L-(U-14C) tyrosine metabolism of the perfused cat brain with high plasma phenylalanine or without plasma tyrosine.

Abstract

Cat brain perfusion was carried out with standard artificial blood containing 2 mg/dl of L-tyrosine and also with standard blood not containing tyrosine, for 70 minutes in each group. In addition, another group was perfused with the tyrosine-containing artificial blood plus 50 mg/dl of L-phenylalanine. Each of these experiments was conducted to see how such blood would affect the tyrosine metabolism of the brain. The results are summarized briefly. 1 Tn the perfusion without addition of tyrosine, the tyrosine content of the brain decreased markedly. Furthcr, there was an outflow of the brain tyrosine into the venous blood. The free tyrosine of the brain is mainly supplied from the blood tyrosine. 2 In the high plasma phenylalanine perfusion, the transport of the blood tyrosine into the brain was inhibited competitively by the blood phenylalanine, but output of tyrosine from the brain to the blood was not disturbed. 3 Tn the high plasma phenylalanine perfusion, the incorporation of tyrosinc into the brain protein fraction from the brain acid soluble fraction was lower than that ofthe control group. 4 During the high plasma phenylalanine perfusion, there was observed a marked increase of phenylalanine, and a decrease of tyrosine, threonine, isoleucine and leucine in the brain.