A polymorphism in the norepinephrine transporter gene is associated with affective and cardiovascular disease through a microRNA mechanism

Norepinephrine released from sympathetic nerves is removed from the neuroeffector junction via the action of the norepinephrine transporter (NET). NET impairment is evident in several clinically important conditions including major depressive disorder (MDD), panic disorder (PD), essential hypertension and the postural orthostatic tachycardia syndrome (POTS). We aimed to determine whether a single nucleotide polymorphism (SNP) in the 3' untranslated region (UTR) of the NET gene is associated with NET impairment and to elucidate the mechanisms involved. The analyses were carried out in two cohorts of European ancestry, which included healthy controls and MDD, PD, hypertensive and POTS patients. Compared with controls, cases had significantly higher prevalence of the T allele of rs7194256 (C/T), arterial norepinephrine, depression and anxiety scores, larger left ventricular mass index, higher systolic and diastolic blood pressures, and heart rate. Bioinformatic analysis identified that the microRNA miR-19a-3p could bind preferentially to the sequence created by the presence of the T allele. This was supported by results of luciferase assays. Compared with controls, cases had significantly lower circulating miR-19a-3p, which was associated with pathways related to blood pressure and regulation of neurotransmission. In vitro norepinephrine downregulated miR-19a-3p. In conclusion, the T allele of the rs7194256 SNP in the 3'UTR of the NET gene is more prevalent in diseases where NET impairment is evident. This might be explained by the creation of a binding site for the microRNA miR-19a-3p. A defect in NET function may potentiate the sympathetic neurochemical signal, predisposing individuals with affective diseases to increased risk of cardiovascular disease development.

Norepinephrine transporter expression is inversely associated with glycaemic indices: a pilot study in metabolically diverse persons with overweight and obesity

Objective

The objective of this study was to examine the cross‐sectional relationship between the expression of norepinephrine transporter (NET), the protein responsible for neuronal uptake‐1, and indices of glycaemia and hyperinsulinaemia, in overweight and obese individuals.

Methods

Thirteen non‐medicated, non‐smoking subjects, aged 58 ± 1 years (mean ± standard error of the mean), body mass index (BMI) 31.4 ± 1.0 kg m⁻², with wide‐ranging plasma glucose and haemoglobin A1c (HbA1c, range 5.1% to 6.5%) participated. They underwent forearm vein biopsy to access sympathetic nerves for the quantification of NET by Western blot, oral glucose tolerance test (OGTT), euglycaemic hyperinsulinaemic clamp, echocardiography and assessments of whole‐body norepinephrine kinetics and muscle sympathetic nerve activity.

Results

Norepinephrine transporter expression was inversely associated with fasting plasma glucose (r = −0.62, P = 0.02), glucose area under the curve during OGTT (AUC_0–120, r = −0.65, P = 0.02) and HbA1c (r = −0.67, P = 0.01), and positively associated with steady‐state glucose utilization during euglycaemic clamp (r = 0.58, P = 0.04). Moreover, NET expression was inversely related to left ventricular posterior wall dimensions (r = −0.64, P = 0.02) and heart rate (r = −0.55, P = 0.05). Indices of hyperinsulinaemia were not associated with NET expression. In stepwise linear regression analysis adjusted for age, body mass index and blood pressure, HbA1c was an independent inverse predictor of NET expression, explaining 45% of its variance.

Conclusions

Hyperglycaemia is associated with reduced peripheral NET expression. Further studies are required to identify the direction of causality.

Effect of sunlight and season on serotonin turnover in the brain

Alterations in monoaminergic neurotransmission in the brain are thought to underlie seasonal variations in mood, behaviour, and affective disorders. We took blood samples from internal jugular veins in 101 healthy men, to assess the relation between concentration of serotonin metabolite in these samples and weather conditions and season. We showed that turnover of serotonin by the brain was lowest in winter (p=0.013). Moreover, the rate of production of serotonin by the brain was directly related to the prevailing duration of bright sunlight (r=0.294, p=0.010), and rose rapidly with increased luminosity. Our findings are further evidence for the notion that changes in release of serotonin by the brain underlie mood seasonality and seasonal affective disorder.

Epidural haematoma after dural puncture in a parturient with neurofibromatosis

A case of epidural analgesia in a parturient with neurofibromatosis (von Recklinghausen's disease) complicated by dural puncture and epidural haematoma is described and the management of the case is discussed. The case emphasizes the need for antenatal assessment of parturients with neurofibromatosis in order that the necessary investigations can be arranged and informed consent for analgesia and anaesthesia can be obtained.

Low-dose estrogen supplementation improves vascular function in hypogonadal men

It is widely accepted that in women, estrogens provide protection against the development of cardiovascular disease. However, the cardiovascular role of estrogens in men remains uncertain, despite preliminary evidence that endogenous estrogens produced by aromatization of androgenic precursors are of physiological importance. Hypogonadal men have very low levels of circulating estrogen. We studied the responsiveness of forearm resistance arteries to vasoconstrictor and vasodilator agents in 12 men (mean+/-SEM age, 68.7+/-2.6 years) rendered hypogonadal as a result of treatment for prostatic cancer, before and after 8 weeks of estrogen supplementation (estradiol valerate 1 mg daily; n=7) or placebo (n=5). Forearm blood flow was measured by venous occlusion plethysmography, and vasoactive agents were infused through a brachial artery cannula in doses that did not affect blood pressure or heart rate. Estrogen supplementation was well tolerated, with no adverse effects. After estrogen treatment, mean estradiol levels increased from <30 to 308+/-65 pmol/L, and both systolic and diastolic blood pressures were reduced. HDL cholesterol levels increased significantly, and vasoconstrictor responses to the NO synthase inhibitor N(G)-monomethyl-L-arginine (1, 2, 4 micromol/min) were enhanced. Vasoconstrictor responses to angiotensin II (8, 16, 32 ng/min) were markedly attenuated by estrogen treatment, as were vasoconstrictor responses to norepinephrine (25, 50, 100 ng/min). Estrogen did not alter the vasodilator responses to acetylcholine (9.25, 18.5, 37 microgram/min) or to the endothelium-independent agent sodium nitroprusside (1.6 microgram/min). Responses to all vasoactive agents were unchanged after administration of placebo. We conclude that low-dose estrogen supplementation in hypogonadal men is well tolerated, lowers blood pressure, and may affect vascular reactivity in a manner that is potentially beneficial, through several mechanisms, including enhancement of basal NO release and attenuation of vasoconstrictor responses to angiotensin II and norepinephrine. These findings suggest the need to consider a possible clinical role for estrogenic compounds in cardiovascular risk reduction in some groups of men.

Effect of cardiac sympathetic nervous activity on mode of death in congestive heart failure

AIMS

To investigate whether strong cardiac sympathetic activity contributes primarily to sudden death or to worsening heart failure, and to determine the relationship of the size of cardiac noradrenaline stores to the mode of death.

