Content and delivery preferences for information to support the management of high blood pressure

Blood pressure(BP) management interventions have been shown to be more effective when accompanied by appropriate patient education. As high BP remains poorly controlled, there may be gaps in patient knowledge and education. Therefore, this study aimed to identify specific content and delivery preferences for information to support BP management among Australian adults from the general public. Given that BP management is predominantly undertaken by general practitioners(GPs), information preferences to support BP management were also ascertained from a small sample of Australian GPs. An online survey of adults was conducted to identify areas of concern for BP management to inform content preferences and preferred format for information delivery. A separate online survey was also delivered to GPs to determine preferred information sources to support BP management. Participants were recruited via social media. General public participants (n = 465) were mostly female (68%), >60 years (57%) and 49% were taking BP-lowering medications. The management of BP without medications, and role of lifestyle in BP management were of concern among 30% and 26% of adults respectively. Most adults (73%) preferred to access BP management information from their GP. 57% of GPs (total n = 23) preferred information for supporting BP management to be delivered via one-page summaries. This study identified that Australian adults would prefer more information about the management of BP without medications and via lifestyle delivered by their GP. This could be achieved by providing GPs with one-page summaries on relevant topics to support patient education and ultimately improve BP management.

Exploration of diet, physical activity, health knowledge and the cardiometabolic profile of young adults with intellectual disability

BACKGROUND

Young adults with intellectual disability (ID) are experiencing early mortality, and it is suggested that they are living with undiagnosed cardiovascular and metabolic risk factors (hereafter referred to as cardiometabolic).

METHODS

We investigated the association between modifiable risk factors and cardiometabolic health profile in adults with ID aged 18-45 years through clinical evaluation of traditional cardiometabolic parameters, and assessment of physical activity levels, diet and associated health knowledge.

RESULTS

We found that young adults with ID have an increased obesity (mean body mass index; ID group: 32.9 ± 8.6 vs. control group: 26.2 ± 5.5, P = 0.001), are engaging in less physical activity than the age-matched general population (total activity minutes per week; ID group: 172.2 ± 148.9 vs. control group: 416.4 ± 277.1, P < 0.001), and overall have unhealthier diets. Additionally, knowledge about nutrition and physical activity appears to be an important predictor of cardiometabolic risk in this population. If young people with ID are to improve their cardiometabolic health to reduce morbidity and early mortality, we need to further explore how to consistently apply health messaging to get lasting behavioural change in this population.

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.

Neuroendocrine adaptations to bariatric surgery

The global epidemic of obesity and its related disease in combination with robust physiological defence of intentional weight loss generates a pressing need for effective weight loss therapies. Bariatric surgery, which works very effectively at delivering substantial sustained weight loss, has been an enigma with respect to mechanism of action. Naive concepts of restriction and malabsorption do not explain the efficacy of the most commonly used bariatric procedures. This century has seen increased interest in unravelling the mystery of the mechanisms underlying surgery associated weight loss with a focus on integrative gastrointestinal (GI) physiology, gut-brain signalling, and beyond weight loss effects on metabolism. GI interventions, some very minor, can alter GI wall stretch and pressure receptors; a range of GI hormones affecting hunger and satiety; bile acid metabolism and signalling; the characteristics of GI microbiome; portal vein nutrient sensing; and circulating concentrations of amino acids. Understanding the mechanisms involved should present targets for less invasive effective therapies.

Fat-free mass loss generated with weight loss in overweight and obese adults: What may we expect?

There is concern that intentional weight loss may generate excessive loss of fat-free mass (FFM). Idealists target minimal loss of FFM, while others consider that FFM loss of up to 25% of weight loss is acceptable. In a cross-sectional study of 275 weight-stable, overweight or obese adults, we used whole-body dual-energy X-ray absorptiometry to measure FFM. A range of models was used to estimate the expected ΔFFM/Δweight ratio required to attain the body composition of a weight-stable individual at a lower body mass index (BMI). Higher BMI was associated linearly with higher FFM in men and women. Proportional ΔFFM/Δweight was influenced by sex, BMI and age. Direct scatter plot analysis, quadratic curve fit modelling and linear FFM-BMI modelling provided similar estimates for each model of ΔFFM/Δweight ratio, with 40% for men and 33% for women. These results show that the 25% rule is inappropriate and our estimates are higher than those generally reported after intentional weight loss indicating favourable preservation of FFM.

