Dissociation of in vitro sensitivities of glucose transport and antilipolysis to insulin in NIDDM
It is unclear from previous studies whether qualitative or only quantitative differences exist in insulin action in adipocytes obtained from obese subjects with non-insulin-dependent diabetes mellitus (NIDDM) when compared with equally nondiabetic subjects. In addition, the role of changes in insulin binding as a cause of insulin resistance in NIDDM is still controversial. We compared the sensitivities of glucose transport and antilipolysis to insulin and measured insulin binding in abdominal adipocytes obtained from 45 obese nondiabetic (% fat, 41 ?? 1), 25 obese diabetic (% fat, 40 ?? 1), and 15 nonobese (% fat, 30 ?? 1) female southwestern American Indians. Compared with the nonobese group, the sensitivities of glucose transport and antilipolysis were reduced in both the obese nondiabetic and obese diabetic groups. Compared with the obese nondiabetic subjects, the ED50 for stimultion of glucose transport was higher in the obese patients with NIDDM (171 ?? 38 vs. 92 ?? 10 pM, P lt; 0.005). In contrast, the Ed50s for antilipolysis were similar in obese diabetic patients (32 ?? 6 pM) and obese nondiabetic subjects (27 ?? 3 pM). No difference was found in insulin binding in patients with NIDDM when compared with the equally obese nondiabetic subjects. These data indicate 1) the mechanism of insulin resistance differs in NIDDM and obesity, and 2) the selective loss of insulin sensitivity in NIDDM precludes changes in insulin binding as a cause of insulin resistance in this disorder.