METHODS AND RESULTS

The study population comprised 116 patients with congestive heart failure (ejection fraction 19+/-7%) and a mean follow-up of 18+/-19 months. Cardiac sympathetic nervous function was measured using coronary sinus blood sampling and noradrenaline isotope dilution methodology. Cardiac sympathetic activity was estimated from cardiac noradrenaline spillover, and noradrenaline stores from the overflow of the tritiated noradrenaline metabolite [(3)H]dihydroxyphenylglycol, which is produced by monoamine oxidase inside nerve endings. Small cardiac noradrenaline stores (below median) predicted death from worsening heart failure (hazard ratio=4.18, P<0.05), particularly if cardiac noradrenaline spillover was elevated (hazard ratio=2.36 per tertile, P<0.01), indicating progression of disease associated with defective sympathetic innervation. In contrast, large stores (hazard ratio=2.81, P<0.05), especially if coupled with increased noradrenaline spillover (hazard ratio=1.64 per tertile, P<0.05), were related to sudden death.

CONCLUSION

High cardiac sympathetic activity is a risk factor for sudden death, particularly in the presence of intact cardiac sympathetic innervation. Conversely, progression of myocardial disease and heart failure is closely associated with depletion of sympathetic nerves in the heart, especially if rates of noradrenaline release paradoxically remain high.

Acute Effects of Continuous Positive Airway Pressure on Cardiac Sympathetic Tone in Congestive Heart Failure

Background —Depressed ventricular performance and neurohormonal activation are key pathophysiological features of congestive heart failure (CHF). Although angiotensin-converting enzyme inhibitors and β-adrenoceptor blockers exert beneficial effects in CHF, mortality remains unacceptably high, and the development of further therapeutic approaches is warranted. Recent data suggest that continuous positive airway pressure (CPAP) may be of benefit in the treatment of CHF, although the mechanism for this action is incompletely understood.

Methods and Results —In the present study, we examined the effect of short-term CPAP (10 cm H 2 O for 10 minutes) on hemodynamics (Swan Ganz catheter) and total systemic and cardiac sympathetic activity (norepinephrine spillover method) in 14 CHF patients in New York Heart Association class III. The application of CPAP was associated with a fall in cardiac output (4.8±0.3 to 4.4±0.2 L/min; P <0.05) and a significant reduction in cardiac norepinephrine spillover (370±58 to 299±55 pmol/min; P <0.05), although total systemic norepinephrine spillover was unchanged.

Conclusion —The short-term application of CPAP results in an inhibition of cardiac sympathetic nervous activity. Further investigation into the potential value of long-term CPAP in CHF patients is warranted.

Mechanisms of Carvedilol Action in Human Congestive Heart Failure

Abstract —The precise mechanism by which β-adrenoceptor blockers exert their beneficial actions in patients with heart failure remains unclear. Several possibilities have been proposed, including heart rate reduction, β2-adrenoceptor–mediated modulation of catecholamine release, antagonism of the receptor-mediated toxic actions of norepinephrine on the myocardium, and favorable effects on myocardial energetics. In the present study we evaluated the effect of 3 months of carvedilol therapy on hemodynamics, total systemic and cardiac norepinephrine spillover (isotope dilution method), and myocardial metabolism (myocardial oxygen consumption and carbon dioxide release) in 10 patients with severe congestive heart failure. Although carvedilol treatment was associated with a significant improvement in left ventricular ejection fraction (17±1% to 28±3%; P <0.01) and left ventricular stroke work (87±13 to 119±21 g · m per beat; P <0.05), this effect was unrelated to changes in total systemic or cardiac norepinephrine spillover. The rise in left ventricular stroke work was accompanied by a modest rise in myocardial oxygen consumption per beat (0.33±0.04 to 0.42±0.04; P =0.05), although contractile efficiency was unchanged. The favorable effects of carvedilol on ventricular function in the failing heart are not explained by alterations in norepinephrine release or by changes in myocardial contractile efficiency.

Effects of intravenous brain natriuretic peptide on regional sympathetic activity in patients with chronic heart failure as compared with healthy control subjects

OBJECTIVES

We sought to assess the effects of brain natriuretic peptide (BNP) on systemic and regional sympathetic nervous activity (SNA) in both patients with congestive heart failure (CHF) and healthy control subjects.

BACKGROUND

Although the response of SNA to atrial natriuretic peptide (ANP) has been well documented, the response of SNA to BNP is largely unknown.

METHODS

We assessed cardiac and whole-body SNA using the norepinephrine (NE) tracer dilution method before and after infusion of two doses of BNP (3 and 15 ng/kg body weight per min) in 11 patients with stable CHF (ejection fraction 24 +/- 2%) and 12 age-matched healthy control subjects. In addition, renal SNA and hemodynamic variables were assessed at baseline and after the higher BNP dose.

RESULTS

Low dose BNP did not change blood pressure or whole-body NE spillover, but reduced cardiac NE spillover in both groups by 32 +/- 13 pmol/min (p < 0.05). In both groups, high dose BNP reduced pulmonary capillary pressure by 5 +/- 1 mm Hg (p < 0.001) and mean arterial pressure by 6 +/- 3 mm Hg (p < 0.05), without a concomitant increase in whole-body NE spillover; however, cardiac NE spillover returned to baseline levels. Renal NE spillover remained virtually unchanged in healthy control subjects (501 +/- 120 to 564 +/- 115 pmol/min), but was reduced in patients with CHF (976 +/- 133 to 656 +/- 127 pmol/min, p < 0.01).

CONCLUSIONS

Our results demonstrate a sympathoinhibitory effect of BNP. Cardiac sympathetic inhibition was observed at BNP concentrations within the physiologic range, whereas high dose BNP, when arterial and filling pressures fell and reflex sympathetic stimulation was expected, systemic and cardiac SNA equated to baseline values. There was inhibition of renal SNA in patients with CHF, but not in healthy control subjects. Whether this effect is specific to BNP or related to reduced filling pressure remains to be determined.

Evidence for functional presynaptic alpha-2 adrenoceptors and their down-regulation in human heart failure

OBJECTIVES

The aim of this study was to investigate the role of peripheral presynaptic alpha-2 adrenergic receptors in modulating norepinephrine (NE) release in congestive heart failure (CHF).

BACKGROUND

Activation of the sympathetic nervous system is a hallmark of CHF. Clonidine, an imidazoline and adrenergic agonist with high selectivity for the alpha-2 adrenoceptor, has been shown to reduce generalized sympathetic activity in heart failure after parenteral administration. If it could be shown that peripheral presynaptic alpha-2 adrenoceptors are inhibitory to NE release, then they could be targeted for future therapy, and as a corollary, potentially circumvent unwanted side effects arising from stimulation of alpha-2 adrenoceptors in the brain. Additionally, it could be concluded that these receptors form the basis for an auto-inhibitory feedback to further NE release.

METHODS

Fifteen healthy volunteers and 10 patients with heart failure received intra-arterial clonidine via the brachial artery (0.05 microg and 0.48 microg/100 ml forearm/min). Radio-tracer techniques were employed for studying NE kinetics.

