Effects of oral and intravenous administrations of dopamine and L-dopa on plasma levels of two isomers of dopamine sulfate in man

The levels of two isomers of dopamine sulfate, dopamine-3-O-sulfate (DA3S) and dopamine-4-O-sulfate (DA4S), in human plasma were measured by HPLC-fluorometry. The basal plasma levels of DA3S and DA4S in the early morning were 13.8 +/- 1.9 and 3.2 +/- 0.5 pmoles/ml, respectively (means +/- S.E.M.). Oral administrations of dopamine (50 mg/body) and 1-dihydroxyphenylalanine (L-DOPA, 250 mg/body) increased the plasma levels of these dopamine sulfates almost 100-fold to 1807 +/- 266 and 1674 +/- 195 pmoles/ml of DA3S, and 466 +/- 83 and 321 +/- 76 pmoles/ml of DA4S. Intravenous dopamine infusion (5 micrograms/kg/min for 30 min) markedly increased the plasma free dopamine concentration, as expected, but increased the levels of DA3S and DA4S only slightly to 110 +/- 32 and 25 +/- 9 pmoles/ml, respectively. In contrast, intravenous L-DOPA (25 mg/body) resulted in a slight increase of free dopamine followed by marked increases of DA3S and DA4S to 691 +/- 219 and 139 +/- 40 pmoles/ml, respectively. These data indicate that O-sulfation of dopamine, especially 3-O-sulfation, is the main pathway for metabolism of intravenously and orally administered L-DOPA and orally ingested dopamine. This sulfation is suggested to occur in the gut wall.