Simultaneous radioenzymatic determination of phenylethylamine, phenylethanolamine, tyramine and octopamine in plasma of patients with hepatic encephalopathy.

A sensitive radioenzymatic assay for the simultaneous determination of phenylethylamine, phenylethanolamine, tyramine and octopamine in plasma samples is reported. After extraction with ethanol, the amines are subjected to enzymatic N-methylation with labelled S-adenosylmethionine, preceded in the case of phenylethylamine and of tyramine, by an enzyme-catalyzed beta-hydroxylation step. The procedure is completed by extraction with toluene containing different amounts of isoamylalcohol, followed by controlled evaporation of the solvent. A generalized and highly significant increase in the concentration of all the four amines was found in plasma samples from patients suffering from hepatic encephalopathy.