Measurement of 3,4-dihydroxyphenylacetic acid and 3-methoxytyramine specific activity rat striatum.

A method is described for the simultaneous determination in rat striatum of the specific activities of tyrosine, dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and 3-methoxytyramine (3-MT) after administration of [3H]tyrosine. [3H]Tyrosine was given intraventricularly to nonanesthetized rats, and the animals were killed by exposure to microwave radiations. Combined chromatographic elutions on Dowex 50W-X4 columns and alumina or solvent extractions were devised to separate the compounds. Fluorimetric, mass-fragmentographic, and radiometric techniques were used for their detection. Recovery was 94% for tyrosine, 72% for dopamine, 63% for DOPAC, and 50% for 3-MT. Concentrations of the labeled compounds in rat striatum 15 min after the [3H]tyrosine injection were at least five to eight times higher than background. Identity of the final fractions containing 3-MT and DOPAC tissue extracts was verified by thin-layer chromatography. α-Methyltyrosine pretreatment of rats markedly reduced the formation of labeled dopamine. DOPAC, and 3-MT from [3H]tyrosine.