| Research Abstract |
Circulating dopamine is mainly present in conjugated forms, and its sulfate esters are the predominant conjugates in human plasma. The physiological significance of these dopamine conjugates is unknown. For examination of this problem, a sensitive and specific method is required for their determination. Thus, we developed a sensitive and specific HPLC-fluorometric method for determination of dopamine, dopamine-3-O- (3-O) and dopamine-4-O-sulfate (4-O) in biological samples, and we applied the method to pharmacological and clinical studies as follows.
Levels of dopamine-3-O-sulfate in the adrenal, kidneys, liver, small intestine and heart of the mongrel dogs were 1.17+0.55, 0.13+0.02, 0.05+0.02, 0.03+0.01 and 0.01+0.002 nmoles/g (Mean+S.D), respectively. The activities of phenolsulfotransferase, an enzyme responsible for dopamine-sulfate synthesis, and arylsulfatase, an enzyme responsible for desulfation of the dopamine sulfates, were found all the tissues examined in the dog. When the two isomers were infused into the dog vein, they disappeared from the blood with the half time of about 60 min, and only a small portion of the administered 4-O was desulfated to form dopamine. During the infusion, neither isomer had effects on blood pressure, heart rate or urine output.
The level of 3-O in human plasma was found to be influenced by food intake, and to increase 10- to 20-fold after meals. The plasma levels of the two isomers on early morning were determined to be 16.8+1.9 for 3-O and 3.2+0.5 for 4-O (pmoles/ml). The levels in patients with essential hypertension was significantly higher than the normotensive controls. When dopamine or L-DOPA was administered orally to healthy men, a rapid and marked increase of the levels of dopamine sulfates were observed.
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