COMT inhibition by high-dose entacapone does not affect hemodynamics but changes catecholamine metabolism in healthy volunteers at rest and during exercise

We studied the effects of catechol-O-methyltransferase (COMT) inhibition with entacapone on hemodynamics and catecholamine metabolism in healthy volunteers at rest and during a bicycle exercise test. Entacapone was given orally during two periods of seven days each to eleven healthy male volunteers; on the first period 400 mg t.i.d. and on the second 800 mg t.i.d. A submaximal exercise test giving a heart rate of about 163-167 beats/min with the highest predetermined work load was performed on a bicycle ergometer, and blood pressure, heart rate and ECG were recorded. The concentrations of adrenaline, noradrenaline, 3,4-dihydroxyphenylglycol (DHPG), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC) in plasma were determined. Blood pressure, heart rate, ECG, and plasma concentrations of unconjugated adrenaline and noradrenaline were not influenced after single and repeated dosing of entacapone. The plasma concentrations of DHPG (a monoamine oxidase (MAO)-dependent metabolite) increased maximally by 245% compared to the control day. DOPAC (a MAO-dependent metabolite) increased maximally by 144% and MHPG (a COMT-dependent metabolite) decreased by 54%. The increase in DHPG and DOPAC was significantly greater with the 800 mg dose than with the 400 mg dose. The decrease in MHPG was significantly greater with the repeated dosing than with the single dose of entacapone. COMT inhibition by entacapone seems not to affect hemodynamics or plasma concentrations of unconjugated adrenaline and noradrenaline in healthy volunteers either at rest or during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Isosorbide 5-mononitrate reverses high blood pressure in NG-nitro-L-arginine methyl ester treated rats

1. The present study has evaluated the effect of iosorbide 5-mononitrate (IS-5-MN) and L-arginine on blood pressure profile during chronic administration of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). 2. After a 7 day period of stabilization, normotensive male Wistar rats (n = 10) were selected and given L-NAME (50 micrograms/ml) in drinking water. Control rats (n = 10) were studied simultaneously for direct comparison of cardiovascular parameters. Blood pressure (systolic, SBP; diastolic, DBP) and heart rate were measured using a photoelectric tail cuff pulse detector; SBP and DBP were, in normotensive rats 106 +/- 2 and 78 +/- 2 mmHg (n = 10), respectively. The average water consumption per animal was about 35 ml/day resulting in a mean intake of L-NAME of about 10 mg/kg/day. 3. Twenty four hours after exposure to L-NAME, both SBP and DBP were found to be increased by 20 mm Hg; heart rate slightly decreased. During the next 13 days both SBP and DBP increased progressively reaching 170 +/- 3 and 116 +/- 3 mm Hg, respectively. 4. On day 14, six animals of either group were sacrificed and the heart, kidneys, liver, spleen, mesenteric and caudal arteries, brain stem, hypothalamus and parietal cortex were taken from determination of noradrenaline and dopamine content; blood from the renal vein was also collected and plasma concentrations of noradrenaline, adrenaline and 3,4-dihydroxyphenylethylglycol (DOPEG) determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual effect of nicotine on cardiac noradrenaline release during metabolic blockade

