McChesney R, Habermann J, Greengard O
Department of Pediatrics, Mount Sinai School of Medicine, New York, N.Y.
Biol Neonate. 1988;54(5):275-84. doi: 10.1159/000242863.
At the same severe elevations in blood phenylalanine (Phe) levels maintained for 4 h, much higher cerebral Phe concentrations were found in 4-day-old than in 16- or 70-day-old rats. In order to compare this developmental change with 14C-Phe influx mediated by the L transport system, the rapid intracarotid injection method was adapted for use in neonatal rats. The brain uptake index (BUI) thus determined for the first time through the suckling period was significantly higher on the 4th day of age than on the 7th or 24th day, while no significant change occurred during subsequent life. This early period of change in influx across the blood-brain barrier overlapped with the age period of decrease of the hyperphenylalaninemia-associated accumulation of Phe in the brain. The results indicate that by the time when intermittent feeding begins, the brain has developed a considerable ability (a) to protect itself against physiological (e.g. postprandial) fluctuations in circulating Phe levels, and (b) to restrict the cerebral accumulation of Phe from pathologically elevated blood concentrations such as those in phenylketonuria.
在将血苯丙氨酸（Phe）水平维持在相同的严重升高状态4小时的情况下，发现4日龄大鼠脑内的Phe浓度远高于16日龄或70日龄大鼠。为了将这种发育变化与L转运系统介导的14C-Phe流入进行比较，对快速颈内注射法进行了改良，以用于新生大鼠。通过哺乳期间首次测定的脑摄取指数（BUI）在4日龄时显著高于7日龄或24日龄时，而在随后的生命过程中没有发生显著变化。血脑屏障流入的这一早期变化时期与高苯丙氨酸血症相关的脑内Phe积累减少的年龄时期重叠。结果表明，在开始间歇性喂养时，大脑已经发展出相当的能力：（a）保护自身免受循环中Phe水平的生理波动（如餐后波动）影响；（b）限制从病理性升高的血浓度（如苯丙酮尿症中的血浓度）中脑内Phe的积累。
