Peters J C, Harper A E
J Nutr. 1985 Mar;115(3):382-98. doi: 10.1093/jn/115.3.382.
Food intake, plasma and brain amino acid concentrations, liver amino acid catabolic enzyme activities, and whole-brain neurotransmitter and metabolite concentrations were measured in young rats adapted for 11 d to diets containing from 5 to 75% (in increments of 5%) casein. Food intake was depressed initially in rats fed diets containing 5, 10% or greater than 35% casein. For the duration of the experiment, food intakes of the groups fed the higher protein diets improved on successive days; the length and severity of the depression were proportional to the protein content of the diet fed. Rats fed low levels of protein grew poorly, and their food intake remained depressed. The gradual improvement in growth and food intake of rats fed diets containing more than 35% casein was accompanied by dramatic increases in the activities of serine-threonine dehydratase (SDH, EC 4.2.1.16) and glutamate-pyruvate aminotransferase (GPT, EC 2.6.1.1) in liver. The increase in amino acid catabolic activity was accompanied by decreases in the concentrations of most amino acids in plasma and brain. However, concentrations of branched-chain amino acids, in both plasma and brain, increased in direct proportion to the protein concentration of the diet fed. As a result of these reciprocal responses, the total concentration of indispensable amino acids in brain (IAA) was maintained within a narrow range of values, despite a sixfold range of protein intakes. Whole-brain concentrations of norepinephrine, dopamine and serotonin were not correlated with dietary protein concentration, total food intake or protein intake. Brain concentrations of homovanillic acid and 5-hydroxyindoleacetic acid were correlated inversely with protein intake and that of 3,4-dihydroxyphenylacetic acid was correlated directly with food intake. Protein intake appeared to be related to the animal's ability to maintain brain total IAA content between some upper and lower limits. Our results indicate that this was accomplished initially through downward adjustment of protein intake and subsequently through an increase in catabolic capacity for the amino acids.
对适应含5%至75%（以5%递增）酪蛋白饮食11天的幼鼠，测量了食物摄入量、血浆和脑内氨基酸浓度、肝脏氨基酸分解代谢酶活性以及全脑神经递质和代谢物浓度。最初，喂食含5%、10%或高于35%酪蛋白饮食的大鼠食物摄入量降低。在实验期间，喂食高蛋白饮食组的食物摄入量在连续几天有所改善；摄入量降低的时长和严重程度与所喂饮食的蛋白质含量成正比。喂食低蛋白水平的大鼠生长不良，其食物摄入量持续降低。喂食含高于35%酪蛋白饮食的大鼠，其生长和食物摄入量的逐渐改善伴随着肝脏中丝氨酸 - 苏氨酸脱水酶（SDH，EC 4.2.1.16）和谷氨酸 - 丙酮酸转氨酶（GPT，EC 2.6.1.1）活性的显著增加。氨基酸分解代谢活性的增加伴随着血浆和脑中大多数氨基酸浓度的降低。然而，血浆和脑中支链氨基酸的浓度与所喂饮食的蛋白质浓度成正比增加。由于这些相反的反应，尽管蛋白质摄入量有六倍的范围，但脑中必需氨基酸（IAA）的总浓度保持在狭窄的数值范围内。全脑中去甲肾上腺素、多巴胺和5 - 羟色胺的浓度与饮食蛋白质浓度、总食物摄入量或蛋白质摄入量均无相关性。脑内高香草酸和5 - 羟吲哚乙酸的浓度与蛋白质摄入量呈负相关，而3,4 - 二羟基苯乙酸的浓度与食物摄入量呈正相关。蛋白质摄入量似乎与动物将脑内总IAA含量维持在某些上限和下限之间的能力有关。我们的结果表明，这最初是通过下调蛋白质摄入量实现的，随后是通过增加氨基酸的分解代谢能力来完成的。
