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Background: Interactions between the endocannabinoid system (ECS) and neurotransmitter systems might mediate the risk of developing a schizophrenia spectrum disorder (SSD). Consequently, we investigated in patients with SSD and healthy controls (HC) the relations between (1) plasma concentrations of two prototypical endocannabinoids (N-arachidonoylethanolamine [anandamide] and 2-arachidonoylglycerol [2-AG]) and (2) striatal dopamine synthesis capacity (DSC), and glutamate and y-aminobutyric acid (GABA) levels in the anterior cingulate cortex (ACC). As anandamide and 2-AG might reduce the activity of these neurotransmitters, we hypothesized negative correlations between their plasma levels and the abovementioned neurotransmitters in both groups., Methods: Blood samples were obtained from 18 patients and 16 HC to measure anandamide and 2-AG plasma concentrations. For all subjects, we acquired proton magnetic resonance spectroscopy scans to assess Glx (i.e. glutamate plus glutamine) and GABA + (i.e. GABA plus macromolecules) concentrations in the ACC. Ten patients and 14 HC also underwent [ 18 F]F-DOPA positron emission tomography for assessment of striatal DSC. Multiple linear regression analyses were used to investigate the relations between the outcome measures., Results: A negative association between 2-AG plasma concentration and ACC Glx concentration was found in patients ( p = 0.008). We found no evidence of other significant relationships between 2-AG or anandamide plasma concentrations and dopaminergic, glutamatergic, or GABAergic measures in either group., Conclusions: Our preliminary results suggest an association between peripheral 2-AG and ACC Glx levels in patients.

In this work, we report a fluorescence strategy for detecting dopamine (DA) and sensing tyrosinase (TYR) activity on the basis of the dual-emission carbon dots (DECDs), which contain two emitters: the blue emitters (BE, maximum emission at 385nm) and yellow emitters (YE, maximum emission at 530nm). Gold nanoparticles (AuNPs) can effectively quench the two emissions of DECDs. The addition of DA aggregates AuNPs effectively, leading to the fluorescence recovery of dual emitters gradually. This strategy exhibits a high selectivity toward DA and shows good linear ranges, such as 0.5-3μM for BE and 0.1-3μM for YE. Additionally, the proposed method is successfully applied to the determination of DA in real samples with satisfactory recoveries. Subsequently, this DECDs-AuNPs platform is further taken advantage to assess TYR activity by the aid of TYR's capability for oxidation of DA into dopaquinone, which will not induce the agglomeration of AuNPs, so the fluorescence quenching of DECDs is associated with TYR activity. Finally, the mechanism of the reaction is discussed in detail, and the results suggest that both amine and phenolic hydroxyl groups of DA bring the aggregation of AuNPs., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background: In this study, we developed and validated a HPLC-MS/MS method capable of simultaneously determining levodopa, carbidopa, entacapone, tolcapone, 3-O-methyldopa and dopamine in human plasma. RESULTS & METHODOLOGY: Chromatographic separation was achieved using a C8 column with a mobile phase consisting of a gradient of water and acetonitrile:methanol (90:10 v/v), both containing 0.1% formic acid. The developed method was selective, sensitive (LD<7.0 ng ml(-1)), linear (r>0.99), precise (RSD<11.3%), accurate (RE<11.8%) and free of residual and matrix effects. The developed method was successfully applied in plasma patients with Parkinson's disease using Stalevo®., Conclusion: The new method can be used for the clinical monitoring of these substances and applied to adjustments in drug dosages.

This study tested whether familial dysautonomia (FD) involves progressive loss of noradrenergic nerves. Plasma levels of catechols, including dihydroxyphenylglycol (DHPG), norepinephrine (NE), dopamine (DA), and DOPA, were measured in 7 adult patients with FD and 50 healthy control subjects. FD patients were re-tested after a mean follow-up period of 13 years. Compared to controls, FD patients had low plasma levels of DHPG (P < 0.001), high DOPA and DA levels (P = 0.01, P = 0.0002), and high NE:DHPG (P < 0.0001), DA:NE (P = 0.0003), and DOPA:DHPG (P < 0.0001) ratios. At follow-up there were no changes in plasma levels of individual catechols; however, there were further increases in DOPA:DHPG ratios (mean 24 +/- 7%, P = 0.01). In FD, plasma catechol profiles are sufficiently stable, at least over a decade, to be used as a biomarker of disease involvement. An increasing DOPA:DHPG ratio suggests slight but consistent, progressive loss of noradrenergic neurons.

Measurements of plasma-free normetanephrine and metanephrine provide a sensitive test for diagnosis of pheochromocytoma but may fail to detect tumors that produce predominantly dopamine. Such tumors are extremely rare, usually found as extraadrenal paragangliomas. This report describes measurements of plasma concentrations of free methoxytyramine, the O-methylated metabolite of dopamine, in 120 patients with catecholamine-producing tumors, including nine with extraadrenal paragangliomas secreting predominantly dopamine. In seven of these nine patients, tumors were found incidentally or secondary to the space-occupying complications of the lesions. Plasma concentrations of free methoxytyramine and dopamine were increased in all nine patients, including two with normal plasma and urinary normetanephrine and metanephrine and normal urinary outputs of dopamine. Relative increases above normal for plasma methoxytyramine (104-fold) and dopamine (56-fold) were much greater (P < 0.001) than those for urinary dopamine (3-fold). Insensitivity of the latter for identification of dopamine-secreting tumors was due to dependence of the urinary amine on renal extraction and decarboxylation of circulating 3,4-dihydroxyphenylalanine. Measurements of plasma-free methoxytyramine, in addition to normetanephrine and metanephrine, are unlikely to improve diagnosis of pheochromocytomas in hypertensive patients with symptoms of catecholamine excess but may be useful in selected patients for identification of tumors that produce predominantly dopamine.

