FREE 3‐METHOXY‐4‐HYDROXYPHENYLETHYLENEGLYCOL IN THE CENTRAL NERVOUS SYSTEM OF THE RAT: SEMI‐AUTOMATED FLUOROMETRIC ASSAY, TURNOVER AND EFFECTS OF DRUGS

Abstract

AbstractA semi‐automated fluorometric assay technique for free 3‐methoxy‐4‐hydroxyphenylethyl‐eneglycol (MOPEG) in rat brain and spinal cord is described.The method is based on a simple manually‐performed two‐step purification procedure using column chromatography on Sephadex G 10 and DEAE‐Sephadex A 25 (borate form) respectively. After isolation MOPEG is converted into a fluorophore in a continuous flow system using ethylene diamine condensation in the presence of an oxidant. The MOPEG assay is highly sensitive (detection limit 2 ng/sample) and linear, with an overall recovery of approx 75%.Specificity is demonstrated by testing a number of compounds and confirmed by gas chromatography‐mass spectrometry analysis. Treatment with clozapine and haloperidol (both neuroleptics), reser‐pine (impairing intraneuronal storage) or phenoxybenzamine (α‐adrenoceptor blocking agent) increased the content of MOPEG both in brain and spinal cord. Cerebral levels of MOPEG were decreased after injection of a single dose of the tricyclic antidepressant desipramine and after chronic destruction of the locus coeruleus by electrolytic lesion or by the administration of the neurotoxic drug 6‐hydroxy‐dopamine. Animals killed by microwave irradiation did not show lower MOPEG contents in brain than decapitated animals.These results indicate that MOPEG is a measure for changes in central noradrenaline turnover and that drugs affect MOPEG in the brain and spinal cord similarly. Fractional rate constants of MOPEG in the rat brain and spinal cord were estimated with the exponential decline curves produced by treatment with pargyline. Turnover rates of 193 pmol/g/h and 167 pmol/g/h in the brain and spinal cord respectively were calculated.