Biomedical subjects

D S Goldstein

Publications and source records attributed to D S Goldstein.

At least 163 records · Page 9Linked to original sources

PubMed1993

In vivo hypothalamic release and synthesis of catecholamines in spontaneously hypertensive rats.

Juvenile spontaneously hypertensive rats (SHR) have higher plasma levels of catechols and markedly larger catechol responses to yohimbine than do normotensive Wistar-Kyoto rats, indicating increased sympathoadrenal outflow and increased alpha 2-adrenergic receptor-mediated restraint of peripheral catecholamine release during hypertension development in SHR. Yohimbine-induced catecholamine release and metabolism in the posterolateral hypothalamus of the brain were assessed in juvenile (6 to 7 weeks) and adult (15 to 16 weeks) SHR and Wistar-Kyoto rats. In vivo microdialysis was used to obtain samples for measurements of norepinephrine, dihydroxyphenylglycol, methoxyhydroxyphenylglycol, and dihydroxyphenylacetic acid in conscious animals before and after yohimbine injection (1 mg/kg IV) beginning 24 hours after probe implantation. Catecholamine synthesis was examined from elevations of 3,4-dihydroxyphenylalanine levels after probe perfusion with NSD-1015, an inhibitor of L-aromatic acid decarboxylase. In adults, SHR had higher dialysate norepinephrine (277 +/- 38 versus 181 +/- 35 pg/mL), dihydroxyphenylglycol (3260 +/- 509 versus 2231 +/- 201 pg/mL), methoxyhydroxyphenylglycol (2659 +/- 369 versus 1890 +/- 144 pg/mL), and dihydroxyphenylacetic acid (46,312 +/- 5512 versus 13,187 +/- 1963 pg/mL) levels and markedly larger increases in 3,4-dihydroxyphenylalanine levels after NSD-1015 than Wistar-Kyoto rats. In juveniles, SHR had larger proportionate increments in microdialysate norepinephrine levels after yohimbine than Wistar-Kyoto rats (85% versus 25%). Although juvenile SHR and Wistar-Kyoto rats had similar NSD-1015-elicited increments in 3,4-dihydroxyphenylalanine levels, systemic yohimbine enhanced the NSD-1015-elicited 3,4-dihydroxyphenylalanine elevations in juvenile SHR but not in Wistar-Kyoto rats. These findings suggest augmented norepinephrine release and catecholamine synthesis in the posterolateral hypothalamus of adult SHR and augmented alpha 2-adrenergic receptor restraint of both norepinephrine release and catecholamine synthesis in juvenile SHR.

Aging↗

PubMed1993

Adrenalectomy augments in vivo release of norepinephrine in the paraventricular nucleus during immobilization stress.

Adrenalectomy (ADX) activates CRH neurons in the paraventricular nucleus (PVN) of the hypothalamus and increases hypothalamic norepinephrine (NE) turnover in vitro. Immobilization (IMMO) markedly increases the release of NE into extracellular fluid in the PVN. The present study assessed whether ADX affects the release of NE in the PVN in vivo in conscious rats at baseline and during IMMO and whether cortisol (CORT) treatment attenuates the effects of ADX. Concentrations of NE, the NE metabolites dihydroxyphenylglycol and methoxyhydroxyphenylglycol, and the dopamine metabolite dihydroxyphenylacetic acid were measured in microdialysate samples beginning 24 h after implantation of a microdialysis probe in the PVN. Seven to 10 days after ADX or ADX plus CORT (20 mg/kg.day via osmotic minipump), animals underwent IMMO for 2 h. Adrenalectomized rats had slightly higher baseline microdialysate NE, dihydroxyphenylglycol, methoxyhydroxyphenylglycol, and dihydroxyphenylacetic acid levels and much larger IMMO-induced responses of these compounds than did sham-operated rats. CORT treatment abolished the ADX-induced augmentation of these responses. The results indicate that ADX, by removing endogenous glucocorticoids, augments IMMO-induced release and turnover of NE and amplifies the responses of catecholamine synthesis. Glucocorticoids, therefore, appear to exert feedback inhibition on stress-induced increments in the release of NE and catecholamine biosynthesis in the PVN.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Endogenous glucocorticoids restrain catecholamine synthesis and release at rest and during immobilization stress in rats.

