Gluconeogenesis and Glycogenolysis - Role and Regulation

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DESCRIPTION (provided by applicant): The objective of this application is to better understand the hormonal and neural regulation of glucose production (gluconeogenesis and glycogenolysis) in vivo in the normal and insulin resistant state. The specific aims are to understand 1) the physiologic relevance of brain insulin signaling in the control of hepatic glucose production, 2) the mechanisms by which the body defends itself against hypoglycemia through modulation of hormone secretion and action, and 3) the interplay between gluconeogenesis and glycogenolysis in determining hepatic glucose production in the insulin resistant state with a view to directing therapeutic intervention. Studies will be carried out in fasted conscious dogs prepared surgically and fitted with a variety of sampling and infusion catheters (e.g. adrenalectomy, catheters placed in the portal and hepatic veins, vertebral and carotid arteries, 3rd cerebral ventricle, etc.) as required by the protocol. Glucose metabolism will be assessed using A-V difference (liver, gut, hind limb) and tracer (3H-glucose) techniques. Gluconeogenesis and glycogenolysis will be determined using A-V difference and isotopic (2H2O,3H-glucose, 13C-alanine) methods. In addition, to explore molecular mechanisms of control, biopsies (liver, hypothalamus, muscle, fat, etc) will be taken for assessment of various cellular signaling cascades, mRNA expression, protein levels and enzyme activities. Hormonal levels will be controlled using somatostatin or adrenalectomy and hormone replacement. Neural mediators will be controlled using blocker infusion or surgical denervation. Substrate levels will be controlled by exogenous infusion or pharmacologic manipulation. The results from the proposed studies should enhance our understanding of the control of glucose production in vivo and thereby facilitate the development of solutions to metabolic problems evident in the diabetic and obese patient. PUBLIC HEALTH RELEVANCE: Overproduction of glucose by the liver is a major contributor to hyperglycemia in diabetes and may result from hepatic and central insulin resistance; this grant will address the mechanisms by which insulin regulates the liver. Low blood sugar following insulin treatment is the major limitation to tight control of glycemia in the individual with diabetes; this project will further elucidate the mechanisms by which the body defends itself against hypoglycemia. Diet induced obesity is associated with insulin resistance and is a major cause of diabetes; this project will explore the mechanisms involved in the development of insulin resistance and potential treatment strategies will be investigated.