Effects of amino acid supplementation and exercise on muscle protein synthesis

支链氨基酸(BCAA)具有多种生理功能。许多研究者关注支链氨基酸的功能之一，即氨基酸可能有效地对抗运动引起的肌肉酸痛和损伤。我们研究了补充5g支链氨基酸对深蹲运动引起的延迟性肌肉酸痛(DOMS)的影响，发现运动前15分钟摄入支链氨基酸显著降低了DOMS，这表明支链氨基酸作为运动补充是有用的。在另一项研究中，我们观察到氯贝特促进大鼠体内支链氨基酸的分解代谢可能会减少肝脏蛋白质的合成。在使用C2C12培养的肌肉细胞的实验中也得到了类似的观察结果。这些发现提示支链氨基酸是调节蛋白质合成的重要因素，一般认为支链氨基酸的分解代谢是由糖尿病促进的。在之前报道的论文中，只考虑了1型糖尿病，而几乎没有关于2型糖尿病的报告。在我们的研究中，通过测定支链氨基酸分解代谢途径中限速酶--支链α-酮酸脱氢酶复合体的肝脏活性来检测支链氨基酸的分解状态，并检测了支链氨基酸对酶活性的影响。以OLETF大鼠作为2型糖尿病动物模型，OLETF大鼠肝脏BCKDH复合体活性明显低于正常对照组，提示2型糖尿病对BCAA分解代谢有下调作用。补充BCAA可上调OLETF大鼠肝脏BCKDH复合体活性分析的BCAA分解代谢状态。这些发现表明支链氨基酸可能具有改善2型糖尿病病情的潜力。

Branched-chain amino acids(BCAAs)have a number of physiological functions. Many researchers pay attention to one of the BCAA functions that the amino acids may be effective against the muscle soreness and damage induced by exercise. We examined effects of 5 g BCAA supplementation on delayed-onset muscle soreness (DOMS) induced by squat exercise and found that BCAA ingestion 15 min before exercise significantly reduced DOMS, suggesting usefulness of BCAAs as a supplement for sports.In another study, we observed that promotion of the BCAA catabolism by administration of clofibrate into rats may decrease the hepatic protein synthesis. The similar observations were obtained in the experiment using C2C12 cultured muscle cells. These findings suggest that BCAAs are important factors in regulation of the protein synthesis.It is generally believed that BCAA catabolism is promoted by diabetes mellitus. In the papers reported previously, only type-1 diabetes was considered and almost no reports concerning type-2 diabetes are available. In our study, the BCAA catabolic state was examined by measuring the hepatic activity of the rate-limiting enzyme in the BCAA catabolic pathway, branched-chain α-keto acid dehydrogenase (BCKDH) complex, and effects of BCAA supplementation on the enzyme activity was also examined. OLETF rats are used as a type-2 diabetic animal model Hepatic BCKDH complex activity was significantly lower in OLETF rats than in normal control rats, suggesting that the BCAA catabolism is downregulated by type-2 diabetes. It was also found that the BCAA catabolic state analyzed from hepatic BCKDH complex activity was upregulated by BCAA supplementation in OLETF rats. These findings suggest that BCAAs may have a potential for improving the type 2-diabetic conditions.