Plasma Dihydroxyphenylglycol Research Articles

Ultrafine particles and ozone perturb norepinephrine clearance rather than centrally generated sympathetic activity in humans

Cardiovascular risk rapidly increased following exposure to air pollution. Changes in human autonomic regulation have been implicated based on epidemiological associations between exposure estimates and indirect autonomic nervous system measurements. We conducted a mechanistic study to test the hypothesis that, in healthy older individuals, well-defined experimental exposure to ultrafine carbon particles (UFP) increases sympathetic nervous system activity and more so with added ozone (O3). Eighteen participants (age >50 years, 6 women) were exposed to filtered air (Air), UFP, and UFP + O3 combination for 3 hours during intermittent bicycle ergometer training in a randomized, crossover, double-blind fashion. Two hours following exposure, respiration, electrocardiogram, blood pressure, and muscle sympathetic nerve activity (MSNA) were recorded at supine rest, during deep breathing, and during a Valsalva manoeuvre. Catechols and inflammatory marker levels were measured in venous blood samples. Induced sputum was obtained 3.5 h after exposure. Combined exposure to UFP + O3 but not UFP alone, caused a significant increase in sputum neutrophils and circulating leucocytes. Norepinephrine was modestly increased while the ratio between plasma dihydroxyphenylglycol (DHPG) and norepinephrine levels, a marker for norepinephrine clearance, was reduced with UFP + O3. Resting MSNA was not different (47 ± 12 with Air, 47 ± 14 with UFP, and 45 ± 14 bursts/min with UFP + O3). Indices of parasympathetic heart rate control were unaffected by experimental air pollution. Our study suggests that combined exposure to modest UFP and O3 levels increases peripheral norepinephrine availability through decreased clearance rather than changes in central autonomic activity. Pulmonary inflammatory response may have perturbed pulmonary endothelial norepinephrine clearance.

Acute effects of breaking up prolonged sitting on fatigue and cognition: a pilot study

ObjectivesTo compare the acute effects of uninterrupted sitting with sitting interrupted by brief bouts of light-intensity walking on self-reported fatigue, cognition, neuroendocrine biomarkers and cardiometabolic risk markers in overweight/obese adults.DesignRandomised...

Clinical Pharmacology Tyramine Challenge Study to Determine the Selectivity of the Monoamine Oxidase Type B (MAO‐B) Inhibitor Rasagiline

Rasagiline is a selective, monoamine oxidase (MAO)-B inhibitor indicated for treatment of Parkinson's disease. This double-blind, placebo-controlled study determined the tyramine sensitivity factor (TSF) and degree of MAO-A inhibition (ie, reduction in plasma dihydroxyphenylglycol) in healthy volunteers who received phenelzine (15 mg, 3 times daily; positive control), selegiline (5 mg, twice daily), or rasagiline (1-6 mg, once daily) for 14 days or rasagiline 2 mg/d for 30 days. The selegiline/rasagiline groups were randomized to placebo or active drug. TSF was highest with phenelzine (17.3) and lowest with placebo (1.5). TSF with selegiline was 2.5. TSFs for rasagiline were as follows: 2.0 for 1 mg/d; 3.3 and 2.4 for 2 mg/d administered for 14 and 30 days, respectively; 4.5 for 4 mg/d; and 5.1 for 6 mg/d. Plasma dihydroxyphenylglycol concentrations suggested that rasagiline 1 mg/d had no effect, whereas rasagiline 2 mg/d had only minimal effect. In contrast, rasagiline 4 and 6 mg/d reduced dihydroxyphenylglycol to a degree approaching that achieved by the positive control phenelzine. Results demonstrate that rasagiline selectively inhibits MAO-B and is not associated with increased tyramine sensitivity at the indicated dose (1 mg/d). These data allowed removal of dietary tyramine restriction from rasagiline US labeling.

