Studies on the central or peripheral origin of free and sulfated 3,4-dihydroxyphenylacetic acid in rat plasma.

The concentrations of free and sulfated 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in rat plasma to investigate their potential central or peripheral origin. Stimulation of central dopamine (DA) metabolism by a long-acting neuroleptic, pipotiazine (PPZ) selectively increased plasma levels of DOPAC sulfate whereas peripheral inhibition of monoamine oxidase by debrisoquin sulfate decreased free DOPAC levels only. These data suggest that the two forms of plasma DOPAC (free and sulfate) may have independent topographic origins. Peripheral DA pools seem to be the most likely sources for plasma free DOPAC whereas central dopaminergic neurons mainly contribute to plasma sulfated DOPAC. Our findings thus demonstrate that plasma DOPAC sulfate may be a useful indicator for central DA function in rat. Although further experiments are necessary to extrapolate our findings from rat to man, arguments are given indicating that measurements of plasma DOPAC sulfate might be of interest in human pathological and pharmacological investigations.