More than 64% of US adults are overweight, with nearly 31% (over 61 million) meeting criteria for obesity. There is a clear link between obesity and development of diabetes, heart disease, many cancers, and depression. It is now clear that obesity primarily results from a genetic predisposition to become overweight coupled with behavioral changes and environmental factors that promote increased caloric intake and sedentary lifestyles. Thus, defining the physiological mechanisms that control food intake provides direction in the search for pathogenic mechanisms of obesity and strategies for prevention and treatment of obesity-related diseases. Glucagon-like peptide-1(7-36)-amide (called GLP-1) is a so-amino acid peptide produced by endocrine cells along the gut from stomach to rectum, pancreatic alpha-cells, and discrete populations of brain neurons in the nucleus of the solitary tract, adjacent dorsomedial medullary reticular formation, and olfactory bulb. In rodents, GLP-1 potently reduces food intake and body weight when given systemically or into the brain, and administration of the GLP-1 receptor antagonist exendin(9-39) into the brain increases food intake and body weight. Obese humans appear to have a blunted plasma GLP-1 response to food intake;yet low doses of GLP-1 decrease food intake similarly in lean and obese humans. These results suggest that GLP-1 may act physiologically to reduce food intake and body adiposity, and that insufficient production of GLP-1 may promote obesity. Food intake releases at least two forms of GLP-1 into the circulation: GLP-1 and GLP-1(7-36)-Gly;other predicted/detected GLP-1 forms in gut tissue and blood include GLP-1(7-36)-Gly- Arg-Arg, GLP-1(1-36)-amide, GLP-1(1-36)-Gly, and GLP-1(1-36)-Gly-Arg-Arg. Studies will use established rat models to test the hypotheses that GLP-1 form(s) secreted by the gut in response to a meal act as signal(s) to the brain to produce satiety and reduce adiposity, and that insufficient production and/or action of these signal(s) contribute to the production of obesity.
Specific aims are to: i) Determine whether GLP-1, when infused intravenously, is the most potent and efficacious GLP-1 form for reducing food intake. 2) Determine whether anorexigenic GLP-1 form(s) act synergistically with other putative satiety and adiposity regulatory factors [cholecystokinin, amylin, oxyntomodulin, peptide YY(3-36), leptin] to reduce food intake. 3) Use novel proteomic methods, antagonists of GLP-1 forms (receptor antagonist, immunoneutralizing antiserum), and abdominal vagal denervation to determine whether GLP-1 form(s) act through endocrine and/or paracrine control of vagal signaling from gut to brain to reduce food intake. 4) Determine whether production and/or action of anorexigenic GLP-1 form(s) are reduced in diet-induced obese rats. 5) Determine whether specific patterns of chronic administration of anorexigenic GLP-1 form(s), alone or in combination with the other putative satiety and adiposity regulatory factors, can produce a sustained reduction in daily food intake and adiposity in diet-induced obese rats.