Catecholamine metabolomic and secretory phenotypes in phaeochromocytoma

Phaeochromocytomas and paragangliomas (PPGLs) are highly heterogeneous tumours with variable catecholamine biochemical phenotypes and diverse hereditary backgrounds. This analysis of 18 catecholamine-related plasma and urinary biomarkers in 365 patients with PPGLs and 846 subjects without PPGLs examined how catecholamine metabolomic profiles are impacted by hereditary background and relate to variable hormone secretion. Catecholamine secretion was assessed in a subgroup of 156 patients from whom tumour tissue was available for measurements of catecholamine contents. Among all analytes, the free catecholamine O-methylated metabolites measured in plasma showed the largest tumour-related increases relative to the reference group. Patients with tumours due to multiple endocrine neoplasia type 2 and neurofibromatosis type 1 (NF1) showed similar catecholamine metabolite and secretory profiles to patients with adrenaline-producing tumours and no evident hereditary background. Tumours from these three patient groups contained higher contents of catecholamines, but secreted the hormones at lower rates than tumours that did not contain appreciable adrenaline, the latter including PPGLs due to von Hippel-Lindau (VHL) and succinate dehydrogenase (SDH) gene mutations. Large increases of plasma dopamine and its metabolites additionally characterised patients with PPGLs due to the latter mutations, whereas patients with NF1 were characterised by large increases in plasma dihydroxyphenylglycol and dihydroxyphenylacetic acid, the deaminated metabolites of noradrenaline and dopamine. This analysis establishes the utility of comprehensive catecholamine metabolite profiling for characterising the distinct and highly diverse catecholamine metabolomic and secretory phenotypes among different groups of patients with PPGLs. The data further suggest developmental origins of PPGLs from different populations of chromaffin cell progenitors.

Association of anosmia with autonomic failure in Parkinson disease

Olfactory dysfunction and autonomic failure are gaining recognition as nonmotor manifestations of Parkinson disease (PD). This observational study assessed whether in PD anosmia and autonomic failure are related to each other or to neuroimaging evidence of striatal dopamine deficiency. Olfactory function was assessed by the University of Pennsylvania Smell Identification Test (UPSIT) in 23 patients with sporadic PD. Baroreflex-cardiovagal gain was quantified from the relationship between cardiac interbeat interval and systolic pressure during the Valsalva maneuver and baroreflex-sympathoneural function by responses of systolic pressure to the Valsalva maneuver and of hemodynamics and plasma norepinephrine (NE) and dihydroxyphenylglycol (DHPG) levels to orthostasis. 6-[(18)F]Fluorodopamine PET and plasma and skeletal muscle microdialysate NE and DHPG were used to indicate cardiac and extracardiac noradrenergic innervation and brain 6-[(18)F]fluorodopa PET to indicate striatal dopaminergic innervation. Parkinsonism was assessed by UPDRS scores. Compared to patients with PD and normal to moderately decreased sense of smell, patients with anosmic PD had lower mean baroreflex-cardiovagal gain (p = 0.04), larger falls in systolic pressure during the Valsalva maneuver and orthostasis (p = 0.04, p = 0.02), smaller orthostatic increments in plasma NE and DHPG (p = 0.003, p = 0.03), lower cardiac septal:hepatic and renal cortical:hepatic ratios of 6-[(18)F]fluorodopamine-derived radioactivity (p = 0.01, p = 0.06), and lower microdialysate NE and DHPG (p = 0.01; p = 0.006). Neither clinical severity of parkinsonism nor the putamen:occipital cortex ratio of 6-[(18)F]fluorodopa-derived radioactivity was related to the UPSIT category. In Parkinson disease, anosmia is associated with baroreflex failure and cardiac and organ-selective extracardiac noradrenergic denervation, independently of parkinsonism or striatal dopaminergic denervation.

S9.4 Parkinson disease with orthostatic hypotension: Distinctions from Parkinson disease without orthostatic hypotension and from pure autonomic failure

About 40% of patients with Parkinson disease (PD) have orthostatic hypotension (OH). This study reviewed clinical and laboratory data from PD+OH patients compared to PD patients without OH or patients with pure autonomic failure (PAF), a rare Lewy body disease in which OH occurs without parkinsonism. Laboratory assessments used physiologic measures (e.g., baroreflex-cardiovagal gain), neurochemical assays (e.g., concentrations of norepinephrine and its deaminated metabolite, dihydroxyphenylglycol (DHPG), in plasma and skeletal muscle microdialysate), tissue noradrenergic innervation examined by 6-[18F]fluorodopamine positron emission tomographic scanning (PET) of the head, thorax, and abdomen, and striatal dopaminergic innervation by brain 6-[18F]fluorodopa PET. PD+OH patients were older than PD patients without OH, both at the time of testing and at the time of onset of the movement disorder; had worse olfactory dysfunction; and were more likely to have constipation, erectile failure, decreased sweating, dementia, and magnetic resonance imaging evidence of cerebral cortical atrophy. PD+OH patients had higher supine systolic blood pressures, lower baroreflex–cardiovagal slopes, and higher prevalances of abnormal systolic pressure responses to the Valsalva maneuver and of atrial ectopy and sinus bradycardia. Among patients off levodopa, plasma norepinephrine concentrations were lower and increased by less during orthostasis in PD+OH than in PD without OH. Plasma and skeletal muscle microdialysate concentrations of DHPG were lower in PD+OH. PD+OH was associated with lower organ:liver ratios of 6-[18F]fluorodopamine-derived radioactivity, for the interventricular septum and free wall, renal cortex, thyroid, and spleen. Compared to PAF patients, PD+OH patients had higher plasma norepinephrine, DHPG, and epinephrine levels, lower putamen:occipital cortex and caudate:occipital cortex ratios of 6-[18F]fluorodopa-derived radioactivity, and similar substantia nigra:occipital cortex ratios. Taken together, the results indicate that PD+OH differs from PD without OH in terms of age, severity of olfactory dysfunction, baroreflex–cardiovagal failure, supine hypertension, evidence of cortical atrophy, and cardiac and extracardiac noradrenergic denervation. PD+OH differs from PAF in terms of striatal but not nigral dopaminergic deficiency. PAF, PD+OH, and PD without OH therefore seem to be characterized by different relative extents of central and peripheral catecholaminergic denervation.

