Slices of striatal tissue obtained from salinc-injected rats were incubated with 'Hphenylalanine in the presence of pargylinc. This resulted in the formation of 3Hm-tyraniine, 'H-p-tyramine, and 3H-phenylethylamine. Pretreatment of the rats with a-methyl-p-tyrosine reduced the formation of 'H-m-tyramine and 'H-ptyramine, but enhanced the formation of 3H-phenylethylamine.
After incubation of striatal tissue obtained from saline-injected rats with 3Hptyrosine, only 'H-p-tyraminc was produced. In this case, a-methyl-p-tyrosine pretreatment enhanced 3H-p-tyramine formation.
Striatal slices incubated with 3H-m-tyramine or 'H-p-tyramine did not yield any significant quantity of 'H-phenylethylamine; nor was ''C-phenylethylamine converted to ''C-m-tyramine or ''C-p-tyramine. Pretreatment of the rats with the monoamine oxidase inhibitor pargyline did not appreciably affect these findings.
After incubation with 3H-dopamine very small quantities of 'H-m-tyramine and 3H-p-tyramine were formed, the ratio between them being 7: 1.
It is concluded that the major biosynthetic route for m-tyramine formation in the rat straitum is by hydroxylation of phenylalanine, probably by tyrosine hydroxylase to m-tyrosine, followed by decarboxylation, probably by L-aromatic amino acid decarboxylase, to m-tyramine. para-Tyramine is formed by decarboxylation of p-tyrosine, and phenylethylamine similarly by decarboxylation of phenylalanine .