THE RATE OF FORMATION OF 3-METHOXY-4-HYDROXYPHENYLETHYLENEGLYCOL SULFATE IN BRAIN AS AN ESTIMATE OF THE RATE OF FORMATION OF NOREPINEPHRINE

¹ Laboratory of Preclinical Pharmacology, National Institute of Mental Health, Saint Elizabeths Hospital, William A. White Building, Washington, D.C.

One of the major metabolites of norepinephrine in rat brain is 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MOPEG-SO₄). The rate of formation in brain of MOPEG-SO₄ was estimated by: 1) determining the rate of its accumulation after treatment with probenecid and 2) determining the initial rate of decline of MOPEG-SO₄, after inhibition of monoamine oxidase with pargyline. The rate of formation of MOPEG-SO₄, appeared to be about 20 to 35% of the rate previously reported for norepinephrine. We also observed that increasing the turnover of norepinephrine by injection of phenoxybenzamine increased the rate of formation and the concentration of MOPEG-SO₄ in brain. Cold exposure, which also accelerates the rate of formation of norepinephrine in brain, increased the concentration of MOPEG-SO₄ in brain. Neither treatment had an appreciable effect on the steady-state concentration of norepinephrine. Measuring MOPEG-SO₄ formation by the above procedures or simply measuring the concentration of MOPEG-SO₄ may be a useful technique for revealing changes in the synthesis of norepinephrine in rat brain.

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