Generalized and neurotransmitter‐selective noradrenergic denervation in Parkinson's disease with orthostatic hypotension

Patients with Parkinson's disease (PD) often have manifestations of autonomic failure. About 40% have neurogenic orthostatic hypotension (NOH), and among PD+NOH patients virtually all have evidence of cardiac sympathetic denervation; however, whether PD+NOH entails extra-cardiac noradrenergic denervation has been less clear. Microdialysate concentrations of the main neuronal metabolite of norepinephrine (NE) and dihydroxyphenylglycol (DHPG) were measured in skeletal muscle, and plasma concentrations of NE and DHPG were measured in response to i.v. tyramine, yohimbine, and isoproterenol, in patients with PD+NOH, patients with pure autonomic failure (PAF), which is characterized by generalized catecholaminergic denervation, and control subjects. Microdialysate DHPG concentrations were similarly low in PD+NOH and PAF compared to control subjects (163 +/- 25, 153 +/- 27, and 304 +/- 27 pg/mL, P < 0.01 each vs. control). The two groups also had similarly small plasma DHPG responses to tyramine (71 +/- 58 and 82 +/- 105 vs. 313 +/- 94 pg/mL; P < 0.01 each vs. control) and NE responses to yohimbine (223 +/- 37 and 61 +/- 15 vs. 672 +/- 130 pg/mL, P < 0.01 each vs. control), and virtually absent NE responses to isoproterenol (20 +/- 34 and 14 +/- 15 vs. 336 +/- 78 pg/mL, P < 0.01 each vs. control). Patients with PD+NOH had normal bradycardia responses to edrophonium and normal epinephrine responses to glucagon. The results support the concept of generalized noradrenergic denervation in PD+NOH, with similar severity to that seen in PAF. In contrast, the parasympathetic cholinergic and adrenomedullary hormonal components of the autonomic nervous system seem intact in PD+NOH.

Effect of endothelin receptor antagonists on ventricular susceptibility in postinfarcted rats

This study investigated whether selective endothelin (ET) type A (ET(A)) or nonselective ET(A)/ET(B) receptor blockade exerted antiarrhythmic effects through attenuated sympathetic reinnervation after infarction. Twenty-four hours after ligation of the left anterior descending artery, male Wistar rats received either vehicle, ABT-627 (selective ET(A) receptor antagonist), bosentan (nonselective ET(A)/ET(B) receptor antagonist), or hydralazine for 4 wk. The measurement of myocardial ET-1 levels at the remote zone revealed a significant increase in vehicle-treated infarcted rats compared with sham-operated rats, consistent with increased activities of ET-1 after infarction. Sympathetic nerve function changes assessed by the norepinephrine content of myocardium and the dialysate and plasma dihydroxyphenylglycol levels were parallel to ET-1 levels. Immunohistochemical analysis for tyrosine hydroxylase, growth-associated protein 43, and neurofilament also confirmed the change of nerve function. This was accompanied with a significant upregulation of nerve growth factor protein expression and mRNA in the vehicle-treated infarcted rats, which reduced after the administration of either ET(A) or ET(A)/ET(B) blockade to a similar extent. The beneficial effects of ET receptor antagonists on sympathetic nerve function and structures were dissociated from their blood pressure-lowering effect because ET receptor antagonists and hydralazine reduced arterial pressure similarly. Arrhythmic severity during programmed stimulation in ET receptor antagonists-treated rats was significantly lower than that in vehicle-treated infarcted rats. Our data indicate that the ET system, especially via ET(A) receptors, plays an important role in attenuating sympathetic reinnervation after infarction. Independent of their hemodynamic effects, a chronic use of either ET(A) or ET(A)/ET(B) antagonists may modify the arrhythmogenic response to programmed electrical stimulation.

