Plasma Dihydroxyphenylglycol Research Articles

Noradrenaline biosynthesis and metabolism during development and recovery from pacing-induced heart failure in the dog.

We have modified an assay utilizing ion-pair high-performance liquid chromatography with electrochemical detection to measure dihydroxyphenylalanine and dyhydroxyphenylglycol simultaneously with noradrenaline. We measured these agents at control, 1 and 3 weeks following the onset of rapid ventricular pacing, as well as 4 weeks after the cessation of a 3-week period of pacing. Our findings were as follows. Plasma noradrenaline increased significantly at 1 week and increased further after 3 weeks of pacing (control, 202 +/- 16; 1 week, 528 +/- 62; 3 weeks, 750 +/- 139 pg.mL-1). Plasma dihydroxyphenylalanine did not change throughout, while plasma dihydroxyphenylglycol was significantly elevated at 3 weeks (513 +/- 48 vs. 388 +/- 35 pg.mL-1 for the control). Four weeks after discontinuation of pacing, all parameters did not differ from the control. These results imply that during the development of heart failure, the rise in circulating noradrenaline does not reflect simply an increase in catecholamine synthesis, but that there are more dynamic changes associated with noradrenaline spill-over, uptake, and metabolism.

Oral yohimbine increases blood pressure and sympathetic nervous outflow in hypertensive patients.

Yohimbine is an alpha 2-adrenoceptor antagonist that is FDA approved for treatment of impotence. The drug is an indolalkylamine alkaloid chemically similar to reserpine and is believed to act through sympatholysis. We examined effects of oral yohimbine on blood pressure (BP) and plasma levels of catechols in patients with essential hypertension, a condition in which most drug treatments can produce impotence. In 25 unmedicated hypertensive subjects, vital signs were measured and blood samples were obtained through an indwelling antecubital venous catheter at baseline and 1 and 2 h after subjects ingested 4 5.4-mg tablets of yohimbine. Mean blood pressure (MBP) increased by an average of 5 mm Hg (p < 0.01), plasma norepinephrine (NE) levels increased by 66% (p < 0.001), and plasma dihydroxyphenylglycol (DHPG) levels increased by 25% (p < 0.01) at 1 h after drug administration. The magnitude of the pressor response was unrelated to baseline MBP but positively correlated with the baseline NE level (r = 0.61, p < 0.01) and with the yohimbine-induced increment in plasma NE (r = 0.4, p < 0.01). The results indicate that yohimbine does not inhibit and actually stimulates sympathetically mediated NE release in humans and that the increased NE release produces a pressor response. Yohimbine should be administered with caution to patients with high BP, especially in individuals with evidence for increased basal sympathetic outflow or those undergoing concurrent treatment with tricyclic antidepressants or other drugs that interfere with neuronal uptake or metabolism of NE.

Estimation of noradrenaline concentrations in the axoplasm of noradrenergic neurones in man

The plasma concentrations of noradrenaline (NA) and its primary neuronal metabolite, dihydroxyphenylglycol (DOPEG), were examined during graded orthostasis and NA infusion in 13 healthy subjects to estimate the NA concentration difference between the site of neuronal DOPEG formation and that in plasma. Stimulation of NA release by graded orthostasis resulted in similar absolute increments in plasma NA and DOPEG with both plasma concentrations being dependent on the degree of orthostasis. The mean value of the delta DOPEG/delta NA ratio amounted to 0.999 (0.745; 1.341). NA was infused i.v. during two consecutive 30-min periods at constant rates of 0.43 and 0.86 nmol kg-1 min-1, respectively. This infusion resulted in a delta DOPEG/delta NA ratio of 0.048 (0.036; 0.064) for the first and 0.078 (0.067; 0.090) for the second infusion period (p less than 0.01). For each individual subject, the factor quantifying the NA concentration difference between the site of neuronal DOPEG formation and plasma was calculated from the square root of the ratio of 'delta DOPEG/delta NA during orthostasis to delta DOPEG/delta NA during the low rate of NA infusion'. The average NA concentration at the site of neuronal DOPEG formation (i.e. the axoplasm of noradrenergic neurones) was found to be 4.6-fold higher than that in plasma.

Plasma norepinephrine and dihydroxyphenylglycol in essential hypertension.

