Uptake of Tyrosine by Rat Brain in Vivo

Abstract

Tyrosine penetrated readily into rat brain in vivo. A brain to plasma ratio, comparable to normal was attained at equilibrium irrespective of absolute concentrations in the tissues. L-Tyrosine penetrated much more rapidly than its D isomer or a number of other compounds of closely related structure. The penetration of L-tyrosine was markedly diminished by other aromatic amino acids, and by leucine, isoleucine, valine, histidine, and cysteine. These findings warrant the conclusion that the entry of tyrosine into brain involves a catalytic mechanism.