Battaglia F C
Department of Pediatrics, University of Colorado Health Sciences Center, Denver 80262.
J Anim Sci. 1992 Oct;70(10):3258-63. doi: 10.2527/1992.70103258x.
Fetal amino acid nutrition and metabolism have been studied primarily in pregnant sheep. The umbilical uptake of amino acids changes during gestation, but at both mid- and late gestation the total supply exceeds that required for growth. Weight-specific protein synthetic rate decreases with increasing gestational age, and these changes are proportional to the changes in metabolic rate. The use of multiple tracer methodology coupled with measurement of net tracer fluxes into and out of fetal and placental tissues can be used to delineate amino acid metabolism in considerable detail. Such studies demonstrate that even essential amino acids can be oxidized extensively by the fetus. The oxidation rate of leucine exceeds its rate of accretion in tissue proteins. Glycine metabolism is unique in several ways; there is a large umbilical uptake of glycine without a measurable uterine uptake. In late gestation there is no significant umbilical uptake of serine, although there is a significant uterine uptake, suggesting net uteroplacental utilization. Glycine is oxidized within the fetal liver and used for serum production. The interorgan exchange of amino acids between the fetal liver and placenta is clearly of major importance for serine and glycine metabolism and is likely to be of major importance for most nonessential amino acids.
胎儿氨基酸营养与代谢主要在妊娠绵羊中进行了研究。氨基酸的脐摄取在妊娠期会发生变化，但在妊娠中期和晚期，总供给量均超过生长所需。单位体重的蛋白质合成率随胎龄增加而降低，且这些变化与代谢率的变化成比例。运用多种示踪方法并结合对胎儿和胎盘组织内外净示踪剂通量的测量，可相当详细地描绘氨基酸代谢情况。此类研究表明，即便必需氨基酸也可被胎儿大量氧化。亮氨酸的氧化速率超过其在组织蛋白中的蓄积速率。甘氨酸代谢在多个方面独具特色；甘氨酸有大量脐摄取，而子宫摄取量却无法测量。在妊娠晚期，丝氨酸虽有显著的子宫摄取，但脐摄取量并不显著，提示存在子宫胎盘净利用。甘氨酸在胎儿肝脏内被氧化并用于血清生成。胎儿肝脏与胎盘之间氨基酸的器官间交换对于丝氨酸和甘氨酸代谢显然至关重要，并且可能对大多数非必需氨基酸也至关重要。
