Iakovou D, Linardou A, Philippides H, Chomatas H, Palaiologos G
Prog Clin Biol Res. 1982;102 Pt C:303-16.
Glucose is the major fuel of the adult brain under normal conditions. The most abundant free amino acids of the brain are: Glutamate, taurine N-acetylaspartate, glutamine, aspartate and 4-aminobutyrate. Deprivation of glucose from the incubation medium of brain cortex slices decreases mainly glutamate and glutamine content. Substitution of pyruvate for glucose maintains the content of aspartate and glutamate but not of glutamine. Therefore the entire glucose molecule is indispensable for the maintenance of the glutamine content. When branched chain amino acids, (BCAA), leucine, isoleucine and valine (0.5 mM) are added to the incubation medium in the presence of glucose the content of glutamine only is increased, all other amino acids are decreased. This suggests that BCAA spare protein as in muscle and produce glutamine. Branched chain amino acids in the presence of pyruvate do not spare protein but they still produce glutamine. Furthermore it seems that they potentiate the protein sparing effect of glucose in brain. In all these experiments glutamate and aspartate content in the incubation medium ranges from 3-10% of their total content (tissue plus media). On the other hand 40-60% of each of the other amino acids is found outside. The presence of 3-hydroxybutyrate and glucose in the incubation medium of brain cortex slices from normal rats spares protein but can maintain constant the content of glutamate, aspartate and glutamine. In addition 3-hydroxybutyrate blocks the release into the medium of glutamate and aspartate.
在正常情况下，葡萄糖是成人大脑的主要燃料。大脑中最丰富的游离氨基酸有：谷氨酸、牛磺酸、N - 乙酰天冬氨酸、谷氨酰胺、天冬氨酸和4 - 氨基丁酸。从大脑皮层切片的孵育培养基中去除葡萄糖主要会降低谷氨酸和谷氨酰胺的含量。用丙酮酸替代葡萄糖可维持天冬氨酸和谷氨酸的含量，但不能维持谷氨酰胺的含量。因此，整个葡萄糖分子对于维持谷氨酰胺含量是不可或缺的。当在有葡萄糖存在的情况下，将支链氨基酸（BCAA）、亮氨酸、异亮氨酸和缬氨酸（0.5 mM）添加到孵育培养基中时，只有谷氨酰胺的含量增加，其他所有氨基酸的含量都降低。这表明支链氨基酸在大脑中如同在肌肉中一样节省蛋白质并产生谷氨酰胺。在有丙酮酸存在的情况下，支链氨基酸不能节省蛋白质，但它们仍然会产生谷氨酰胺。此外，它们似乎还能增强葡萄糖在大脑中的蛋白质节省作用。在所有这些实验中，孵育培养基中谷氨酸和天冬氨酸的含量占其总含量（组织加培养基）的3 - 10%。另一方面，其他每种氨基酸有40 - 60%存在于细胞外。在正常大鼠大脑皮层切片的孵育培养基中添加3 - 羟基丁酸和葡萄糖可节省蛋白质，但能使谷氨酸、天冬氨酸和谷氨酰胺的含量保持恒定。此外，3 - 羟基丁酸会阻止谷氨酸和天冬氨酸释放到培养基中。