Parkinson disease is characterized by the loss of dopaminergic neurons, thus decreasing the system's ability to produce and store dopamine (DA). Such ability is often investigated using 18F-fluorodopa (FD) positron emission tomography. A commonly used model to investigate the DA synthesis and storage rate is the modified Patlak graphical approach. This approach allows for both plasma and tissue input functions, yielding the respective uptake rate constants K(i) and K(occ). This method requires the presence of an irreversible compartment and the absence of any nontrapped tracer metabolite. In the case of K(occ), this last assumption is violated by the presence of the FD metabolite 3-O-methyl-[18F]fluoro-dopa (3OMFD), which makes the K(occ) evaluation susceptible to a downward bias. It was found that both K(i) and K(occ) are influenced by DA loss and thus are not pure measures of DA synthesis and storage. In the case of K(occ), the presence of 3OMFD exacerbates the effect of DA egress, thus introducing a disease-dependent bias in the K(occ) determination. These findings imply that K(i) and K(occ) provide different assessments of disease severity and that, as disease progresses, K(i) and especially K(occ) become more related to DA storage capacity and less to the DA synthesis rate.

Background: Short-term exposure to high-altitude hypoxia increases hypoxic ventilatory sensitivity (HVS) in healthy humans. Dopamine (DA) is the implicated neurotransmitter in carotid body (CB) chemoreceptor response, and the microenvironmental conditions in CB tissue are comparable to blood. Continuous DA infusion affected ventilation in animals and humans. Age-related oscillations in blood DA levels may influence peripheral chemoreflexes., Objective: Hypoxic ventilatory responses (HVR) relative to blood DA concentration and its precursor, dihydroxyphenylalanine (DOPA) was measured in young and elderly men during short-term altitude adaptation., Methods: Nine elderly climbers (group 1:61+/-1.4 years) and 7 young healthy subjects (group 2: 23+/-2 years) were tested at sea level on day 0, on day 3 after passive transport to 2,200 m, and on day 14 after climbing to 4,200 and 5,642 m., Results: Sea level HVR in group 1 was 47% lower than in group 2, accompanied by higher blood DOPA (300%) and DA (37%) content. Initial DA and DOPA concentrations showed a negative correlation with initial HVR but a positive correlation with age. Passive transport to middle altitude (2,200 m) increased HVS, doubling HVR slopes in groups 1 and 2 and producing increased maximum expired minute ventilation during isocapnic rebreathing (29 and 28%, respectively). Day 3 2,200-meter blood DOPA content decreased by 22% in group 1 and increased by 300% in group 2. DA increased in both groups., Conclusion: The relationship between HVR and the reciprocal DA and DOPA values seen in both groups is associated with age, producing decreased DA receptor sensitivity and enhanced DA reuptake during adaptation to high altitude., (Copyright 2000 S. Karger AG, Basel.)

Adaptation to intermittent hypoxia can enhance a hypoxic ventilatory response (HVR) in healthy humans. Naturally occurring oscillations in blood dopamine (DA) level may modulate these responses. We have measured ventilatory response to hypoxia relative to blood DA concentration and its precursor DOPA before and after a 2-week course of intermittent hypoxic training (IHT). Eighteen healthy male subjects (mean 22.8+/-2.1 years old) participated in the study. HVRs to isocapnic, progressive, hypoxic rebreathing were recorded and analyzed using piecewise linear approximation. Rebreathing lasted for 5-6 min until inspired O2 reached 8 to 7%. IHT consisted of three identical daily rebreathing sessions separated by 5-min breaks for 14 consecutive days. Before and after the 2-week course of IHT, blood was sampled from the antecubital vein to measure DA and DOPA content. The investigation associated pretraining high blood DA and DOPA values with low HVR (r = -0.66 and -0.75, respectively), elevated tidal volume (r = 0.58 and 0.37) and vital capacity (r = 0.69 and 0.58), and reduced respiratory frequency (r = -0.89 and -0.82). IHT produced no significant change in ventilatory responses to mild hypoxic challenge (Peto2 from 110 to 70-80 mm Hg; 1 mm Hg = 133.3 Pa) but elicited a 96% increase in ventilatory response to severe hypoxia (from 70-80 to 45 mm Hg). Changes in HVRs were not accompanied by statistically significant shifts in blood DA content (24% change), although a twofold increase in DOPA concentration was observed. Individual subject's changes in DA and DOPA content were not correlated with HVR changes when these two parameters were evaluated in relation to the IHT. We hypothesize that DA flowing to the carotid body through the blood may provoke DA autoreceptor-mediated inhibition of endogenous DA synthesis-release, as shown in our baseline data.

11C-labeled 3,4-Dihydroxy-phenyl-L-alanine (L-DOPA) and L-fluorodopa were used as tracers for the functional state of the presynaptic dopamine system in anesthetized monkeys with positron emission tomography. The radiotracer disposition in brain tissue and plasma were studied and effects induced by pharmacologic challenges were evaluated. 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (6R-BH4) increased the striatal influx rate constant, e.g., striatal K(i) for L-[beta-11C]DOPA, but it induced no effect on the K(i)-value using L-[beta-11C]-6-fluorodopa. Studies of radiolabeled tracer and metabolites in plasma showed substantial differences between the two tracers. At baseline conditions, 60% unchanged L-[beta-11C]DOPA was detected in plasma 50 minutes after tracer injection and the 3-O-methylated fraction accounted for 25% of total radioactivity. For L-[beta-11C]-6-fluorodopa, the relation was inverse; about 25% unchanged tracer and 60% 3-O-methyl metabolite were present in plasma after 50 minutes. A site-specific 11C-labeling in the carboxylic position in the molecules revealed a significant specific retention of radioactivity in striatum with L-[car-boxy-11C]-6-fluorodopa but not with L-[carboxy-11C]DOPA. The 3-O-methyl metabolite of L-DOPA is known to pass the blood-brain barrier and may interfere with the calculation of the K(i)value using a brain reference region. Thus, extensive 3-O-methylation in circulation of the fluorinated analog could obscure the detectability of potential functional change in striatal K(i) of the tracer when using a reference tissue model for calculation.

