The central theme of this research proposal is to further elucidate the mechanism of insulin resistance in obesity and NIDDM, with particular emphasis on post-receptor defects in insulin's action on glucose disposal. To accomplish this, we plan a broadly based in vitro and in vivo approach. We will determine the in vivo Km and Vmax for overall glucose disposal in both obesity and NIDDM and will combine this with in vitro studies of adipocytes in which glucose transport Km and Vmax is assessed along with the number and distribution of cellular glucose carriers, the level of insulin mediator substance, and insulin receptor kinase activity. Detailed studies of insulin receptor structure, internalization, processing, and degradation will be conducted in cells from obese and NIDDM patients will also be treated with a 3 week period of CSII, to normalize glucose levels. After this, the effects of insuliln therapy on the various in vivo and vitro aspects of insulin resistance will be assessed by repeat studies. In this proposal we will also examine the mechanisms of various therapies such as insulin treatment, sulfonylurea treatment, and weight reduction in obese or NIDDM patients. We also propose that abnormalities in the kinetics of insulin action play a role in insulin resistance and plan to test this by measuring the rate of activation and deactivation of insulin's effects to stimulate glucose disposal and inhibit hepatic glucose production. The role of intermittant versus sustained hyperinsulinemia in causing post-receptor defects will also be assessed, and new methods to measure the rate of non-insulin mediated glucose disposal in vivo are proposed for NIDDM. We also plan to re-examine the Randle hypothesis by measuring the effects of elevated FFA levels on in vivo insulin action and the potential beneficial effects of medium chain triglycerides. Finally, the influence of CSII treatment on the therapeutic effects of sulfonylureas in NIDDM will be explored. Since insulin resistance is a major characteristic feature of obese and NIDDM patients, it is hoped that a better understanding of the in vivo and in vitro mechanisms underlying this metabolic abnormality will lead to better knowledge of the pathogenesis of these disorders, and a more rationale of therapeutic modalities.
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