Brain tryptophan, plasma free tryptophan and distribution of plasma neutral amino acids

Although rat brain tryptophan is strikingly elevated following portacaval shunt, plasma total tryptophan is unchanged and plasma free tryptophan is not elevated to the same degree as brain tryptophan. Investigation of the concentrations of the neutral amino acids (phenylalanine, tyrosine, methionine, threonine, leucine, isoleucine, and valine) revealed that their distribution and the sum of their concentrations were altered following portacaval shunt, and that this pattern was similar to that seen in humans with cirrhosis of the liver. It is suggested that both the elevation in plasma free tryptophan and the decrease in the competing neutral amino acids, act together to increase the transport of tryptophan into brain when portal blood is diverted around the liver. The implications of these findings in therapy of hepatic coma is discussed.