Muscle glucose uptake of obese Zucker rats trained at two different intensities

Exercise training reduces the muscle insulin resistance of the obese Zucker rat. The purpose of the present study was to determine whether the magnitude of this training response is exercise intensity specific. Obese Zucker rats were randomly divided into sedentary (SED), low-intensity (LI), and high-intensity (HI) exercise groups. For the LI rats, exercise training consisted of running on a rodent treadmill at 18 m/min up an 8% grade for 90 min. Rats in the HI group ran at 24 m/min up an 8% grade for four 17-min bouts with 3 min between bouts. Both exercise groups performed the same amount of work and trained 5 days/wk for 7 wk. To evaluate muscle insulin resistance, rat hindlimbs were perfused for 30 min with perfusate containing 6 mM glucose (0.15 μCi of D-[¹⁴C(U)] glucose/ml) and either a maximal (10.0 mU/ml) or a submaximal (0.50 mU/ml) insulin concentration. Perfusions were performed 48-56 h after the last exercise bout and a 12-h fast. In the presence of 0.5 mU/ml insulin, the rate of muscle glucose uptake was found to be significantly faster for the HI (9.56 ± 0.66 μmol · h^-1 · g^-1) than for the LI (7.72 ± 0.65 μmol · h^-1 · g^-1) and SED (6.64 ± 0.44 μmol · h^-1 · g^-1) rats. The difference in glucose uptake between the LI and SED rats was not significant. In the presence of 10.0 mU/ml insulin, the rate of glucose uptake was significantly faster for the HI (16.43 ± 1.02 μmol · h^-1 · g^-1) than for the LI rats ( 13.76 ± 0.84 μmol · h^-1 · g^-1) and significantly faster for the LI than for the SED rats (11.02 ± 0.35 μmol · h^-1 ·g^-1). Rates of glucose oxidation and glucose incorporation into glycogen in the plantaris followed patterns similar to glucose uptake, whereas lactate production did not differ between treatment groups. The results suggest that the exercise-induced improvement in the muscle insulin resistance of the obese Zucker rat was due, in part, to an increase in insulin responsiveness and was exercise intensity specific.