Rabbit brain metabolism of phenylethylamine and tyramine: drug effects

Kinetic study on p-tyramine metabolism in humans using stable isotope-labeled tracers

A sensitive method for the determination of p-tyramine was developed using gas chromatography-chemical ionization mass spectrometry. This method was combined with a stable isotope tracer technique to study p-tyramine metabolism in humans. [2H]5-Phenylalanine was administered orally to men (5 mg/kg) as a tracer and the amounts of [2H]4-p-tyramine excreted into urine were determined at each hour. Excretion of [2H]4-p-tyramine was maximal between 1 and 2 hours following administration, at about 15 ng/kg.h in healthy adult men. Possible application in the study of metabolic disorders in human was demonstrated.

Hydroxylation of phenylethylamine by rat liver preparations. Inhibition studies

1. Rat liver 100,000 g pellet microsomal fraction p-hydroxylate phenylethylamine to tyramine in a relatively slow proceeding, NADPH-requiring reaction; Km 2.1 x 10(-5) M and Vmax 0.32 nmol/mg protein/20 min. 2. This reaction is inhibited, either competitively, noncompetitively or uncompetitively by a number of behaviorally active monomethylated and monohalogenated derivatives of phenylethylamine. 3. Whereas formation of tyramine was not significantly affected by L-phenylalanine or its p-chloro derivative, it was competitively inhibited by imipramine, iprindole and alprazolam. 4. It is suggested that at least some of the effects of these drugs may result from their ability to interfere with phenylethylamine metabolism.

Phenylethylamine metabolism to tyramine by postmortem human brain preparations

Human brain preparations obtained from either the putamen, thalamus, hippocampus or lateral occipital gyrus p-hydroxylate phenylethylamine to tyramine, a reaction carried out by a microsomal (100,000 xg pellet) membrane bound, NADPH-requiring enzyme. This is a minor metabolic pathway occurring in chronic psychiatric patients, as well as in age-comparable controls.