Nicotine-induced noradrenaline was investigated in perfused guinea pig hearts subjected to metabolic blockade that was caused either by anoxia or by cyanide intoxication. Noradrenaline, neuropeptide Y, and dihydroxyphenylethyleneglycol (DOPEG) were determined in the coronary venous overflow Neuropeptide Y is a sympathetic cotransmitter of noradrenaline, and concomitant release of both transmitters indicates an exocytotic, calcium-dependent release mechanism, whereas neuropeptide Y overflow does not occur during nonexocytotic noradrenaline release. Nonexocytotic, calcium-independent noradrenaline release, however, is associated with an increase of DOPEG overflow, which is the main intraneuronal metabolite of noradrenaline formed by monoamine oxidase if oxygen is present. Anoxia per se caused a nonexocytotic release of noradrenaline starting after 10 min of anoxia and reaching peak levels at 30 min. During anoxia, nicotine (3 and 10 mumol/l) accelerated and enhanced noradrenaline overflow, i.e., the period between the onset of anoxia and the begin of noradrenaline release was shortened and peak levels were increased. Nicotine-induced noradrenaline release was accompanied by neuropeptide Y overflow. The action of nicotine was further evaluated during energy depletion caused by cyanide. As anoxia did, cyanide administration alone resulted in noradrenaline release. In accordance with a nonexocytotic mechanism and due to the presence of oxygen, this release of noradrenaline was accompanied by an increase of DOPEG. When added 10 min after the onset of energy depletion, nicotine (10 mumol/l) caused a brief but marked enhancement of exocytotic noradrenaline release, since this release was calcium-dependent and was accompanied by a significant rise of neuropeptide Y overflow. In absence of extracellular calcium to avoid exocytosis, concomitant administration of nicotine (3-100 mumol/l) and cyanide caused a concentration-dependent acceleration of both the overflow of noradrenaline and DOPEG, whereas overflow of neuropeptide Y was not increased, thus indicating a nonexocytotic release mechanism. In conclusion, the application of nicotine during myocardial energy depletion increases overflow of noradrenaline by both calcium-dependent exocytotic release and calcium-independent nonexocytotic release mechanisms.

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 because 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.

Occipital horn syndrome and a mild Menkes phenotype associated with splice site mutations at the MNK locus

We have found mutations in the Menkes disease gene (MNK) which impair, but do not abolish, correct mRNA splicing in patients with less severe clinical phenotypes. In one family, four males aged 2-36 years with a distinctive Menkes variant have a mutation at the +3 position of a splice donor site near the 3' end of the Menkes coding sequence that is associated with exon skipping and a stable mutant transcript. In an unrelated 15-year-old male with typical occipital horn syndrome, a point mutation at the -2 exonic position of a splice donor site in the middle of the gene causes exon-skipping and activation of a cryptic splice acceptor site. In both mutations, maintenance of some normal splicing is demonstrable by RT-PCR, cDNA sequencing and ribonuclease protection.

In vitro release of [3H]noradrenaline by tyramine from the superior cervical ganglion and in the nictitating membrane of the cat

1. The release and the metabolism of [3H]noradrenaline ([3H]NA) induced by tyramine was studied in the superior cervical ganglion (cell bodies) and in the nictitating membrane (nerve endings) of the cat. 2. Exposure of the ganglia to 58.0 and 174.0 microM tyramine resulted in the release of 13.7 and 11.8% respectively of the total tissue radioactivity. In the nictitating membrane, the fractional release of radioactivity was directly proportional to the concentration of tyramine (5.8, 58.0 and 174.0 microM). 3. In ganglia [3H]DOPEG accounted for 55.8% of the radioactivity released by 58.0 microM tyramine and only 10.5% of the radioactivity was unmetabolized NA. In presence of 174.0 microM tyramine, [3H]NA increased to 28.0% of the total radioactivity and [3H]DOPEG and [3H]OMDA decreased to 45.3 and 18.9% respectively. 4. In the nerve endings, the contribution of [3H]NA, [3H]DOMA and [3H]NMN increased with the concentration of tyramine while [3H]DOPEG decreased. 5. The deamination is the first step of the metabolic inactivation of [3H]NA induced by tyramine in the cell body of the postganglionic adrenergic neuron while in the nerve endings [3H]NA is preferentially O-methylated.

[Neurochemical studies of adrenergic reinnervation after heart transplantation]

Heart transplantation causes sympathetic cardiac denervation. Measurements of plasma concentrations of the main presynaptic noradrenaline metabolite, dihydroxyphenylglycol (DOPEG, the plasma pool of which is exclusively neuronal in origin), were used to examine sympathetic reinnervation of the transplanted human heart. We determined arterial and coronary-venous plasma concentrations of DOPEG in 27 heart transplant recipients (transplant age ranging from 0.5 to 5 years) and in 9 control patients. In each of the control patients the DOPEG concentration was higher in coronary venous plasma than in arterial plasma (mean arterio-venous increment: 57.3 +/- 8.7%; p < 0.001). However, in heart transplant recipients, 18 out of 27 patients showed an arteriovenous increment in plasma DOPEG (mean increment in all patients 12.6 +/- 2.0%; p < 0.05). The ratio of the coronary-venous to arterial DOPEG concentration was positively correlated with the time after transplantation (p = 0.02 for individual results and p < 0.01 for mean group results). Thus, our data provide evidence for a time-dependent partial sympathetic reinnervation of the transplanted heart.

