Dopamine sulfate formation and phenol sulfotransferase activity in dog and human platelets

The potential of intact human platelets for sulfoconjugation of norepinephrine in vitro

The aim of the present study was to investigate the potential of human platelets for sulfoconjugation of plasma norepinephrine. For this purpose the uptake and the efflux of norepinephrine and norepinephrine sulfate were studied in vitro in intact human platelets. Incubation of platelets with 0.5 mumol/l norepinephrine led to a rapid uptake of norepinephrine within 1 min (22.76 +/- 4.14 pmol/2.5 x 10(9) platelets/min), whereby 63.7% was transformed to norepinephrine sulfate. The substrate kinetics showed a different slope of norepinephrine uptake with increasing norepinephrine concentrations in the incubation medium (0.1-0.5 mumol/l). At 0.1 mumol/l norepinephrine the uptake was more efficient than at higher norepinephrine concentrations. Incubation with norepinephrine sulfate slightly decreased intraplatelet norepinephrine sulfate (p < or = 0.01). Incubation of human platelets in a catecholamine free medium led to an efflux of norepinephrine and norepinephrine sulfate (21.8%, 11.2% of total intraplatelet content, respectively). The present findings indicate a net uptake of norepinephrine into the platelets. At physiological norepinephrine concentrations the uptake seems to be achieved predominantly by an active transport mechanism. Moreover, data indicate a net efflux of norepinephrine sulfate. Therefore it is concluded that human platelets might contribute to the formation of plasma norepinephrine sulfate by norepinephrine uptake, intraplatelet sulfoconjugation and release of norepinephrine sulfate.

Effect of dopamine and dopamine-antagonist infusion on blood platelet count, size and release reaction in hypertensive and normotensive subjects

To examine the effect of dopamine on in vivo platelet function and a possible platelet contribution to the clearance of dopamine we measured platelet count, platelet size and plasma concentration of the platelet specific protein beta-thromboglobulin (BTG) in groups of 40 year old untreated hypertensive and normotensive men. One hypertensive (n = 10) and one normotensive (n = 10) group received dopamine infusion at doses from 0.5 to 2.0 micrograms/kg/min which increased plasma dopamine 100-fold from baseline. Two other groups of hypertensive (n = 10) and normotensive (n = 11) subjects received 10 mg of the dopamine antagonist metoclopramide intravenously, upon which serum prolactin concentration increased 10-fold. No significant effect on platelet function in any group was observed during these interventions. Platelet phenol-sulphotransferase may contribute to dopamine conjugation. However, the selected platelet parameters correlated only weakly with dopamine kinetics during the infusion. Neither dopamine nor a dopamine antagonist altered the selected platelet parameters, nor did these parameters influence the clearance of dopamine during a short-lasting pharmacological infusion.

Free and conjugated plasma homovanillic acid in schizophrenic patients

It has recently been suggested that the plasma level of homovanillic acid (HVA) may provide an index of central dopaminergic activity in humans. Clinical studies have shown that in schizophrenic patients, plasma HVA levels increase with the severity of psychopathology. However, these studies only considered the plasma free HVA fraction whereas investigations on conjugated HVA in humans are sparse and results remain controversial. The aim of this study was to measure both plasma free and conjugated HVA in healthy volunteers and drug-free schizophrenic patients. The mean values and the ranges of plasma free HVA in volunteers and patients were similar to those described in the literature. A substantial and significant increase in plasma free HVA was observed in schizophrenic patients compared with normal subjects. In contrast, plasma conjugated HVA was significatively decreased in schizophrenics. The plasma total HVA was nevertheless higher in schizophrenics compared with controls. No significant correlations were observed between plasma HVA levels and the clinical features of schizophrenic patients rated by various psychiatric scales. These findings suggest that there is an imbalance between plasma free and conjugated HVA in schizophrenic patients, who present an increase in total HVA when compared with controls. Paranoid schizophrenic patients, who present mainly positive symptoms, show the most marked plasma free/conjugated HVA imbalance.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

Preparation of dopamine 3-O-sulphate and dopamine 4-O-sulphate as reference substances and high-performance liquid chromatographic trace determination

Simple syntheses of the biologically important but hitherto difficult to obtain dopamine sulpho conjugates dopamine 3-O-sulphate (I) and dopamine 4-O-sulphate (II), as analytical reference substances, starting from dopamine hydrochloride are described. A method for the determination of I and II with reversed-phase high-performance liquid chromatographic separation and coulometric detection in human urine together with calibration and current-voltage curves are presented. Detection limits of approximately 100 pg of I or II and unequivocal substance identifications even in very complex substrates such as human urine are reported.

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.

Analytical techniques for the determination of phenolic amine neurotransmitter conjugates

This paper reviews methods developed in the author's laboratory for the measurement of the two sulfate conjugates of dopamine in biological material. The methods are sensitive enough for most applications relating to dopamine sulfate. Some are applicable to measurement of sulfate conjugates of other phenolic amines.

Direct measurement of dopamine O-sulfate in plasma and cerebrospinal fluid

This paper describes a method for measurement of dopamine 3-O-sulfate (DA3S) and dopamine 4-O-sulfate (DA4S) in dog and human plasma and dog cerebrospinal fluid. C18 solid-phase extraction columns were utilized for sample preparation. DA3S and DA4S were separated by high-performance liquid chromatography and then quantified by dual-electrode electrochemical detection. [3H]Dopamine O-sulfate (DAS) was used as internal standard. Recovery of authentic DAS added to dog plasma and carried through the entire procedure was 49.9 +/- 6.3% for DA3S (n = 9) and 42.2 +/- 4.3% for DA4S (n = 8). The lower limit of detection (signal-to-noise ratio of 3) was 20 fmol for each DAS isomer. The within-assay coefficient of variation for DA3S in dog plasma averaged 5.8% (range 2.0-12%, n = 5). The between-assay coefficient of variation for DA3S in dog plasma was 3.8% (n = 3). DAS levels in plasma of conscious dogs were 20.3 +/- 6.9 pmol/ml DA3S and 5.91 +/- 3.5 pmol/ml DA4S (n = 5). Cerebrospinal fluid levels were 3.06 +/- 3.22 pmol/ml DA3S and 0.10 +/- 0.18 pmol/ml DA4S in dogs anesthetized with methoxyflurane and nitrous oxide (n = 3). This procedure is also appropriate for use with human plasma; DAS levels were 24.3 +/- 12.8 pmol/ml DA3S and 9.07 +/- 3.9 pmol/ml DA4S (n = 6).