Urinary MHPG sulfate as a marker of central norepinephrine metabolism: a commentary.

Measurement of total (free + conjugated) 3 methoxy-4-hydroxyphenylglycol (MHPG) in urine has long been used to assess the metabolism of central norepinephrine (NE). However, available data indicate that total MHPG is not a sensitive marker because the portion of urinary MHPG which derives from brain NE is less than was previously assumed. Several arguments support the view that central MHPG excretion is best represented by the urinary MHPG sulfate fraction. Accordingly, a new strategy has been introduced in last years, involving the separate determination of sulfate and glucuronide conjugates of MHPG as respective markers of central and peripheral NE metabolism. Various biochemical and pharmacological data obtained in healthy subjects and in patients with mental diseases support this hypothesis.