The biosynthesis of p-tyramine, m-tyramine, and beta-phenylethylamine by rat striatal slices

Abstract

Slices of striatal tissue obtained from saline-injected rats were incubated with 3H-phenylalanine in the presence of pargyline. This resulted in the formation of 3H-m-tyramine, 3H-p-tyramine, and 3H-phenylethylamine. Pretreatment of the rats with alpha-methyl-p-tyrosine reduced the formation of 3H-m-tyramine and 3H-p-tyramine, but enhanced the formation of 3H-phenylethylamine. After incubation of striatal tissue obtained from saline-injected rats with 3H-ptyrosine, only 3H-p-tyramine was produced. In this case, alpha-methyl-p-tyrosine pretreatment enhanced 3H-p-tyramine formation. Striatal slices incubated with 3H-m-tyramine or 3H-p-tyramine did not yield any significant quantity of 3H-phenylethylamine; nor was 14C-phenylethylamine converted to 14C-m-tyramine or 14C-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 3H-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 striatum 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.