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1 Department of Internal Medicine and Endocrinology, and 2 Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520
Individuals with type 1 diabetes
demonstrate a hypoglycemia-specific defect in glucagon secretion. To
determine whether intraislet hyperinsulinemia plays a role in the
genesis of this defect, glucagon-secretory responses to moderate
hypoglycemia induced by either insulin or a novel combination of the
noninsulin glucose-lowering agents 5-aminoimidazole-4-carboxamide
(AICAR) and phlorizin were compared in diabetic BB rats (an
animal model of type 1 diabetes) and nondiabetic BB rats. The
phlorizin-AICAR combination was able to induce moderate and equivalent
hypoglycemia in both diabetic and nondiabetic BB rats in the absence of
marked hyperinsulinemia. Diabetic BB rats demonstrated impaired
glucagon and epinephrine responses during insulin-induced hypoglycemia
compared with nondiabetic rats. In contrast, both glucagon (9- to
10-fold increase) and epinephrine (5- to 6-fold increase) responses
were markedly improved during phlorizin-AICAR hypoglycemia. Combining
phlorizin, AICAR, and insulin attenuated the glucagon response to
hypoglycemia by 70% in the diabetic BB rat. Phlorizin plus AICAR had
no effect on counterregulatory hormones under euglycemic conditions. We
conclude that
-cell glucagon secretion in response to hypoglycemia
is not defective if intraislet hyperinsulinemia is prevented. This suggests that exogenous insulin plays a pivotal role in the etiology of
this defect.
type 1 diabetes; counterregulation; epinephrine; insulin; 5-aminoimadazole-4-carboxamide; adenosine 5'-monophosphate-activated protein kinase
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