OBJECTIVE. Optimal nutrition is of utmost importance for the preterm infant's later health and developmental outcome. Amino acid requirements for preterm infants differ from those for term and older infants, because growth rates differ. Some nonessential amino acids, however, cannot be sufficiently synthesized endogenously. Cyst(e)ine is supposed to be such a conditionally essential amino acid in preterm infants. The objective of this study was to determine, at 32 and 35 weeks’ postmenstrual age, cyst(e)ine requirements in fully enterally fed very low birth weight preterm infants with gestational ages of 29 weeks.METHODS. Infants were randomly assigned to 1 of the 5 graded cystine test diets that contained generous amounts of methionine. Cyst(e)ine requirement was determined with the indicator amino acid oxidation technique ([1-13C]phenylalanine) after 24-hour adaptation.RESULTS. Fractional [1-13C]phenylalanine oxidation was established in 47 very low birth weight preterm infants (mean gestational age: 28 weeks ± 1 week SD; birth weight: 1.07 kg ± 0.21 kg SD). Increase in dietary cyst(e)ine intake did not result in a decrease in fractional [1-13C]phenylalanine oxidation.CONCLUSIONS. These data do not support the hypothesis that endogenous cyst(e)ine synthesis is limited in very low birth weight preterm infants with gestational ages of 29 weeks, both at 32 and 35 weeks postmenstrual age. It is safe to conclude that cyst(e)ine requirement is 18 mg/kg per day in enterally fed very low birth weight preterm infants who are older than 32 weeks’ postmenstrual age and whose methionine intake is adequate. Therefore, cyst(e)ine is probably not a conditionally essential amino acid in these infants.
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机译：目的。最佳营养对于早产儿的后期健康和发育结果至关重要。早产儿的氨基酸需求与早产儿和较大婴儿的氨基酸需求不同，因为其生长速率不同。但是，某些非必需氨基酸不能内源地充分合成。胱氨酸（e）被认为是早产儿的条件必需氨基酸。这项研究的目的是确定在月经后32和35周时，完全肠内喂养的出生体重<29周的极低体重早产儿的胱氨酸需求量。婴儿被随机分配到含有大量蛋氨酸的5种分级胱氨酸测试饮食中的1种。适应24小时后，通过指示剂氨基酸氧化技术（[1-13C]苯丙氨酸）确定了胱氨酸（e）的需求量。结果。在47例极低出生体重的早产儿（平均胎龄：28周±1周SD;出生体重：1.07 kg±0.21 kg SD）中建立了[1-13C]苯丙氨酸的部分氧化。饮食中摄入胱氨酸（e）的摄入增加并不会降低[1-13C]苯丙氨酸的氧化分数。结论。这些数据不支持这样的假设，即在月经后32和35周时，胎龄小于29周的极低出生体重早产儿，内源性半胱氨酸的合成受到限制。可以得出结论，对于经肠道喂养的出生后体重很轻的早产儿，其月经后年龄超过32周，并且蛋氨酸摄入量足够，因此每天需要摄入的胱氨酸（e）小于18 mg / kg。因此，在这些婴儿中，胱氨酸（e）可能不是有条件的必需氨基酸。
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