Hypoglycemia Associated Autonomic Failure in Type 1 DM, Q5

Overview

When a patient with Type 1 diabetes exercises, he or she is more prone to low blood sugar, or hypoglycemia. It is known that antecedent exercise can blunt defense responses, called counterregulatory responses to subsequent hypoglycemia in Type 1 DM, causing him or her to be vulnerable to another bout of hypoglycemia. Epinephrine is one of the important hormones in the defense of blood glucose during both exercise and hypoglycemia. We will test the hypothesis that antecedent exercise will blunt the metabolic, neuroendocrine and cardiovascular effects of subsequent epinephrine infusion in Type 1 DM.

We have recently performed studies to determine whether the critical metabolic actions of epinephrine are blunted in Type 1 DM. These studies have obvious clinical relevance because strategies aimed at increasing circulating levels of epinephrine will not be effective if the metabolic counterregulatory mechanisms (increased endogenous glucose production (EGP), increased lipolysis and reduced glucose uptake) of the hormone are also blunted. Epinephrine was infused to reach circulating levels of \~ 1000 pg/ml (This level of epinephrine is equivalent to values of the hormone observed during hypoglycemia of 50 mg/dl in healthy males and T1DM men with average glucose control) in groups of either intensively treated (HBA1C \< 7.0%), conventionally treated (HBA1C \> 9.0%) type 1 DM and age, weight matched healthy controls. In the intensively treated DM group, epinephrine's actions to increase EGP, lipolysis and to restrain glucose uptake were significantly reduced (\<60%). The mechanism for our finding needs to be determined. Our hypothesis is that antecedent exercise can cause repetitive activations of Autonomic-adrenomedullary responses that lead to downregulation of β-adrenoreceptor mechanisms. Therefore, the combination of blunted epinephrine effects, increased insulin action and reduced levels of the catecholamine might fully explain the vexing clinical question of post exercise hypoglycemia in Type 1 DM. In this application, we will test the hypothesis that antecedent exercise will blunt the metabolic, neuroendocrine and cardiovascular effects of subsequent epinephrine infusion in Type 1 DM.

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