Determination of Plasma and Tissue Levels of Tyramine by Radioimmunoassay 1 2

Abstract

Summary

Antibodies were prepared against tyramine. The antigen was prepared as follows: p-Aminohippuric acid was coupled to mBSA using a carbodiimide reagent. The amino group was diazotized and attached to the aromatic ring of TYR. The immunogen in Freund's complete adjuvant was injected into rabbits. The specificity of the resulting antibody was determined by radioimmunoassay. Using random-labeled TYR-³H, TYR, its metabolites, phenethyla-mine analogs, catecholamines, and certain amino acids were evaluated by a competitive binding assay method. With this technique 4 ng of TYR inhibited the binding of TYR-³H by 50%. The radioimmunoassay of TYR was used to measure the plasma, urine, and tissue levels of TYR in rabbits. The plasma disappearance curve of TYR revealed a biphasic pattern with t _1/2 of 2 min and 54 min. The highest concentration of TYR was found in adrenals and spleen. The factthat the major metabolites of TYR and a series of pharmacologically important sym-pathomimetics and catecholamines did not interfere, makes the radioimmunoassay of TYR a useful, simple, sensitive, and specific method for the direct analysis of TYR in biological materials.