Evaluation of dopamine metabolism in rat striatum by a gas chromatographic technique

Dopamine metabolism in rat striatum was evaluated by gas chromatographic quantitation of 3,4-dihydroxy-phenylacetic acid (DOPAC) and homovanillic acid (HVA). The level of DOPAC (5.21 nmoles/g ± 0.40 S.E.M., n = 12) exceeded that of HVA (3.63 nmoles/g ± 0.25 S.E.M., n = 12). 2 hr following administration of probenecid (200 mg/kg i.p.) the level of striatal HVA was approximately doubled whereas the level of DOPAC was not significantly elevated. Parggline (75 mg/kg i.p.) produced a rapid depletion of DOPAC and HVA. The rate of disappearance of DOPAC (t ^{1 2} = 10 min) exceeded that of HVA (t ^{1 2} = 18 min). Rates of metabolite formation were computed assuming steady state kinetics. The rate of formation of DOPAC (20.5 nmoles/g/hr) was much greater than that of HVA (10.1 nmoles/g/hr). We conclude that DOPAC is the major dopamine metabolite in rat striatum and that its measurement may provide the best index of functional of neuronal activity in this species.