Role of the sympathetic nervous activity in hypertension-update in 2014

Many reviews focused on the role of sympathetic nervous activity in hypertension have been published. Recently a new treatment, radiofrequency renal denervation for the treatment of resistant hypertension has been developed and examined in several clinical trials such as the Symplicity HTN and EnligHTN studies. In the Symplicity HTN-1 study the efficacy for lowering blood pressure remained satisfactory at 3 years follow up and many ancillary ameliorative effects have been reported including cardiovascular, psychosocial, and metabolic effects. The purpose of this review is to provide the current findings on the relationships between sympathetic nerve activity and hypertension, especially focus on the importance of renal sympathetic nervous activity for the onset and development of hypertension. In addition, the methods to assess sympathetic nervous activity are reviewed.

The renal denervastion was developed for the treatment-resistant hypertensive patients, and excessive confidence of the efficacy and safety existed by the end of 2013, although several issues on the efficacy and safety were reported in 2014. Furthermore, long-term efficacy and impact on renal function have been unclear. Those issues have to be clear for clinical usage. This review will also address the recent data from the renal denervation.

Ephedrine activates brown adipose tissue in lean but not obese humans

AIMS/HYPOTHESIS

Brown adipose tissue (BAT) activation increases energy consumption and may help in the treatment of obesity. Cold exposure is the main physiological stimulus for BAT thermogenesis and the sympathetic nervous system, which innervates BAT, is essential in this process. However, cold-induced BAT activation is impaired in obese humans. To explore the therapeutic potential of BAT, it is essential to determine whether pharmacological agents can activate BAT.

METHODS

We aimed to determine whether BAT can be activated in lean and obese humans after acute administration of an orally bioavailable sympathomimetic. In a randomised, double-blinded, crossover trial, we administered 2.5 mg/kg of oral ephedrine to nine lean (BMI 22 ± 1 kg/m²) and nine obese (BMI 36 ± 1 kg/m²) young men. On a separate day, a placebo was administered to the same participants. BAT activity was assessed by measuring glucose uptake with [¹⁸F]fluorodeoxyglucose and positron emission tomography-computed tomography imaging.

RESULTS

BAT activity was increased by ephedrine compared with placebo in the lean, but unchanged in the obese, participants. The change in BAT activity after ephedrine compared with placebo was negatively correlated with various indices of body fatness.

CONCLUSIONS/INTERPRETATION

BAT can be activated via acute, oral administration of the sympathomimetic ephedrine in lean, but not in obese humans.

The effects of dietary weight loss with or without exercise training on liver enzymes in obese metabolic syndrome subjects

AIM

Insulin resistance and visceral adiposity are predisposing factors for fatty liver disease. The main objectives of this study were (i) to compare the effects of caloric restriction (CR) alone or together with moderate-intensity aerobic exercise training (CR+EX) on liver enzymes, a surrogate marker of liver injury, in obese metabolic syndrome (MetS) subjects and (ii) to identify anthropometric, metabolic, cardiovascular and dietary predictors of changes in liver enzymes.

METHODS

Sedentary men and women (n = 63), aged 55 ± 6 (s.d.) years with body mass index 32.7 ± 4.1 kg/m(2) and confirmed MetS, were randomized to 12-week CR, CR+EX or no treatment (Control).

RESULTS

Weight loss averaged 7.6% in the CR and 9.1% in the CR+EX group (time effect, p < 0.001; group effect, p = 0.11); insulin sensitivity improved by 49 and 45%, respectively (both p < 0.001). Fitness (maximal oxygen consumption) increased by 19% in the CR+EX group only (p < 0.001). Alanine aminotransferase (ALT) levels decreased by 20% in the CR and 24% in the CR+EX group (time effect, both p < 0.001; group effect, p = 0.68); corresponding values for γ-glutamyltransferase (GGT) were -28 and -33%, respectively (time effect, both p < 0.001; group effect, p = 0.28). Reduction in abdominal fat mass (measured by DXA from L1 to L4) independently predicted ΔALT (r = 0.42, p = 0.005) and ΔGGT (r = 0.55, p < 0.001), whereas change in dietary saturated fat intake was independently associated with ΔALT (r = 0.35, p = 0.03).

CONCLUSIONS

Reductions in central adiposity and saturated fat intake are key drivers of improvement in liver enzymes during lifestyle interventions. Exercise training did not confer significant incremental benefits in this study.