Clinical pharmacokinetics of the norepinephrine precursor L-threo-DOPS in primary chronic autonomic failure

Oral L-threo-3,4-dihydroxyphenylserine (L-DOPS), a synthetic catechol amino acid, increases standing blood pressure and improves standing ability in patients with neurogenic orthostatic hypotension, by conversion of L-DOPS to norepinephrine (NE) outside the brain. This study assessed the pharmacokinetics of L-DOPS, NE, and dihydroxyphenylglycol (DHPG), the main neuronal metabolite of NE, in patients with primary chronic autonomic failure from pure autonomic failure (PAF) or multiple system atrophy (MSA). In 5 MSA and 4 PAF patients, antecubital venous blood was drawn during supine rest and plasma levels of catechols measured at various times for 48 hours after a single oral dose of 400 mg of L-DOPS. Plasma L-DOPS peaked at 1.9 microg/ml (9 micromol/L) about 3 hours after drug administration, followed by a monoexponential decline with a half-time of 2-3 hours in both patient groups. Plasma NE and DHPG also peaked at about 3 hours, but at much lower concentrations (4 and 42 nmol/L). Compared to the MSA group, the PAF group had a smaller calculated volume of distribution of L-DOPS and up to 10-fold lower plasma NE levels at all time points. Plasma NE was above baseline in MSA even at 48 hours after L-DOPS. The relatively long half-time for disappearance of L-DOPS compared to that of NE explains their very different attained plasma concentrations. The similar NE and DHPG responses in PAF and MSA suggests production of NE from LDOPS mainly in non-neuronal cells. Persistent elevation of plasma NE in MSA suggests residual release of NE from sympathetic nerves.

Effects of real and simulated microgravity on response of sympathoadrenal system to various stress stimuli.

Changes in plasma levels of epinephrine (EPI) and norepinephrine (NE) were investigated in humans exposed to physical exercise (WL), to psychic stressor (mental arithmetic test, MAT), and to oral glucose administration (oGTT) before and during a stay in microgravity (real space flight, SF) or in simulated microgravity (head-down bed rest, HDBR). A permanent cannula inserted into the cubital vein and a special appliance, Plasma-03, were used for blood collection, plasma separation, and freezing of samples during SF. Plasma EPI, NE, dihydroxyphenylglycol (DHPG), and dihydroxyphenylalanine (DOPA) levels were measured by the high-pressure liquid chromatography (HPLC) method. Basal plasma EPI, NE, DHPG, and DOPA levels were found within the range of control values during SF. Preflight WL produced high increase in plasma NE and moderate elevation of plasma EPI, DHPG, and DOPA levels. Exaggerated exercise induced increases in plasma NE, DHPG, EPI, and DOPA levels were demonstrated in real microgravity. A return to preflight responses of sympathoadrenal system was seen after the landing. Plasma EPI, NE, and DHPG responses to MAT were relatively small, but increased during SF. During the oGTT the plasma EPI levels were slightly reduced in microgravity. Similarly as in SF, WL in HDBR was followed by significantly exaggerated responses of plasma catecholamines. These results show that both somatic and psychological stressors are able to induce an increased activation of sympathoadrenal system during SF or simulated microgravity in HDBR.

Neurology (53)

Sympathetic innervation and function in reflex sympathetic dystrophy. (National Institutes of Health, Bethesda, MD) Ann Neurol 2000;48:49–59.This study examined sympathetic neurocirculatory function and the role of sympathetic postganglionic nerve traffic in maintaining the pain in 30 patients with reflex sympathetic dystrophy. Most had had the condition for more then 1 year, and 14 had undergone sympathectomy for the pain. Positron emission tomographic scanning after administration of 13N‐ammonia was used to assess local perfusion, and 6‐[18F]fluorodopamine was used to assess sympathetic innervation. Rates of entry of norepinephrine in the regional venous drainage (spillovers) and regional plasma levels of L‐dihydroxyphenylalanine (the immediate product of the rate‐limiting enzymatic step in norepinephrine biosynthesis) and dihydroxyphenylglycol (the main neuronal metabolite of norepinephrine) were measured with and without intravenous trimethaphan for ganglion blockade. 13N‐ammonia‐derived radioactivity was less on the affected side than on the unaffected side, whereas 6‐[18F]fluorodopamine‐derived radioactivity was symmetrical. Thus, perfusion‐adjusted 6‐[18F]fluorodopamine‐derived radioactivity was higher on the affected side. Norepinephrine spillover and smaller arteriovenous increments in plasma levels of L‐dihydroxyphenylalanine and dihydroxyphenylglycol did not differ significantly between affected and unaffected limbs, although 4 patients had noticeably less norepinephrine spillover and smaller arteriovenous increments in plasma dihydroxyphenylglycol on the affected side. Trimethaphan decreased the pain in only 2 of 12 nonsympathectomized patients. The results indicate that patients with chronic unilateral reflex sympathetic dystrophy have decreased perfusion of the affected limb, symmetrical sympathetic innervation and norepinephrine synthesis, variably decreased release and turnover of norepinephrine in the affected limb, and failure of ganglion blockade to improve the pain in most cases. These findings suggest augmented vasoconstriction, intact sympathetic terminal innervation, possibly impaired sympathetic neurotransmission, and pain usually independent of sympathetic neurocirculatory outflows.

