The main function of the Animal Metabolic Physiology Core is to teach and provide consultation on ex vivo and in vivo methods to investigate insulin and leptin action. Increasingly, the biologic roles of the products of newly discovered genes are being tested by transgenic over expression and gene knockout approaches. Thus, the need for characterization of new mouse models is growing. The Animal Metabolic Physiology Core is designed to meet the needs for characterization of rodent models that have alterations in glucose homeostasis, insulin action, leptin action, and/or body composition. The specific objectives of the Core are: 1) to teach: and 2) to provide consultation to investigators in designing and carrying out in vivo studies of insulin and leptin action, glucose homeostasis, lipid metabolism, and body composition and in vitro studies of insulin and leptin action, glucose transport and metabolism, and lipid metabolism. The Core also performs a limited number of these studies on selected mouse or rat models created by or obtained by investigators who are members of the Center. The services of the Core include ex vivo methods such as adipocyte isolation, and dissection andincubation of isolated skeletal muscles to study glucose transport, insulin signaling, leptin signaling, and glucose and fatty acid metabolism. The in vivo methods of insulin action and glucose homeostasis include insulin tolerance test, glucose tolerance test and signaling assays after insulin injection or infusion. The in vivo methods to investigate biological actions of leptin include measurement of food intake, energy expenditure and leptin signaling. The Core also provides several specialized pieces of equipment such as a dual energy x-ray absorptiometry (DEXA) scanner for non-invasive analysis of body composition and a Coulter Counter for counting adipocyte number. The Core has added consultation and teaching of new assays including leptin signaling in vivo and ex vivo, fatty acid oxidation in various tissues in vivo, lipogenesis and euglycemic-hyperinsulinemic clamp studies. Other new services include teaching how to dissect different regions of the hypothalamus for mechanistic studies related to obesity, food intake or energy balance and how to surgically place intravenous (iv), intraperitoneal (ip), and intrahypothalamic (ihp) catheters for the study of metabolism and signaling. The Core Director, Barbara B. Kahn, M.D., the Associate Core Director, Odile Peroni, Ph.D., and the other members of the Core (Research Associates Drs. Ed Hadro and Anna Lee) have extensive experience with the in vivo, ex vivo and in vitro assays offered by the Core. They are developing new assays for the characterization of new transgenic and knockout mouse models of insulin resistance and diabetes.