Identification and distribution of m- and p-hydroxyphenylacetic acids in the brain of the rat.

The m and p isomers of hydroxyphenylacetic acid have been identified and quantitated in whole rat brain and in several regions using a capillary column high resolution gas chromatography - mass spectrometry procedure. Their concentrations were: for m-hydroxyphenylacetic acid (mean +/- S.E., number of determinations in parentheses)-whole brain, 2.3 +/- 0.3 ng/g (7); hypothalamus, 1.2 +/- 0.3 ng/g (5); caudate nucleus, 5.5 +/- 0.6 ng/g (5); brain stem, 1.8 +/- 0.1 ng/g (5); cerebellum, 1.2 +/- 0.1 ng/g (5) and the "rest," 1.7 +/- 0.1 ng/g (5); and for p-hydroxyphenylacetic acid-whole brain, 10.6 +/- 0.7 ng/g (7); hypothalamus, 4.5 +/- 0.1 ng/g (4); caudate nucleus, 28.3 +/- 1.6 ng/g (5); brain stem, 8.6 +/- 0.6 ng/g (5); cerebellum, 8.1 +/- 0.4 ng/g (5), and the "rest," 5.3 +/- 0.5 ng/g (5). This heterogeneous distribution parallels closely that exhibited by their respective precursor amines, m- and p-tyramine.