Counterregulatory deficits occur within 24 h of a single hypoglycemic episode in conscious, unrestrained, chronically cannulated mice

Abstract

Jacobson, Lauren, Tasneem Ansari, and Owen P. McGuinness. Counterregulatory deficits occur within 24 h of a single hypoglycemic episode in conscious, unrestrained, chronically cannulated mice. Am J Physiol Endocrinol Metab 290: E678 -E684, 2006; doi: 10.1152/ajpendo.00383.2005.-Hypoglycemia-induced counterregulatory failure is a dangerous complication of insulin use in diabetes mellitus. Controlled hypoglycemia studies in gene knockout models, which require the use of mice, would aid in identifying causes of defective counterregulation. Because stress can influence counterregulatory hormones and glucose homeostasis, we developed glucose clamps with remote blood sampling in conscious, unrestrained mice. Male C57BL/6 mice implanted with indwelling carotid artery and jugular vein catheters were subjected to 2 h of hyperinsulinemic glucose clamps 24 h apart, with a 6-h fast before each clamp. On day 1, blood glucose was maintained (euglycemia, 178 Ϯ 4 mg/dl) or decreased to 62 Ϯ 1 mg/dl (hypoglycemia) by insulin (20 mU ⅐ kg Ϫ1 ⅐ min Ϫ1 ) and variable glucose infusion. Donor blood was continuously infused to replace blood sample volume. Baseline plasma epinephrine (32 Ϯ 8 pg/ml), corticosterone (16.1 Ϯ 1.8 g/dl), and glucagon (35 Ϯ 3 pg/ml) were unchanged during euglycemia but increased significantly during hypoglycemia, with a glycemic threshold of ϳ80 mg/dl. On day 2, all mice underwent a hypoglycemic clamp (blood glucose, 64 Ϯ 1 mg/dl). Compared with mice that were euglycemic on day 1, previously hypoglycemic mice had significantly higher glucose requirements and significantly lower plasma glucagon and corticosterone (n ϭ 6/group) on day 2. Epinephrine tended to decrease, although not significantly, in repeatedly hypoglycemic mice. Pre-and post-clamp insulin levels were similar between groups. We conclude that counterregulatory responses to acute and repeated hypoglycemia in unrestrained, chronically cannulated mice reproduce aspects of counterregulation in humans, and that repeated hypoglycemia in mice is a useful model of counterregulatory failure.hypoglycemia-associated autonomic failure; hypoglycemia unawareness; catecholamines; norepinephrine; glucocorticoids HYPOGLYCEMIA-ASSOCIATED COUNTERREGULATORY FAILURE is an increasingly common complication of intensive insulin therapy and poses new obstacles to glucose control in insulindependent diabetes. Counterregulatory failure is evident as decreases in either the absolute level or the threshold for activation of sympathoadrenal, glucocorticoid, and glucagon responses to hypoglycemia (3). Of these responses, the glucagon and sympathoadrenal responses are the most critical because of the rapidity with which they are activated and serve to increase blood glucose (4). Counterregulatory failure is not unique to individuals with type 1 diabetes and can be demonstrated experimentally in nondiabetic subjects after only one to two episodes of hypoglycemia (5, 6). However, because type 1 diabetes patients lack the ability to decrease insulin and often lose hypoglycemia-in...

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] .…”

Hypothalamic ventromedial COUP-TFII protects against hypoglycemia-associated autonomic failure

“…4A). This phenotype is reminiscent of a defective CRR to insulin-induced hypoglycemia (31). In SF1-COUP-TFII mice, the more drastic drop in blood glucose following a single insulin injection is associated with a lower glucagon secretion 60 min after injection (Fig.…”

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

“…In mice, when blood glucose levels fall below ~80 mg/dl the counter-regulatory response to insulin is activated (Jacobson et al, 2006a). If a particular mouse model exhibits a defect in the counter-regulatory response, this could be misinterpreted as enhanced insulin action.…”