Evidence for marked sensitivity to the antilipolytic action of insulin in obese maturity-onset diabetics

Changes in plasma free fatty acids (FFA) observed during oral glucose tolerance tests in 12 obese maturity-onset diabetic Pima Indians with insulin response to oral glucose averaging only 7 ± 19 μU/ml above fasting were compared to those of 11 obese nondiabetic Pima Indians and 10 obese nondiabetic Caucasions who had mean insulin responses of 252 ± 34 and 73 ± 18 μU/ml, respectively. Fasting free fatty acid levels in the diabetics were higher, but they showed decreases similar to controls (278 ± 55 versus 284 ± 32 for nondiabetic Pima controls and 262 ± 43 μeq/liter below fasting for nondiabetic Caucasions). Plasma glycerol levels showed decreases parallel to those of free fatty acids, indicating that the FFA changes in the diabetics were attributable to inhibition of lipolysis rather than to increased removal. During intravenous glucose tolerance tests (IVGTT) in these diabetics, insulin levels decreased initially and there was no decline in FFA. In a second group of less severe diabetics (N = 6), whose increments in insulin during intravenous glucose tolerance tests averaged 15 ± 4.1 μU/ml above fasting, FFA decreases were again comparable to Pima and Caucasion nondiabetics (214 ± 53, 234 ± 37, and 183 ± 51 μeq/liter below fasting, respectively). These findings demonstrate marked sensitivity to the antilipolytic effects of insulin in individuals considered to be resistant to its glucose-lowering action.