The aim of the present study was to examine whether essential hypertension is associated with altered plasma concentrations of dihydroxyphenylglycol, the principal presynaptic metabolite of norepinephrine. Forearm venous plasma dihydroxyphenylglycol and norepinephrine were determined at rest and during graded orthostasis in 47 normotensive control subjects and 58 outpatients with essential hypertension. There was no group difference in age. At supine rest as well as during sitting and standing, hypertensive subjects had plasma norepinephrine concentrations similar to those in normotensive control subjects, but plasma dihydroxyphenylglycol concentrations were higher than those in normotensive control subjects. Both groups showed a linear relation between plasma dihydroxyphenylglycol (ordinate) and plasma norepinephrine (abscissa). The resulting regression line was steeper (p less than 0.02) and its ordinate intercept higher (p less than 0.01) in hypertensive than in control subjects. Eleven normotensive and 14 hypertensive subjects were also tested 3 hours after desipramine (1.5 mg/kg orally) was administered to inhibit neuronal norepinephrine reuptake. The drug did not alter plasma norepinephrine, but did reduce plasma dihydroxyphenylglycol and did abolish plasma dihydroxyphenylglycol responses to upright posture in both groups of subjects. The mean plasma dihydroxyphenylglycol concentration observed in the presence of desipramine again was higher in the hypertensive than in the control group (p less than 0.01) and closely agreed, in both groups, with the dihydroxyphenylglycol concentration given by the ordinate intercept of the dihydroxyphenylglycol versus norepinephrine regression line in the absence of desipramine.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma noradrenaline in cirrhosis: a study of kinetics and temporal relationship to ascites formation

The kinetics of plasma noradrenaline (NA) were studied in 14 patients with cirrhosis and ascites and 13 normal subjects. [3H]noradrenaline ([3H] NA) was infused intravenously to steady state and the spillover of NA into plasma and its clearance from plasma calculated. The increase in plasma NA in the cirrhotic patients was due to an increase in NA spillover (14.5 vs 3.9 nmol min-1m-2; P less than 0.001). NA plasma clearance was also increased in the cirrhotic patients (3.5 vs 2.11 min-1m-2; P less than 0.01). Plasma NA and dihydroxyphenylglycol (DHPG), a metabolite of NA of which a portion is formed after re-uptake of NA into sympathetic nerve endings, were then measured in 23 patients with cirrhosis and ascites, 17 patients with cirrhosis who had never had ascites, and 34 normal subjects. Both plasma NA and DHPG were significantly increased in the patients with ascites (NA 4.7, DHPG 14.7 nmol l-1 and in the patients with cirrhosis but no ascites (NA 3.8, DHPG 12.0 nmol l-1) compared with normal subjects (NA 1.9, DHPG 8.8 nmol 1-1). Therefore, the increase in plasma NA in cirrhosis is due to increased activity of the sympathetic nervous system rather than interference with the metabolism of NA or impaired neuronal uptake of NA. This increase appears to precede the development of ascites.

Noradrenaline reuptake and plasma dihydroxyphenylglycol during sustained changes in sympathetic activity in rabbits

The effects of sustained changes in sympathetic activity, produced by intracisternal (i.c.) infusion of yohimbine or clonidine, on the formation of the intraneuronal noradrenaline metabolite, dihydroxyphenylglycol (DHPG), and on the efficiency of noradrenaline reuptake were examined in conscious rabbits. Noradrenaline spillover was estimated by radiotracer dilution analysis of i.v. infused [ 3H]noradrenaline. Noradrenaline reuptake was estimated from the amount of DHPG derived from recaptured neurotransmitter and the effects of desipramine-induced neuronal uptake blockade on noradrenaline clearance and plasma [ 3H]DHPG. The efficiency of neuronal reuptake was assessed from relationships between noradrenaline reuptake and spillover. Sustained sympathetic activation with i.c. yohimbine increased the amount of plasma DHPG that was derived from recaptured noradrenaline as well as that derived from other sources. Acute administration of desipramine decreased both components so that the decrease in plasma DHPG overestimated the amount derived from recaptured noradrenaline. Thus, estimation of the component of plasma DHPG that was derived from recaptured noradrenaline was most accurately achieved by examination of relationships between plasma noradrenaline and DHPG. Noradrenaline reuptake and spillover into plasma were decreased by i.c. infusion of clonidine and increased by i.c. infusion of yohimbine. Neither i.c. infusion of clonidine nor yohimbine altered relationships between noradrenaline reuptake and spillover indicating that the efficiency of neuronal reuptake was unaltered by sustained changes in sympathetic activity.

