Roberts S A, Ball R O, Filler R M, Moore A M, Pencharz P B
Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada.
Pediatr Res. 1998 Dec;44(6):907-14. doi: 10.1203/00006450-199812000-00014.
Tyrosine is considered to be an indispensable dietary amino acid in the neonate, yet achieving adequate parenteral tyrosine intake is difficult due to its poor solubility. Increasing the supply of phenylalanine is the most common means of compensating for low tyrosine levels. Unfortunately, plasma phenylalanine concentrations are sometimes elevated in infants receiving high phenylalanine intake. This led us to study the phenylalanine and tyrosine metabolism in 16 neonates randomized to receive total parenteral nutrition with either a high or a moderate phenylalanine-containing amino acid solution. A primed, 24-h continuous stable isotope infusion of L-[1-13C]phenylalanine and L-[3,3-2H2]tyrosine was given to enable the measurement of phenylalanine and tyrosine kinetics. Results demonstrated that 1) phenylalanine hydroxylation was significantly greater in infants receiving high phenylalanine, 2) phenylalanine oxidation and percent dose oxidized was also significantly greater in infants receiving high phenylalanine, 3) apparent phenylalanine retention was greater in neonates receiving high phenylalanine, and 4) alternate catabolites of phenylalanine and tyrosine metabolism were significantly greater in infants receiving high phenylalanine compared with moderate phenylalanine. We conclude that neonates respond to increased parenteral phenylalanine intake by increasing their hydroxylation and oxidation rates. The greater oxidation of phenylalanine in infants receiving high phenylalanine in conjunction with the urinary excretion of alternate catabolites of phenylalanine and tyrosine suggests that the high phenylalanine intake may be in excess of needs. However, the lower apparent phenylalanine retention observed in infants receiving moderate phenylalanine suggests that the total aromatic amino acid level of moderate phenylalanine may be deficient for neonatal needs.
酪氨酸被认为是新生儿不可或缺的膳食氨基酸，但由于其溶解性差，难以实现充足的肠外酪氨酸摄入。增加苯丙氨酸供应是补偿低酪氨酸水平的最常见方法。不幸的是，接受高苯丙氨酸摄入的婴儿血浆苯丙氨酸浓度有时会升高。这促使我们对16名随机接受含高或中等苯丙氨酸的氨基酸溶液进行全肠外营养的新生儿的苯丙氨酸和酪氨酸代谢进行研究。给予一次负荷剂量后，连续24小时稳定输注L-[1-¹³C]苯丙氨酸和L-[3,3-²H₂]酪氨酸，以测量苯丙氨酸和酪氨酸动力学。结果表明：1）接受高苯丙氨酸的婴儿苯丙氨酸羟化作用明显更强；2）接受高苯丙氨酸的婴儿苯丙氨酸氧化及氧化剂量百分比也明显更高；3）接受高苯丙氨酸的新生儿苯丙氨酸表观潴留量更大；4）与中等苯丙氨酸组相比，接受高苯丙氨酸的婴儿苯丙氨酸和酪氨酸代谢的替代分解代谢产物明显更多。我们得出结论，新生儿通过提高其羟化和氧化速率来应对肠外苯丙氨酸摄入量的增加。接受高苯丙氨酸的婴儿中苯丙氨酸的更大氧化作用，以及苯丙氨酸和酪氨酸替代分解代谢产物的尿排泄表明，高苯丙氨酸摄入量可能超过需求。然而，接受中等苯丙氨酸的婴儿中观察到的较低苯丙氨酸表观潴留量表明，中等苯丙氨酸的总芳香族氨基酸水平可能无法满足新生儿的需求。
