The central theme of this research proposal is to continue our studies to further elucidate the mechanisms of insulin resistance in obesity and NIDDM, with particular emphasis on post-binding defects in insulin's action on glucose disposal. To accomplish this, we plan a broadly based combined in vitro and in vivo approach. We will carry out studies of the insulin receptor kinase using receptor from adipocytes and skeletal muscle from fact in NIDDM. We also propose detailed studies of the structure and function of adipocyte glucose transporters. These studies will assess the mechanisms of decreased glucose transporter intrinsic activity. We also plan to assess the in vivo Km and Vmax for overall whole body glucose disposal and more importantly, for skeletal muscle glucose disposal using the femoral arteriovenous catheterization technique. Using this arteriovenous difference technique we will also measure time course and dose response curves for insulin stimulated glucose uptake in normal and insulin resistant states. The dose response for extraction of insulin across the leg will also be measured to determine whether insulin leaves the leg plasma circulation via a receptor or non-receptor mediated process. Concomitant measurements of the volume of distribution of glucose and glucose transit time at different insulin and glucose transit time at different insulin and glucose levels will also be made. Finally, we have recently reported a polymorphism in the insulin receptor gene which is associated with the NIDDM phenotype and even more closely associated with insulin resistance. A series of family studies and further population studies are proposed to further explore the genetics of NIDDM and to assess the relationship between the presence of this insulin receptor gene polymorphism and in vivo and in vitro insulin resistance. Molecular studies are also planned to clone and express the receptor gene from a NIDDM subject homozygous for the polymorphism. Since insulin resistance is an important pathophysiologic feature of obesity and NIDDM, it is our hope that a better understanding of the basic mechanisms underlying this metabolic abnormality will lead to the better knowledge of the pathogenesis of these disorders and a more rationale design of therapeutic modalities.
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