IMPAIRED INSULIN-MEDIATED SKELETAL-MUSCLE BLOOD-FLOW IN PATIENTS WITH NIDDM

Patients with non-insulin-dependent diabetes mellitus (NIDDM) exhibit decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Because IMGU is equal to the product of the arteriovenous glucose difference (AVG-DELTA) across and blood flow (F) into muscle (IMGU = AVG-DELTA x F), reduced tissue permeability (AVG-DELTA) and/or glucose and insulin delivery (F) can potentially lead to decreased IMGU. The components of skeletal muscle IMGU were studied in six obese NIDDM subjects (103 +/- 9 kg) and compared with those previously determined in six lean (weight 68 +/- 3 kg), and six obese (94 +/- 3 kg) with normal glucose tolerance. The insulin dose-response curves for whole body and leg muscle IMGU were constructed using the combined euglycemic clamp and leg balance techniques during sequential insulin infusions (range of serum insulin 130-80,000 pmol/L). In lean, obese, and NIDDM subjects, whole body IMGU, femoral AVG-DELTA, and leg IMGU increased in a dose-dependent fashion over the range of insulin with an ED50 of 400-500 pmol/L in lean, 1000-1200 pmol/L in obese, and 4000-7000 pmol/L in NIDDM subjects (P < 0.01 lean vs. obese and NIDDM). In lean and obese subjects, maximally effective insulin concentrations increased leg blood flow -2-fold from basal with an ED50 of 266 pmol/L and 957 pmol/L, respectively (P < 0.01 lean vs. obese). In contrast, leg F did not increase from the basal value in NIDDM subjects (2.7 +/- 0.1 vs. 3.5 +/- 0.5 dl/min, NS). In the physiological range of insulin concentrations NIDDM subjects had lower body IMGU, leg F, femoral AVG-DELTA, and leg IMGU than obese and lean subjects, but at maximally effective insulin concentrations, femoral AVG-DELTA did not differ between obese and NIDDM subjects. Thus, 1) both reduced skeletal muscle tissue permeability and blood flow are found in NIDDM subjects and 2) impaired insulin-mediated augmentation of skeletal muscle blood flow in obese NIDDM patients is due to the diabetic state per se and not to the obesity status. Whether reduced skeletal muscle blood flow is the result or the cause of insulin resistance in patients with NIDDM remains to be elucidated.