Sucrose-induced insulin resistance in the rat: modulation by exercise and diet

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Abstract
Isocaloric substitution of sucrose for starch results in hyperinsulinemia and deterioration of glucose tolerance, suggesting a loss of insulin sensitivity. In this study we have quantitated the insulin resistance which develops with sucrose feeding, and evaluated the ability of dietary fiber, or an increase in skeletal muscle activity, to inhibit, or even prevent, the detrimental effect of sucrose feeding on in vivo insulin action. Thus, 6-wk-old rats were fed one of the following regimens for three weeks: a 64% cornstarch diet (C), a 32% cornstarch + 32% sucrose diet (S), the (S) diet containing added wheat bran fiber (S/F), and the (S) diet given to rats running spontaneously in exercise wheel cages (S/ET). Insulin sensitivity was evaluated by comparing steady-state plasma glucose (SSPG) concentrations at constant plasma insulin levels ∼70 µU/ml attained during the continuous infusion of epinephrine (0.08 µg/kg/min), propranolol (1.7 µg/kg/min), glucose (8 mg/kg/min), and insulin (2.5 mU/kg/min) to each experimental group. The results show that rats fed the S diet had a significant increase (p < 0.01) in mean (± SEM) SSPG concentration compared with rats fed the C diet (255 ± 14 versus 165 ± 3 mg/dl). SSPG concentrations, although lower (p < 0.05) in rats fed S/F (205 ± 8 mg/dl), were still higher (p < 0.05) than the C levels (165 ± 3 mg/dl). However, S/ET completely inhibited the increase in SSPG concentration seen in rats fed S and the values were actually lower (p < 0.05) than in rats fed C (100 ± 10 versus 165 ± 3 mg/dl). In conclusion 1) sucrose feeding results in a loss of insulin sensitivity in normal rats; 2) addition of fiber attenuates, but does not completely prevent, the loss of insulin sensitivity associated with feeding sucrose; 3) exercise training prevents the loss of insulin sensitivity seen in sucrose-fed rats, and actually improves glucose uptake beyond that seen in the control group. These results document the profound effect of environmental factors on in vivo insulin action.