Norepinephrine and dihydroxyphenylglycol effluxes from sympathetic nerve endings during hypoxia and reoxygenation in the isolated rat heart

The present experiments were carried out in isolated rat hearts perfused according to the Langendorff method at a constant pressure of 10 kPa. The aim was to measure norepinephrine (NE) overflow and its deaminated metabolite dihydroxyphenylglycol (DOPEG) by changing the composition of the buffer perfusing the heart to simulate hypoxia. When aerobic and glycolytic pathways were simultaneously reduced, NE and DOPEG overflow increased 711 and 145%, respectively, after 30 min, compared with control values of 0.45 +/- 0.06 and 0.66 +/- 0.7 ng.min-1.g-1 of heart (n = 8, p < 0.05). Whereas NE leakage decreased sharply after reoxygenation and glucose addition, DOPEG continued to increase up to 260% after 5 min of normal reperfusion. This mechanism was calcium independent and inhibited by 80% with desipramine (1 microM), confirming the role of the uptake I carrier, which reversed its normal transport direction. Neuropeptide Y, a marker of exocytotic release, did not increase in the perfusate with the progression of hypoxia, which supports the hypothesis of a nonexocytotic release. Tyramine (1 microM) significantly enhanced NE outflow by displacing the amine from its storage vesicles through a calcium-independent mechanism, indicating that a pool of NE was still available. In the presence of 1 microM clorgyline (a monoamine oxidase A inhibitor) but not deprenyl (a monoamine oxidase B inhibitor), NE outflow increased 934% and DOPEG only 40% at 30 min (n = 6, p < 0.05 versus control hearts).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased alpha 2-adrenoceptor mediated regulation of adult rat brain noradrenaline overflow after chronic neonatal exposure to propranolol; a microdialysis study

Direct and persistent effects of chronic neonatal administration of the beta-adrenoceptor antagonist propranolol on brain noradrenergic activity were investigated by measuring tissue concentrations of noradrenaline and its metabolites and in vivo overflow of noradrenaline during adulthood. Rat pups were chronically treated with propranolol from postnatal day 1 to day 10. Determination of monoamine metabolism after the last injection showed an increase in noradrenaline metabolism in frontal cortex, limbic system and hippocampus of propranolol-exposed rats, but 47 days after this last injection it was apparent that these effects were not long-lasting. Moreover, basal noradrenaline overflow in vivo in the hippocampus of 40-55 day-old propranolol-exposed rats did not differ from that in controls. However, the regulation of noradrenaline release seemed to have been altered, since a pharmacological challenge with the alpha 2-adrenoceptor antagonist idazoxan induced an enhanced increase in the in vivo noradrenaline overflow in propranolol-exposed rats compared to controls. It is suggested that the neonatal beta-blockade induced a supersensitivity of the presynaptic alpha 2-adrenoceptor. The precise mechanism underlying this effect has to be elucidated.

Dexmedetomidine premedication before intravenous regional anesthesia in minor outpatient hand surgery

STUDY OBJECTIVE

To assess the efficacy and safety of intravenous (i.v.) dexmedetomidine, an alpha-2 agonist, as a premedication before i.v. regional anesthesia.

DESIGN

Randomized, double-blind, placebo-controlled study with two parallel groups.

SETTING

Day-case surgery unit, Department of Surgery, Turku University Hospital, Turku, Finland.

PATIENTS

30 healthy ASA physical status I outpatients scheduled for minor hand surgery with i.v. regional anesthesia.

