetic controls were similar to those reported in conscious mice [28,29]. Our novel demonstration of an impaired glucagon response to IIH in diabetic NOD mice, coupled with those already published in BB diabetic rats [30] and in humans with type 1 diabetes [31,32], makes it clear that an early impairment of the glucagon response to IIH is a general feature of autoimmune diabetes.…”

Hyperinsulinemic-euglycemic Clamps in Conscious, Unrestrained Mice

“…Furthermore, elevated catecholamines resulting from tail sampling can impair insulin secretion and enhance glucagon secretion 22 . The insulin clamp protocol can also be modified to allow for glucose levels to fall to relative hypoglycemia to assess counter-regulatory response 2,23,24 . Arterial catheterization can also be used to assess the dynamics of glucose metabolism during exercise [25][26][27][28][29][30] .…”

Standard operating procedures for describing and performing metabolic tests of glucose homeostasis in mice

“…1, the hyperinsulinemic-hypoglycemic clamp, or hypoglycemic clamp, is a useful test of the counter-regulatory response to hypoglycemia (Jacobson et al, 2006a;Jacobson et al, 2006b;Berglund et al, 2008). The protocol for hypoglycemic clamps is identical to that of insulin clamps, except that a larger insulin infusion dose is used (typically 20 mU kg -1 minute -1…”