Sex differences in postnatal growth and renal development in offspring of rabbit mothers with chronic secondary hypertension

Previously, we demonstrated that adult blood pressure was increased in offspring of rabbit mothers with chronic secondary renal hypertension. Our study identified sex-specific differences in the programming of hypertension, with female, not male, offspring, having increased blood pressure at 30 wk of age. The aim of this study was to characterize the maternal hypertension during pregnancy to determine potential programming stimuli. Further, we examined the impact of chronic maternal hypertension on offspring birth weight, nephron number, and renal noradrenaline content (as an index of renal innervation density). Three groups of mothers and their offspring were studied: two-kidney, one-wrap (2K-1W, n = 9 mothers) hypertensive, two-kidney, two-wrap (2K-2W, n = 8) hypertensive, and a sham-operated group (n = 9). Mean arterial blood pressure was increased by approximately 20 mmHg throughout pregnancy in both hypertensive groups compared with sham mothers (P(G) < 0.001). Plasma renin activity (PRA; P(G) < 0.05) and aldosterone (P(G) < 0.05) levels were increased during gestation in the 2K-1W, but not the 2K-2W mothers. Birth weight was increased by approximately 20% in offspring of both groups of hypertensive mothers (P(T) < 0.001), though this was associated with a reduction in litter size. Renal noradrenaline content was increased ( approximately 40%, P < 0.05) at 5 wk of age in female 2K-1W offspring compared with sham offspring. Glomerular number was not reduced in female offspring of either group of hypertensive mothers; however, glomerular tuft volume was reduced in female 2K-2W offspring (P < 0.05), indicative of a reduction in glomerular filtration surface area. In conclusion, the two models of renal hypertension produced differential effects on the offspring. The impact of a stimulated maternal renin-angiotensin system in the 2K-1W model of hypertension may influence development of the renal sympathetic nerves and contribute to programming of adult hypertension.

The role of catecholamines in memory impairment in chicks following reduced gas exchange in ovo

We have shown previously that reducing gas exchange to chick embryos by half wrapping eggs with an impermeable membrane from either days 14-18 (W14-18) or days 10-18 (W10-18) of the 21 day incubation results in post-hatch memory deficits. In the W10-18 chicks, short-term memory following training is impaired, whereas in the W14-18 chicks, memory is intact for 30 min but does not consolidate into long-term storage. The reduction in gas exchange caused by half wrapping eggs resulted in alterations in hematocrit, O2 and CO2 tensions suggesting that the embryos are hypoxic and hypercapnic. Our aim was to test the hypothesis that increases in circulating levels of catecholamines in ovo, as a result of hypoxia, lead to a disturbance of the central noradrenergic pathways resulting in cognitive impairment. Noradrenaline is critical for memory consolidation and a disturbance during development could compromise cognitive ability. In the present study, plasma noradrenaline levels were significantly elevated compared with control levels 2 days after hatch in W14-18 chicks. There was also a decrease in tissue noradrenaline concentration in the anterior forebrain in both W14-18 and W10-18 chicks. The differential ability of centrally administered beta2- and beta3-adrenoceptor agonists to overcome the memory deficit post-training, suggests altered responsiveness of central beta2-adrenoceptors to noradrenaline in W14-18 chicks. By comparing the W10-18 and W14-18 chicks with those from eggs wrapped from W10-14 we show that it is the timing of the prenatal hypoxia, rather than its duration, that determines the nature of cognitive dysfunction. We conclude that prenatal hypoxia induced by restriction of gas exchange can disrupt or alter central noradrenergic transmission causing cognitive impairment.

Seasonal differences in the effect of isolation and restraint stress on the luteinizing hormone response to gonadotropin-releasing hormone in hypothalamopituitary disconnected, gonadectomized rams and ewes

Stress responses are thought to act within the hypothalamopituitary unit to impair the reproductive system, and the sites of action may differ between sexes. The effect of isolation and restraint stress on pituitary responsiveness to GnRH in sheep was investigated, with emphasis on possible sex differences. Experiments were conducted during the breeding season and the nonbreeding season. In both experiments, 125 ng of GnRH was injected i.v. every 2 h into hypothalamopituitary disconnected, gonadectomized rams and ewes on 3 experimental days, with each day divided into two periods. During the second period on Day 2, isolation and restraint stress was imposed for 5.5 h. Plasma concentrations of LH and cortisol were measured in samples of blood collected from the jugular vein. In the second experiment (nonbreeding season), plasma concentrations of epinephrine, norepinephrine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylglycol were also measured. In both experiments, there was no effect of isolation and restraint stress on plasma concentrations of cortisol in either sex. During the breeding season, there was no effect of isolation and restraint stress on plasma concentrations of LH in either sex. During the nonbreeding season, the amplitude of the first LH pulse after the commencement of stress was significantly reduced (P < 0.05) in rams and ewes. In the second experiment, during stress there was a significant increase (P < 0.05) in plasma concentrations of epinephrine in rams and ewes and significantly higher (P < 0.05) basal concentrations of norepinephrine in ewes than in rams. These results suggest that in sheep stress reduces responsiveness of the pituitary gland to exogenous GnRH during the nonbreeding season but not during the breeding season, possibly because of mediators of the stress response other than those of the hypothalamus-pituitary-adrenal gland axis.