The relationship between age and venous plasma concentrations of noradrenaline, catecholamine metabolites, DOPA and neuropeptide Y-like immunoreactivity in normal human subjects

Forearm venous plasma concentrations of noradrenaline (NA), catecholamine metabolites (dihydroxyphenylglycol (DHPG), dihydroxyphenylacetic acid (DOPAC], dihydroxyphenylalanine (DOPA) and neuropeptide Y-like immunoreactivity (NPY-LI) were studied in 22 men aged 20 to 81 years in the supine position and after 30 min of standing posture. Venous plasma NA, DHPG and NPY-LI increased significantly in the standing position, whereas venous plasma DOPAC and venous plasma DOPA remained unchanged. Increments in venous plasma NA and DHPG upon standing up, as well as venous plasma NA in the standing-up position, increased significantly with age. The ratio between increments in venous plasma DHPG and venous plasma NA did not change with age. Venous plasma NPY-LI and venous plasma DOPA did not change with age, whereas venous plasma DOPAC decreased significantly. Changes in venous plasma NPY-LI were negatively correlated with changes in pulse pressure. These results confirm previous studies that sympathetic activity increases with age. The unchanged ratio between increments in venous plasma DHPG and venous plasma NA suggests that intra-neuronal deamination of recaptured NA is unchanged in the elderly. The lower basal venous plasma DOPAC concentration may suggest a reduced basal intraneuronal synthesis of NA in old age.

Simultaneous determination of plasma noradrenaline and adrenaline kinetics

Liquid chromatographic fractionation and detection of exogenous radiolabelled and endogenous catechols was used to examine simultaneously the plasma kinetics of noradrenaline and adrenaline in the conscious rabbit. Plasma clearances and release of noradrenaline and adrenaline into plasma were compared before and during nitroprusside-induced hypotension and 2-deoxyglucose-induced glucopenia, stimuli purported to differentially affect catecholamine release from sympathetic neurons and the adrenal medulla. Plasma concentrations of dihydroxyphenylglycol (DHPG) were also measured to assess presynaptic sympathetic function. Plasma clearances of adrenaline correlated with, but were significantly less than those of noradrenaline. Plasma clearances of both catecholamines showed significant decreases during nitroprusside-induced hypotension and 2-deoxyglucose-induced glucopenia. Glucopenia and hypotension increased the release into plasma of noradrenaline and adrenaline, but the adrenaline response relative to the noradrenaline response was greater during glucopenia than during hypotension. Plasma DHPG concentrations increased during glucopenia and hypotension, consistent with increased neuronal reuptake of noradrenaline and therefore a neuronal source--as opposed to an adrenal source--of most of the noradrenaline appearing in plasma during the stimuli. The increase in plasma DHPG relative to that of noradrenaline was greater after 2-deoxyglucose than after nitroprusside suggesting that the presynaptic handling of noradrenaline during glucopenia was different from that during hypotension or that the two stimuli released DHPG from regionally distinct sources.

Plasma dihydroxyphenylglycol for estimation of noradrenaline neuronal re-uptake in the sympathetic nervous system in vivo.

1. Neuronal re-uptake is the primary means for terminating the actions of endogenously released noradrenaline. A portion of the recaptured noradrenaline is deaminated to form dihydroxyphenylglycol. The present report describes a technique using plasma dihydroxyphenylglycol for estimation of the rate of neuronal reuptake of endogenous noradrenaline in vivo. 2. Neuronal re-uptake of noradrenaline in the sympathetic nervous system of the rat was estimated from the effects of neuronal uptake blockade with desipramine on three variables: (i) the plasma clearance of intravenously infused 3H-labelled noradrenaline, (ii) the plasma concentration of endogenous dihydroxyphenylglycol, and (iii) the plasma concentration of 3H-labelled dihydroxyphenylglycol formed from infused 3H-labelled noradrenaline. 3. Desipramine decreased plasma dihydroxyphenylglycol by 36%, this representing the fraction of dihydroxyphenylglycol in plasma that was derived from recaptured noradrenaline. After desipramine, the decrease in the rate of neuronal uptake of 3H-labelled noradrenaline was 9.7 times that of the decrease in the plasma spillover of 3H-labelled dihydroxyphenylglycol. Since the appearances in plasma of dihydroxyphenylglycol from unlabelled and 3H-labelled noradrenaline were similar, the neuronal re-uptake of endogenous noradrenaline could be assumed to be 9.7 times as much as the plasma spillover of dihydroxyphenylglycol that was derived from recaptured noradrenaline (0.15 nmol min-1 kg-1). 4. The rate of neuronal re-uptake of endogenous noradrenaline was estimated to be 1.45 nmol min-1 kg-1, whereas the plasma spillover of noradrenaline was 0.127 nmol min-1 kg-1. Thus, only a small fraction (less than 9%) of the noradrenaline released into the synaptic cleft spills over into the circulation.

