A method for the assay of conjugated 3,4-dihydroxyphenylglycol, a major noradrenaline metabolite in the rat brain.

We present the first published procedure for the measurement of endogenous conjugated 3,4-dihydroxyphenylglycol (DOPEG) in the rat brain. Conjugated DOPEG is estimated from brain extracts after enzymic hydrolysis, isolation of hydrolysed DOPEG on alumina, methylation of DOPEG to 3-methoxy-4-hydroxyphenylglycol (MOPEG) and gas chromatographic quantification of MOPEG. The level of conjugated DOPEG in the CNS of rats (65.7 +/- 0.7 ng/g whole brain tissue corrected for recovery) almost equals the level of conjugated MOPEG. The sensitivity of the method is about 6 ng/g brain tissue. After inhibition of monoamine oxidase with clorgyline (30 mg/kg) conjugated DOPEG and MOPEG both disappeared from the brain with a half-life of about 1 h. Turnover calculations indicate that conjugated DOPEG and MOPEG are the two major noradrenaline end-metabolites in the rat brain. The method of estimating conjugated DOPEG also allows the measurement of noradrenaline, dopamine and total MOPEG in an extract from one half of a rat brain.