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.

Paring down on Descartes: a review of brain noradrenaline and sympathetic nervous function

1. The conceptual framework of mind-body interaction can be traced back to the seminal observations of the French philosopher and mathematician René Descartes (1596-1650). Descartes succeeded in eliminating the soul's apparent physiological role and established the brain as the body's control centre. 2. While the pivotal role played by the central nervous system (CNS) in the maintenance of physiological and psychological health has long been recognized, the development of methods designed for the direct examination of human CNS processes has only recently come to fruition. 3. There exists a substantial body of evidence derived from clinical and experimental studies indicating that CNS monoaminergic cell groups, in particular those using noradrenaline as their neurotransmitter, participate in the excitatory regulation of the sympathetic nervous system and the development and maintenance of the hypertensive state. 4. In essential hypertension, particularly in younger patients, there occurs an activation of sympathetic nervous outflows to the kidneys, heart and skeletal muscle. The existence of a correlation between subcortical brain noradrenaline turnover and total body noradrenaline spillover to plasma, resting blood pressure and heart rate provides further support for the observation that elevated subcortical noradrenergic activity subserves a sympathoexcitatory role in the regulation of sympathetic preganglionic neurons of the thorocolumbar cord.

Central nervous system norepinephrine metabolism in hypertension

Although the pivotal role played by the brain in the maintenance of optimal physiologic and psychologic health has long been recognized, methods for the direct examination of human central nervous system processes have only recently been developed. A growing body of evidence indicates that central nervous systemmonoaminergic cell groups, in particular those utilizing norepinephrine as their neurotransmitter, participate in the excitatory regulation of the sympathetic nervous system and the development of the hypertensive state.

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.

Effect of intrauterine growth restriction on blood pressure, glucose tolerance and sympathetic nervous system activity in the rat at 3-4 months of age

OBJECTIVE

Epidemiological studies suggest that intrauterine growth restriction (IUGR) due to maternal undernutrition during pregnancy represents a major risk factor for hypertension and diabetes in adult age. However, placental insufficiency, rather than maternal malnutrition, is the main cause of IUGR in the Western world. We therefore studied the relationship between birth weight and adult blood pressure and glucose tolerance in an established animal model of placental insufficiency.

DESIGN

IUGR was induced by uterine artery ligation in pregnant rats and the offspring were studied at 3-4 months of age.

METHODS

In one subgroup of animals (n = 41, birth weight range 3.2-6.6 g) blood pressure was recorded over 72 h using telemetry and hypothalamic tissue levels of noradrenaline was measured. In another subgroup (n = 30, birth weight range 3.0-6.8 g) the activity of the sympathetic nervous system (SNS) was assessed by noradrenaline isotope dilution techniques and glucose tolerance determined by an intravenous glucose load.

RESULTS

Adult blood pressure was independent of birth weight Haemodynamic responses of IUGR rats to moderate sound stress was unaltered. In male rats neither SNS activity, hypothalamic noradrenaline concentrations nor glucose tolerance was associated with birth weight In contrast, IUGR in female rats was associated with increased SNS activity, elevated fasting blood glucose as well as lower insulin and higher glucose levels in response to a glucose load.

CONCLUSION

IUGR is not linked to an elevated blood pressure at 3-4 months of age in this model. However, in female rats, IUGR is associated with increased SNS activity and impaired glucose tolerance in adult life.

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.