Protein intake-induced natriuresis previously related to increased urinary dopamine excretion was reexamined in an extensive controlled study comparing healthy and hypertensive subjects. In healthy subjects, ingestion of 1 g/kg wt tuna induced natriuresis that was associated, between postprandial hours 1 and 2, with increased plasma tyrosine [191 +/- 13% (mean +/- SE); P < 0.01], 3, 4-dihydroxyphenylalanine (104 +/- 12%, P < 0.05 in plasma; 162 +/- 20%, P < 0.05 in urine), plasma free dopamine (156 +/- 32%; P < 0. 05), and dopamine sulfate (191 +/- 11%, P < 0.001 in plasma; 199 +/- 15%, P < 0.01 in urine) but affected urinary free dopamine excretion only at limits of significance. Hypertensive subjects had less (P < 0.02) natriuresis and, despite comparable plasma tyrosine and dopamine sulfate increases, no increase in plasma and urinary 3, 4-dihydroxyphenylalanine and plasma free dopamine. Their plasma and urinary free epinephrine responses were less (P < 0.05) than the borderline increases in control subjects. Compared with control subjects, they significantly increased plasma 3, 4-dihydroxyphenylalanine sulfate (P < 0.05), epinephrine sulfate (P < 0.05), and the dopamine sulfate-to-free dopamine ratio (P < 0.02). Postprotein natriuresis is thus associated with nutritional priming-induced plasma but not urinary free dopamine increase. Hypertensive subjects have attenuated natriuretic and plasma free dopamine responses and less free epinephrine increase. This may partly result from higher circulating 3,4-dihydroxyphenylalanine, dopamine, and epinephrine sulfoconjugates leaving fewer free amines for biological actions.

Routine determination of [18F]DOPA and its metabolites in plasma is essential for assessment and quantification of presynaptic dopamine function in vivo using a modeling approach with positron emission tomography (PET). The determination of unchanged [18F]DOPA from human and non-human primate plasma using solid-phase extraction (SPE) with Sep-Pak cartridges during PET dopaminergic studies is described here. The results from the studies showed that this new approach in comparsion to a method such as thin-layer chromatography (TLC) possessed a simplicity, rapidity and accuracy as well as good correlation between the two techniques (p<0.0001). A proposed procedure involving radioanalysis on alumina plates (Al2O3) was also developed with an excellent correlation compared to the conventional C18 plates (r=0.96). Thus it could be concluded that the SPE on either C18 or alumina cartridges (Waters) compared to radio-TLC analysis on C18 and alumina systems, appears to be a useful analytical method suitable for correcting the input arterial function in routine clinical PET neurotransmission studies.

1. Plasma concentrations of 3,4-dihydroxyphenylalanine (DOPA), dopamine sulphate (DA-S), and 3,4-dihydroxyphenylacetic acid (DOPAC) in humans have been claimed to be indexes of sympathetic nervous activity, but the source and significance of plasma DOPA, DOPAC and DA-S have not been completely elucidated. 2. The effects of ordinary meals on plasma concentrations of total dopamine, mainly DA-S, DOPAC and DOPA were studied in seven healthy subjects. Venous blood was collected every hour for 25 h, while subjects were either fasting or received three meals at 9.00 hours, 13.00 hours and 18.00 hours. Catecholamines and metabolites were determined by reverse-phase HPLC with electrochemical detection. Neutral amino acids were measured by ion-exchange chromatography with photometric detection. 3. The food contained relatively little DOPA as compared with phenylalanine, tyrosine, isoleucine and tryptophan. The content of DA and DA-S varied considerably, with the greatest amount in the evening meal of open sandwiches. 4. Plasma DOPA decreased significantly after the meals at 13.00 hours and 18.00 hours, whereas concentrations of the other amino acids increased as expected. 5. Plasma DA-S increased significantly after meals and especially after the evening meal. Increments in DA-S above basal values after a meal were closely related to the content of DOPA+DA+DA-S in the meal. Plasma DOPAC increased significantly after the evening meal. 6. The decrease in plasma DOPA observed after a meal was probably due to uptake of DOPA by muscle tissue. Changes in plasma DA-S and DOPAC during this 25-h study reflected to a large extent the content of DOPA, DA and DA-S in the meals.

1. The present study has examined the daily urinary excretion of L-DOPA, dopamine and its metabolites (DOPAC, 3-MT and HVA) during normal salt (NS) and high salt(HS) diets. 2. Daily urinary excretion of L-DOPA, DA, DOPAC, 3-MT and HVA during the 4-day period of NS diet averaged, respectively, 7.6 +/- 0.4, 71 +/- 5, 217 +/- 22, 570 +/- 90 and 1217 +/- 110 nmol/kg/day. The slight increase in the urinary excretion of DA, DOPAC and 3-MT (16% to 42% increase), when rats were fed a HS diet, did not achieve statistical significance. 3. In contrast, the urinary levels of L-DOPA during the HS diet period (11 +/- 1 nmol/kg/day) were found to be significantly higher than during the NS diet period; the maximal increase in the urinary excretion of L-DOPA (93% increase) was observed in the first day and then a progressive decline was observed towards the end of the HS intake period. 4. During the first 5 days of the HS intake period, the urine output of noradrenaline (NA) was found to increase (27% to 83%) and then to progressively decline to baseline values (13.5 +/- 0.7 nmol/ kg/day). Urinary excretion of adrenaline (AD) during the HS intake period was found to increase (72% to 146%); the mean daily urinary excretion of AD during the NS diet period averaged 2.5 +/- 0.4 nmol/ kg/day. NS and DA contents in the kidney of rats on a NS diet were not significantly different from that of rats in a HS diet. 6. It is concluded that long-term HS intake in Wistar rats fail to change the urinary excretion of DA and of its metabolites (DOPAC, 3-MT and HVA). Furthermore, the discrepant profile in the urinary excretion of L-DOPA and DA during HS intake might be related to a reduction in the tubular uptake of the amino acid, rather than reflecting a decrease in its decarboxylation.

