Insulin sensitivity of adipose tissue in vitro and the response to exogenous insulin in obese human subjects.

The effect of varying concentrations of insulin on 1-14C-glucose conversion to 14CO2 was measured in subcutaneous adipose tissue samples obtained from 16 obese human subjects (10 nondiabetic, 6 diabetic). An index of insulin sensitivity in vitro, Kins, was calculated as the concentration of insulin stimulating one-half maximal 14CO2 production. An index of insulin sensitivity in vivo, Kitt, was calculated as the rate constant for decrease in blood glucose after rapid intravenous administration of 0.05 U/kg insulin. There was, over-all, a significant correlation between Kins and Kitt, indicating that insulin sensitivity of 1-14C-glucose oxidation by adipose tissue in vitro reflects the general state of sensitivity of glucose metabolism to insulin in vivo in obese human subjects. The mean values for both Kins and Kitt in the nondiabetic subjects were significantly different from those in the diabetic subjects, indicating greater sensitivity to insulin in the former group. The nondiabetic group was also distinguished by a significantly greater plasma insulin:blood glucose ratio in the oral glucose tolerance test. These results support the view that tissue insulin sensitivity as well as pancreatic beta cell response play an important role in determining glucose tolerance in obesity.