Beckman D A, Brent R L, Lloyd J B
Division of Developmental Biology, Jefferson Medical College, Philadelphia, PA, USA.
Placenta. 1997 Jan;18(1):79-82. doi: 10.1016/s0143-4004(97)90074-6.
Fetal and maternal plasma were assayed for the concentration of free leucine, acid-insoluble radioactivity and acid-soluble radioactivity at intervals after an intravenous bolus injection of [3H]leucine into anaesthetized pregnant rats at 17.5 days post-conception. The concentrations of total free leucine and of free [3H]leucine in maternal and fetal plasma were effectively unchanged from 5 to 180 min post-injection. Plasma free leucine concentrations in the fetus were five times those in the mother. The concentration of free [3H]leucine in fetal plasma was similar to that in maternal plasma. Thus the specific radioactivity of free leucine in fetal plasma is substantially lower than that in maternal plasma, indicating that a significant portion of the free leucine in plasma of the 17.5-day rat fetus comes from a source other than the free leucine in the maternal plasma. The data are consistent with a major contribution of amino acids coming from the degradation of extraembryonic protein in the yolk sac. Other possible sources of unlabelled leucine are discussed.
在妊娠17.5天的麻醉孕鼠静脉推注[³H]亮氨酸后，间隔一定时间测定母鼠和胎鼠血浆中游离亮氨酸、酸不溶性放射性和酸溶性放射性的浓度。注射后5至180分钟，母鼠和胎鼠血浆中总游离亮氨酸和游离[³H]亮氨酸的浓度实际上没有变化。胎鼠血浆中游离亮氨酸的浓度是母鼠的五倍。胎鼠血浆中游离[³H]亮氨酸的浓度与母鼠血浆中的相似。因此，胎鼠血浆中游离亮氨酸的比放射性显著低于母鼠血浆中的比放射性，这表明17.5天龄大鼠胎儿血浆中的游离亮氨酸有很大一部分并非来自母鼠血浆中的游离亮氨酸。这些数据与来自卵黄囊中胚外蛋白质降解产生的氨基酸的主要贡献一致。还讨论了未标记亮氨酸的其他可能来源。