Plasma levels of norepinephrine (NE), dihydroxyphenylglycol (DHPG), dihydroxyphenylalanine (DOPA), dopamine (DA), and dihydroxyphenylacetic acid (DOPAC)--all of which are free catechols--and sulfoconjugated DA (DASO4) were determined in 14 normal subjects and 18 patients with neurogenic orthostatic hypotension caused by either multiple system atrophy (MSA) (n = 11) or pure autonomic failure (n = 7). All free catechols were normal in patients with MSA, whereas NE, DHPG, DA, and DOPAC levels were significantly lower in patients with pure autonomic failure. The levels of DA-SO4, however, did not statistically differ among the three groups. The different plasma levels of free catechols in MSA and pure autonomic failure are consistent with the view that peripheral sympathetic neurons are relatively preserved in MSA, whereas they are severely affected in pure autonomic failure. Because DASO4 does not appear to be affected in pure autonomic failure, it appears likely that this metabolite is derived mainly from non-neural sources, such as the gastrointestinal tract, rather than from the sympathoadrenomedullary system.

Objective: To investigate endogenous cerebrospinal fluid catecholamines in Parkinson's disease., Material and Methods: Basal concentrations of free norepinephrine (NE), dopamine (DA), epinephrine (E), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylalanine (DOPA) in cerebrospinal fluid (csf) and plasma were measured using reverse-phase HPLC with electrochemical detection in 16 patients with Parkinson's disease and 21 control patients with low back pain., Results: Parkinsonian patients had significantly decreased values of csf NE and DOPAC, the strong relationship between plasma and csf NE was disrupted and neither was there any age related increase of plasma NE. In l-DOPA treated patients plasma DA and DOPA concentrations were raised and csf DOPAC values were inversely related to severity of disease (Hoehn and Yahr score). Csf E concentrations were also reduced in parkinsonian patients whereas csf DA concentrations were unchanged. Csf DOPA concentrations were insignificantly decreased in parkinsonian patients., Conclusions: These results point towards a diffuse neuronal dysfunction in Parkinson's disease and indicate that lumbar csf NE and csf DOPAC are of central nervous origin.

In mammals, the sympathetic neurotransmitter is norepinephrine (NE), and the main adrenomedullary hormone is epinephrine (EPI). The sources and physiological roles of the third endogenous catecholamine, dopamine (DA), outside the brain have been obscure. Several lines of evidence suggest that in the periphery, rather than DA serving only as the precursor for the active compounds, released from sympathetic nerves and the adrenal medulla, DA may also act as an autocrine/paracrine regulator of local organ function. Thus, in the kidneys, most of DA formation appears to be from proximal tubular uptake of plasma DOPA, and binding of locally formed DA to dopaminergic receptors decreases Na/K ATPase activity and thereby accentuates natriuresis. In the gastric mucosa, DA may modulate sodium absorption and acid secretion. Recent clinical and laboratory animal evidence has indicated that the lungs and mesenteric organs contribute substantially to total body production and metabolism of DA. Generation of DA in non-noradrenergic, non-adrenergic cells can explain why human urine contains higher concentrations of DA and its metabolites than of NE and its metabolites. The vast preponderance of plasma DA in humans is sulfoconjugated. Since patients with sympathoneural failure have normal plasma levels of DA sulfate, one may speculate that the sulfoconjugating mechanism is relatively independent of sympathetic nerves and acts to localize DA effects and inactivate DA entering the circulation. These considerations lead to the concept of a third peripheral catecholaminergic system, where DA derived from plasma DOPA acts as an autocrine/paracrine substance and is inactivated by conjugation.

Neuroblastoma (NB) is a tumor which arises from neural crest cells. In the developing neural crest cells, the induction of 3,4-dihydroxyphenylalanine (DOPA) decarboxylase is more delayed than that of tyrosine hydroxylase and dopamine-beta-hydroxylase. If NB cells are arrested in an early stage of neural crest development, the induction of DOPA decarboxylase is insufficient and the accumulation and secretion of DOPA can be caused. The biochemically immature phenotype is thought to represent the undifferentiated characteristics of the cells and might correlate with the grade of malignancy. To investigate whether the hypothesis is clinically applicable or not, we have measured plasma DOPA, dopamine and urinary catecholamine metabolites in NB patients. The levels of plasma DOPA, dopamine, urinary homovanillic acid (HVA) and vanillactic acid (VLA) were significantly higher in patients with unfavorable NBs and the higher plasma DOPA level was significantly associated with the patients' age (> 1 year old), tumor stage (III, IV) and DNA diploidy. Serial determination of plasma DOPA was a good monitor of the disease course. These results are compatible with the hypothesis on DOPA decarboxylase deficiency and DOPA secretion in undifferentiated, unfavorable NBs. In conclusion, the plasma DOPA can be used to predict patients' prognosis as well as to follow up patients with NB.

A method for simultaneous measurement of free and conjugated forms of adrenalin, noradrenaline, dopamine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylacetic acid in the blood plasma and urine by high-pressure liquid chromatography with electrochemical detector has been developed. The levels of the said substances in 36 normal volunteers and 20 patients with mental disorders are presented. Simultaneous measurements of excretion of free catecholamines and their conjugates permitted a more complete characterization of catecholamine metabolism, which is important for understanding the mechanisms of disorders in catecholamine system in various diseases.

The evidence that some older patients with essential hypertension have low urinary dopamine excretion has brought into question the levels of urinary dopamine and plasma dopa, the major source of urinary dopamine, in young patients with essential hypertension. Twenty-four-hour urine sodium, creatinine, dopamine and noradrenaline and plasma dopa were evaluated in 48 patients with essential hypertension aged 18 to 27 years and 25 normotensive subjects. In comparison with age-matched normotensive subjects, the hypertensive patients had higher urinary dopamine (1920 +/- 80 vs 1520 +/- 130 nmol/day, p < 0.01) and noradrenaline (216 +/- 11 vs 179 +/- 12 nmol/day, p < 0.05) excretion. There was a significant correlation between urinary dopamine and noradrenaline excretion. There was no difference in plasma dopa levels between normotensive and hypertensive subjects. These results suggest that the elevated conversion of dopa to dopamine in the kidney is leading to increased urinary dopamine excretion in young patients with essential hypertension.

