Expression Of Protein Kinase B Of Skeletal Muscle In Insulin Resistant Rats

Objective: The protein kinase B (PKB/Akt) is a protein product coded by oncogene v-akt of retrovirus Akt-8. It plays a role in promotion of growth, proliferation and anti-apoptosis of cells. Especially, it has a great effects on carbohydrate metabolism. The pathway of phosphatidylinositol 3-kinase (PI3-K) is one of the mainly signal transduction of pathways which can conduct the action of insulin into interior of cells. As a kinase of Serine/Threonine which lies in the downstream of PI3-K, the PKB can regulate the metabolic response of insulin such as uptake of glucose, synthesis of glycogen, glycolysis and so on by influencing the signal transduction of insulin. So, we put forward the hypothesis that the expression and the activity of PKB are associated significantly with the formation and development of insulin resistance. In this study, we induced the rats to develop insulin resistance by feeding rats with high fat diet, then detected the changes of PKB expression induced by insulin in skeletal muscle of insulin resistant rats, revealed the relation between insulin resistance and expression of protein kinase B induced by insulin.Methods: 29 cases of healthy and clean male SD rats (body weight range from 140 grams to 180 grams) were randomly divided into group A (control) and group B (insulin resistance model). The rats were fed with normal diet in group A and high fat diet in group B. After 8 weeks, the rats in group B were randomly divided into groupB1 and group B2 again. The rats in group B1 continued to be fed with high fat diet, but in group B2 were given the intervention by fed with normal diet. The body weight, fasting blood sugar and plasma insulin of rats were measured in the different phases. After 4 weeks, all rats were sacrificed after 15 minutes when injected with regular insulin (10 units per kilogram weight) into abdominal cavity. The fat of epididymidis, mesentery, folded peritoneum and the fat pad of kidney were isolated as visceral fat mass. The ultrastructural changes of isolated skeletal muscles of rats in group A and group B1 were observed with electron microscope. The PKB expression of skeletal muscle induced by insulin in group A, B1, B2 were respectively detected with Western Immunoblotting.Results: The rats fed with continuous high fat diet (group B1) had a great increase in visceral fat mass and displayed obvious visceral obesity. Its fasting blood sugar increased slightly and plasma insulin increased significantly, but the insulin sensitivity indices decreased obviously, which showed that the rats in group B1 had developed obvious insulin resistance. Compared with normal control group, the skeletalmuscle of insulin resistance existed pathologic changs of ultrastructure and their expression of protein kinase B of skeletal muscle induced by insulin decreased significantly (OD values 8.24 + 0.11 vs 9.36 + 0.18, P<0.01 ) . However, insulin resistance of group B2 with normal diet intervention about 4 weeks was improved significantly, their expression of protein kinase B induced by insulin increased obviously compared with group B, (OD values 8.40 + 0.09 vs 8.24 + 0.11, P<0.05) , but decreased significantly compared with normal control group (OD values 8.40 + 0.09 vs 9.36 + 0.18, P<0.0I) .Conclusion: The results suggest that high fat feeding SD rats can develop obvious insulin resistance and pathologic changs of ultrastructure of skeletal muscle. Their total expression of protein kinase B of skeletal muscle is lower than normal. The reduction of PKB expression can weaken the action of insulin. This may be the one of reasons of developing insulin resistance.