the plasma concentration of mhpg observed in these study subjects ( n = 34 ) correlated ( rs = 0.77 , p less than 0.01 ) more strongly with the ratio of plasma catecholamine precursor amino acids ( tyrosine and phenylalanine ) to other neutral amino acids ( tryptophan , leucine , isoleucine , and valine ) known to compete with catecholamine precursor amino acids for uptake into the brain than with plasma concentration of tyrosine plus phenylalanine alone ( rs = 0.63 , p less than 0.01 ) .
C0301715
neutral amino acids
C0002520
amino acids