RESULTS

Intra-arterial clonidine caused a dose-dependent decrease in forearm spillover of NE in healthy individuals (low dose, high dose: 26%, 49%: p < 0.05, p < 0.001, respectively). In the patient group, no decrease in forearm spillover was demonstrated after local administration. The difference in response between the two groups was statistically significant (p = 0.004).

CONCLUSIONS

Peripheral sympathoneural alpha-2 adrenoceptors are functionally important in inhibiting NE release in the healthy human. In heart failure, this function is lost. This finding offers further insights into the mechanisms responsible for high circulating levels of NE in patients with heart failure. In addition, it suggests that selective targeting of peripheral presynaptic alpha-2 adrenoceptors will not achieve sympathoinhibition in heart failure.

Comparative effects of mibefradil and nifedipine gastrointestinal transport system on autonomic function in patients with mild to moderate essential hypertension

BACKGROUND

L-type dihydropyridine calcium channel blockers (CCBs) have been implicated in increased cardiovascular events in patients with hypertension, perhaps due to adverse effects on autonomic nervous system (ANS) function. Blockade of T-type calcium channels may limit ANS dysfunction by inhibition of T channel-mediated neuroendocrine effects.

OBJECTIVE AND DESIGN

This double-blind, parallel group study compared the effect of nifedipine gastrointestinal transport system (GITS) (L-type CCB) versus mibefradil (T-type CCB) on ANS function in patients with mild-moderate essential hypertension.

METHODS

Sixteen patients (10 male, 6 female; age 57.2 +/- 2.3 years), diastolic blood pressure (DBP) < 95 mmHg were randomized to nifedipine 30 mg daily or mibefradil 50 mg daily (2 weeks), then nifedipine 60 mg daily or mibefradil 100 mg daily (4 weeks). Sympathetic nervous system activity (SNSA) was assessed using norepinephrine kinetics. Parasympathetic nervous system activity (PSNA) was assessed from 24 h Holter recordings of heart rate variability (HRV). Non-invasive baroreflex sensitivity (BRS) provided integrated assessment of ANS.

RESULTS

Patient groups were well matched at baseline. Achieved DBP was lower in patients treated with mibefradil compared with nifedipine, (83.4 +/- 1.7 versus 95.25 +/- 3.3 mmHg). There were no significant differences in SNSA and BRS between groups, however the root mean square of successive differences and high frequency power (HFP) were increased in mibefradil compared with nifedipine-treated patients [(+ 1.07 +/- 1.6 versus -3.36 +/- 1.2 ms, P < 0.05) and (+ 0.28 +/- 0.1 versus -0.23 +/- 0.1 ms2, P < 0.01), respectively]. Furthermore, Ln HFP/Ln total power was increased from week 0 to week 6 in the mibefradil-treated group, (0.71 +/- 0.02 versus 0.74 +/- 0.03, P = 0.046).

CONCLUSION

No differences existed between effect of L- and T-type CCBs on SNSA and BRS. However, T-type CCBs increased PSNA, independent of achieved changes in heart rate.

Phenotypic evidence of faulty neuronal norepinephrine reuptake in essential hypertension

Previous reports suggest that neuronal norepinephrine (NE) reuptake may be impaired in essential hypertension, perhaps because of dysfunction of the NE transporter, although the evidence is inconclusive. To further test this proposition, we applied phenotypically relevant radiotracer methodology, infusion of tritiated NE and quantification of NE metabolites, to 34 healthy lean subjects (body mass index <27.0 kg/m(2)), 19 overweight (body mass index >28.0 kg/m(2)) but otherwise healthy normotensive subjects, 13 untreated lean patients with essential hypertension, and 14 obesity-related hypertensives. Spillover of NE from the heart was increased in lean hypertensives only (mean+/-SD 33.4+/-20.6 versus 16.1+/-11.7 ng/min in lean normotensives, P<0.05), but this could have resulted from high cardiac sympathetic nerve firing rates, faulty NE reuptake, or both. The arterial plasma concentration of 3-methoxy-4-hydroxylphenylglycol, an extraneuronal metabolite of NE, was elevated in lean hypertensives only (3942+/-1068 versus 3055+/-888 pg/mL in healthy subjects, P:<0.05). The fractional extraction of plasma tritiated NE in passage through the heart, determined on the basis of neuronal NE uptake, was reduced in lean essential hypertensives (0.65+/-0.19 versus 0.81+/-0.11 in healthy subjects, P<0.05). Cardiac release of the tritiated NE metabolite [(3)H]dihydroxylphenylglycol, produced intraneuronally by monoamine oxidase after uptake of [(3)H]NE by the transporter, was reduced in lean hypertensives only (992+/-1435 versus 4588+/-3189 dpm/min in healthy subjects, P<0.01) These findings suggest that neuronal reuptake of NE is impaired in essential hypertension. Through amplification of the neural signal, such a defect could constitute a neurogenic variant of essential hypertension. In obesity-related hypertension, there was no phenotypic evidence of NE transporter dysfunction.

Human ageing and the sympathoadrenal system

Over the past three decades the changes in sympathoadrenal function that occur with age in healthy adult humans have been systematically studied using a combination of neurochemical, neurophysiological and haemodynamic experimental approaches. The available experimental evidence indicates that tonic whole-body sympathetic nervous system (SNS) activity increases with age. The elevations in SNS activity appear to be region specific, targeting skeletal muscle and the gut, but not obviously the kidney. The SNS tone of the heart is increased, although this appears to be due in part to reduced neuronal reuptake of noradrenaline (norepinephrine). In contrast to SNS activity, tonic adrenaline (epinephrine) secretion from the adrenal medulla is markedly reduced with age. This is not reflected in plasma adrenaline concentrations because of reduced plasma clearance. Despite widely held beliefs to the contrary, sympathoadrenal responsiveness to acute stress is not exaggerated with age in healthy adults. Indeed, adrenaline release in response to acute stress is substantially attenuated in older men. The mechanisms underlying the age-associated increases in SNS activity have not been established, but our preliminary data are consistent with increased subcortical central nervous system (CNS) sympathetic drive. These changes in sympathoadrenal function with advancing age may have a number of important physiological and pathophysiological consequences for human health and disease.

Nitric oxide mediated modulation of norepinephrine transport: identification of a potential target for S-nitrosylation

1. Carrier mediated uptake (uptake-1) transport of norepinephrine (NE) plays a key role in the regulation of sympathetic neurotransmission. Recent investigations indicate that nitric oxide (NO) may modulate uptake-1 activity, possibly in a cyclic GMP independent manner. 2. Carrier mediated transport of [(3)H-NE] and [(3)H-dopamine, DA] was examined in CHO cells transfected with cDNA for the NE and DA transporters (NET, DAT) respectively. 3. While exposure to the NO donor S-nitroso-N-acetylpenicillamine (100 microM, SNAP) significantly reduced [(3)H-NE] uptake (P<0.001), no effect on [(3)H-DA] transport was apparent. 4. Comparison of the amino acid sequences for NET and DAT identified cysteine residue 351 in NET, which was not present in DAT. Site-directed mutagenesis of Cys 351 to Ser produced a functional NET that was resistant to the inhibitory effects of SNAP. 5. The presence of SNAP mediated nitrosylation of the cysteine residue in an 8-mer model peptide based around Cys 351 in NET was confirmed by both biochemical and mass spectroscopic means. 6. These data indicate the potential regulatory role for NO in modulating sympathetic neurotransmission, and further confirm the importance of non-cyclic GMP dependent mechanisms in mediating the actions of NO.