Plasma dihydroxyphenylglycol (DHPG) as an index of diabetic autonomic neuropathy.

Forearm venous plasma noradrenalin and dihydroxyphenylglycol (DHPG) concentrations were measured in eight diabetic patients with and eight diabetic patients without neuropathy. Plasma noradrenalin was on average the same in patients with and without neuropathy and correlated to serum creatinine. Plasma DHPG concentrations were significantly reduced in patients with autonomic neuropathy as compared to patients without neuropathy (P less than 0.05). A low plasma DHPG/noradrenalin ratio in forearm venous blood identified all patients with autonomic neuropathy except one (P less than 0.02). Measuring the plasma DHPG/noradrenalin ratio may circumvent the problem of unrepresentative noradrenalin release from the forearm.

Plasma dihydroxyphenylglycol and the intraneuronal disposition of norepinephrine in humans.

We examined plasma levels of the sympathetic neurotransmitter norepinephrine (NE) and its deaminated metabolite dihydroxyphenylglycol (DHPG) during supine rest in healthy human subjects and in sympathectomized patients, during physiological (tilt) or pharmacological (yohimbine, clonidine) manipulations known to affect sympathetically mediated NE release, during blockade of neuronal uptake of NE (uptake-1) using desipramine, and during intravenous infusion of NE. Healthy subjects had a mean arteriovenous increment in plasma DHPG in the arm (10%, P less than 0.05), whereas sympathectomized patients had a mean arteriovenous decrement in DHPG in the affected limb (mean decrease 21%, P less than 0.05 compared with healthy subjects). Tilt and yohimbine, which stimulate, and clonidine, which inhibits, release of endogenous NE, produced highly correlated changes in plasma NE and DHPG (r = 0.94). Pretreatment with desipramine abolished DHPG responses to yohimbine while enhancing NE responses. To attain a given increase in plasma DHPG, about a tenfold larger increment in arterial NE was required during NE infusion than during release of endogenous NE. When plasma NE was markedly suppressed after administration of clonidine, plasma DHPG decreased to a plateau level of 700-800 pg/ml. The results indicate that (i) plasma DHPG in humans is derived mainly from sympathetic nerves; (ii) increments in plasma DHPG during stimulation of NE release result from uptake of NE into sympathetic nerve endings and subsequent intraneuronal conversion to DHPG; (iii) plasma DHPG under basal conditions probably is determined mainly by net leakage of NE into the axonal cytoplasm from storage vesicles; and (iv) increments in NE concentrations at neuronal uptake sites can be estimated by simultaneous measurements of DHPG and NE during NE infusion and NE release. Measurement of NE and DHPG provides unique clinical information about sympathetic function.

Simultaneous liquid-chromatographic determination of 3,4-dihydroxyphenylglycol, catecholamines, and 3,4-dihydroxyphenylalanine in plasma, and their responses to inhibition of monoamine oxidase.

This is a reversed-phase liquid-chromatographic method, with electrochemical detection, for simultaneously measuring, in plasma, the concentrations of the catecholamine precursor dihydroxyphenylalanine (DOPA); the endogenous catecholamines norepinephrine, epinephrine, and dopamine; and the deaminated catecholamine metabolites dihydroxyphenylacetic acid (DOPAC) and dihydroxyphenylglycol (DHPG). We used this method to assess effects of monoamine oxidase (EC 1.4.3.4) inhibition in humans. Plasma DHPG concentrations as determined by the present method (mean 826, SEM 61 ng/L) were similar to those found by other methods. Inhibition of monoamine oxidase (by administering deprenyl or tranylcypromine) decreased plasma DHPG by greater than 65%, plasma DOPAC by greater than 50%, and plasma DOPA by about 20%, without consistently affecting norepinephrine or epinephrine. Simultaneous measurement of DOPA, catecholamines, and DHPG may be useful for examining the synthesis, release, and intraneuronal metabolism of norepinephrine. The assay method is rapid, reliable, and simple, and it provides a more comprehensive assessment of noradrenergic nervous function than does measurement only of catecholamines.

