This project continues studies on counterregulatory hormone-insulin interactions in diabetes. The current proposal focuses on the mechanisms protecting the brain from hypoglycemia and how they are altered by insulin dependent diabetes (IDDM) and its limiting attempts at restoring euglycemia in IDDM. The hypoglycemic insulin clamp technique will be used to assess glycemic thresholds for counterregulation and impaired brain function (measured by neurophysiological and neurobehavioral tests). To evaluate our procedures, we will examine whether a) the duration of hypoglycemia effects hormonal or CNS endpoints; b) epinephrine itself influences measurements of CNS function, and c) hyperinsulinemia per se modulates glycemic thresholds. Conditions modulating glycemic thresholds during hypoglycemia will be evaluated including: 1) modulating glycemic thresholds during hypoglycemia will be evaluated including: 1) antecedent glycemic control of IDDM; 2) chronic hypoglycemia 3) opiate-blockade; and 4) age. These studies test the hypothesis that strict glycemic control of IDDM and recurrent hypoglycemia lower, whereas chronic hyperglycemia, opiate blockade, and age (childhood) raise glycemic thresholds. The islet clamp technique will be used to evaluate whether intensive insulin treatment of IDDM reduces the metabolic actions of epinephrine. The mechanisms underlying deranged glucagon secretion in IDDM will also be examined. Amino acid stimulated glucagon release will be assessed during euglycemia and hypoglycemia, at varying levels of hyperinsulinemia.
The aim i s to determine why strictly controlled IDDM patients fail to secrete glucagon in response to amino acids under conditions of hyperinsulinemic hypoglycemia, in marked contrast to normal subjects. In addition, the spontaneously diabetic BB rat will be used as a model of defective counterregulation in IDDM. We will determine at what stage in the early development of IDDM do impaired glucagon responses to hypoglycemia appear and whether defective hormonal responses in diabetic rats are ameliorated when hypoglycemia is produced by agents that do not simultaneously raise insulin levels (insulin-like growth factor I and mercaptopicolinic acid). Overall, these studies will provide clinically relevant data on the mechanisms underlying hypoglycemia during treatment of IDDM and the influence of antecedent glycemic control on brain function during reductions in circulating glucose. Such data are important for establishing therapeutic goals and for minimizing the risks of treatment of IDDM.
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