The urinary excretion of free dopamine, norepinephrine, and epinephrine could reflect the contribution of the neural release and filtration of these catecholamines as well as the intrarenal tubular synthesis and metabolism of dopamine. Because these catecholamines are rapidly metabolized, the excretion of the free amines represents only a fraction of the total release and synthesis by the kidney. The present study determined the effect of increasing dietary phosphate intake on the excretion of free dopamine, norepinephrine, and epinephrine and their primary stable metabolites. Seven male rats were placed in metabolic balance cages and fed 12 gm/day of normal phosphate diet (NPD) (0.7% inorganic phosphorus [Pi]) for 4 days and then fed a high phosphate diet (HPD) (1.8% Pi) for 4 days. Twenty-four-hour urine samples were collected for determination of free catecholamines, their major stable metabolites, and electrolyte excretions. The urinary excretion data for the seven rats was combined for all 4 days of each dietary regimen. Increasing phosphate intake from 0.7% to 1.8% significantly increased free dopamine excretion by 23%, from 5.6 +/- 0.2 to 6.8 +/- 0.1 micrograms/day (n = 7, p < 0.05). This increase in free dopamine excretion was associated with similar increases in urinary excretion of dopamine glucuronide, 21.6 +/- 1.3 to 27.9 +/- 1.8 micrograms/day (32%) and the dopamine metabolite DOPAC, 9.4 +/- 0.5 to 12.1 +/- 0.6 micrograms/day (30%) and total dopamine excretion from 32.9 +/- 1.7 to 41.0 +/- 1.9 micrograms/day (27%). Plasma DOPA levels were unchanged by increased dietary phosphate intake; however, plasma norepinephrine levels decreased significantly. Excretion of free or sulfated norepinephrine was not changed by increased phosphate intake. However, excretion of MHPG, a metabolite of norepinephrine and epinephrine, decreased significantly, from 33.7 +/- 2.1 to 23.9 +/- 0.8 micrograms/day, n = 7, p < 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Dihydroxyphenylalanine is the precursor of all endogenous catecholamines. In laboratory animals, renal uptake and decarboxylation of circulating dihydroxyphenylalanine accounts for most of dopamine in urine. Dopamine is natriuretic, and in rats, dietary salt loading increases renal dihydroxyphenylalanine uptake by increasing the rate of entry (spill-over) of dihydroxyphenylalanine into arterial plasma. In experimental animals and in humans, dietary salt loading increases urinary excretion of dihydroxyphenylalanine and dopamine. The present study examined in humans the extent to which circulating dihydroxyphenylalanine is the source of urinary dopamine and of the dopamine metabolite dihydroxyphenylacetic acid, and whether, as in animals, dietary salt loading affects dihydroxyphenylalanine spillover. 2. L-Dihydroxyphenylalanine (0.33 micrograms min-1 kg-1) was infused intravenously for 300 min after 7 days of a low-salt (mean 41 mmol/day) or a high-salt (mean 341 mmol/day) diet in 12 healthy subjects. Concentrations of dihydroxyphenylalanine, dopamine and dihydroxyphenylacetic acid were measured in urine and in antecubital venous plasma. Infusion of L-dihydroxyphenylalanine produced a steady-state mean dihydroxyphenylalanine level about 10 times the endogenous level. About 30% of infused dihydroxyphenylalanine estimated to be delivered to the kidneys via the arterial plasma was excreted as dopamine, and about 30% was excreted as dihydroxyphenyl-acetic acid. 3. Dietary salt loading increased urinary excretion rates of dihydroxyphenylalanine [from 0.08 +/- (SEM) 0.01 to 0.14 +/- 0.03 nmol/min, t = 2.80, P < 0.02] and dopamine (from 1.03 +/- 0.19 to 1.30 +/- 0.28 nmol/min, t = 2.35, P < 0.05), whereas dihydroxyphenylalanine spillover appeared to be unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

The "wearing-off" phenomenon is a clinically recognized adverse effect of long-term L-DOPA therapy in Parkinson's disease. Several causes of this phenomenon have been proposed, but no direct evidence has yet been obtained. The present study was therefore conducted to investigate the effects of long-term L-DOPA administration on the dopamine system. We examined in rats the time course of the levels of L-DOPA and its metabolites in the serum and striatum, the activities of tyrosine hydroxylase and catechol O-methyltransferase, and the D1 and D2 dopamine receptor bindings in the striatum until 12 h after the final dose on the 28th day of repeated oral L-DOPA administration, and compared the results with those after a single L-DOPA administration. The results revealed that long-term L-DOPA administration induced (1) acceleration of DOPA absorption at the gut and the blood-brain barrier, (2) reduction of dopamine retention in the striatum, and (3) loss of "supersensitive response" of dopamine receptors. "Supersensitive response" induced by single L-DOPA administration was preceded by the increase of D1 messenger RNA. We suggest that these changes after long-term L-DOPA administration are causes of the "wearing-off" phenomenon in Parkinson's disease.

