Lou H C
John F Kennedy Institute, Glostrup, Denmark.
Acta Paediatr Suppl. 1994 Dec;407:86-8. doi: 10.1111/j.1651-2227.1994.tb13461.x.
Phenylalanine and tyrosine constitute the two initial steps in the biosynthesis of dopamine, which, in its turn, is the metabolic precursor of noradrenaline and adrenaline. The extracellular phenylalanine concentration influences brain function in phenylalanine deficiency (PHD) by decreased dopamine synthesis. It has been shown to induce EEG slowing, and prolonged the performance time on neuropsychological tests. The tyrosine concentration in the CNS is reduced in PHD, possibly implying insufficient substrate (= tyrosine) for catecholamine synthesis due to competition inhibition, for instance across the blood brain barrier. In experimental studies it has been shown that the synthesis and release of dopamine can be influenced by an increase in the availability of tyrosine. In PHD an extra dietary intake of three doses of tyrosine (160 mg/kg/24h) induced a shortening of reaction time and decreased variability, and in a double-blind crossover study a similar dose has been reported to induce an improvement on psychological tests. In a study with lower doses of tyrosine (110 mg/kg/24 h) no effect was found on reaction time tests. These findings need to be substantiated, and more detailed information should be obtained.
苯丙氨酸和酪氨酸是多巴胺生物合成的两个起始步骤，而多巴胺又是去甲肾上腺素和肾上腺素的代谢前体。细胞外苯丙氨酸浓度在苯丙氨酸缺乏症（PHD）中会因多巴胺合成减少而影响脑功能。研究表明，它会导致脑电图减慢，并延长神经心理学测试的表现时间。PHD患者中枢神经系统中的酪氨酸浓度降低，这可能意味着由于竞争抑制，例如穿过血脑屏障，儿茶酚胺合成的底物（即酪氨酸）不足。实验研究表明，酪氨酸可用性的增加会影响多巴胺的合成和释放。在PHD中，额外摄入三剂酪氨酸（160毫克/千克/24小时）可缩短反应时间并降低变异性，并且在一项双盲交叉研究中，据报道类似剂量可改善心理测试结果。在一项使用较低剂量酪氨酸（110毫克/千克/24小时）的研究中，未发现对反应时间测试有影响。这些发现需要得到证实，并且应该获取更详细的信息。