The 'adrenaline hypothesis' of hypertension revisited: evidence for adrenaline release from the heart of patients with essential hypertension

OBJECTIVE

Whether adrenaline acts as a sympathetic nervous cotransmitter in humans and stimulates beta2-adrenoceptors to augment neuronal noradrenaline release remains a subject of considerable dispute. The aim of this study was to test if adrenaline is released from regional sympathetic nerves (in the heart) in patients with essential hypertension, and to investigate whether locally released adrenaline might enhance cardiac noradrenaline release.

METHODS

Using dual isotope dilution methodology, adrenaline and noradrenaline plasma kinetics was measured for the whole body and in the heart in 13 untreated patients with essential hypertension and 27 healthy volunteers. All research participants underwent cardiac catheterization under resting conditions.

RESULTS

At rest, there was negligible adrenaline release from the sympathetic nerves of the heart in healthy subjects, 0.27 +/- 1.62 ng/min. In contrast, in patients with essential hypertension, adrenaline was released from the heart at a rate of 1.46 +/- 1.73 ng/min, equivalent on a molar basis to approximately 5% of the associated cardiac noradrenaline spillover value. Cardiac noradrenaline spillover was higher in hypertensive patients, 24.9 +/- 17.0 ng/min compared to 15.4 +/- 11.7 ng/min in healthy volunteers (P< 0.05). Among patients, rates of cardiac adrenaline and noradrenaline spillover correlated directly (r= 0.59, P< 0.05).

CONCLUSIONS

This study, in demonstrating release of adrenaline from the heart in patients with essential hypertension, and in disclosing a proportionality between rates of cardiac adrenaline and noradrenaline release, provides perhaps the most direct evidence to date in support of the 'adrenaline hypothesis' of essential hypertension.

Reduced myocardial nerve growth factor expression in human and experimental heart failure

Maintenance of cardiac performance is tightly controlled by the autonomic nervous system. In congestive heart failure (CHF), although the adverse pathophysiological effects of cardiac sympathetic overactivity are increasingly recognized, the paradoxical finding of reduced sympathetic innervation density in the failing heart remains unexplained. Given these observations, we tested the hypothesis that a reduction in the myocardial production of nerve growth factor (NGF), which is important for the maintenance of sympathetic neuronal survival, could explain the conflicting neurochemical and neuroanatomical profile of CHF. In healthy humans (n=11), there was a significantly greater transcardiac venoarterial plasma NGF gradient than in CHF patients (n=11, P<0.05). In a rat model of CHF, a 40% reduction (P<0.05) NGF mRNA expression was apparent in association with a 24% reduction in tissue NGF content (P<0.05). In conjunction, evidence of reduced sympathetic innervation in the failing heart was apparent, as measured histologically by catecholamine fluorescence and by expression of the neuronal NGF receptor trkA. Norepinephrine (10 micromol/L) exposure reduced both NGF mRNA and protein expression in isolated cardiomyocytes, suggesting that myocardial NGF downregulation may represent an adaptive response to sympathetic overactivity. These data indicate that NGF expression in the heart is dynamic and may be altered in cardiovascular disease states. In CHF, reduced NGF expression may account for alterations in sympathetic neuronal function and neuroanatomy. The full text of this article is available at http://www.circresaha.org.

Total body catecholamine kinetics before and after birth in spontaneously hypoxemic fetal lambs

To study the effect of fetal hypoxemia on perinatal norepinephrine and epinephrine total body kinetics, 13 near-term fetal lambs were instrumented with vascular catheters under general anesthesia. One week later, norepinephrine and epinephrine kinetics were measured in normoxemic (n = 7) or spontaneously hypoxemic fetuses (n = 6) with isotope dilution methodology. Hypoxemic fetuses had lower body (P < 0.02) and placental (P = 0.01) weights and a threefold elevation in plasma norepinephrine (P < 0.005) and epinephrine (P < 0.025) associated with correspondingly higher total body norepinephrine (P < 0.005) and epinephrine (P < 0.05) spillovers. After birth, total body norepinephrine and epinephrine spillover increased 45% and 3.2-fold, respectively, in normoxemic animals (both P < 0.001). However, in the hypoxemic group, norepinephrine total body spillover was unchanged between fetal and 1-h lambs and then fell in 4-h lambs (P < 0.005). In addition, total body epinephrine release rose postnatally (P < 0.05) but less than in the normoxemic group (P < 0.02). No differences in norepinephrine or epinephrine total body clearance occurred between normoxemic and hypoxemic groups in either fetal or newborn lambs. These findings indicate that in hypoxemic and growth-restricted fetuses 1) elevated circulating norepinephrine and epinephrine levels are related to increased sympathoadrenal activity and 2) birth is associated with an initial maintenance and subsequent decline in global sympathetic activity but a blunting of adrenal medullary activation.

Sympathetic activation triggers ventricular arrhythmias in rat heart with chronic infarction and failure

OBJECTIVE

To seek direct evidence for a cause-effect relation between sympathetic activation and arrhythmogenesis.

METHODS

Rats underwent open-chest surgery with either coronary artery occlusion or sham operation, and were studied 8 weeks later using in situ heart perfusion and nerve stimulation methods.

RESULTS

Infarcted rats showed cardiac functional impairment and increased heart and lung weight. The extent of these changes correlated well with infarct size (IS). In in situ perfused hearts, sympathetic nerve stimulation (2 and 4 Hz, 45 s duration) induced a frequency-dependent release of norepinephrine (NE). NE release was lower in MI than that in control groups. In hearts with large IS (> or = 40%, n = 19) ventricular arrhythmias were rare at baseline, but nerve stimulation evoked the onset of ventricular premature beats (95%), tachycardia (37%) and fibrillation (26%), IS and stimulation frequency were key determinants for the inducibility of arrhythmias. Lower K- concentration enhanced arrhythmia inducibility. beta-blockade inhibited the frequency of arrhythmias produced by nerve stimulation.

CONCLUSION

In infarcted rat hearts sympathetic activation is a potent trigger for the onset of ventricular tachyarrhythmias.

Neural mechanisms in human obesity-related hypertension

OBJECTIVE

Two hypotheses concerning mechanisms of weight gain and of blood pressure elevation in obesity were tested. The first hypothesis is that in human obesity sympathetic nervous system underactivity is present, as a metabolic basis for the obesity. The second hypothesis, attributable to Landsberg, is that sympathetic nervous activation occurs with chronic overeating, elevating blood pressure. These are not mutually exclusive hypotheses, since obesity is a heterogeneous disorder.