INTERVENTIONS

Patients were assigned to one of two groups to receive either dexmedetomidine 1 microgram/kg i.v. (n = 15) or saline placebo i.v. (n = 15) 10 minutes before exsanguination and inflation of a tourniquet. Regional blockade was induced with 0.5% lidocaine 3 mg/kg (maximum 200 mg). Additional fentanyl 1 microgram/kg intraoperatively and oxycodone 0.05 mg/kg postoperatively were administered for analgesia if needed.

MEASUREMENTS AND MAIN RESULTS

Dexmedetomidine preoperatively induced 16% to 20% decreases in systolic blood pressure (p < 0.001), diastolic blood pressure (p < 0.001), and heart rate (p < 0.001), which were mainly abolished within the 4-hour postoperative follow-up period. A clinically significant decrease in arterial oxygen saturation was not observed. The subjective intensity of pain during tourniquet inflation was similar in both groups, but fewer intraoperative (p = 0.009) opioid analgesics were needed in the dexmedetomidine group. Dexmedetomidine decreased sympathoadrenal responses: plasma norepinephrine concentration decreased to one-fourth of the baseline level (p < 0.001), and one of its main metabolites, 3,4-dihydroxyphenylglycol, decreased by 27% (p < 0.001). Dexmedetomidine also prevented an increase in plasma epinephrine concentration following tourniquet inflation (p = 0.003). Dexmedetomidine induced subjective sedation (p = 0.002), but the Maddox Wing test did not show any statistically significant differences between the groups. General effectiveness was graded superior in the dexmedetomidine group (p < 0.001).

CONCLUSIONS

Dexmedetomidine is an effective premedication before i.v. regional anesthesia because it reduces patient anxiety, sympathoadrenal responses, and opioid analgesic requirements.

Effect of TJ-68 (shakuyaku-kanzo-to) on polycystic ovarian disease

OBJECTIVE

To investigate the effect of an herbal medicine, Shakuyaku-Kanzo-To (TJ-68), on endocrine variables in patients with polycystic ovarian disease (PCOD).

SETTING

Medical university hospital.

PATIENTS AND INTERVENTIONS

Thirty-four Japanese women with PCOD were treated daily with 7.5 g of TJ-68 for 24 weeks. Testosterone (T), free-testosterone (free-T), sex hormone binding globulin (SHBG), LH, FSH, estrone, 17 beta-estradiol, 3,4-dihydroxyphenylglycol (DOPEG), and 3, 4-dihydroxyphenylacetic acid (DOPAC) were examined.

RESULTS

No side effects were observed in any cases. At 4 weeks after initiation of treatment, serum T and free-T levels significantly decreased, while SHBG was not significantly elevated. Meanwhile, after 12 weeks of treatment, the mean serum T level of the patients who became pregnant decreased to 35% of that before the treatment, but levels did not change in the patients who failed to conceive. There was no significant difference in estrone/estradiol ratio before and after treatment, but the estradiol/testosterone ratio increased significantly after 4 weeks of treatment. The LH/FSH ratio after 24 weeks of treatment was significantly lower than that before treatment. DOPEG and the DOPEG/DOPAC ratio significantly decreased after 4 weeks of treatment.

CONCLUSIONS

It is suggested that TJ-68 acts directly on the ovary first, increasing the activity of aromatase, which promotes the synthesis of estradiol from testosterone, thus lowering serum T levels. Furthermore, the effect on catecholamines results in gradually improving the dissociate phenomenon of LH/FSH ratio. Therefore, TJ-68 is an effective herbal medicine for decreasing serum free-T levels and achieving pregnancy in patients with PCOD.