Sympathetic innervation and function in reflex sympathetic dystrophy

Patients with reflex sympathetic dystrophy have posttraumatic pain disproportionate to the injury and spreading beyond the distribution of any single peripheral nerve. We examined sympathetic neurocirculatory function and the role of sympathetic postganglionic nerve traffic in maintaining the pain in 30 patients with reflex sympathetic dystrophy. Most had had the condition for more than 1 year, and 14 had undergone sympathectomy for the pain. Positron emission tomographic scanning after administration of 13N-ammonia was used to assess local perfusion, and 6-[18F]fluorodopamine was used to assess sympathetic innervation. Rates of entry of norepinephrine in the regional venous drainage (spillovers) and regional plasma levels of L-dihydroxyphenylalanine (the immediate product of the rate-limiting enzymatic step in norepinephrine biosynthesis) and dihydroxyphenylglycol (the main neuronal metabolite of norepinephrine) were measured with and without intravenous trimethaphan for ganglion blockade. 13N-Ammonia-derived radioactivity was less on the affected side than on the unaffected side, whereas 6-[18F]fluorodopamine-derived radioactivity was symmetrical. Thus, perfusion-adjusted 6-[18F]fluorodopamine-derived radioactivity was higher on the affected side. Norepinephrine spillover and arteriovenous increments in plasma levels of L-dihydroxyphenylalanine and dihydroxyphenylglycol did not differ significantly between affected and unaffected limbs, although 4 patients had noticeably less norepinephrine spillover and smaller arteriovenous increments in plasma dihydroxyphenylglycol on the affected side. Trimethaphan decreased the pain in only 2 of 12 nonsympathectomized patients. The results indicate that patients with chronic unilateral reflex sympathetic dystrophy have decreased perfusion of the affected limb, symmetrical sympathetic innervation and norepinephrine synthesis, variably decreased release and turnover of norepinephrine in the affected limb, and failure of ganglion blockade to improve the pain in most cases. These findings suggest augmented vasoconstriction, intact sympathetic terminal innervation, possibly impaired sympathetic neurotransmission, and pain usually independent of sympathetic neurocirculatory outflows.

α 2-Adrenoceptor-mediated restraint of norepinephrine synthesis, release, and turnover during immobilization in rats

Stress-related release of norepinephrine (NE) in the brain and periphery probably underlies several neuroendocrine and neurocirculatory responses. NE might influence its own synthesis, release, and turnover, by negative feedback regulation via α 2-adrenoceptors. We examined central and peripheral noradrenergic function by measuring concentrations of NE, dihydroxyphenylglycol (DHPG), and dihydroxyphenylacetic acid (DOPAC) in hypothalamic paraventricular nucleus (PVN) microdialysate and arterial plasma simultaneously during immobilization (IMMO) in conscious rats. The α 2-adrenoceptor antagonist yohimbine (YOH) was injected i.p. or perfused locally into the PVN via the microdialysis probe. The i.p. YOH increased plasma NE, epinephrine (EPI), DHPG, dihydroxyphenylalanine, and DOPAC levels by 4.3, 7.3, 2.5, 0.6 and 1.8-fold and PVN microdialysate NE, DHPG, and DOPAC by 1.2, 0.6 and 0.5-fold. The i.p. YOH also enhanced effects of IMMO on plasma and microdialysate NE, DHPG, and DOPAC. YOH delivered via the PVN microdialysis probe did not affect microdialysate or plasma levels of the analytes at baseline and only slightly augmented microdialysate NE responses to IMMO. The results indicate that α 2-adrenoceptors tonically restrain NE synthesis, release, and turnover in sympathetic nerves and limit IMMO-induced peripheral noradrenergic activation. In the PVN, α 2-adrenoceptors do not appear to contribute to these processes tonically and exert relatively little restraint on IMMO-induced local noradrenergic activation.