DESIGN AND METHODS

Whole body and regional sympathetic nervous system activity, in the kidneys and heart, was measured at rest using noradrenaline isotope dilution methodology in a total of 86 research voluteers in four different subject groups, in lean and in obese people who either did, or did not, have high blood pressure.

RESULTS

In the lean hypertensive patients, noradrenaline spillover for the whole body, and from the heart and kidneys was substantially higher than in the healthy lean volunteers. In normotensive obesity, the whole body noradrenaline spillover rate was normal, mean renal noradrenaline spillover was elevated (twice normal), and cardiac noradrenaline spillover reduced by approximately 50%. In obesity-related hypertension, there was elevation of renal noradrenaline spillover, comparable to that present in normotensive obese individuals but not accompanied by suppression of cardiac noradrenaline spillover, which was more than double that of normotensive obese individuals (P<0.05), and 25% higher than in healthy volunteers. There was a parallel elevation of heart rate in hypertensive obese individuals.

CONCLUSIONS

The sympathetic underactivity hypothesis of obesity causation now looks untenable, as based on measures of noradrenaline spillover, sympathetic nervous system activity was normal for the whole body and increased for the kidneys; the low sympathetic activity in the heart would have only a trifling impact on total energy balance. The increase in renal sympathetic activity in obesity may possibly be a necessary cause for the development of hypertension in obese individuals, although clearly not a sufficient cause, being present in both normotensive and hypertensive obese individuals. The discriminating feature of obesity-related hypertension was an absence of the suppression of the cardiac sympathetic outflow seen in normotensive obese individuals. Sympathetic nervous changes in obesity-related hypertension conformed rather closely to those expected from the Landsberg hypothesis.

Decontamination of laryngoscopes: a survey of national practice

We conducted a postal questionnaire to survey methods of laryngoscope cleaning in units throughout Great Britain. We found that there was great variation in practice. Most units autoclave laryngoscope blades at some time, but less than one-quarter do so between each case. A wide range of methods is used to clean the blade in units where autoclaving was not undertaken. Most units had no guidelines relating to laryngoscope treatment between uses.

Antiadrenergic effect of chronic amiodarone therapy in human heart failure

OBJECTIVES

The aim of the present study was to evaluate the influence of amiodarone on neurochemical parameters of sympathetic nervous activity in patients with congestive heart failure.

BACKGROUND

Unlike most antiarrhythmic agents, amiodarone has been shown to exert a beneficial effect on survival in some studies of patients with congestive heart failure. The pharmacology of this agent is complex, and as such, the mode of its action is unclear in humans. Some experimental studies suggest that amiodarone exerts a sympatholytic effect.

METHODS

To evaluate the effect of amiodarone on sympathetic nervous activity, we measured the total systemic and cardiac norepinephrine (NE) spillover rate by isotope dilution in 58 patients with severe heart failure (left ventricular ejection fraction 20 +/- 1%), 22 of whom were receiving chronic amiodarone treatment. Release rates for dihydroxyphenylalanine (DOPA, a precursor of NE), and endogenous and radiolabeled dihydroxyphenylglycol (DHPG and 3H-DHPG, intraneuronal metabolites of NE and 3H-NE, respectively) were also determined to assess sympathetic neuronal integrity.

RESULTS

Amiodarone-treated patients had significantly lower cardiac spillover rates for NE (42%, p = 0.001), DOPA (74%, p < 0.001), DHPG (44%, p < 0.01) and 3H-DHPG (51%, p < 0.01) than those patients not treated with amiodarone. Hemodynamic assessment of amiodarone-treated patients revealed higher cardiac output (4.4 +/- 0.2 vs. 3.7 +/- 0.2 liters/min, p < 0.01), and slightly lower pulmonary capillary wedge pressure (18 +/- 2 vs. 22 +/- 1, p = NS) than in untreated patients. After correction for the potential confounding effect of hemodynamic differences, amiodarone-treated patients continued to demonstrate significantly lower spillover rates of NE, DOPA and DHPG from the heart.

CONCLUSIONS

These data indicate that amiodarone may exert beneficial effects on the failing human heart through a sympatholytic process, and this action appears to be relatively cardioselective.

Recent insight into therapy of congestive heart failure: focus on ACE inhibition and angiotensin-II antagonism

One possible intervention to interrupt the deleterious effects of the renin-angiotensin system is suppression of angiotensin II (Ang II) formation by inhibition of angiotensin-converting enzyme (ACE). However, ACE inhibition incompletely suppresses Ang II formation and also leads to accumulation of bradykinin. Angiotensin II type 1 (AT1) receptors are believed to promote the known deleterious effects of Ang II. Therefore, AT1 receptor antagonists have been recently introduced into therapy for hypertension and congestive heart failure (CHF). Although there are significant differences between the effects of AT1 receptor antagonists and ACE inhibitors including the unopposed stimulation of angiotensin II type 2 (AT2) receptors by AT1 receptor antagonists, the discussion of whether ACE inhibitors, AT1 receptor antagonists or the combination of both are superior in the pharmacotherapy of CHF is still largely theoretical. Accordingly, AT1 receptor antagonists are still investigational. Angiotensin-converting enzyme inhibitors remain first line therapy in patients with CHF due to systolic dysfunction. However, in patients not able to tolerate ACE inhibitor induced side effects, in particular cough, AT1 receptor antagonism is a good alternative. In clinical practice, emphasis should be placed on increasing the utilization of ACE inhibitors, as more than 50% of patients with CHF do not receive ACE inhibitors. In addition, the majority of those on ACE inhibitors receive doses lower than the dosage used in the large clinical trials. Although not yet completely proved, it is likely that high doses of ACE inhibition are superior to low doses with respect to prognosis and symptoms.

Estrogen supplementation attenuates glucocorticoid and catecholamine responses to mental stress in perimenopausal women

Estrogens are reported to provide protection against the development of cardiovascular disease in women, but the mechanisms underlying these effects are not well defined. We hypothesized that estrogen might affect the hormonal responses to stress. We therefore studied cortisol, ACTH, epinephrine, norepinephrine, and norepinephrine spillover and hemodynamic responses to a 10-min mental arithmetic test in 12 perimenopausal women randomized to 8 weeks of estrogen supplementation (estradiol valerate, 2 mg daily; n = 7) or placebo (n = 5). Total body and forearm norepinephrine spillover were measured by radiotracer methodology. After supplementation with estradiol, the increases in both systolic and diastolic blood pressure in response to mental stress were reduced, and cortisol, ACTH, plasma epinephrine and norepinephrine, and total body norepinephrine spillover responses to stress were significantly attenuated (P < 0.05 in each case). Forearm norepinephrine spillover was unchanged by estrogen, and there was no change in any of the responses after placebo. We conclude that estrogen supplementation in perimenopausal women attenuates blood pressure, glucocorticoid, and catecholamine responses to psychological stress.

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.