Cardiovascular and metabolic adjustments during stress involve participation of the sympatho-adrenal and hypothalamic-pituitary-adrenocortical systems, which interact at several levels. The present study investigated the effects of removal of endogenous glucocorticoids on indices of norepinephrine release and metabolism and of catecholamine biosynthesis in sympathetic nerves, at baseline and in response to immobilization stress (IMMO) in rats. Plasma levels of the catecholamine precursor dihydroxyphenylalanine, norepinephrine (NE), the NE metabolites dihydroxyphenylglycol and methoxyhydroxyphenylglycol, dopamine, and the dopamine metabolites dihydroxyphenylacetic acid and homovanillic acid were measured in adrenalectomized, adrenal-medullectomized, or sham-operated conscious rats, with or without glucocorticoid treatment (25 mg/kg.24 h cortisol for 7 days by osmotic minipumps), at rest and after 5, 20, 60, and 120 min of IMMO. Adrenalectomy eliminated plasma levels of epinephrine and corticosterone and augmented IMMO-induced increments in levels of NE, dihydroxyphenylglycol, methoxyhydroxyphenylglycol, dihydroxyphenylalanine, dihydroxyphenylacetic acid, and homovanillic acid. Adrenal-medullectomy reduced plasma epinephrine, but not corticosterone, to undetectable levels at baseline and did not augment stress-induced responses of any of the measured compounds. Cortisol administration (plasma levels approximately 600 pmol/ml) reversed the augmentation of catecholaminergic responses in adrenalectomized rats. The results indicate that adrenalectomy stimulates several aspects of sympatho-neural function, including stress-induced increments in NE release, reuptake, metabolism, and turnover and in catecholamine biosynthesis. This augmentation was absent in adreno-medullectomized rats, indicating that the loss of adrenomedullary hormones after adrenalectomy does not appear to contribute to the augmentation. Since cortisol treatment reversed or prevented this augmentation, loss of feedback inhibition by endogenous glucocorticoids appears to be the basis of the enhanced responses. Thus, the results suggest that endogenous glucocorticoids restrain responses of catecholamine turnover, synthesis, release, reuptake, and metabolism in sympathetic nerves in this stress model.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Chemical mediators of autonomic nervous system activity.

Several modifications have improved the sensitivity and specificity of neurochemical tests to diagnose and distinguish multiple system atrophy and pure autonomic failure. These include [3H]-norepinephrine infusion to estimate plasma norepinephrine clearance; neuroendocrine stimulation tests; and simultaneous measurements of levels of levodopa, catecholamines, and catecholamine metabolites. New clinical imaging approaches have the potential to visualize alterations in neurotransmitter function in the brain and periphery. Patients with multiple system atrophy have decreased striatal radioactivity after injection of positron-emitting ligands at dopamine receptors or uptake sites, and patients with diffuse sympathetic denervation have decreased myocardial radioactivity after injection of radioactive sympathoneural imaging agents.

Autonomic Nervous System↗

PubMed1993

Extraneuronal metabolism of endogenous and exogenous norepinephrine and epinephrine in rats.

Normetanephrine (NMN) and metanephrine (MN) are produced by the actions of catechol-O-methyltransferase on norepinephrine (NE) and epinephrine (E). Because catechol-O-methyltransferase is not present appreciably in neurons, plasma concentrations of NMN and MN provide a marker of extraneuronal catecholamine metabolism. In the present study, plasma NMN and MN were examined in rats before and during immobilization stress or i.v. infusion of NE and E to compare the extraneuronal metabolism of circulating and neuronally released catecholamines. At rest, plasma concentrations of NMN (0.44 +/- 0.03 pmol/ml) were 34% those of NE (1.40 +/- 0.11 pmol/ml) and MN concentrations (0.15 +/- 0.02 pmol/ml) were 33% those of E (0.48 +/- 0.11 pmol/ml). Immobilization and catecholamine infusion both increased plasma NMN and MN in parallel with increases in the precursor amines. Relative to increases in precursor amines, the MN response to infusion of catecholamines was 50% greater than the NMN response. Increases in plasma MN, relative to those in E, were similar during infusion of catecholamines and immobilization stress. In contrast, the NMN response to immobilization, relative to the NE response, was 3-fold larger than the NMN response to catecholamine infusion. Larger MN responses than NMN responses to infusion of catecholamines may reflect preferential extraneuronal uptake or O-methylation of E over NE or more efficient metabolism of NMN than MN. The larger NMN response to release of endogenous stores than to infusion of exogenous amine indicated that 30% of NMN is derived from circulating NE and 70% from NE in transit from sites of release to the circulation.