Regional differences in the in vivo regulation of the extracellular levels of noradrenaline and its metabolites in rat brain

Microdialysis was used to determine extracellular levels of both noradrenaline and its metabolites in several brain regions of rats under basal conditions and in response to drugs selective for the alpha 2-adrenoceptor to study regional differences in the regulation of noradrenaline overflow. Basal overflow of noradrenaline was about 1.3 fmol/min in frontoparietal cortex, amygdala and hippocampus and in the medial prefrontal cortex 2.4 fmol/min was measured, whereas the overflow of the noradrenaline metabolites 3,4-dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol was 10-fold higher. After correction for recovery and membrane length no regional differences in the basal overflow of noradrenaline (NA) were found. There were, however, regional differences in the drug-induced effects: locally applied moxonidine decreased extracellular noradrenaline stronger in the frontoparietal cortex than in the medial prefrontal cortex. The increase in noradrenaline overflow caused by idazoxan (10(-4) M) was stronger in frontoparietal cortex than in amygdala and hippocampus. The metabolites were also generally decreased by moxonidine and increased by idazoxan, although less markedly. The present study shows that the regulation of noradrenaline overflow by the presynaptic alpha 2-autoreceptor was stronger in cortical regions than in amygdala and hippocampus. In those latter regions the uptake mechanism probably plays a relatively more important role in the regulation of noradrenaline overflow.

Evidence for partial sympathetic cardiac reinnervation following cardiac transplantation

Heart transplantation causes total cardiac denervation. Measurements of plasma concentrations of the main presynaptic noradrenal metabolite, dihydroxyphenylglycol (DOPEG, exclusively neuronal in origin), were used to examine the possibility of sympathetic reinnervation of the transplanted human heart. We determined arterial and coronary-venous plasma concentrations of DOPEG in 15 heart transplant recipients (28-68 years of age at the time of transplantation with the transplant ageing from 0.5 to 4 years at the time of investigation) and in nine control patients (45-75 years of age). In each of the control patients the DOPEG concentration was higher in coronary venous plasma than in arterial plasma (mean arteriovenous increment: 60 +/- 10%; P < 0.001). In the heart transplant recipients nine patients showed an arteriovenous increment in plasma DOPEG. For the mean group results it was found that the ratio of the coronary-venous to arterial DOPEG concentration was positively correlated with the time after transplantation (r = 0.92; n = 5; P < 0.05). Thus, our data provide neurochemical evidence for partial sympathetic reinnervation in some of the heart transplants. Moreover, it is suggested that the time after transplantation is unlikely to be the only determinant for the occurrence and extent of sympathetic reinnervation.

A CRF antagonist attenuates stress-induced increases in NA turnover in extended brain regions in rats

We investigated the effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF9-41 (ahCRF), on increases in noradrenaline (NA) turnover caused by immobilization stress in rat brain regions. Pretreatment with ahCRF (50 or 100 micrograms) significantly attenuated increases in levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of NA in rat brain, in the locus coeruleus (LC) region, and attenuated the MHPG-SO4/NA ratio after immobilization stress for 50 min in the cerebral cortex, hippocampus, amygdala, midbrain and hypothalamus. However, stress-induced increases in plasma corticosterone levels were not decreased significantly by pretreatment with ahCRF. These results suggest that CRF, released during stress, causes increases in NA release in extended brain regions of stressed rats.

Evidence for increased noradrenaline release from subcortical brain regions in essential hypertension

OBJECTIVE

To test whether the activation of the sympathetic nervous system that is common in essential hypertension derives from subcortical noradrenergic neuronal excitation.

DESIGN AND METHODS

We performed a radionuclide cerebral venous sinus scan, using technetium-99m, to establish which internal jugular vein predominantly drained the cortical (the major jugular vein) and which the subcortical (minor jugular vein) brain regions. Blood samples were then collected simultaneously from catheters placed percutaneously in the brachial artery or radial artery and high in the internal jugular vein in 11 untreated hypertensive patients and 18 normotensive subjects, for determination of the plasma concentrations of noradrenaline, its precursor dihydroxyphenylalanine (DOPA) and its metabolite dihydroxyphenylglycol (DHPG) to calculate their rates of overflow into the cerebrovascular circulation.