The previously observed defective dopamine (DA) generation from 3,4-dihydroxyphenylalanine (DOPA) can also be seen in patients treated for many years by hydralazine. This may be due to a hydralazine-induced depletion of pyridoxine, an essential coenzyme of the aromatic L-amino acid decarboxylase (LAAD). Eleven hydralazine-treated stable essential hypertensive (EH) patients, initially found to have a defect in the DOPA decarboxylation to DA, tested by a single DOPA administration (500 mg, orally), were retested by the same test 4 days after pyridoxine pretreatment (100 mg/day) for data on blood pressure (BP), pulse rate, and renal and plasma catecholamines and their metabolites, as well as plasma atrial natriuretic factor (ANF), cyclic GMP (cGMP), plasma renin activity (PRA), and plasma aldosterone (PA). Initially, hydralazine-treated stable EH patients manifested, following DOPA administration, lower DOPA decarboxylation to DA than control subjects. Pyridoxine pretreatment accelerated DA generation from exogenous DOPA and attenuated the DOPA-induced increases in plasma and urinary DOPA and its metabolite 3-O-methyl-DOPA, but accentuated the increase in free DA and its main metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), while BP, ANF, cGMP, PRA, and PA remained unaffected. The DOPA-induced increments of urinary DA were, in contrast to plasma DA changes, blunted by pyridoxine pretreatment. The attenuation of the sodium excretion by pyridoxine pretreatment exceeded that of the DA excretion, suggesting that pyridoxine suppressed a natriuretic factor, other than ANF, or activated a sodium-retaining factor, other than renin or aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty newborns, 12 with prenatal exposure to cocaine and an unexposed control group of 8, were studied to determine concentrations of circulating catecholamines and their relationship to newborn behavior. Birth weight of the cocaine-exposed neonates was significantly lower than that of the control group. Gestational age, length, and head circumference of the cocaine-exposed neonates were also lower, although the differences did not reach statistical significance. Between 24 and 48 hours of age, circulating concentrations of norepinephrine, dopamine, and the catecholamine precursor dihydroxyphenylalanine were measured and behavior was assessed using the Neonatal Behavioral Assessment Scale. Mean dihydroxyphenylalanine concentrations were increased in the cocaine-exposed newborns (10.3 ng/mL vs 5.9 ng/mL, P = .055), while there was no difference between the groups in mean norepinephrine or dopamine concentrations. There was a significant negative correlation between norepinephrine concentration and orientation cluster score for the cocaine-exposed newborns (r2 = .6979, P = .005). norepinephrine concentration did not correlate with the score for any other behavioral cluster, nor did dopamine or dihydroxyphenylalanine concentration correlate with the score for any cluster. These preliminary data from a pilot study suggest that catecholamine activity is increased in cocaine-exposed newborns and may play a role in neurobehavioral disturbances associated with prenatal exposure to this drug.

To explore whether an altered metabolic pathway of dihydroxyphenylalanine (DOPA) may be related to some previously observed dopamine abnormalities in borderline hypertension, we measured basal and DOPA-induced (500 mg orally) changes in blood pressure and pulse rate as well as in three hourly plasma and urine samples. We found that borderline hypertensive patients compared with controls 1) showed a higher baseline urinary excretion of methoxytyramine, a marker of exocytotic dopamine release, with a greater DOPA-induced decrease of systolic blood pressure without reflex tachycardia; 2) had in response to DOPA a blunted plasma DOPA and free dopamine increase but an accentuated plasma dopamine sulfate and urinary DOPAC excretion; and 3) eliminated comparable quantities of dopamine in urine despite a lower rise in the glomerular DOPA load. Furthermore, although DOPA elicited natriuresis in both groups, its effect was greater in borderline hypertensive patients, who lacked the urinary sodium correlation with urinary dopamine excretion seen in control subjects. These data are compatible with increased basal exocytotic dopamine release and accelerated neuronal and renal (extraneuronal) dopamine generation from administered DOPA in borderline hypertension. The DOPA-induced hypernatriuresis exceeding augmented dopamine in borderline hypertensive patients, contrasting with the urinary sodium and dopamine correlation in control subjects, suggests that DOPA induced an additional natriuresis in borderline hypertensive patients by a decrease in renal sympathetic tone because of its central inhibition of sympathetic outflow, which also may account for the absence of reflex tachycardia.

A high-performance liquid chromatographic method for the analysis of gamma-L-glutamyl-L-dihydroxyphenylalanine (gludopa) and its major metabolites L-dihydroxyphenylalanine (L-DOPA), dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) is described. High sensitivity is achieved with a multi-cell coulometric detector utilising the specific electrochemical properties of gludopa (limit of detection 10 pg on-column). The retention time of gludopa was both pH-dependent and sensitive to negatively charged ion-pairing agents. An alumina-based solid-phase sample preparation technique with dihydroxybenzylamine as internal standard is described for plasma and urine (limit of detection 40 pg/ml) and an ultrafiltration technique is described for tissues (limit of detection 1-10 ng/g). After treatment with 50 mg/kg gludopa, in excess of twenty separate catecholic metabolic peaks can be detected in rat urine, whereas in humans after 9 mg/kg the only catechols detected were L-DOPA, dopamine and DOPAC.

5-S-Cysteinyldopa, dopa, and dopamine levels were determined by HPLC and electrochemical detection in serum, urine, kidney, spleen, heart, and sympathetic ganglion of guinea-pig. The kidney showed high levels of 5-S-cysteinyldopa, but also of dopa and dopamine, thus demonstrating the role of the renal ti-sue in the excretion of these substances. The concentrations found in spleen and heart may indicate specific catechol-containing structures in these organs.

A method for gas chromatographic analysis of plasma dopa and dopamine is described. Deproteinized plasma was shaken with acid washed aluminium oxide at pH 8.8. Dopa and dopamine were eluted from alumina with weak acids and evaporated to dryness. The pentafluoropropionic derivative of dopamine and the trifluoroacetic derivate of dopa were made and injected into a gas chromatograph equipped with a 63Ni electron capture detector. Alpha-methyl derivatives of each substance were used as internal standards. Linearity of plasma working curves of each substance was good. This method was applied to the assay of plasma samples from Parkinsonian patients under treatment with L-dopa with or without peripheral dopa decarboxylase inhibitors. The method described is sensitive and simple enough to monitor the blood levels of dopa and dopamine of these patients.

