Is 3,4-dihydroxyphenylglycol the major route of central norepinephrine metabolism in rat brain?

Central norepinephrine (NE) metabolism was assessed by measuring 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxyphenylethyleneglycol (DHPG) in different rat brain areas after saline or probenecid (300 mg/kg) administration. Under probenecid, results showed an increased accumulation of total MHPG and DHPG, and a clear preponderance of DHPG levels over MHPG in almost all the brain areas examined. Estimation of their formation rates confirmed that in basal conditions DHPG is formed more rapidly. This study supports the notion that, without ruling out the importance of MHPG, brain DHPG may be a useful index of central NE activity.