RESULTS

In normotensive subjects blood flow determined by thermodilution was significantly higher in the major than in the minor jugular vein. The noradrenaline spillovers into the major and minor jugular veins calculated during infusions of L-[3H]-7-noradrenaline were similar in healthy subjects. The noradrenaline spillover from subcortical regions into the minor jugular vein was significantly higher in the hypertensives than in the normal subjects, as was the overflow of DHPG. In contrast, cortical noradrenaline and DHPG overflows into the major jugular vein were similar in hypertensive and normotensive subjects. Overflow of DOPA into the minor jugular vein, which derives largely from precursor turnover in dopaminergic neurons, was similar in hypertensive and normotensive subjects. Subcortical noradrenaline spillover correlated with neurochemical indices of sympathetic nervous system activity, with total body noradrenaline spillover (r = 0.56, P < 0.05) in normal and hypertensive subjects combined, and with renal noradrenaline spillover in the six hypertensive patients tested (r = 0.91, P < 0.05).

CONCLUSION

These results suggest that increased subcortical noradrenaline release is a possible cause of peripheral sympathetic activation in essential hypertension.

Influence of dietary myoinositol on myocardial vulnerability and norepinephrine release in a diabetic animal model

In a canine model of diabetes enhanced ventricular vulnerability (VFT) has been associated with reduced myocardial myoinositol and increased release of norepinephrine (NE). To assess the role of the polyol, a dietary supplement of myoinositol was fed for 1 year to a diabetic group. Diabetes was induced with alloxan, 30 mg/kg. Controls (Group 1) were compared with diabetics without (Group 2) and with the inositol supplement (Group 3). After 1 year the animals were anesthetized to assess VFT. Basal heart rate and arterial pressure were comparable. The VFT in Group 1 was 43 +/- 2.6 ma, 26.7 +/- 2.8 ma in Group 2 (P < 0.02) and 39 +/- 3.5 ma in Group 3 (P < 0.02 vs. Group 2). Since the cardiac sympathetic system may promote arrhythmogenesis, the release of NE into the coronary sinus (CS) has been determined. To assess basal NE release serial arterial (A) and (CS) samples were taken at 5 min intervals for 20 min during infusion of 3H-NE. There was no significant difference between the diabetic groups in the level of arterial NE (HPLC). The mean for NEA-CS was higher in Group 2 (-228 +/- 33 pg/ml) compared to normals (-75 +/- 19 P < 0.02). In Group 3 the mean NE in the coronary venous effluent was -33 +/- 9 pg/ml, significantly less than Group 2. Infusion of 3H-NE was attended by significantly higher 3H-NEcs levels in Group 2. While dihydroxyphenylglycol (DHPG) was increased, 3H DHPG was not, suggesting that an impaired uptake mechanism contributed to the increased NEcs.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical application of noradrenaline spillover methodology: delineation of regional human sympathetic nervous responses

The proportionality which in general exists between rates of sympathetic nerve firing and the overflow of noradrenaline into the venous drainage of an organ provides the experimental justification for the use of measurements of noradrenaline in plasma as a biochemical measure of sympathetic nervous function. Static measurements of noradrenaline plasma concentration have several limitations. One is the confounding influence of noradrenaline plasma clearance on plasma concentration. Other drawbacks include the distortion arising from antecubital venous sampling (this represents but one venous drainage, that of the forearm), and the inability to detect regional differentiation of sympathetic responses. Clinical regional noradrenaline spillover measurements, performed with infusions of radiolabelled noradrenaline and sampling from centrally placed catheters, and derived from regional isotope dilution, overcome these deficiencies. The strength of the methodology is that sympathetic nervous function may be studied in the internal organs not accessible to nerve recording with microneurography. Examples of the regionalization of human sympathetic responses disclosed include the preferential activation of the cardiac sympathetic outflow with mental stress, cigarette smoking, aerobic exercise, cardiac failure, coronary insufficiency, essential hypertension and in ventricular arrhythmias, and the preferential stimulation or inhibition of the renal sympathetic nerves with low salt diets and mental stress, and with exercise training, respectively. By application of the same principles, regional release of the sympathetic cotransmitters neuropeptide Y and adrenaline can be studied in humans. Cotransmitter release, however, is detected only with some difficulty. In restricted circumstances we find evidence of regional cotransmitter release to plasma, such as the release of neuropeptide Y from the heart at the very high rates of sympathetic nerve firing occurring with aerobic exercise, and cardiac adrenaline release also with exercise and after loading of the neuronal adrenaline pool by intravenous infusion of adrenaline.

