Saito K, Nagamura Y, Ohta Y, Sasaki E, Ishiguro I
Department of Biochemistry, School of Medicine, Fujita Health University, Aichi, Japan.
Life Sci. 1991;49(7):527-34. doi: 10.1016/0024-3205(91)90070-r.
In order to characterize the system of L-tryptophan (TRP) transport into liver during the growing period of 10 to 42 days, the changes of tryptophan 2,3-dioxygenase (TDO) activity, levels of serum, liver, brain, and muscle TRP, and the rate and mode of TRP uptake into isolated hepatocytes were examined in male Wistar rats. Liver TDO activity increased rapidly at 16 days of age. A marked and rapid decrease in free serum TRP level occurred before weanling, while a small decrease in total serum TRP level was found after weanling. The change of liver TRP level was similar to that of free serum TRP level and correlated well. There was a significant inverse correlation between liver TDO activity and either free serum TRP level or liver TRP level. A rapid change in TRP level did not occur in brain and muscle during the growing period. The concentrations of brain and muscle TRP correlated better with those of total serum TRP than with those of free serum TRP. The rate of TRP uptake into hepatocytes isolated from rats aged 10 days was lower than that from rats aged 21 and 42 days. The former hepatocytes were lacking in a high-affinity saturable transport component for TRP uptake which was present in the latter ones. The present results indicate that a great change in the system of TRP transport into liver occurs in growing rats, and that in suckling rats a high level of free serum TRP contributes to the efficient transport of the amino acid into the liver.
为了表征10至42日龄生长期间L-色氨酸（TRP）转运至肝脏的系统，在雄性Wistar大鼠中检测了色氨酸2,3-双加氧酶（TDO）活性、血清、肝脏、脑和肌肉中TRP水平的变化，以及TRP摄取至分离的肝细胞中的速率和模式。肝脏TDO活性在16日龄时迅速增加。断奶前游离血清TRP水平显著快速下降，而断奶后总血清TRP水平有小幅下降。肝脏TRP水平的变化与游离血清TRP水平相似且相关性良好。肝脏TDO活性与游离血清TRP水平或肝脏TRP水平之间存在显著负相关。生长期间脑和肌肉中的TRP水平未发生快速变化。脑和肌肉中TRP的浓度与总血清TRP的相关性优于与游离血清TRP的相关性。从10日龄大鼠分离的肝细胞中TRP的摄取速率低于21日龄和42日龄大鼠。前者的肝细胞缺乏后者中存在的用于TRP摄取的高亲和力可饱和转运成分。目前的结果表明，生长中的大鼠肝脏中TRP转运系统发生了巨大变化，并且在乳鼠中，高水平的游离血清TRP有助于氨基酸有效地转运至肝脏。
