Effects Of Puerarin On Plasma Membrane GLUT4 Content In Insulin-resistant Rat Skeletal Muscle

Objective: The peripheral insulin resistance, which can lead to hyperinsulinemia and impaired glucose tolerance, is a significant pathogenesis of Type 2 diabetes. Insulin resistance results largely from an impairment of insulin-stimulated glucose uptake into skeletal muscle, the major site of insulin-mediated glucose disposal. Early application of medication to insulin-resistant people prevents or delays the development of impaired glucose tolerance and insulin resistance in skeletal muscle. At present, the medication of insulin resistance is mainly concentrated on western medicine. But study of the traditional Chinese medicine in this field is very limited. Puerarin is monomer that extracted from the root of Pueraria lobata (Wild) Ohwi. Many clinical researches have suggested that Puerarin can ameliorate insulin resistance through various mechanisms. However, its post-receptor mechanism is yet unknown. Glucose transporter 4 (GLUT4) in plasma membrane, the main insulin-sensitive glucose transporter, mediates trans-membrane transport of glucose (the rate-limiting step of glucose metabolism) in skeletal muscle. It has been considered as an appropriate candidate for insulin resistance. In the present study, we have tested the hypothesis that Puerarin can alleviate insulin resistance and the effect of Puerarin is associated with increased cell-surface level of GLUT4 in insulin-resistant rat skeletal muscle.Methods: The rat model of insulin resistance was made by feeding Sprague-Dawley rat high-fat diet for 8 weeks. The animals were divided into three groups at random (ten for each group): group I: controls: fed chow diet for 12 weeks; group II: high-fat diet: fed high-fat diet for 12 weeks; group III: high-fat diet + Puerarin treatment: fed high-fat diet for 8 weeks and insulin-resistant rat model was formed. Then the rats were injected with 100mg Puerarin Injection per kg body weight through abdominal cavity once a day for 4 weeks. Measure fasting plasma glucose and fasting serum insulin levels before and after Puerarin treatment, respectively. Insulin treatment was achieved by intraperitoneal injection of insulin (10 unit insulin per kg body weight) 15 minute before killing the animals. The right hindlimb thigh skeletal muscle was rapidly dissected. Then the expression of GLUT4 protein in the plasma membrane from all the animals was assessed with western blot method.Results: High-fat diet for 8 weeks resulted in hyperinsulinemia, moderate hyperglycemia and loss of insulin sensitivity. Under insulin stimulus, the GLUT4 content in the plasma membrane in insulin-resistant rats was significantly lower (about53%) than that of controls (P<0.01). Puerarin Injection partly corrected fasting plasma glucose and fasting serum insulin levels, and increased the GLUT4 content in the plasma membrane by 1.18-fold in insulin-resistant rats skeletal muscle.Conclusion: High-fat diet can lead to the decrease of GLUT4 level in plasma membrane, which may partly result from impaired transport of GLUT4 in skeletal muscle. Puerarin Injection can ameliorate insulin resistance, and the mechanism may be involved in increased cell-surface level of GLUT4 through decreasing fasting plasma glucose and fasting serum insulin levels, improving GLUT4 trafficking and intracellular insulin signaling.