Insulin Resistance And β-cell Function In The Individuals With Impaired Glucose Regulation

ObjectiveImpaired glucose regulation (IGR) is meant to be an intermediate metabolic state between normal and diabetic glucose homeostasis. It includes three different subcategories: isolated impaired fasting glucose (IFG) , isolated impaired glucose tolerance (IGT) and combined IFG and IGT. In the individuals with IGR, how the degree of insulin resistance or β - cell dysfunction is? Are there differences between IFG and IGT? These questions remain to be elucidated. In particular, it is unknown what are the Chinese subjects characterized by? Therefore , we performed this cross - section study in use of hyperinsulin euglycemic clamp which is the internationally accepted as " golden standard" to determine insulin resistance and intravenous glucose tolerance test which is regarded as more liable index than those derived from OGTT data to evaluate early disturbance in insulin secretion.SubjectsAccording to oral 75g glucose tolerance test (OGTT) , 31 subjects in Shenyang were divided into four groups:normal glucose tolerance (NGT) group: FPG < 6. lmmol/l,2hPG <7. 8mmol/l;isolated impaired fasting glucose (I - IFG) group: FPG 6.1 ~6.9mmol/l, 2hPG<7.8mmol/l;isolated impaired glucose tolerance (I - IGT) group: FPG <6. lmmol/1, 2hPG 7.8~11.0mmol/l;combined impaired glucose tolerance ( C - IGT) group: FPG 6. 1 ~ 6. 9mmol/l,2hPG 7.8-11. Ommol/1.MethodsFor every subject, we performed the hyperinsulin euglycemic clamp test and the intravenous glucose tolerance test to evaluate the degree of insulin resistance and the insulin secretion of the first and the second phase, respectively.1. The euglycemic clamp test:After a 10 - hour fast, the subjects were given a continuous infusion of insulin (Novolin R, Denmark) at a constant speed of 40mU/m2( body surface area )/min and a variable infusion rate of 25% glucose adjusted by the plasma glucose level at the same time. During the period of the experiment, blood samples were taken at 5 — lOmin intervals for immediate determination of plasma glucose concentration by glucose oxidase analyzer(BIOSEN 5030,German) . The plasma glucose concentration was maintained at approximately 5mmol/l by the periodic adjustment of the glucose infusion rate. When getting into the steady state of constant euglycemia and glucose infusion rate, the glucose infusion rate (GIR) at that time was calculated as a quantitative index of insulin sensitivity.2. The intravenous glucose tolerance test;When fasting, 25% glucose (0.5g/kg) was infused intravenously in three minutes. Plasma samples for determination of plasma glucose and insulin level were taken before initiating infusion and at 1,3,5,10,30,60,120min after the infusion. Plasma glucose level was measured by the same method as above. Serum insulin level was determined by radio - immuoassay. Sum up the amount of insulin secretion at 1 - lOmin as the first - phase insulin secretion (1 st PH) to evaluate acute insulin secretion response, and 30 - 120min as the second -phase insulin secretion (2 nd PH).ResultsInsulin resistance - GIR...