Plasma dopa and the catecholamines--dopamine, norepinephrine, and epinephrine--were assayed by a radioenzymatic method in 15 children with active neuroblastoma and in eight others without evidence of disease to assess the value of these determinations in the diagnosis and management of the tumor. Thirty-four children with solid tumors and hemopoietic malignancies served as our controls. Elevated plasma dopa levels were observed in 13 children with active neuroblastoma (87%); dopamine and norepinephrine were elevated in 1/4 of these patients. In the group of children with neuroblastoma without evidence of disease, dopa and catecholamine levels were within the range observed in the controls. Total urinary catecholamines, homovanillic acid (HVA) and/or vanilmandelic acid (MVA) were elevated in 11 of the 15 (73%) neuroblastoma patients with active disease. While serial plasma dopa determinations correlated with the course of the disease in practically all patients and thus were useful in their follow-up, the catecholamines were of limited value in assessing tumor status. Our results suggest that plasma dopa, assayed by a radioenzymatic method, may be more reliable than the traditional urinary catecholamine determinations in the diagnosis of neuroblastoma, and it appears useful in the management of this disease.

We report a reliable method for determining DOPA levels in plasma and cerebrospinal fluid. The method is based on complete conversion of DOPA to dopamine and quantification by HPLC-ECD of the dopamine formed. Lower limit of detection was 0.5 nmol/l. No differences in plasma DOPA levels were found between normal children (0-15 yr, n = 60), normal adults (n = 39) and patients with essential hypertension (n = 40) or Parkinson's disease (no DOPA therapy, n = 30). In normal individuals and in patients with essential hypertension venous plasma levels were higher than arterial levels (10.2 vs 9.3 nmol/l, p less than 0.001, V/A ratio 1.11 (SD 0.08), n = 15). Sympathetic stimuli (standing, tilting, bicycle exercise, tyramine) did not influence DOPA levels. In untreated depressed patients (n = 10) and in non-parkinsonian neurological patients (n = 12) cerebrospinal fluid levels of DOPA were 4.5 (SD 2.4) and 5.2 (SD 1.3) nmol/l respectively. A direct method for the measurement of DOPA by HPLC-ECD after deproteinization of plasma is also described and compared with the conversion method. Good agreement was found when plasma DOPA levels exceeded 0.25 mumol/l (y(conversion method) = 0.943x (direct method) + 0.118; n = 60; r = 0.985). The direct method, because of greater simplicity and the possibility of simultaneous measurement of the DOPA metabolite 3-O-methyldopa, is the method of choice with plasma samples from DOPA-treated patients. In non-DOPA treated individuals the conversion method is superior and has proved to be an accurate and sensitive method for the determination of DOPA levels in plasma and cerebrospinal fluid.

We describe a new method for the simultaneous assay of 3,4-dihydroxyphenylalanine (L-dopa) and dopamine in serum. Both compounds have been determined quantitatively at concentrations as low as 10 mug/liter with a coefficient of variation of less than 4%. Peak heights were linearly related to concentration up to 10 mg/liter for each compound. Assay of human sera gave within-run and day-to-day coefficients of variation of 2.8% and 3.1% for L-dopa, and 2.9% and 3.7% for dopamine. The linear relationship between readings nA, y-axis) and concentration (mug/liter) is described by the following equations: y = (21.0 +/- 0.082)x + (0.46 +/- 0.31 SD) for L-dopa and y = (17.0 +/- 0.10)x + (0.08 +/- 0.04 SD) for dopamine. The procedure combines liquid/solid extraction, liquid chromatography, and controlled-potential electrochemistry. The simplicity, sensitivity, and accuracy of this method make it suitable for routine clinical analysis of serum samples to optimize bioavailability for individual patients. After the extraction procedure is completed, samples can be analyzed at the rate of 10/h.

1. We estimated the extent to which circulating dopa (3,4-dihydroxyphenylalanine) is the source of urinary dopamine (DA; 3,4-dihydroxyphenethylamine). Tritiated dopa ([3H]dopa) was infused for 90 min into the left renal artery of seven anaesthetized foxhounds, and levels of labelled and unlabelled dopa and DA were measured in the ureteral urine and in the femoral arterial and left renal venous plasma. 2. Only a small percentage of [3H]dopa delivered to the kidneys was excreted as [3H]DA (0.59% from the left kidney, 0.68% from the right); however, the arterial concentration of endogenous dopa (1220 pg/ml) and the renal plasma flows (144 and 141 ml/min by p-aminohippurate clearances) were such that all of the urinary excretion of endogenous DA (about 1 ng/min from each kidney) could be accounted for by uptake and decarboxylation of circulating endogenous dopa. 3. Plasma dopa is the main source of urinary DA.

Peculiarities of dopamine metabolism were investigated in 27 patients with various forms of active schizophrenic process. The investigations were carried out by determining the content of dopamine and its metabolites in the blood and urine. In all the patients a considerable rise of the dopamine blood level (284.7 of normal) was revealed: prevalent were bound forms of this amine. The free dopamine content in the blood rose still higher in cases of psychomotor excitation. The dopamine content in the patients' urine was lowered. The determinations of dopamine metabolites, such as, dihydroxyphenylacetic acid, and homovanillic acid showed an insufficiency of dopamine deamination: this was an evidence of a deficient activity of monoamine oxidase. Administration of L-DOPA to schizophrenic patients did not cause a rise of the dopamine blood level (in distinction from normal). The author suggests that the discovered disturbances of dopamine metabolism play a certain role in the pathogenesis of schizophrenia.