Adrenal Medulla↗

PubMed1993

Determination of metanephrines in plasma by liquid chromatography with electrochemical detection.

Metanephrines are O-methylated metabolites of catecholamines. We report the use of liquid chromatography with electrochemical detection to determine plasma concentrations of normetanephrine (NMN) and metanephrine (MN). Plasma NMN and MN in 32 normal volunteers and inpatients were compared with concentrations in 23 patients with pheochromocytoma. Metanephrines were adsorbed from plasma onto a cation-exchange column and eluted with ammoniacal methanol. The dried residue was dissolved in mobile phase and injected onto a reversed-phase column. Recoveries of NMN and MN from 1 mL of plasma averaged 50-70%, and results varied linearly with quantity injected over a range of 0.13-55 pmol. The detection limit was 25 fmol for NMN and 50 fmol for MN. Intra-assay CVs were < 5%. In normal volunteers and inpatients, plasma concentrations of NMN ranged between 0.12 and 0.73 nmol/L (mean 0.38 nmol/L), and MN between 0.06 and 0.63 nmol/L (mean 0.19 nmol/L). Plasma NMN concentrations were increased in all 23 patients with pheochromocytoma (range 1-172 nmol/L), whereas MN concentrations (range 0.10-382 nmol/L) were increased in only 9 patients. The assay method is reliable and sensitive and offers an approach to examine the extraneuronal metabolism of catecholamines. The method may also be useful in the diagnosis of pheochromocytoma.

Adrenal Gland Neoplasms↗

PubMed1992

Effects of alprazolam on pituitary-adrenal and catecholaminergic responses to metabolic stress in humans.

Concurrent effects of benzodiazepines on stress-induced activation of the three classical "stress" systems: pituitary-adrenal, adrenomedullary, and sympathoneural systems have not been extensively investigated in humans. In the present study, the effects of alprazolam (1.5 mg) on plasma levels of adrenocorticotropin hormone (ACTH), epinephrine, norepinephrine, dihydroxyphenylglycol (DHPG, the intraneuronal metabolite of norepinephrine), and mood states were examined in 10 healthy volunteers undergoing glucoprivic stress. Glucoprivic stress was induced by intravenous administration of the glucose analog, 2-deoxyglucose (2DG), at a dose (50 mg/kg) that impairs cellular glucose metabolism and produces a state comparable to hypoglycemia. Alprazolam and 2DG were administered in a double-blind, placebo-controlled manner. 2DG produced robust elevations in plasma ACTH and epinephrine levels, modest elevations in plasma norepinephrine levels, and decreases in plasma DHPG levels. Alprazolam significantly attenuated the 2DG-induced increases in plasma ACTH and epinephrine, but did not significantly effect plasma norepinephrine and DHPG. These data suggest that benzodiazepines attenuate metabolic stress-induced activation of the pituitary-adrenal and adrenomedullary systems but do not effect 2DG-related effects on peripheral sympathoneural function. The possible mechanisms involved are discussed.

Adrenocorticotropic Hormone↗

PubMed1992

Noradrenergic activation in the paraventricular nucleus during acute and chronic immobilization stress in rats: an in vivo microdialysis study.

In vivo microdialysis was used to study the effects of single (2 h) or repeated (2 h for 7 consecutive days) immobilization (IMMO) stress on extracellular fluid concentrations of norepinephrine (NE) and the deaminated metabolites of NE and dopamine, dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC) in the paraventricular nucleus of conscious rats. During IMMO, NE, DHPG, and DOPAC levels increased markedly, with similar peak values and time courses in the repeatedly stressed and previously unstressed groups. NE levels during a 2-h baseline period were lower in the repeatedly stressed group than in the unstressed group (99 +/- 9 pg/ml vs. 167 +/- 13 pg/ml, P less than 0.05), whereas DHPG (1,697 +/- 263 pg/ml vs. 1,424 +/- 194 pg/ml) and DOPAC (5,989 +/- 863 pg/ml vs. 4,428 +/- 1150 pg/ml) levels tended to be higher, so that the NE/DHPG ratio at baseline was significantly lower in the repeatedly stressed group (P less than 0.05). The results indicate that IMMO stress enhances NE release, reuptake, metabolism, and synthesis in the PVN. Repeated exposure to IMMO may decrease the microdialysate NE/DHPG ratio by inhibiting exocytotic release or enhancing neuronal reuptake of NE. In either case, the results suggest that repeated exposure to stress alters the release and disposition of NE in the PVN of conscious animals.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Plasma levels of catecholamines and corticotrophin during acute glucopenia induced by 2-deoxy-D-glucose in normal man.