Presynaptic antisympathetic action of amiodarone and its metabolite desethylamiodarone.

Amiodarone has a "reserpine-like" sympatholytic action in the heart. The aims of this study were to test whether desethylamiodarone (DEA), the in vivo bioactive metabolite of amiodarone, has this action and whether this action could be demonstrated in a neuronal preparation. Experiments were performed in intact rats, perfused hearts, or brain synaptosomes treated with DEA and amiodarone, and concentrations of norepinephrine (NE) and dihydroxyphenylglycol (DHPG), the intraneuronal metabolite of NE, were assayed in plasma, coronary effluent, and synaptosomes. In perfused hearts, DEA at 1, 3, and 10 microM increased DHPG overflow by threefold, sixfold, and ninefold, respectively (all p < 0.01 vs. control). DEA at 1 microM was more potent than amiodarone in increasing DHPG overflow. DEA at 1 and 3 microM also inhibited NE release evoked by sympathetic nerve stimulation (p < 0.05). In intact rats, intravenous DEA at 15 mg/kg elicited onefold increase in plasma DHPG level, and oral pretreatment with amiodarone did not interfere with the sympatholytic action of intravenous amiodarone. In synaptosomes, 40-min incubation with amiodarone, DEA (both 10 microM), and reserpine reduced synaptosomal NE content by 42, 45, and 60%, respectively. Thus similar to its parent drug, DEA exerts a presynaptic sympatholytic action in rat hearts in vivo and in vitro. This action of amiodarone and DEA also was observed in synaptosomes.

Peripheral catecholamine alterations in adolescents with polycystic ovary syndrome.

Polycystic ovary syndrome (PCO) is one of the most common endocrine disorders affecting women. Several lines of evidence have suggested the involvement of the sympathetic nervous system (SNS) in this condition. The present work was designed to assess neurochemically SNS activity in patients during the early stages of PCO. Fourteen patients with PCO (aged 14 to 21 years) were studied on a random day and 9 normal regularly cycling adolescents (aged 14 to 20 years) were studied during the early follicular phase (days 2 to 5). Hormonal profile was determined in basal conditions. LH and FSH were also measured after i.v. administration of 100 micrograms GnRH. Plasma concentrations of dihydroxyphenylalanine (Dopa), noradrenaline (NA), adrenaline (A), total dopamine (DA) and dihydroxyphenylglycol (DHPG) were determined in basal conditions and in response to GnRH by HPLC with electrochemical detection or a radioenzymatic method. Basal urinary Dopa, catecholamines and catechol metabolites (DHPG, vanillylmandelic acid (VMA), 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), metanephrine (MN) and normetanephrine (NMN)) were determined by HPLC with electrochemical detection. Basal plasma LH, testosterone, androstenedione, oestrone and LH/FSH ratio were higher (P < 0.01) and serum sex hormone-binding globulin (SHBG) were lower (P < 0.01) in PCO patients than in control subjects. Basal and GnRH-stimulated plasma free Dopa, A, NA and total DA were similar in patients and controls. Plasma DHPG was lower (P < 0.01) in PCO patients (4.20 +/- 0.30 nmol/l) than in controls (8.0 +/- 1.0 nmol/l) throughout the study. Urinary A, NA, DA, Dopa, MN, MHPG, HVA, and VMA were similar in patients and controls. Urinary DHPG was lower (P < 0.01) in PCO patients (0.50 +/- 0.02 mumol/d) than in controls (0.73 +/- 0.09 mumol/d). On the other hand PCO patients had a higher urinary excretion of NMN than controls (PCO: 1.20 +/- 0.10; C: 0.78 +/- 0.10 mumol/d, P < 0.05). Our results show the same endocrinological features in adolescent PCO patients as those reported in adults. The results also demonstrate a peripheral catecholaminergic alteration which suggests an alteration in noradrenaline deamination and/or uptake in adolescent patients. This study however does not permit us to conclude that PCO is primarily caused by this sympathetic alteration.