Human obesity is associated with a chronic elevation in brain 5-hydroxytryptamine turnover

The afferent signals that evoke changes in energy intake with regard to body weight regulation are presumed to arise partly from body stores, with the most likely candidate being adipose tissue depots. However, clinical investigation of the neuronal circuitry involved in the central nervous system's processing of such satiety signals remains largely unexplored. Using percutaneously placed catheters in either the right or left internal jugular veins, we were able to quantify the release of central nervous system monoamine and indoleamine neurotransmitters in 64 weight-stable male subjects with varying degrees of adiposity. Veno-arterial plasma concentration differences and internal jugular blood or plasma flow were used, according to the Fick Principle, to quantify the amount of neurotransmitter stemming from the brain. By combining this technique with a noradrenaline and adrenaline isotope dilution method for examining neuronal transmitter release, we were able to examine the association between central nervous system neurotransmitters and efferent sympathetic nervous outflow and adrenomedullary function in human obesity. We found that brain 5-hydroxytryptamine (serotonin) turnover is chronically elevated in proportion to adiposity and is increased postprandially to a similar degree in lean and obese individuals. There was no difference in the degree of sympathetic nervous activity or rate of adrenaline secretion in the subjects examined. It therefore seems that in human obesity, in the face of a chronic elevation in peripheral satiety signals, brain serotonergic processes are switched on accordingly, but the subsequent physiological response involving a reduction in food intake, increased thermogenesis and sympathetic activity is in some way impeded.

Contribution of lungs to desipramine-induced changes in whole body catecholamine kinetics in newborn lambs

To characterize pulmonary and total body norepinephrine and epinephrine kinetics in the immediate newborn period, the effects of desipramine were studied in six fetal lambs chronically instrumented at 133-134 days gestation (term 147 days) and delivered 1 wk later by cesarean section under spinal anesthesia. Norepinephrine and epinephrine kinetics were determined with isotope dilution methodology 4 h after birth and repeated 30 min after desipramine (2 mg/kg iv). At baseline, the lungs accounted for 35 +/- 10 and 47 +/- 13% of whole body norepinephrine clearance (93 +/- 8 ml. min-1. kg-1) and spillover (188 +/- 29 ng. min-1. kg-1) and 15 +/- 2 and 19 +/- 7% of whole body epinephrine clearance (82 +/- 4 ml. min -1. kg -1) and release (22.7 +/- 2.7 ng. min-1. kg-1), respectively. Desipramine decreased pulmonary norepinephrine and epinephrine clearance and spillover to near-zero levels, whereas whole body norepinephrine clearance fell by 51 +/- 3% (P < 0.001), norepinephrine spillover by 54 +/- 6% (P < 0.005), epinephrine clearance by 30 +/- 6% (P < 0.01), and epinephrine spillover by 34 +/- 11% (P < 0.05). These results indicate that, in the immediate newborn period, pulmonary removal and release of norepinephrine and epinephrine is mediated by a desipramine-sensitive process that accounts for a major portion of associated reductions in whole body norepinephrine and epinephrine clearance and release.

Protection of neuronal uptake-1 inhibitors in ischemic and anoxic hearts by norepinephrine-dependent and -independent mechanisms

Cardiac ischemia and anoxia induce massive norepinephrine (NE) release, which is mediated by a reverse operation of uptake-1 and can be suppressed by uptake-1 inhibitors. We studied effects of uptake-1 inhibitors on incidence of ventricular fibrillation (VF%) and myocardial contracture in perfused rat hearts under ischemic or anoxic conditions. NE release occurred in hearts during ischemia or anoxia and was largely inhibited by desipramine, imipramine, and cocaine. The generation of inositol 1,4,5-trisphosphate (InsP3) during reperfusion also was abolished by desipramine. During anoxia/reoxygenation, VF (93 and 71%, respectively) and myocardial contracture occurred and were significantly inhibited by desipramine and by NE depletion. Regional ischemia and reperfusion induced high VF% (86 and 100%, respectively), which was reduced or abolished by desipramine and imipramine at 0.03 and 0.3 microM. During the ischemic phase, cocaine was similarly antiarrhythmic, as was a combination of timolol and prazosin, but NE depletion was not. In NE-depleted hearts, cocaine or the combination of timolol and prazosin showed limited effect on VF%, whereas both desipramine and imipramine abolished VF. In anesthetized rats in vivo, ischemic VF% was reduced by desipramine (30 vs. 92%; p < 0.01). In conclusion, uptake-1 inhibitors protect hearts against ischemia/reperfusion- and anoxia/reoxygenation-induced arrhythmias, partly because of the inhibition of locally mediated NE release. Other actions of desipramine and imipramine may contribute to the overall efficacy.

Control of the forearm microcirculation: interactions with measures of obesity and noradrenaline kinetics

1. Obesity influences the responsiveness of the microcirculation; constriction is augmented probably reflecting heightened sympathetic nervous activity. 2. The responsiveness of the microcirculation in the forearm to constriction and dilation was therefore examined in 14 men and women with varying degrees of abdominal adiposity, to determine the potential effects of sympathetic nervous activity and adiposity on flow. Changes in basal blood flow were measured by venous occlusion plethysmography during intra-arterial infusions of noradrenaline, acetylcholine and sodium nitroprusside and after temporary ischaemia. Total body noradrenaline spillover was also measured, as an index of sympathetic neuronal activity. 3. Parameters of obesity were found to influence the responsiveness of the microcirculation. Changes in vascular resistance with noradrenaline (100 ng/min) were positively correlated with body weight, body mass index and waist circumference (r=0.63, P=0.02), whereas waist circumference was negatively correlated with post-ischaemia vasodilatation (r=-0.76, P=0.002). Acetylcholine-induced vasodilatation was inversely related to body mass index (r=-0.53, P=0.053). 4. Basal blood flow did not correlate with adiposity. Furthermore, vasodilatation with 800 ng/min sodium nitroprusside was inversely correlated with total body noradrenaline spillover (r=-0. 77, P<0.001); and changes in flows with noradrenaline (constriction) and post-ischaemia (dilation) were inversely related (r=-0.56, P=0. 035). 5. These findings, taken together, are consistent with increased local sympathetic neuronal responsiveness and diminished nitric-oxide-mediated dilation in the forearm vasculature with increasing body adiposity.

Depression of efferent parasympathetic control of heart rate in rats with myocardial infarction: effect of losartan

Heart failure is associated with attenuation of parasympathetic nervous function and enhanced renin-angiotensin activity. We tested whether there was a dysfunction in the efferent cholinergic neurotransmission in the heart of rats with chronic myocardial infarction (MI) and the potential role of angiotensin II (Ang II) receptors in such changes. Rats with MI and sham-operation were anesthetized, and heart rate (HR) reduction in response to vagal nerve stimulation was measured before and after losartan administration (10 mg/kg, i.v.) in the presence or absence of physostigmine to inhibit acetylcholinesterase. Infarcted rats had an average infarct size (IS) of 38% of the left ventricle (LV), depressed LV dP/dtmax, elevated LVEDP, and cardiac hypertrophy. Nerve stimulation (1-16 Hz) reduced HR in a frequency-dependent manner. The bradycardiac responses were significantly attenuated in infarcted versus control rats (p < 0.01), indicating an impaired efferent vagal tone. In contrast, the bradycardic response to exogenous acetylcholine was similar in both groups, implying an unchanged muscarinic receptor responsiveness in hearts with MI. HR response to nerve stimulation was potentiated by losartan in infarcted rats by 21 +/- 4 versus 4 +/- 2 beats/min (p < 0.01) but was unaffected in control rats. This effect of losartan was inversely related to the extent of attenuation of vagally mediated HR reduction. IS was correlated with both the extent of attenuation in vagally mediated bradycardia and the effect of losartan. In conclusion, the efferent vagal control of HR is attenuated in rats with MI and heart failure. This attenuation may be partly due to a presynaptic inhibition of acetylcholine release through the tonic activation, by Ang II, of neuronal AT1 receptors.

