The long term objective of this laboratory is to understand the mechanism of insulin action in the liver in normal and insulin resistant states, both in animal models and man.
The specific aim of this proposal is to study the mechanism of insulin resistance and disordered carbohydrate and lipid metabolism in uremia. The contribution of the liver to these processes is largely unknown and the liver is the most important target organ of insulin action and plays a central role in carbohydrate and lipid metabolism. Freshly isolated and primary cultures of rat hepatocytes from a rat model of severe chronic uremia are used to study these problems. In addition, a major new effort of this proposal is to perform similar studies using hepatocytes and adipocytes from uremic and non-uremic patients. Events close to the insulin binding site of the receptors, i.e., generation of the putative messenger of insulin action and phosphorylation of the insulin receptor, as well as the structure and processing of the receptor itself will be studied before the intracellular domain can be assigned as the site for the defect in uremia. Analytical and enzymatic methods will be used to ascertain if the carbohydrate intolerance of uremia is due to increased glucose production, decreased glucose utilization, or a combination of both. Although de novo lipid synthesis is decreased in uremia, the increased serum FFA may be esterified and then secreted as VLDL by the liver. This hypothesis will be directly tested to study the contribution of the liver in the hypertriglyceridemia of uremia. In an attempt to understand the relationship between carbohydrate and lipid metabolism in uremia, two important regulatory loci will be studied: (1) Pyruvate dehydrogenase activity, the critical enzyme link between these two major pathways; and (2) Fructose 2,6 bisphosphate level, a recently discovered key compound in the control of glucose metabolism. The study of the mechanism of these processes in the insulin resistant state of uremia may enhance our understanding of the high morbidity and mortality of these patients and perhaps help to develop a better therapeutic approach to their problems.