Acute cellular glucopenia after 2-deoxy-D-glucose administration profoundly stimulates hypothalamic-pituitary-adrenocortical and adrenomedullary activity. Whether glucopenia stimulates sympathoneural release of noradrenaline is unclear. We studied 20 healthy subjects who received 2-deoxy-D-glucose (50 mg/kg in 100 ml isotonic saline) or isotonic saline (100 ml) i.v. for 30 min on each of 2 test days. Heart rate and blood pressure were measured with antecubital venous blood obtained via an indwelling catheter for assays of plasma catecholamines (noradrenaline; adrenaline; dihydroxyphenylalanine; dihydroxyphenylglycol; and dihydroxyphenylacetic acid), corticotrophin, cortisol, and glucose. 2-deoxy-D-glucose decreased diastolic blood pressure by 20% (from 69 +/- 2 to 55 +/- 2 mmHg) and increased adrenaline levels by 30-fold [21 +/- 6 (SEM) to 634 +/- 73 pg/ml], corticotrophin by sevenfold (5.1 +/- 1.2 to 35.8 +/- 4.9 pg/ml), glucose and cortisol by two-fold (82 +/- 5 to 163 +/- 9 mg/dl and 15 +/- 2 to 31 +/- 2 micrograms/dl), and noradrenaline by about 30% (224 +/- 15 to 295 +/- 24 pg/ml, p < 0.05), whereas plasma dihydroxyphenylglycol levels decreased (765 +/- 56 to 628 +/- 42 pg/ml). Small decreases in dihydroxyphenylalanine and dihydroxyphenylacetic acid levels after 2-deoxy-D-glucose did not differ from those after saline. Responses of adrenaline levels were positively correlated with those of noradrenaline (r = 0.47, p < 0.05) and glucose (r = 0.45, p = 0.06), but not of corticotrophin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1992

Sympathoadrenal contribution to plasma dopa (3,4-dihydroxyphenylalanine) in rats.

1. To determine the sources of dopa (3,4-dihydroxyphenylalanine) in plasma, we measured regional arteriovenous differences, tissue concentrations and urinary excretion of dopa during systemic intravenous infusions of I-[3H]dopa into anaesthetized intact rats and rats pretreated with the sympathetic neurotoxin, 6-hydroxydopamine. 2. In intact rats, large arteriovenous increments in plasma dopa concentrations were noted in the femoral (47%) and adrenal (141%) beds, with a small arterial-portal venous increment (11%), whereas in the kidney there was a substantial (47%) arteriovenous decrement in plasma dopa levels. Skeletal muscle appeared to be a major source of dopa in arterial plasma. 3. Treatment with 6-hydroxydopamine abolished the afferent-efferent increment of plasma dopa concentrations in the femoral bed. The arteriovenous decrement of plasma dopa concentrations in the kidney was preserved, and the arteriovenous increment in the adrenal bed was decreased by about half. Arterial plasma dopa levels fell by 41%. 4. Regional extraction percentages of I-[3H]dopa were used to estimate the clearances and rates of appearance (spillovers) of dopa in plasma. Dopa spillover was detected in the femoral, renal, splanchnic and adrenal beds, with skeletal muscle accounting for about 44% and the kidneys accounting for about 18% of dopa in arterial plasma. Whereas chemical sympathectomy decreased the femoral and renal spillover of dopa by 90% or more, arterial dopa levels and estimated dopa spillover into arterial plasma were decreased by only about 45%. 5. The kidneys accounted for 22% of dopa clearance from arterial plasma. From the renal extraction of I-[3H]dopa and the urinary excretion of [3H]dopamine, it was estimated that 77% of dopa removed in the kidneys was excreted as dopamine in intact animals and 69% was excreted as dopamine in sympathectomized animals. Conversely, about 80% of urinary endogenous dopamine was derived from plasma dopa, regardless of 6-hydroxydopamine treatment. 6. The results indicate that endogenous dopa in arterial plasma is derived substantially but not exclusively from sympathetic nerve endings that are destroyed by 6-hydroxydopamine, especially in skeletal muscle and the kidneys. Regional dopa spillover therefore probably reflects regional catecholamine biosynthesis. In rats, urinary dopamine is derived mainly from renal decarboxylation of circulating dopa.

