Type 2 diabetes is a complex disease which is caused by a slow progression of decreased glucose tolerance, followed by hyperglycemia. it is of great interest to understand the complex patterns of changes in metabolic function which precede overt hyperglycemia. Three components which can contribute to glucose intolerance are insulin resistance, impaired B-cell function, and reduced glucose effectiveness. The latter process is the ability of glucose itself to enhance carbohydrate disposal and suppress endogenous glucose output. We have obtained data supporting the concept that in normal individuals B-cell function increases to compensate for insulin resistance caused by hereditary or environmental factors. In fact, the mathematical product of insulin sensitivity and insulin secretion is approximately constant. The mechanisms responsible for the hyperbolic relationship between insulin sensitivity and insulin secretion are studied in this proposal. The time course of changes in glucose tolerance and B-cell response will be monitored to elucidate the events which account for the hyperbolic interaction, and to identify the signals in blood which are responsible for this striking relationship. Whether a similar, but less efficient hyperbolic relationship can be maintained when B-cell function is impaired will be examined. Also, we will examine the importance of individual metabolic precesses to glucose effectiveness. The role of glucose production by liver or kidney, as well as glucose uptake by insulin independent and insulin dependent tissues will be assessed. Also examined will be the changes which take place in function of individual tissues when glucose effectiveness changes. These studies should provide an integrated picture of the means by which the intact organism maintains normal maintenance of glucose tolerance when small changes in B-cell function are imposed, and could well provide new insights into the pathogenesis and potential treatment targets for Type 2 diabetes and the prediabetic state.
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