Study on the mechanisms responsible for improvements of glucose and amino acid metabolism by exercise

众所周知，运动在保持和/或促进健康方面有有益的效果。然而，运动效果的机制是有限的阐明。在这项研究中，我们研究了衰老和运动训练对胰岛素信号级联反应中酶的基因表达和蛋白质含量的影响。利用大鼠的实验结果表明，运动训练通过维持骨骼肌中胰岛素受体底物-1(IRS-1)和磷脂酰肌醇3-激酶(PI3-K)的高水平蛋白以及IRS-1的基因表达来抑制由衰老引起的胰岛素抵抗。葡萄糖是所有哺乳动物细胞的主要能量来源。细胞内的葡萄糖代谢受两种酶的调节：葡萄糖转运蛋白IV(GLUT-IV)和丙酮酸脱氢酶复合体(PDC)，前者催化细胞内葡萄糖的摄取，后者位于糖酵解和柠檬酸循环的连接处。GLUT-IV含量和PDC活性随胰岛素敏感性降低而降低。由于运动训练可增加胰岛素敏感性和促进葡萄糖代谢，我们研究了运动训练对大鼠骨骼肌这些参数的影响。本研究结果表明，运动训练通过增加骨骼肌中GLUT-IV含量和PDC活性来增加葡萄糖代谢，支链氨基酸代谢受限速酶支链α-酮酸脱氢酶复合体的调节。我们检测了运动训练对糖尿病大鼠肝脏BCKDC活性和基因表达的影响，发现运动训练抑制了糖尿病大鼠肝脏BCKDC活性和基因表达的增加，提示糖尿病对支链氨基酸分解代谢的抑制作用增强。

It is well known that exercise has a beneficial effect in keeping and/or promoting health. However, the mechanisms responsible for the effects of exercise are limitedly elucidated. In this study, we examined effects of ageing and exercise training on gene expression and protein contents of the enzymes in the insulin signaling cascade. The results obtained using rats suggest that insulin resistance caused by ageing was suppressed by exercise training through sustaining the high levels of proteins of insulin receptor substrate-1 (IRS- 1) and phosphatidylinositol 3-kinase (PI3-kinase), and gene expression of IRS-1 in skeletal muscle.Glucose is a major source of energy for all of the mammalian cells. The glucose metabolism in the cells is regulated by two enzymes: glucose transporter-IV (Glut-IV) catalyzing glucose uptake into the cells and pyruvate dehydrogenase complex (PDC) which located at the position connecting between glycolysis and citric acid cycle. The Glut-IV content and PDC activities decrease in association with decreasing the insulin sensitivity. Since it has been reported that exercise training increases insulin sensitivity and promotes glucose metabolism, we examined effects of exercise training on these parameters in rat skeletal muscle. The results in the present study suggest that exercise training increases glucose metabolism by increasing Glut-IV content and PDC activity in the skeletal muscle.Branched-chain amino acid metabolism is regulated by the rate-limiting enzyme branched-chain α-keto acid dehydrogenase complex (BCKDC). We examined exercise training on activity and gene expression of hepatic BCKDC in diabetic rats, and found that exercise training suppressed the increases in activity and gene expression of hepatic BCKDC in the rats, suggesting suppression of branched-chain amino acid catabolism increased by diabetes.