Adrenal Glands↗

PubMed1992

Effects of handling or immobilization on plasma levels of 3,4-dihydroxyphenylalanine, catecholamines, and metabolites in rats.

In conscious animals, handling and immobilization increase plasma levels of the catecholamines norepinephrine (NE) and epinephrine (EPI). This study examined plasma concentrations of endogenous compounds related to catecholamine synthesis and metabolism during and after exposure to these stressors in conscious rats. Plasma levels of 3,4-dihydroxyphenylalanine (DOPA), NE, EPI, and dopamine (DA), the deaminated catechol metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC), and their O-methylated derivatives methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured using liquid chromatography with electrochemical detection at 1, 3, 5, 20, 60, and 120 min of immobilization. By 1 min of immobilization, plasma NE and EPI levels had already reached peak values, and plasma levels of DOPA, DHPG, DOPAC, and MHPG were increased significantly from baseline, whereas plasma DA and HVA levels were unchanged. During the remainder of the immobilization period, the increased levels of DOPA, NE, and EPI were maintained, whereas levels of the metabolites progressively increased. In animals immobilized briefly (5 min), elevated concentrations of the metabolites persisted after release from the restraint, whereas DOPA and catecholamine levels returned to baseline. Gentle handling for 1 min also significantly increased plasma levels of DOPA, NE, EPI, and the NE metabolites DHPG and MHPG, without increasing levels of DA or HVA. The results show that in conscious rats, immobilization or even gentle handling rapidly increases plasma levels of catecholamines, the catecholamine precursor DOPA, and metabolites of NE and DA, indicating rapid increases in the synthesis, release, reuptake, and metabolism of catecholamines.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Effect of ionizing radiation on sympathetic nerve function in rat parotid glands.

Ionizing radiation (IR) irreversibly damages salivary glands. The pathologic mechanism is unknown. Previously we reported that parotid serous acinar cells may not be the primary site of damage by IR. The purpose of this study was to determine if IR alters sympathetic nerve function in rat parotid glands. Male adult rats received a single dose of radiation (20 Gy) to the head and neck. Three days after IR, parotid saliva secretion induced by norepinephrine (NE) was completely blocked. Catecholamine uptake and metabolism were studied by injecting [3H] dopamine ([3H]DA) into irradiated rats, as a bolus. After 60 min, animals were sacrificed and the parotid gland, submandibular gland, and left ventricle removed. Tissue contents of [3H]DA and [3H]NE, identified by HPLC, were unaffected by IR. The results indicate that IR abolishes acinar responsiveness to NE without affecting parotid sympathetic nerve function.

Animals↗

PubMed1992

Effects of water immersion on sympathoadrenal and dopa-dopamine systems in humans.

Water immersion to the neck increases central blood volume and evokes a marked diuresis and natriuresis. The present study examined simultaneously effects of water immersion on activities of three endogenous systems thought to participate in sodium homeostasis: the sympathetic nervous system, the atrial natriuretic peptide system, and the renal dopa-dopamine system. Hourly urine collections and antecubital venous blood samples were obtained from 10 normal subjects before, during, and after sitting in a water-immersion tank for 3 h; four control subjects were studied while seated without immersion. Urine volume was increased by more than threefold after 1 h of immersion (from 1.2 +/- 0.2 ml/min at baseline to 5.9 +/- 0.7 ml/min, P less than 0.001) and peaked during the second hour. Urinary sodium excretion increased by more than twofold (from 103 +/- 17 mu eq/min at baseline to 196 +/- 36 mu eq/min at 1 h, P less than 0.001) and peaked during the third hour. Plasma levels and urinary excretion of norepinephrine (NE) and epinephrine were suppressed consistently during immersion (P less than 0.05). There was a marked, prompt, and sustained increase in plasma levels of immunoreactive atrial natriuretic factor (irANF) from 6.9 +/- 1.9 pg/ml baseline to 17.3 +/- 4.3 pg/ml at 1 h (P less than 0.001). Urinary excretion of dopa, dopamine, and 3,4-dihydroxyphenylglycol, a neuronal metabolite of NE, changed in a triphasic pattern, with decreased excretion during the first hour of immersion (P less than 0.01), small but consistent increases during the next 2 h, and decreased excretion, to below baseline, during recovery (P less than 0.01 for dopa and dopamine).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1992

Sympathetic nervous function in human heart as assessed by cardiac spillovers of dihydroxyphenylglycol and norepinephrine.

