Stegink L D, Reynolds W A, Pitkin R M
JPEN J Parenter Enteral Nutr. 1981 Nov-Dec;5(6):485-7. doi: 10.1177/0148607181005006485.
Available data indicate little reutilization of 3-methylhistidine (3-MH) in the rat and man. These data led to the use of urinary 3-MH excretion as a measure of muscle protein catabolism in those animal species. However, 3-MH excretion does not accurately measure protein catabolism in the sheep, pig, and rabbit. This is due, at least in part, to the fact that renal amino acid (AA) transport systems reabsorb 3-MH from the glomerular filtrate. The monkey differs from man in that its plasms contains significant quantities of 3-MH, suggesting an active renal transport system for this AA. The present study measured maternal and fetal plasma 3-MH levels in 33 pregnant rhesus monkeys to determine whether the non-human primate placenta contained transport sites concentrating this AA to the fetal plasma. Mean fetal plasma 3-MH concentrations were 16.4 +/- 6.71 micrometers/100 ml, while maternal levels were 9.45 +/- 3.69 micrometers/100 ml. The fetal to maternal gradient was maintained between 1.6 to 1.7 during the course of maternal infusions of various AA. Since placental AA transport systems are similar to those in the kidney and intestine, the data also suggest the presence of AA transport systems for 3-MH in the monkey, indicating that urinary 3-MH excretion would be a poor method for measuring muscle protein catabolism in this species.
现有数据表明，大鼠和人类对3-甲基组氨酸（3-MH）的再利用很少。这些数据使得尿中3-MH排泄量被用作衡量这些动物物种肌肉蛋白分解代谢的指标。然而，3-MH排泄量并不能准确衡量绵羊、猪和兔子的蛋白质分解代谢。这至少部分是由于肾氨基酸（AA）转运系统会从肾小球滤液中重吸收3-MH。猴子与人类的不同之处在于其血浆中含有大量的3-MH，这表明该氨基酸存在活跃的肾转运系统。本研究测量了33只怀孕恒河猴母体和胎儿血浆中的3-MH水平，以确定非人灵长类动物胎盘是否含有将这种氨基酸浓缩到胎儿血浆中的转运位点。胎儿血浆中3-MH的平均浓度为16.4±6.71微摩尔/100毫升，而母体水平为9.45±3.69微摩尔/100毫升。在母体输注各种氨基酸的过程中，胎儿与母体的梯度维持在1.6至1.7之间。由于胎盘氨基酸转运系统与肾脏和肠道中的相似，这些数据还表明猴子体内存在3-MH的氨基酸转运系统，这表明尿中3-MH排泄量将是测量该物种肌肉蛋白分解代谢的一种糟糕方法。