Regulation of Peripheral Catecholamine Responses to Acute Stress in Young Adult and Aged F-344 Rats

Young adult (3-month-old) and aged (24-month-old) Fischer-344 male rats received i.v. infusions of 3H-labeled norepinephrine (NE) and epinephrine (EPI) to examine the effects of aging on the neuronal uptake of NE and sympathoadrenal release of NE and EPI. Spillovers of NE and EPI into plasma and their clearance from the circulation were estimated from plasma concentrations of endogenous and 3H-labeled NE and EPI. The efficiency of neuronal uptake was assessed from changes in plasma clearance of NE and concentrations of its intraneuronal metabolite, dihydroxyphenylglycol (DHPG), during immobilization stress or neuronal uptake blockade with desipramine. Stress-induced increases in plasma NE and higher plasma NE concentrations in aged compared to young adult rats were due to both decreases in NE clearance and increases in NE spillover. EPI spillover and clearance were reduced in aged compared to young adult rats, so that plasma EPI levels did not differ between groups. Young adult and aged rats had similar desipramine-induced decreases in NE clearance, whereas desipramine-sensitive decreases and stress-induced increases in plasma DHPG were larger in aged rats. This indicates that neuronal uptake is intact and that increased NE spillover at rest and during stress in aged rats reflects increased NE release from sympathetic nerves. The results show that aging is associated with divergent decreases in EPI release from the adrenal medulla and increases in NE release from sympathetic nerves. Increased plasma concentrations of NE in aged compared to young adult rats also result from decreased circulatory clearance of NE, but this does not reflect any age-related impairment of NE reuptake.

Pharmacodynamics and Pharmacokinetics of Two Dose Regimens of Befloxatone, a New Reversible and Selective Monoamine Oxidase Inhibitor, at Steady State in Healthy Volunteers

The pharmacodynamic equipotency of 2 dose regimens (5 mg twice daily versus 10 mg once daily) of befloxatone, a new reversible and selective monoamine oxidase A (MAO-A) inhibitor, after single and multiple doses for 6 days was examined in a randomized, double-blind, three-way crossover, placebo-controlled trial of 12 healthy volunteers. Plasma levels of the deaminated metabolite 3-4 dihydroxyphenylglycol (DHPG), as measured by high-performance liquid chromatography (HPLC) with coulometric electrochemical detection, were used as an index of MAO inhibition. A single dose of befloxatone produced a significant dose-related reduction in plasma DHPG levels, as shown by the decrease in the 24-hour area under the concentration-time curve (AUC0-24) of DHPG, which peaked 2 hours after administration and persisted over 24 hours. Both dose regimens provided equipotent extent and duration of MAO-A inhibition at steady state, suggesting a once daily dosage should be sufficient for most patients. The pharmacokinetic bioavailability at steady state of both dose regimens was also similar. The concentration-time effect curve after a single dose revealed a hysteresis corresponding to the delay necessary to elicit MAO inhibition and/or elimination of DHPG. The relationship between plasma levels of DHPG and/or elimination of plasma concentrations of DHPG and befloxatone after a single dose can be modeled using the Emax model with a mean EC50 of 4.75 ng/mL, and suggests the presence of a maximal response from the single dose. This model permits prediction of steady-state levels of DHPG.

Interrelationships among measures of autonomic activity and cardiovascular risk factors during orthostasis and the oral glucose tolerance test

Overstimulation of sympathetic nervous system activity is related to atherosclerotic cardiovascular disease risk, but the role of parasympathetic activity in this association is not clear. This study evaluated sympathetic and parasympathetic function by spectral analysis of heart rate variability and plasma levels of norepinephrine (NE) epinephrine (EPI), dihydroxyphenylglycol (DHPG), dihydroxyphenylalanine (DOPA) and dihydroxyphenylacetic acid (DOPAC). It also examined the interrelationships among these parameters and established atherosclerotic cardiovascular disease risk factors in 53 men (mean age 59.5 years). During supine rest, low-frequency power correlated positively with high-frequency power (r = 0.58, p < 0.001), plasma NE correlated with plasma DHPG (r = 0.41, p < 0.001) and plasma DOPA with DOPAC (r = 0.47, p < 0.001) but neither low- nor high-frequency power was correlated with plasma levels of any catechol. Among risk factors, plasma NE correlated with fasting insulin and mean arterial blood pressure, and urine NE correlated with body mass index. Both low- and high-frequency power correlated positively with insulin levels. Orthostasis decreased high-frequency power and increased low-frequency power and plasma NE levels. During the oral glucose tolerance test, both high- and low-frequency power increased, plasma NE levels were unchanged, and plasma EPI levels decreased [88.5 +/- 18 (SEM) versus 52.5 +/- 12 pM, p = 0.001]. The results suggest that orthostasis decreases and the oral glucose tolerance test increases parasympathetic outflows, whereas both stimuli increase sympathetic outflows. Among all atherosclerotic cardiovascular disease risk factors, hyperinsulinaemia showed the strongest association with autonomic nervous system activity, especially parasympathetic activity. Estimates of sympathetic responses obtained from power spectral analysis of heart rate variability agree poorly with those from plasma levels of catechols, possibly because of a parasympathetic contribution to low-frequency power and independence of sympathoneural outflows to the arm and heart.