1. Urinary excretion of dopamine (DA) increases during dietary salt loading. The majority of urinary DA is derived from circulating dihydroxyphenylalanine (dopa). Whether the increase in urinary DA excretion during salt loading results from increased efficiency of uptake of dopa by proximal tubular cells of the kidney, facilitation of intracellular conversion of dopa to DA, or increased delivery of dopa to tubular uptake sites, has been unknown. 2. In 10 inpatient normal volunteers on a constant diet, daily excretion of dopa and DA was assessed during normal sodium intake (109 mmol/day) for 1 week, low sodium intake (9 mmol/day) for 1 week and high sodium intake (249 mmol/day) for 1 week. 3. Urinary DA excretion exceeded urinary dopa excretion by about tenfold, and the excretion of both DA and dopa increased by about twofold between the low and high salt diets, with similar proportionate changes. Plasma dopa was unchanged by dietary salt manipulation. 4. The results indicate that increases in urinary DA excretion during dietary salt loading can be accounted for by increased delivery of dopa to sites of uptake by proximal tubular cells. Since dopa is released into the bloodstream by sympathetic nerve endings and by the brain, and since interference with decarboxylation of dopa attenuates natriuretic responses, dopa may function indirectly as a neurohormone involved in homoeostatic regulation of sodium balance.

Dopamine (DA) normally circulates in plasma. The plasma concentration of the free form of DA is approximately equivalent to that of epinephrine (E) and 20% that of norepinephrine (NE). The free form constitutes less than 2% of total plasma DA, and the remainder exists predominantly as sulfate or glucuronide conjugates. DA is found in adrenal medulla and cortex, peripheral nerves, sympathetic ganglia, carotid body, and kidney, but quantitatively the origin of circulating DA remains poorly understood. Plasma concentrations of free DA increase in association with events that increase sympathetic tone, although to a much lesser degree than seen for NE or E. Thus, upright posture, bicycle exercise, a variety of emotional and physical stresses, and hypoglycemia may be associated with increases in plasma free DA. Plasma DA decreases during the course of dietary sodium depletion in humans, in contrast to the plasma NE response, and consistent with a physiological role for DA in the regulation of aldosterone secretion. Plasma DA increases after administration of its precursor L-dihydroxyphenylalanine, together with the decarboxylase inhibitor carbidopa. Plasma NE and (in some studies) plasma DA decrease after administration of the DA receptor agonist bromocriptine. In contrast, plasma DA and one of its major metabolites, homovanillic acid, increase after administration of the DA receptor antagonist haloperidol. Administration of the endogenous opioid peptide beta-endorphin into the brain increases central sympathetic outflow, thus increasing plasma DA concentration, although to a lesser extent than for NE or E. Disordered basal concentrations of DA in plasma or disordered responses of plasma DA have been reported in a number of disease states. Clear understanding of physiological roles of DA in plasma and of its pathophysiology awaits definition.

1 A sensitive radioenzymatic assay was developed, in which DOPA is enzymatically decarboxylated to dopamine and the latter converted to [3H]-methoxytyramine in the presence of [3H]-S-adenosyl-L-methionine and catechol-o-methyltransferase. 2 The assay was specific for DOPA, and was sensitive to 50 pg/ml. 3 Endogenous DOPA was found to be present in the plasma of eight human volunteers at a concentration of 10.46 +/- 2.42 nmol/l. 4 Simultaneous urine collections in the same subjects showed a free dopamine excretion of 68.88 +/- 17.70 nmol/h. There was significant correlation (P less than 0.01) between plasma DOPA concentration and urine free dopamine excretion (r = 0.84). 5 After the oral administration of 250 mg levodopa, plasma DOPA and urine dopamine both increased by a similar proportion (98 +/- 8.4-fold, and 93.4 +/- 6.9-fold respectively). These compare with an increase in plasma dopamine of only 26 +/- 15-fold (P less than 0.01). 6 Following the orale dose DOPA, the increase in plasma DOPA, but not plasma dopamine, could account for the increase in urine dopamine. The calculated clearance of plasma DOPA by renal decarboxylation to dopamine was 114 +/- 20 ml/min. 7 This is not significantly different from the apparent clearance of endogenous DOPA by renal decarboxylation to dopamine, and suggests that there is adequate renal decarboxylase activity for DOPA to be the precursor for renal dopamine formation.

The intracerebroventricular administration of morphine to ovariectomized rats resulted in a marked decrease in the concentration of dopamine in plasma of hypophysial portal blood. A 90% reduction in the rate of release of hypothalamic dopamine into hypophysial portal blood occurred during the 60 min following the intraventricular administration of 60 ng of morphine sulfate. A dose-related decrease in the rate of release of dopamine into the portal vasculature was observed between 7.5 ng and 60 ng of morphine sulfate. Regardless of the quantity of morphine sulfate (1-500 ng) given to the animals, the concentrations of norepinephrine and epinephrine in hypophysial portal plasma and femoral arterial plasma remained unchanged. The efficacy of morphine on the release of dopamine into hypophysial portal blood was not associated with an equal efficacy of the drug on the synthesis of dopamine in tuberoinfundibular neurons, as evaluated by the accumulation of dihydroxyphenylalanine (DOPA) in the median eminence of rats given 3-hydroxybenzylhydrazine (NSD 1015). No effect of morphine was observed on DOPA accumulation in the median eminence of NSD-treated rats that had received 50 ng of morphine sulfate intracerebroventricularly, and only a 50% reduction was observed in the accumulation of DOPA in the median eminence of rats given 500 ng of morphine sulfate. These findings are supportive of the view that morphine inhibits both the release and synthesis of dopamine but is more effective in inhibiting the release than synthesis of dopamine.

Dihydroxyphenylalanine (DOPA), dopamine (DA) and norepinephrine (NE) levels were measured in matched samples of maternal plasma (MV), umbilical arterial (UA) and venous (UV) blood of 25 normal infants born following an uncomplicated vaginal delivery. Levels in maternal plasma in the preterm period (36-40 weeks of gestation) and in 20 non-pregnant control subjects were also determined. DOPA and NE concentrations in the maternal vein at delivery were markedly higher than findings in the preterm period. The levels of DOPA and NE in the umbilical artery were significantly higher than those in the maternal vein at delivery. The DOPA levels in umbilical cord plasma showed arteriovenous differences indicating a net distribution of DOPA from the fetus to the mother. These data strongly suggest that the high DOPA levels in cord blood originate mainly from the fetus.