Internal jugular venous spillover of noradrenaline and metabolites and their association with sympathetic nervous activity

It is recognized that the brain plays a pivotal role in the maintenance of blood pressure and the control of myocardial function. By combining direct sampling of internal jugular venous blood with a noradrenaline isotope dilution method, for examining neuronal transmitter release, and microneurographic nerve recording, we were able to quantify the release of central nervous system noradrenaline and its metabolites and investigate their association with efferent sympathetic nervous outflow in healthy subjects and patients with pure autonomic failure. To further investigate the relationship between brain noradrenaline, sympathetic nervous activity and blood pressure regulation we examined brain catecholamine turnover, based on the internal jugular venous overflow of noradrenaline and its principal central nervous system metabolites, in response to a variety of pharmacological challenges. A substantial increase was seen in brain noradrenaline turnover following trimethaphan, presumably resulting from a compensatory response in sympathoexcitatory forebrain noradrenergic neurones in the face of interruption of sympathetic neural traffic and reduction in arterial blood pressure. In contrast, reduction in central nervous system noradrenaline turnover accompanied the blood pressure fall produced by intravenous clonidine administration, thus representing the blood pressure lowering action of the drug. Following vasodilatation elicited by intravenous adrenaline infusion, brain noradrenaline turnover increased in parallel with elevation in muscle sympathetic nervous activity. While it is difficult to assess the source of the noradrenaline and metabolites determined in our studies, available evidence implicates noradrenergic cell groups of the posterolateral hypothalamus, amygdala, the A5 region and the locus coeruleus as being involved in the regulation of sympathetic outflow and autonomic cardiovascular control.

Sympathetic activity in patients with panic disorder at rest, under laboratory mental stress, and during panic attacks

BACKGROUND

The sympathetic nervous system has long been believed to be involved in the pathogenesis of panic disorder, but studies to date, most using peripheral venous catecholamine measurements, have yielded conflicting and equivocal results. We tested sympathetic nervous function in patients with panic disorder by using more sensitive methods.

METHODS

Sympathetic nervous and adrenal medullary function was measured by using direct nerve recording (clinical microneurography) and whole-body and cardiac catecholamine kinetics in 13 patients with panic disorder as defined by the DSM-IV, and 14 healthy control subjects. Measurements were made at rest, during laboratory stress (forced mental arithmetic), and, for 4 patients, during panic attacks occurring spontaneously in the laboratory setting.

RESULTS

Muscle sympathetic activity, arterial plasma concentration of norepinephrine, and the total and cardiac norepinephrine spillover rates to plasma were similar in patients and control subjects at rest, as was whole-body epinephrine secretion. Epinephrine spillover from the heart was elevated in patients with panic disorder (P=.01). Responses to laboratory mental stress were almost identical in patient and control groups. During panic attacks, there were marked increases in epinephrine secretion and large increases in the sympathetic activity in muscle in 2 patients but smaller changes in the total norepinephrine spillover to plasma.

CONCLUSIONS

Whole-body and regional sympathetic nervous activity are not elevated at rest in patients with panic disorder. Epinephrine is released from the heart at rest in patients with panic disorder, possibly due to loading of cardiac neuronal stores by uptake from plasma during surges of epinephrine secretion in panic attacks. Contrary to popular belief, the sympathetic nervous system is not globally activated during panic attacks.

Panic disorder: coronary spasm as a basis for cardiac risk?

Patients with panic disorder often complain of angina-like chest pain during panic attacks, but this is not usually considered life-threatening. We describe three patients with panic disorder and documented cardiac ischaemia during episodes of chest pain. In two, it progressed to myocardial infarction. As none had atherosclerosis evident at coronary angiography, the mechanism was presumed to be coronary artery spasm. These cases illustrate that pain typical of angina during panic attacks may have an organic cause.

Continuous release of vasodilator prostanoids contributes to regulation of resting forearm blood flow in humans

Continuous release of nitric oxide contributes to the maintenance of resting tone in the human forearm and coronary circulations; however, evidence for a similar role of vasodilator prostanoids such as prostacyclin is lacking. We examined whether continuous release of prostacyclin contributes to basal forearm blood flow. Flow was measured using venous occlusion plethysmography in 38 healthy volunteers [mean age 21.3 +/- 2.5 yr (+/- SD); 13 female, 25 male] at rest, after administration of three incremental intra-arterial infusions of either the cyclooxygenase inhibitor aspirin or placebo, and before and after administration of the endothelium-dependent and -independent dilators acetylcholine (30 micrograms/min) and nitroprusside (1 microgram/min). To assess the effect of aspirin on the production of prostacyclin, plasma 6-keto prostaglandin F1 alpha (6-keto-PGF1 alpha; the stable metabolite of prostacyclin) was measured by simultaneous arterial and venous sampling. Aspirin produced a time- and dose-dependent reduction in forearm blood flow, resulting in a 32% decrease at the highest dose. The effect was maximal after 10 min. Flow at rest and after aspirin doses of 1, 3, and 10 mg/min was 2.6 +/- 0.2, 2.3 +/- 0.2, 2.1 +/- 0.2, and 1.8 +/- 0.2 ml.100 ml forearm tissue-1.min-1, respectively (means +/- SE, P < 0.001). Commensurate with these data, the net forearm production of 6-keto-PGF1 alpha was 52.9 +/- 16.4, 11.7 +/- 8.6, 18.7 +/- 8.5, and 12.0 +/- 12.5 pg.100 ml forearm tissue-1.min-1 for the respective doses (P = 0.04). No time-dependent reduction in flow was seen in subjects with vehicle infusion. Aspirin did not affect the responses to acetylcholine or nitroprusside. These data suggest that continuous release of prostacyclin plays a role in the maintenance of resting forearm blood flow. There appears to be a direct link between the reduction in flow with aspirin and inhibition of prostacyclin production.

