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.
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.
|Coate, Katie C; Kraft, Guillaume; Moore, Mary Courtney et al. (2014) Hepatic glucose uptake and disposition during short-term high-fat vs. high-fructose feeding. Am J Physiol Endocrinol Metab 307:E151-60|
|Gifford, Aliya; Kullberg, Joel; Berglund, Johan et al. (2014) Canine body composition quantification using 3 tesla fat-water MRI. J Magn Reson Imaging 39:485-91|
|Coate, Katie C; Kraft, Guillaume; Irimia, Jose M et al. (2013) Portal vein glucose entry triggers a coordinated cellular response that potentiates hepatic glucose uptake and storage in normal but not high-fat/high-fructose-fed dogs. Diabetes 62:392-400|
|Ramnanan, Christopher J; Kraft, Guillaume; Smith, Marta S et al. (2013) Interaction between the central and peripheral effects of insulin in controlling hepatic glucose metabolism in the conscious dog. Diabetes 62:74-84|
|Ramnanan, C J; Edgerton, D S; Kraft, G et al. (2011) Physiologic action of glucagon on liver glucose metabolism. Diabetes Obes Metab 13 Suppl 1:118-25|
|Ramnanan, Christopher J; Saraswathi, Viswanathan; Smith, Marta S et al. (2011) Brain insulin action augments hepatic glycogen synthesis without suppressing glucose production or gluconeogenesis in dogs. J Clin Invest 121:3713-23|
|Coate, Katie Colbert; Kraft, Guillaume; Lautz, Margaret et al. (2011) A high-fat, high-fructose diet accelerates nutrient absorption and impairs net hepatic glucose uptake in response to a mixed meal in partially pancreatectomized dogs. J Nutr 141:1643-51|
|Edgerton, Dale S; Basu, Rita; Ramnanan, Christopher J et al. (2010) Effect of 11 beta-hydroxysteroid dehydrogenase-1 inhibition on hepatic glucose metabolism in the conscious dog. Am J Physiol Endocrinol Metab 298:E1019-26|
|Coate, Katie Colbert; Scott, Melanie; Farmer, Ben et al. (2010) Chronic consumption of a high-fat/high-fructose diet renders the liver incapable of net hepatic glucose uptake. Am J Physiol Endocrinol Metab 299:E887-98|
|Nelson, Robert H; Edgerton, Dale S; Basu, Rita et al. (2007) Triglyceride uptake and lipoprotein lipase-generated fatty acid spillover in the splanchnic bed of dogs. Diabetes 56:1850-5|
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