The measurement of monoamine metabolites in the plasma of psychiatric patients is now possible thanks to methods that have become available over the past ten years.1.2 As was true to some degree for investigations in cerebrospinal fluid (CSF), clinical research using these measures in plasma has proceeded without full knowledge of their origin and significance.3 Currently, most investigators believe that both central and peripheral sources contribute to plasma homovanillic acid (HVA) and methoxyhydroxyphenylglycol (MHPG) metabolites of dopamine and norepinephine, respectively. Debrisoquin has been used in some studies in an effort to minimize the peripheral
See also pp 553, 561, and 564.
contribution to plasma monoamine metabolite values.4 Diet can be a major contributor to plasma HVA concentrations under certain circumstances,5 and diurnal changes have been noted.6
Despite incomplete information regarding the processes plasma monoamine metabolites may reflect, a number of interesting clinical findings have already