An increased uptake of tryptophan in the brain may increase serotoninergic activity and recently has been suggested to be a cause of fatigue during prolonged exercise. The present study, therefore, investigates whether ingestion of tryptophan or the competing branched-chain amino acids (BCAAs) affect performance. Ten endurance-trained male athletes were studied during cycle exercise at 70-75% maximal power output, while ingesting, ad random and double-blind, drinks that contained 6% sucrose (control) or 6% sucrose supplemented with (1) tryptophan (3 g l-1), (2) a low dose of BCAA (6 g l-1) or (3) a high dose of BCAA (18 g l-1). 2. These treatments greatly increased the plasma concentration of the respective amino acids. Using the kinetic parameters of transport of human brain capillaries, BCAA supplements were estimated to reduce brain tryptophan uptake at exhaustion by 8-12%, while tryptophan ingestion caused a 7- to 20-fold increase. Exercise time to exhaustion was not different between treatments (122 +/- 3 min). 3. The data suggest that manipulation of tryptophan supply to the brain either has no additional effect upon serotoninergic activity during prolonged exhaustive exercise or that manipulation of serotoninergic activity functionally does not contribute to mechanisms of fatigue.
摘要
大脑中色氨酸摄取量增加可能会增强血清素能活性，最近有人提出这是长时间运动期间疲劳的一个原因。因此，本研究调查摄入色氨酸或竞争性支链氨基酸（BCAAs）是否会影响运动表现。对10名耐力训练的男性运动员进行了研究，他们在以最大输出功率的70 - 75%进行自行车运动时，随机且双盲地摄入含有6%蔗糖（对照）或补充了（1）色氨酸（3 g l-1）、（2）低剂量BCAA（6 g l-1）或（3）高剂量BCAA（18 g l-1）的蔗糖饮料。2. 这些处理极大地提高了相应氨基酸的血浆浓度。利用人脑毛细血管转运的动力学参数估计，补充BCAAs可使力竭时大脑色氨酸摄取量降低8 - 12%，而摄入色氨酸会使其增加7至20倍。各处理间力竭运动时间无差异（122 +/- 3分钟）。3. 数据表明，在长时间力竭运动期间，调控大脑色氨酸供应对血清素能活性要么没有额外影响，要么血清素能活性的调控在功能上对疲劳机制没有作用。
