Hyperglycemia compensates for diet-induced insulin resistance in liver and skeletal muscle of rats

Abstract

High-fat and high-sucrose diets increase the contribution of gluconeogenesis to glucose appearance (glc Ra) under basal conditions. They also reduce insulin suppression of glc Ra and insulin-stimulated muscle glycogen synthesis under euglycemic, hyperinsulinemic conditions. The purpose of the present study was to determine whether these impairments influence liver and muscle glycogen synthesis under hyperglycemic, hyperinsulinemic conditions. Male rats were fed a high-sucrose, high-fat, or low-fat, starch control diet for either 1 ( n = 5–7/group) or 5 wk ( n = 5–6/group). Studies involved two 90-min periods. During the first, a basal period (BP), [6-3H]glucose was infused. In the second, a hyperglycemic period (HP), [6-3H]glucose, [6-14C]glucose, and unlabeled glucose were infused. Plasma glucose (BP: 111.2 ± 1.5 mg/dl; HP: 172.3 ± 1.5 mg/dl), insulin (BP: 2.5 ± 0.2 ng/ml; HP: 4.9 ± 0.3 ng/ml), and glucagon (BP: 81.8 ± 1.6 ng/l; HP: 74.0 ± 1.3 ng/l) concentrations were not significantly different among diet groups or with respect to time on diet. There were no significant differences among groups in the glucose infusion rate (mg · kg−1 · min−1) necessary to maintain arterial glucose concentrations at ∼170 mg/dl (pooled average: 6.4 ± 0.8 at 1 wk; 6.4 ± 0.7 at 5 wk), percent suppression of glc Ra (44.4 ± 7.8% at 1 wk; 63.2 ± 4.3% at 5 wk), tracer-estimated net liver glycogen synthesis (7.8 ± 1.3 μg · g liver−1 · min−1 at 1 wk; 10.5 ± 2.2 μg · g liver−1 · min−1at 5 wk), indirect pathway glycogen synthesis (3.7 ± 0.9 μg · g liver−1 · min−1 at 1 wk; 3.4 ± 0.9 μg · g liver−1 · min−1 at 5 wk), or tracer-estimated net muscle glycogenesis (1.0 ± 0.3 μg · g muscle−1 · min−1 at 1 wk; 1.6 ± 0.3 μg · g muscle−1 · min−1 at 5 wk). These data suggest that hyperglycemia compensates for diet-induced insulin resistance in both liver and skeletal muscle.