Circulating dihydroxyphenylglycol and norepinephrine concentrations during sympathetic nervous system activation in patients with pheochromocytoma.

Although increased plasma norepinephrine (NE) concentrations mediate vasoconstriction during episodic hypertension and hypertensive crises in patients with pheochromocytoma (Pheo), the precise origin of this circulating NE (tumor or sympathetic nerves) is not known. Dihydroxyphenylglycol (DHPG), a deaminated metabolite of NE, is formed principally in sympathetic nerve endings. Under basal conditions, plasma NE and DHPG concentrations correlate closely, and during sympathetic nervous system activation, both plasma NE and DHPG concentrations increase. This observation suggests that plasma DHPG concentrations may reflect the source of circulating NE (tumor or sympathetic nerves) during hypertensive episodes in patients with Pheo. Plasma NE and DHPG concentrations were measured simultaneously, and the NE/DHPG ratio was calculated in seven patients with Pheo during 20 min of sympathetic nervous system activation (treadmill exercise) before and after surgical resection of the tumor. Age- and sex-matched normal subjects were also studied. Exercise resulted in a significant increase in plasma NE and DHPG concentrations in patients with Pheo and in normal subjects (Pheo: basal NE, 1827 +/- 639; peak NE, 3016 +/- 769 pg/mL (P = 0.02); normal subjects: basal NE, 266 +/- 27; peak NE, 1166 +/- 197 pg/mL (P = 0.01); Pheo: basal DHPG, 1521 +/- 280; peak DHPG, 2313 +/- 252 pg/mL (P = 0.007); normal subjects: basal DHPG, 870 +/- 50; peak DHPG, 1630 +/- 180 pg/mL (P = 0.01)]. The NE/DHPG ratio increased with exercise in normal subjects (basal, 0.30 +/- 0.02; peak, 0.83 +/- 12; P = 0.005), but did not change in patients with Pheo (basal, 1.22 +/- 0.32; peak, 1.54 +/- 0.27). Exercise also increased plasma NE and DHPG concentrations and the NE/DHPG ratio in five patients studied after surgical resection of the tumor. Systolic blood pressure and heart rate increased significantly during exercise in all three study groups. The increase in plasma NE and HDPG concentrations during exercise-induced sympathetic nervous system stimulation in patients with Pheo is similar to that in normal subjects and may indicate that the sympathetic nervous system plays an important role in the pathogenesis of hypertension and hypertensive crises in patients with Pheo.

New approaches to evaluate sympathoadrenal system activity in experiments on Earth and in space

In previous studies the activity of the sympathoadrenal system (SAS) in cosmonauts during space flights was evaluated by measuring plasma catecholamines (CA) levels and urinary CA and their metabolites concentrations. Plasma CA levels are accepted indicators of SAS activity, however, they are determined by the plasma clearances as well as the rates of CA release (spillover-SO) into the bloodstream. Nowadays methods are available which evaluate not only plasma levels of CA but also their release, spillover, uptake, reuptake, degradation and also CA synthesis in vivo measured by plasma levels of dihydroxyphenylalanine (DOPA). Plasma concentrations of DOPA, the CA noradrenaline (NE), adrenaline (ADR), and dopamine (DA), the deaminated catechol metabolites dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC), and the O-methylated metabolites methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured during immobilization stress (IMO) in conscious rats. Radiotracer methods were used to measure NE SO. IMO markedly increased arterial NE levels but NE SO was less elevated bacause the NE clearance was slightly reduced in IMO rats. Simultaneous measurements of plasma CA and their metabolites provide another means to obtain information about SAS function. For instance, dissociation between changes of plasma DHPG and NE levels can indicate changes in neuronal reuptake of NE. We found marked parallel increases in plasma NE and DHPG levels during acute IMO; however after repeated IMO, plasma NE levels were increased but DHPG responses were less pronounced suggesting a reduced NE reuptake. DOPA, the CA precursor, circulates in plasma at a concentration higher than NE. During stress, increased sympathoneural outflow stimulates DOPA synthesis and release into the circulation supporting the view that changes in plasma DOPA levels during stress reflect in vivo changes in the rate of CA synthesis. We propose to measure the new plasma indicators of SAS activity in cosmonauts and/or in animals before, during and after space flights.