BACKGROUND: Measurement of cardiac norepinephrine spillover may indicate the amount of transmitter at neuroeffector sites but does not distinguish neuronal release or reuptake in determining this amount or provide information about other aspects of sympathetic function. This report examines how cardiac spillover of the norepinephrine metabolite dihydroxyphenylglycol (DHPG) provides additional distinct information about cardiac sympathetic function. METHODS AND RESULTS: Arterial and coronary venous blood samples were taken during cardiac catheterization and intravenous infusion of [3H]norepinephrine in 57 subjects. Subjects were given intravenous yohimbine or underwent mental stress, handgrip exercise, and cycling exercise to activate sympathetic nerves or were given intravenous desipramine to block norepinephrine reuptake. Cardiac DHPG spillover (601 +/- 41 pmol/min) was eightfold greater than norepinephrine spillover (78 +/- 10 pmol/min) at rest and increased during sympathetic activation by 65% of the increase of norepinephrine. This and the desipramine-sensitive cardiac production of [3H]-labeled DHPG from [3H]norepinephrine indicated that 10.5 times more endogenous norepinephrine is recaptured than escapes into plasma; that more than 90% of recaptured norepinephrine is sequestered into storage vesicles; and that under resting conditions, most cardiac spillover of DHPG and turnover of norepinephrine are from metabolism of transmitter leaking from vesicles; the latter process is independent of exocytotic transmitter release with a rate at rest over 100-fold that of norepinephrine spillover and over 10-fold that of norepinephrine reuptake. CONCLUSIONS: Cardiac spillover of DHPG provides information about processes close to or within sympathetic nerve endings that cannot be provided by measurements of norepinephrine spillover alone. This includes quantitative information about the role of neuronal uptake in terminating the actions of norepinephrine at neuroeffector sites and the importance of vesicular-axoplasmic exchange of norepinephrine as a dynamic process contributing to norepinephrine turnover.

Cardiac Output, Low↗

PubMed1992

Hypercortisolemia inhibits yohimbine-induced release of norepinephrine in the posterolateral hypothalamus of conscious rats.

Chronic hypercortisolemia attenuates yohimbine (YOH)-induced increments in plasma levels of the sympathetic neurotransmitter norepinephrine (NE). The present study used in vivo microdialysis to study the effects of hypercortisolemia on YOH-induced release of NE in the brain. Cortisol (25 mg/kg.day) or saline was infused sc into rats for 7 days via an osmotic minipump. Microdialysate and plasma concentrations of NE and its metabolites dihydroxyphenylglycol and methoxyhydroxyphenylglycol were measured before and after YOH (1 mg/kg, iv) administration in conscious animals, with microdialysate and plasma collections beginning 20-24 h after probe implantation. Chronic cortisol treatment resulted in attenuated NE, dihydroxyphenylglycol, and methoxyhydroxyphenylglycol responses in both microdialysate and plasma. The results indicate that YOH increases central neural as well as peripheral release, reuptake, turnover, and metabolism of NE and that hypercortisolemia suppresses these responses.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Plasma dopa responses during stress: dependence on sympathoneural activity and tyrosine hydroxylation.

