Methylmercury transport across the placenta via neutral amino acid carrier
Methylmercury transport across the placenta via neutral amino acid carrier
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DOI：
10.1007/s002040050279
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发表时间：
1996-02-01
影响因子：
6.1
通讯作者：
Hirayama, K
中科院分区：
文献类型：
--
作者：
Kajiwara, Y;Yasutake, A;Hirayama, K
甲基汞（MeHg）可透过胎盘屏障影响子宫内发育中的胎儿，但其在胎盘中的转运机制尚不清楚。为了阐明在胎盘中发挥作用的甲基汞转运系统，在妊娠第18天对妊娠大鼠静脉注射甲基汞。在给药后30和60 min从脐带中采集胎血，并测量其汞浓度。甲基汞被发现以时间和剂量依赖的方式迅速转运到胎儿血液中，并主要分布在那里的血细胞中。中性氨基酸的共同注射有效地抑制了甲基汞的转运，即，L-甲硫氨酸和L-苯丙氨酸，表明甲基汞是积极运输的半胱氨酸共轭物通过中性氨基酸载体系统。蛋氨酸的抑制作用不如苯丙氨酸明显。由于蛋氨酸管理引起的半胱氨酸，这是一个主要的载体在甲基汞运输，在母体血浆中，新合成的半胱氨酸迅速增加，似乎加速汞的吸收。因此，额外半胱氨酸的加速作用将部分补偿作为中性氨基酸的蛋氨酸的竞争作用。
Methylmercury (MeHg) penetrates the placental barrier to affect developing fetuses in the uterus, However, the mechanism of placental MeHg transport is not well defined. To clarify the MeHg transport system that functions in the placenta, pregnant rats were intravenously administered MeHg on day 18 of gestation. The fetal blood was collected from the umbilical cord at 30 and 60 min after the administration, and its mercury concentration was measured. MeHg was found to be rapidly transported to the fetal blood in a time- and dose-dependent manner, and predominantly distributed in the blood cells there. MeHg transport was effectively suppressed by the co-injection of neutral amino acids, i.e., L-methionine and L-phenylalanine, suggesting that MeHg is actively transported as its cysteine conjugate via the neutral amino acid carrier system. The suppression by methionine was not so marked as by phenylalanine. Since methionine administration caused a rapid increase of the cysteine, which functioned as a predominant carrier in MeHg transport, in the maternal plasma, newly synthesized cysteine seemed to accelerate the mercury uptake. Accordingly, the acceleration by the extra cysteine would compensate partly the competitive effect of methionine as a neutral amino acid.