Effects of Endurance Exercise and High-Fat Diet on Insulin Resistance and Ceramide Contents of Skeletal Muscle in Sprague-Dawley Rats

Background: We evaluated the effects of endurance exercise and a high-fat diet on insulin resistance and ceramide contents of skeletal muscle in Sprague-Dawley rats. Methods: We randomly divided 32 rats into four groups: control (CON, n=8), high fat diet (HP, n=8), exercise (Ex, 24 m/min for 2 hours, 5 days/wk, n=8), HF/Ex (n=8). After 4-week treatments, plasma lipid profiles, glucose and insulin concentrations were measured. The triglycerides (TG), ceramide, and glucose transporter 4 (GLUT-4) contents were measured in the skeletal muscle. The rate of glucose transport was determined under submaximal insulin concentration during the muscle incubation. Results: Free fatty acid levels were significantly higher in CON and HF than Ex (P=0.032). Plasma glucose levels in HF were significantly higher than the two Ex groups (P=0.002), and insulin levels were significantly higher in HF than in other three groups (P=0.021). Muscular TG concentrations were significantly higher in HF than CON and Ex and also in HF/Ex than Ex, respectively (P=0.005). Hepatic TG concentrations were significantly higher in HF than other three groups but Ex was significantly lower than HP/Ex (P=0.000). Muscular ceramide content in HF was significantly greater than that in either Ex or HF/Ex (P=0.031). GLUT-4 levels in CON arid HF were significantly lower than those in Ex and HF/Ex (P=0.009, P=0.003). The glucose transport rate in submaximal insulin concentration was lower in CON than in either Ex or HF/Ex (P=0.043), but not different from HF, Conclusion: This study suggests that high fat diet for 4 weeks selectively impairs insulin resistance, but not glucose transport rate, GLUT-4 and ceramide content in skeletal muscle per se. However, endurance exercise markedly affects the content of ceramide and insulin resistance in muscle.