Insulin sensitivity of non-obese asymptomatic diabetics in vivo in relation to insulin responsiveness of their adipose tissue in vitro.

In twenty-four non-obese male subjects a 2-hour glucose infusion test (12 mg/kg/min) with initial bolus injection (0.33 g/kg) was performed as a test of carbohydrate tolerance. Sixteen individuals had a normal and eight a pathological carbohydrate tolerance (asymptomatic diabetes). All subjects received a one-hour insulin infusion (two 30-minutes periods of 8 or 16 mU/kg MC-Actrapid). After two days subcutaneous adipose tissue was removed from the abdominal wall by needle biopsy for characterization of insulin-stimulated (1-14C) glucose incorporation into triglycerides. Under in vivo conditions insulin provoked a decrease of blood glucose concentrations by 31 +/- 3.9% and 11.6 +/- 2.2% as well as of plasma free fatty acids levels by 60 +/- 4.6% and 37 +/- 6.8% in normal persons and asymptomatic diabetics, respectively (p less than 0.01). In vitro the insulin-stimulated incorporation of labeled glucose into triglycerides of adipose tissue was diminished in asymptomatic diabetics. Thus, the results indicate that both the in vivo insulin responsiveness and the in vitro insulin sensitivity of adipose tissue are reduced in early stages of diabetes. The findings suggest that changes in insulin target tissues are equally important in the development of carbohydrate intolerance in non-obese subjects.