Plasma-free and sulfoconjugated MHPG in major depressive disorders: differences between responders to treatment and nonresponders

The plasma levels of free and sulfoconjugated forms of 3-methoxy-4-hydroxyphenylglycol (MHPG) were examined before and after treatment in 16 patients with unipolar major depressive disorders without melancholia. The patients were treated with intravenous administration of clomipramine for 4 weeks. Seven depressive disorder patients who showed marked improvement (the improvement group) revealed significant reduction in their plasma sulfoconjugated MHPG levels. In 6 depressive disorder patients who showed no improvement (the no-improvement group), the plasma sulfoconjugated MHPG levels showed no significant change after treatment. The remaining 3 patients, who showed ambiguous change after treatment, were excluded from the analysis. Levels of plasma-free MHPG showed significant change after treatment in neither the improvement group nor in the no-improvement group. It is suggested that levels of plasma sulfoconjugated MHPG may serve as an indicator of brain noradrenergic activity.

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.

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.

Neuronal metabolism of catecholamines: plasma DHPG, DOMA and DOPAC

Pre-synaptic endings of the sympathetic nervous fibers control the metabolism of catecholamines, particularly inactivating norepinephrine after its neuronal recapture. The present study was carried out to investigate this segment of the metabolism of catecholamines through measurements of DHPG, DOMA and DOPAC concentrations in plasma. A sensitive and specific radio-enzymatic assay was developed of which the major characteristic is to include the plasma sample in the incubation mixture without initial extraction of the deaminated metabolites. In the rat, there was a statistically significant correlation between norepinephrine and DHPG in both anesthetized and conscious conditions and after clonidine or guanethidine induced reduction of sympathetic activity; thus it can be suggested that plasma DHPG is a good index of neuronal metabolism of norepinephrine in this animal. In humans, our data indicate an interesting correlation between norepinephrine and DOMA concentrations in plasma in resting conditions and within three hours after clonidine. Further studies need to be carried out to establish whether DOMA is a better index of neuronal metabolism of norepinephrine than DHPG.

Peripheral catecholamine metabolites and menstrual irregularity in patients with polycystic ovaries

OBJECTIVE

To investigate the catecholamine status of patients with polycystic ovary syndrome.

DESIGN

Three parallel groups with polycystic ovary were diagnosed by ultrasound: (a) 5 patients with regularly ovulatory menstruation; (b) 10 with anovulatory menstruation; (c) 13 with secondary amenorrhea who responded to progestagen with withdrawal bleeding. Blood samples for measurement of LH, testosterone, and catecholamine metabolites were drawn during cycle days 4-7.

RESULTS

(1) Serum LH and testosterone of the patient groups (b) and (c) were significantly higher than those of controls. (2) Plasma 3,4-dihydroxyphenylglycol (DOPEG) and the DOPEG/DOPAC ratio were elevated in patients, and DOPAC levels were reduced. However, there was no significant difference of catecholamine metabolites among the three patient groups.

CONCLUSIONS

The androgen status in polycystic ovary diagnosed by ultrasound is correlated, but catecholamine status is not correlated, with the menstrual irregularity of polycystic ovary syndrome.

Concentrations of noradrenaline at neuronal uptake sites during sympathetic nervous inhibition and activation in rabbits