Human muscle sympathetic activity and cardiac catecholamine spillover: no support for augmented sympathetic noradrenaline release by adrenaline co-transmission

1. Evidence from animal studies indicates that circulating adrenaline may be taken up into sympathetic nerves, facilitating the release of noradrenaline. To test whether adrenaline acts as a co-transmitter in humans we studied eight healthy men (aged 19-23 years) during isometric handgrip before and after an adrenaline infusion (1-3 micrograms/min for > 30 min). Sympathetic activity was assessed using radiotracer kinetic techniques to measure total and cardiac spillovers of noradrenaline and adrenaline, and microneurography to measure muscle sympathetic activity. 2. During the adrenaline infusion systolic blood pressure and heart rate increased significantly and diastolic blood pressure decreased. Total noradrenaline spillover, and arterial and coronary sinus plasma noradrenaline concentrations, increased significantly. Muscle sympathetic nerve traffic increased both during and after the end of the infusion. 3. Thirty minutes after the end of the adrenaline infusion there was adrenaline release from the heart (1.5 +/- 0.4 ng/min, mean +/- S.E.M.) indicating that significant adrenaline loading of cardiac sympathetic nerves had occurred. At this time muscle sympathetic nerve traffic and total body and cardiac noradrenaline spillovers were similar (P > 0.05) to pre-adrenaline infusion values (nerve traffic 24 +/- 4 versus 21 +/- 3 bursts/min; total noradrenaline spillover 698 +/- 98 versus 618 +/- 119 ng/min; cardiac noradrenaline spillover 16.2 +/- 2.8 versus 13.9 +/- 3.9 ng/min). 4. Isometric handgrip contraction evoked similar responses pre- and post-adrenaline infusion in total and cardiac noradrenaline spillovers and in muscle sympathetic activity. 5. The results do not support the theory that adrenaline is a co-transmitter facilitating noradrenaline release from human sympathetic nerves.

The failing human heart does not release nitrogen oxides

It has been suggested that the myocardial production of nitric oxide, as a consequence of expression of the inducible isoform of nitric oxide synthase (NOS), plays an important role in the pathophysiology of heart failure. We determined the net cardiac production of nitrogen oxides (NOx), as a measure of NOS activity, by performing arterial and coronary sinus sampling in healthy control subjects (n=6) and patients with end-stage heart failure (n=10). The arterial plasma NOx concentration was significantly elevated in heart failure patients (58.4 +/- 7.0 vs 36.9 +/- 4.9 microM, p<0.05). However, we found net extraction of NOx across the heart, with no difference between the two groups. Therefore, the heart does not appear to be a source of NOx in heart failure, and this study does not support a pathophysiological role for NOx in this condition.

Differential effect of acute baroreceptor unloading on cardiac and systemic sympathetic tone in congestive heart failure

OBJECTIVES

The present study was designed to identify the hemodynamic factor or factors that reflexly contribute to activation of the cardiac sympathetic nerves in patients with severe congestive heart failure (CHF).

BACKGROUND

We and others have previously shown that activation of the sympathetic nervous system is a key feature of CHF in humans. Furthermore, the degree of sympathetic activation shows marked regional heterogeneity and is most pronounced in the heart. Recent studies have shown a significant positive relation between pulmonary artery pressure and the magnitude of cardiac sympathetic activation. Of particular importance, the degree of cardiac sympathoexcitation has also been shown to be strongly associated with mortality in CHF.

METHODS

We assessed total systemic and cardiac sympathetic activity (norepinephrine [NE] spillover method) in nine patients with severe CHF and significantly elevated pulmonary artery pressure (mean [+/-SEM] pulmonary artery pressure 46 +/- 3 mm Hg) at rest and during a titrated infusion of sodium nitroprusside (SNP).

RESULTS

SNP infusion significantly reduced mean arterial blood pressure, pulmonary artery pressure and pulmonary capillary wedge pressure. During SNP infusion, the total body NE spillover rate (NESR) increased (from 7.9 +/- 1.7 to 11.2 +/- 3.1 nmol/min, p < 0.01), whereas the cardiac NESR decreased (from 522 +/- 86 to 409 +/- 71 pmol/min, p < 0.05). The ratio of cardiac/total NE spillover was also substantially reduced (from 7.8 +/- 1.3 to 4.9 +/- 0.9%, p < 0.001).

CONCLUSIONS

There is a directionally opposite change in whole-body (increase) and cardiac (reduction) sympathetic nervous activity during SNP infusion, most likely due to unloading of arterial baroreceptors and specific cardiopulmonary baroreceptors, respectively, in severe CHF. These observations support the concept of a positive feedback relation between pulmonary artery pressure/filling pressure and cardiac sympathetic tone in CHF and serve to reinforce the importance of vasodilator therapy in this condition.

Effects of intracellular Ca2+ chelating on noradrenaline release in normoxic and anoxic hearts

1. Ischaemia and anoxia induce excessive noradrenaline (NA) release in the heart by a mechanism independent of both nerve activity and extracellular Ca2+. The present study was designed to examine the potential role of intracellular Ca2+ mobilization in anoxic NA release in the heart by chelating intracellular free Ca2+. 2. In normoxic hearts, preloading with an intracellular free Ca2+ chelator (BAPTA) reduced neuronal NA release by 65%, confirming the effectiveness of the loading protocol. Release of NA independent of nerve activity occurred in hearts subjected to a 40 min period of anoxic, substrate-free and nominal Ca(2+)-free perfusion. Loading hearts with BAPTA prior to anoxia failed to reduce NA overflow (1561 +/- 147 vs 1496 +/- 206 pmol/g over 40 min). Infusion with BAPTA (20 mumol/L) during the first 25 min of the anoxic period reduced the quantity of anoxic NA release by approximately 25% from 2013 +/- 124 to 1476 +/- 207 pmol/g (P < 0.05). 3. Our results confirm that anoxic NA release is predominantly a Ca(2+)-independent process with Ca2+ mobilization from endogenous storage playing only a minor contributing role.

Left ventricular norepinephrine and epinephrine kinetics at birth in lambs

Little is known about the changes in the left ventricular (LV) kinetics of the catecholamines norepinephrine and epinephrine occurring at birth and their relationship to perinatal alterations in LV function and whole-body catecholamine kinetics. To address this issue, whole-body and LV catecholamine kinetics (radiotracer dilution methodology) and fetal LV output and myocardial blood flow (radioactive microspheres) were measured in chronically instrumented near-term fetuses and in the same animals 1 and 4 hours after birth. Between fetal and 1-hour lambs, LV external work increased 115% (P<.005); carotid arterial plasma norepinephrine concentration, 148% (P<.01); carotid arterial plasma epinephrine concentration, 546% (P<.005); LV norepinephrine spillover, a measure of LV sympathetic activity, 4.1-fold (P<.005); LV epinephrine spillover, 3-fold (P<.05); total-body spillover of norepinephrine, 52% (P<.025); and total-body spillover of epinephrine, 460% (P<.005). Arterial catecholamine concentrations and total-body catecholamine spillovers were unchanged between 1- and 4-hour lambs, but LV external work fell (P<.05) to a level still 77% greater than in fetal lambs (P<.005); LV norepinephrine spillover returned to near-fetal levels, and LV epinephrine spillover became undetectable. These results suggest that (1) a transient increase in LV sympathetic activity occurs at birth and may contribute to the immediate postnatal augmentation of LV performance, (2) organ differences in the pattern of sympathetic activation occur at birth, and (3) birth-related increases in LV sympathetic activity are accompanied by release of epinephrine from the heart.