Adibi S A
Metabolism. 1976 Nov;25(11):1287-302. doi: 10.1016/s0026-0495(76)80012-1.
Plasma concentrations of the branched-chain amino acids (leucine, isoleucine, and valine) are more prominently affected than the concentrations of other amino acids by changes in dietary-caloric, protein, fat, and carbohydrate-intake in man. For example, within a day of starvation or protein deprivation, there are increases or decreases, respectively, in concentrations of these amino acids in the plasma of healthy human volunteers. The cellular mechanisms of these changes have been investigated in rats, since the changes in the plasma branched-chain amino acid concentrations in response to the previously stated dietary alterations are similar to those found in man. Among the tissues studied (liver, skeletal muscle, heart, kidney, and intestine) only liver and the skeletal muscle exhibit changes in branched-chain amino acid concentrations in response to dietary alteation. Changes in plasma concentrations appear to reflect more intimately those of the muscle than theliver. After 8 days of starvation, there is a 25% decrease in the muscle protein, but after 8 days of protein deprivation, there is no significant change in the muscle mass. Increases in concentrations of branched-chain amino acids in the muscle are much smaller than the amounts of these amino acids lost as protein constituents form the muscle during fasting. Changes in tissue transport, transamination, oxidation, or metabolic conversions of branched-chain amino acids in tissues. It is concluded that increased muscle protein breakdown, which provides substrates for enhanced gluconeogenesis in the liver and enhanced branched-chain amino acid oxidation in the muscle, is the major mechanism of hyperbranched-chain aminoacdemia in starvation. On the other hand, the principal factors in the development of hypobranched-chain aminoacidemia during protein deprivation are absence of exogenous amino acids as well as curtailed muscle protein breakdown.
与其他氨基酸浓度相比，人体饮食热量、蛋白质、脂肪和碳水化合物摄入量的变化对支链氨基酸（亮氨酸、异亮氨酸和缬氨酸）血浆浓度的影响更为显著。例如，在饥饿或蛋白质缺乏的一天内，健康人类志愿者血浆中这些氨基酸的浓度会分别升高或降低。由于大鼠对上述饮食变化的反应中血浆支链氨基酸浓度的变化与人相似，因此已经在大鼠中研究了这些变化的细胞机制。在所研究的组织（肝脏、骨骼肌、心脏、肾脏和肠道）中，只有肝脏和骨骼肌会因饮食改变而出现支链氨基酸浓度的变化。血浆浓度的变化似乎更密切地反映了肌肉而非肝脏的变化。饥饿8天后，肌肉蛋白减少25%，但蛋白质缺乏8天后，肌肉质量没有显著变化。肌肉中支链氨基酸浓度的增加远小于禁食期间作为蛋白质成分从肌肉中流失的这些氨基酸的量。组织中支链氨基酸的转运、转氨作用、氧化或代谢转化发生了变化。得出的结论是，肌肉蛋白分解增加是饥饿时高支链氨基酸血症的主要机制，它为肝脏中增强的糖异生和肌肉中增强的支链氨基酸氧化提供底物。另一方面，蛋白质缺乏期间低支链氨基酸血症发生的主要因素是缺乏外源性氨基酸以及肌肉蛋白分解减少。