Dihydroxyphenylalanine (dopa), the precursor of all the endogenous catecholamines, circulates in plasma at a concentration higher than that of the sympathetic neurotransmitter, norepinephrine (NE). Sources of dopa in plasma and the meaning of plasma dopa levels in terms of sympathoneural function have been unclear. Plasma concentrations of dopa, the catecholamines NE, epinephrine and dopamine, the deaminated catechol metabolites dihydroxyphenylglycol and dihydroxyphenylacetic acid, and the O-methylated metabolites methoxyhydroxyphenylglycol and homovanillic acid were measured during immobilization stress in conscious rats. Animals were pretreated with chlorisondamine to block ganglionic neurotransmission or with alpha-methyl-para-tyrosine to inhibit tyrosine hydroxylation. Immobilization produced rapid, sustained increases in plasma levels of dopa, catecholamines and catecholamine metabolites. Chlorisondamine decreased base-line plasma dopa and NE levels and abolished the increases in plasma dopa and NE levels during immobilization. alpha-Methyl-para-tyrosine administration produced sustained decreases in plasma dopa levels and markedly attenuated immobilization-induced increases in plasma dopa levels. Bilateral adrenalectomy augmented base-line plasma levels of dopa and NE and augmented dopa and NE responses during immobilization. The results indicate that during immobilization stress, increased postganglionic sympathoneural outflow stimulates the synthesis of dopa in sympathetic neurones and enhances release of dopa into the circulation. The data generally support the view that changes in plasma dopa levels during stress reflect in vivo changes in the rate of catecholamine biosynthesis in sympathetic nerve terminals.

Adrenalectomy↗

PubMed1991

Method for measuring endogenous 3-O-methyldopa in urine and plasma.

The present report describes a method using column liquid chromatography with electrochemical detection for assaying concentrations of 3-O-methyldopa in urine and plasma. The technique combines a one-step sample preparation scheme with post-column flow-through electrodes in series, allowing adequate chromatographic separation of 3-O-methyldopa from other endogenous substances in urine. The validity of the method was confirmed by markedly decreased urinary 3-O-methyldopa levels after administration of an inhibitor of catechol-O-methyltransferase to rats, radioactivity in chromatographic fractions corresponding to 3-O-methyldopa in urine of rats undergoing infusion of [3H]-L-DOPA, and correlations between excretion rates of 3-O-methyldopa and catechols in humans. In healthy humans, urinary excretion of 3-O-methyldopa averaged 974 +/- 707 (S.D.) nmol per day, and plasma levels of 3-O-methyldopa averaged 89 +/- 32 nmol/l. The method should be useful in studies about the metabolism of endogenous and exogenous DOPA.

Animals↗

PubMed1991

Regional extraction of circulating norepinephrine, DOPA, and dihydroxyphenylglycol in humans.

Dihydroxyphenylglycol (DHPG) is the main intraneuronal metabolite of the sympathetic neurotransmitter, norepinephrine (NE), and dihydroxyphenylalanine (DOPA) the immediate product of the rate-limiting step in catecholamine biosynthesis. Simultaneous measurements of regional rates of appearance (spillovers) of NE, DOPA, and DHPG in plasma have the potential to provide unique information about aspects of sympathoneural function but have not actually been measured in humans. In the present study, spillovers of DHPG, DOPA, and NE in the heart, head, leg, and lungs, were estimated from regional extraction fractions of infused [3H]-1-NE, DHPG, and [13C6]DOPA or unlabelled DOPA in humans during cardiac catheterization. There was little cardiac extraction of DHPG (7 +/- SEM 2%) or DOPA (8 +/- 4%) but substantial extraction of NE (69 +/- 4%). Values for cardiac spillover of DHPG and DOPA therefore were similar to values for the arteriovenous increment times plasma flow (arteriovenous production rate), whereas the cardiac spillover of NE averaged about 7-times the NE arteriovenous production rate. Cardiac DHPG spillover (28 +/- 3 ng/min) exceeded the spillovers of NE (9 +/- 2 ng/min) and DOPA (15 +/- 4 ng/min). In contrast, cranial DOPA spillover (159 ng/min) exceeded those of NE and DHPG by 8- and 2-fold and accounted for about 1/10 of the total spillover of DOPA into arterial plasma. In the femoral vascular bed, arteriovenous production rates of NE and DHPG were unrelated to femoral spillovers of NE and DHPG. Arterial and regional clearances of [13C6]DOPA were similar to those of unlabelled DOPA. The results suggest that (1) endogenous NE, DOPA, and DHPG all are released into the bloodstream by the heart, head, and limbs of humans; (2) DHPG and DOPA are not co-released with NE; (3) cardiac arteriovenous production rates of DOPA and DHPG can be used to indicate cardiac spillover of these catechols, whereas the cardiac NE arteriovenous production rate substantially underestimates cardiac NE spillover; and (4) estimates of limb spillover of NE and DHPG require concurrent measurements of the corresponding regional clearances.

Arteries↗