Block K P, Harper A E
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison 53706.
J Nutr. 1991 May;121(5):663-71. doi: 10.1093/jn/121.5.663.
Plasma and brain amino acid and plasma branched-chain alpha-keto acid (BCKA) concentrations were measured in rats fed diets containing high levels of individual amino and alpha-keto acids. Consumption of a low-protein (9% casein) diet high in leucine or alpha-ketoisocaproate depressed plasma concentrations of isoleucine and valine and their respective keto acids, alpha-keto-beta-methylvalerate and alpha-ketoisovalerate. High dietary levels of alpha-keto-beta-methylvalerate or alpha-ketoisovalerate (but not of isoleucine or valine) depressed plasma concentrations of the other BCKA and their respective branched-chain amino acids (BCAA). Consumption of a low protein, high phenylalanine diet depressed plasma concentrations of both BCAA and BCKA. Brain large neutral amino acid pools of rats fed all low-protein, high-amino acid diets were depleted. Consumption of diets high in individual BCKA increased brain concentrations of aromatic amino acids. In this study of rats allowed to feed for only 6 h/d, elevated brain phenylalanine concentration was associated with a significant depression of food intake, whereas elevated brain BCAA concentrations were not. Also, elevated plasma BCKA concentrations, comparable with those observed in maple syrup urine disease, were accompanied by elevations in concentrations of aromatic amino acids in brain but not in plasma.
在喂食含有高水平单个氨基酸和α-酮酸饮食的大鼠中，测量了血浆和脑氨基酸以及血浆支链α-酮酸（BCKA）的浓度。食用富含亮氨酸或α-酮异己酸的低蛋白（9%酪蛋白）饮食会降低异亮氨酸和缬氨酸及其各自酮酸α-酮-β-甲基戊酸和α-酮异戊酸的血浆浓度。高膳食水平的α-酮-β-甲基戊酸或α-酮异戊酸（但不是异亮氨酸或缬氨酸）会降低其他BCKA及其各自支链氨基酸（BCAA）的血浆浓度。食用低蛋白、高苯丙氨酸饮食会降低BCAA和BCKA的血浆浓度。喂食所有低蛋白、高氨基酸饮食的大鼠脑大中性氨基酸池被耗尽。食用富含单个BCKA的饮食会增加脑芳香族氨基酸的浓度。在这项仅允许大鼠每天进食6小时的研究中，脑苯丙氨酸浓度升高与食物摄入量显著降低有关，而脑BCAA浓度升高则不然。此外，与枫糖尿症中观察到的血浆BCKA浓度升高相伴的是，脑而非血浆中芳香族氨基酸浓度升高。
