An in vivo tritium release assay of human dopamine beta-hydroxylase

A non-invasive method is described for estimating dopamine beta-hydroxylase (DBH) activity in sympathetic neurons. Our assay is based on the measurement of the in vivo rate of tritiated water (THO) release from dopamine specifically labeled in the beta-position ([beta-3H]DA). In validation of this method, we have establsihed in human subjects that 1) THO release from [beta-3H]DA correlates with [beta-3H]norepinephrine metabolite excretion, and 2) partial inhibition of DBH with disulfiram (5.5 mg/kg for 4 days) causes parallel decreases in these two indices of dopamine beta-hydroxylation. Since there is a strong correlation (r = 0.89; P < 0.05) between the effect of disulfiram on THO release and the effect of the drug on [3H]-norepinephrine metabolite excretion, our data indicate that the rate at which THO is liberated from [beta-3H]DA into the total body water can be used as an in vivo index of DBH activity.