The Effect of Age upon the Entry of Some Amino Acids into the Brain, and their Incorporation into Cerebral Protein

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Abstract
The way in which the influx of amino acids into the brain changes as the age of rats increases from 1-25 wk is reported. Most of the amino acids have a very high rate of influx during the 1st weeks of life, which falls progressively until an adult level is reached by about 8-10 wk of age. The high influx in early life is due to carrier-mediated transport systems which act more rapidly in the young than in the adult. These systems can be saturated by raised levels of amino acid in the blood, both in young and adult animals. The high influx in early life is necessary to provide abundant supplies of amino acids for cerebral-protein formation during the period of rapid brain growth. In adult life, influx declines to a level that is adequate to support the synthesis of cerebral protein, which is still being continuously broken down and renewed at a remarkably high rate.