Dallman P R, Spirito R A
J Clin Invest. 1972 Aug;51(8):2175-80. doi: 10.1172/JCI107024.
This study was designed to determine how the brain, in contrast to most other tissues, maintains an almost normal protein content during a period of dietary protein deficiency. Administration of leucine-(3)H to rats was started during a period of early development (6-18 days) which is characterized by disproportionately rapid brain growth; later (24-33 days) leucine-(14)C was administered, when brain growth diminishes but total body weight gain continues to be rapid. At 35 days of age the ratio of (3)H:(14)C in cerebrum, cerebellum, and brain stem protein averaged between 1.63 and 1.82. In skeletal muscle, liver, myocardium, and intestinal mucosa the mean (3)H:(14)C was 1.07 or less. Then, a diet containing either 26% or 3.4% protein was administered. In animals fed the 26% protein diet, (3)H:(14)C in the three brain segments remained essentially unchanged over a 42 day period. In contrast, in the 3.4% protein group (3)H:(14)C in brain decreased to values approaching those of other tissues in the body: cerebrum, 1.18; cerebellum, 1.20; and brain stem, 1.16. The results suggest that conservation of brain protein is not due entirely to the long life-span of its cellular components or to efficient reutilization of the products of protein catabolism but through utilization of amino acids from degradation of protein elsewhere in the body.
本研究旨在确定与大多数其他组织相比，大脑如何在膳食蛋白质缺乏期间维持几乎正常的蛋白质含量。在大脑发育早期（6 - 18天）开始给大鼠施用亮氨酸 -（3）H，此阶段大脑生长速度极快；之后（24 - 33天）施用亮氨酸 -（14）C，此时大脑生长减缓，但总体体重仍持续快速增加。在35日龄时，大脑、小脑和脑干蛋白质中（3）H：（14）C的平均比值在1.63至1.82之间。在骨骼肌、肝脏、心肌和肠黏膜中，平均（3）H：（14）C为1.07或更低。然后，给动物喂食含26%或3.4%蛋白质的饲料。在喂食26%蛋白质饲料的动物中，三个脑区的（3）H：（14）C在42天内基本保持不变。相比之下，在3.4%蛋白质组中，大脑中的（3）H：（14）C降至接近身体其他组织的值：大脑为1.18；小脑为1.20；脑干为1.16。结果表明，大脑蛋白质的保存并非完全归因于其细胞成分的长寿命或蛋白质分解产物的有效再利用，而是通过利用身体其他部位蛋白质降解产生的氨基酸。