Concentrations of noradrenaline at peripheral neuronal uptake sites were examined during sustained changes in sympathetic nervous activity produced by intracisternal infusion of yohimbine or clonidine in conscious rabbits. The gradient between concentrations of noradrenaline in plasma and at neuronal uptake sites was estimated by comparing the formation of the intraneuronal metabolite of noradrenaline, dihydroxyphenylglycol (DHPG), from intravenously infused and endogenously released noradrenaline. At resting levels of sympathetic activity the noradrenaline concentration at neuronal uptake sites (4.2 +/- 0.5 nmol/l) was 3.4-fold greater than the concentration in arterial plasma (1.3 +/- 0.1 nmol/l). Noradrenaline at neuronal uptake sites increased to 9.4 +/- 1.3 nmol/l after yohimbine and decreased to 2.4 +/- 0.1 nmol/l after clonidine. The noradrenaline concentration gradient was not altered by intracisternal infusion of yohimbine or clonidine. Thus, a positive linear relationship (r = 0.97) was observed between concentrations of noradrenaline at neuronal uptake sites and in plasma. The gradient was positively related to the efficiency of noradrenaline reuptake (r = 0.81). The results show that arterial plasma concentrations of noradrenaline are considerably less than concentrations close to sites of release, but accurately reflect changes in amounts of noradrenaline at release sites during sustained changes in sympathetic activity. The gradient in noradrenaline concentrations between neuronal uptake sites and plasma is largely dependent on the efficiency of neuronal reuptake. Since the gradient is not altered by sympathetic nervous inhibition or activation, the proportion of noradrenaline removed by neuronal and extraneuronal uptake does not appear to be altered by moderate changes in transmitter release.

Effects of single or repeated immobilization on release of norepinephrine and its metabolites in the central nucleus of the amygdala in conscious rats

The release of norepinephrine (NE) and its metabolites in the central nucleus of the amygdala was measured using in vivo microdialysis during immobilization (IMMO) stress in conscious rats. Animals underwent 2-hour periods of IMMO either once or daily for 7 days. Extracellular fluid concentrations of NE, dihydroxyphenylglycol (DHPG), methoxyhydroxyphenylglycol (MHPG), and the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) were measured before, during, and after IMMO. Microdialysate levels of NE and DHPG attained 2- to 3-fold increments during the 1 h of IMMO and declined thereafter, whereas MHPG and DOPAC levels attained maximal levels of about twice basal concentrations during the 2- or 3-h after initiation of IMMO. After the sixth IMMO basal levels of NE, DHPG, MHPG, and DOPAC were decreased, and NE, DHPG, and DOPAC responses during the seventh IMMO failed to attain levels found during the first IMMO, although the absolute changes during IMMO were similar between animals subjected to IMMO once or seven times. The results indicate that acute IMMO increases synthesis, release, and metabolism of NE in the central nucleus of the amygdala and that repetition of IMMO decreases basal catecholamine synthesis and noradrenergic turnover in this brain region, without inhibiting acute noradrenergic responses.

Inhibition of aromatic L-amino acid decarboxylase under physiological conditions: optimization of 3-hydroxybenzylhydrazine concentration to prevent concurrent inhibition of monoamine oxidase

The activity of the enzyme tyrosine hydroxylase (TH; EC 1.14.16.2) is commonly studied indirectly by quantifying the formation of the product, 3,4-dihydroxyphenylalanine (DOPA), after inhibition of aromatic L-amino acid decarboxylase (AAAD; EC 4.1.1.28), the enzyme which metabolizes DOPA. This study was done to determine if the concentration of the hydrazine derivative 3-hydroxybenzylhydrazine (NSD-1015), a drug frequently used in vitro to inhibit AAAD, could be adjusted such that it would inhibit that enzyme, but would not simultaneously inhibit a second, potentially important enzyme, monoamine oxidase (MAO; EC 1.4.3.4). MAO catalyzes the formation of 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG) from dopamine (DA) and norepinephrine (NE), respectively. Five concentrations of NSD-1015 in superfusate (0.01 to 20 microM) were tested in strips of canine portal vein superfused and stimulated in vitro. DOPA, DA, NE, and DOPEG in superfusate and in the veins after superfusion were quantified by HPLC with electrochemical detection. The efficacy of NSD-1015 in inhibiting AAAD and MAO was determined by examining the levels of DOPA and DOPEG, respectively. NSD-1015, only when applied at 0.1 microM, resulted in the marked augmentation of total DOPA levels, but did not affect levels of DOPEG, which suggests that this concentration of the drug inhibits AAAD, but does not inhibit MAO. Therefore, it is concluded that, of the concentrations of NSD-1015 tested, 0.1 microM is the optimum concentration to use in this preparation for studies designed to examine TH activity by measuring DOPA after the inhibition of AAAD.