Uptake of Radiolabeled Essential Amino Acids by Brain Following Arterial Injection

Abstract

Summary

¹⁴C-labeled amino acids were injected into rat common carotid artery mixed with ³H₂O, with decapitation 15 sec later. The ratio of ¹⁴C to ³H in brain was compared with the same ratio in the injected solution allowing expression of brain uptake of amino acid as a percentage of ³H₂O uptake. Eighteen amino acids showed a range of uptake between 2.24 and 54.5%. Those amino acids ordinarily considered nutritionally essential in the rat are taken up to a greater extent than nonessentials. The exception is tyrosine which is not nutritionally essential to the total organism because it is available from hydroxylation of phenylalanine. The large uptake of tyrosine by brain may be related to the absence in brain of phenylalanine hydroxylase thus necessitating an external source.