ISOLATION AND RADIOENZYMIC ESTIMATION OF PICOGRAM QUANTITIES OF DOPAMINE AND NOREPINEPHRINE IN BIOLOGICAL SAMPLES

Abstract

Abstract— A method was developed to measure small amounts of dopamine or norepincphrine in biological samples. It was based on the radioenzymic assay originally described by E ngelman et al. (1968) and improved by other workers: dopamine and norepinephrine are O ‐methylated by catechol‐ O ‐ methyl‐transferase in the presence of [ 3 H] S ‐adenosylmethioniiie as la belled methyl donor. O ‐Methylated derivatives are extracted and estimated. The optimal conditions for the O ‐methylation and the extractions were determined. The most important improvement in the method consisted in the selective isolation of catecholamines on microcolumns of alumina under conditions that allowed their subsequent enzymic assay. The assay described can thus be used on any size of biological sample. The assay was not affected by the prescnce of various agents (tissue extracts, CSF salts and particularly calcium, drugs etc.) which were shown to interfere with the O ‐methylation process, and it allowed the measurement of quantities of dopamine and norepinephrine as low as 0.15 and 0.1 pmol respectively, whatever the origin of the sample (CSF superfusates, cerebral tissue).