Plasma dihydroxyphenylglycol (DHPG) in the in vivo assessment of human neuronal norepinephrine metabolism

We investigated the utility of deaminated norepinephrine (NE) metabolites in the study of human sympathetic nervous pathophysiology. Plasma levels of the NE metabolite dihydroxyphenylglycol (DHPG) appear to be related to intraneuronal NE stores. Plasma DHPG increases when sympathetic nervous activity or circulating NE increase and decreases when neuronal NE is depleted or neuronal NE reuptake is blocked. Changes in plasma dihydroxymandelic acid (DOMA) related less closely to changes in plasma NE. The coupling of measurements of plasma NE with its deaminated metabolites and DHPG may improve understanding of human NE metabolism and neuronal NE reuptake.

Plasma noradrenaline and its deaminated metabolites in essential hypertension and pheochromocytoma.

Dihydroxyphenylglycol (DOPEG) is a metabolite of noradrenaline (NA) in the sympathetic nerve endings, and dihydroxymandelic acid (DOMA) is one in the extraneuronal tissues. The measurement of plasma DOPEG and DOMA were evaluated with NA as one of the clinical indices of sympathetic nerve activity. These were measured in essential hypertension and also applied for diagnosis of pheochromocytoma. Plasma DOPEG levels were correlated with NA. Plasma NA and DOPEG were decreased after oral administration of clonidine (150 micrograms) and plasma DOPEG levels were slowly increased after standing. Therefore, plasma DOPEG seemed to be useful as one of the rather stable indices of the sympathetic nerve activity. Plasma NA and DOPEG levels in WHO stage I essential hypertension were higher than those in normotensive controls. Observed normal plasma noradrenaline and DOPEG levels in stage II reflect the normalized sympathetic tone in this stage. The elevation of plasma NA and DOMA levels in stage III seemed to be at least partly explained by renal function disturbance. In patients with pheochromocytoma, despite of the marked elevation of plasma NA and DOMA, plasma DOPEG showed only three-fold elevation and the ratio DOPEG/NA was reduced. The simultaneous measurement of plasma NA, DOPEG and DOMA is useful to evaluate sympathetic nerve activity in essential hypertension and to differentiate pheochromocytoma in hypertension.

Plasma Levels of Catecholamines and Dihydroxyphenylglycol during Antidepressant Drug Treatment

Plasma norepinephrine, epinephrine, and 3,4-dihydroxyphenylglycol levels were measured in depressed outpatients treated in a double-blind controlled clinical trial with 150 mg/day of amitriptyline or 60 mg/day of phenelzine for 6 weeks. Both antidepressant drug treatments were associated with a significant decline in plasma dihydroxyphenylglycol concentrations, which was more pronounced with phenelzine. Plasma norepinephrine levels also declined during phenelzine but not amitriptyline treatment, and the posttreatment values correlated with clinical improvement with the monoamine oxidase inhibiting drug. Reductions in norepinephrine and dihydroxyphenylglycol correlated highly with the degree of platelet monoamine oxidase inhibition. Mechanisms of these antidepressant drug effects on amine metabolism and their implications are discussed.

Radioenzymatic assay for plasma dihydroxyphenylglycol (DHPG), dihydroxymandelic acid (DOMA) and dihydroxyphenylacetic acid (DOPAC)

An adaptation of the single-isotope radioenzymatic catecholamine assay technique allows simultaneous quantitation of free dihydroxyphenylglycol (DHPG), dihydroxymandelic acid (DOMA), and dihydroxyphenylacetic acid (DOPAC) in small volumes of plasma. Incubation of sample with catechol-O-methyltransferase and S-adenosylmethionine is followed by acidic extractions of metabolites and thin-layer chromatography. O-methylated products of the beta-hydroxylated metabolites DHPG and DOMA are further subjected to periodate cleavage to improve sensitivity. Quantitation by liquid scintillation counting with internal standardization results in a sensitivity of approximately 8, 30 and 70 pg for DHPG, DOMA and DOPAC. Normal values for these three metabolites in resting humans are (mean ± S.D., pg/ml): 1010 ± 280 for DHPG, 2090 ± 720 for DOMA and 3270 ± 1470 for DOPAC.