Influence of voluntary exercise on hypothalamic norepinephrine

We combined hypothalamic tissue and plasma determinations of norepinephrine, dihydroxyphenylalanine, and dihydroxyphenylglycol with measurements of abdominal fat in voluntary running rats to examine the relationship among exercise training, hypothalamic and sympathetic nervous function, and body fat stores. The hypothalamic concentrations of norepinephrine, dihydroxyphenylalanine, and dihydroxyphenylglycol were reduced after exercise training (P < 0.01), with the amount of norepinephrine being strongly associated with the plasma norepinephrine (r = 0.58, P < 0.05) and dihydroxyphenylglycol (r = 0.65, P = 0.01) concentrations. Exercise training resulted in a diminution in abdominal fat mass (P < 0.01). A strong relationship existed between fat mass and hypothalamic norepinephrine content (r = 0.83, P < 0.001). The presence of a positive relationship between the arterial and hypothalamic norepinephrine levels provides presumptive evidence of an association between noradrenergic neuronal activity of the hypothalamus and sympathetic nervous function. The observation that abdominal fat mass is linked with norepinephrine in the hypothalamus raises the possibility that alterations in body fat stores provide an afferent signal linking hypothalamic function and the activity of the sympathetic nervous system.

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.

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.

Cerebral noradrenaline spillover and its relation to muscle sympathetic nervous activity in healthy human subjects

Studies using internal jugular vein blood sampling in human subjects have demonstrated the release of noradrenaline from the brain and have provided a link between central nervous system noradrenergic neuronal activity and renal, cardiac and total body sympathetic activity. The aim of this study was to further categorise the dependence of regional sympathetic nervous function on central nervous system noradrenergic neuronal processes by combining measures of internal jugular venous noradrenaline spillover, as an indicator of brain noradrenaline release, and cerebral blood flow scans with measures of the overall integrated neuronal firing rate for the body as a whole, the spillover of noradrenaline into the coronary sinus and with measurements of resting muscle sympathetic nerve activity. Positive veno-arterial plasma noradrenaline gradients were found across the brain, with the plasma concentration being 17 +/- 3% (p < 0.01) greater in the internal jugular vein. Linear regression analysis revealed a significant relationship between the degree of muscle sympathetic nerve activity and the spillover of noradrenaline from subcortical brain regions (y = 0.1 x + 16.0; r = 0.81, p < 0.02). The rate of spillover of noradrenaline for the body as a whole also bore a significant association with the rate of subcortical noradrenaline spillover (y = 0.01x + 2.33; r = 0.71, p < 0.05). Cortical noradrenaline spillover was not related to any of the sympathetic nervous system parameters measured in this study. The demonstration of a direct relationship between the rate of peroneal nerve firing and the spillover of noradrenaline from subcortical brain regions provides further support for the concept of central nervous system noradrenergic cell groups behaving in a sympathoexcitatory role.

Region-specific neuropeptide Y overflows at rest and during sympathetic activation in humans

Neuropeptide Y coexists with norepinephrine in sympathetic nerves and is coreleased into the circulation on sympathetic activation. Little is known about the regional release of neuropeptide Y in humans under normal conditions or in pathophysiological situations of sympathetic activation or denervation. We measured plasma neuropeptide Y-like immunoreactivity and norepinephrine concentrations in samples taken from the brachial artery; coronary sinus; and internal jugular, antecubital, or hepatic veins in volunteers aged 20 to 64 years. Regional neuropeptide Y overflow at rest was calculated from venoarterial plasma concentration differences and plasma flow, and norepinephrine spillover was determined by [3H]norepinephrine infusion techniques. Cardiac release of neuropeptide Y and norepinephrine was examined in response to various stressors as well as in clinical models of sympathetic activation, cardiac failure, and denervation after cardiac transplantation. In healthy volunteers, cardiac, forearm, and jugular venous sample neuropeptide Y concentrations were similar to arterial levels. Hepatic vein plasma neuropeptide Y was greater than arterial both at rest (119 +/- 5% of arterial, n = 7) and after a meal (132 +/- 12%, n = 7), with neuropeptide Y overflows of 6 +/- 2 and 11 +/- 2 pmol/min, respectively. In contrast, hepatomesenteric norepinephrine spillover was not significantly increased by feeding. Although coronary sinus plasma norepinephrine concentrations increased significantly with the cardiac sympathetic activation accompanying mental arithmetic, coffee drinking, isotonic exercise, and bicycle exercise, only the latter powerful sympathetic stimulus increased neuropeptide Y overflow. Cardiac failure was associated with increased resting release of both norepinephrine and neuropeptide Y from the heart, whereas postcardiac transplant norepinephrine spillover from the heart was reduced. The net overflow of neuropeptide Y to plasma observed at rest across the hepatic circulation, but not the cardiac, forearm, or cerebral circulations, indicates that the gut, the liver, or both make a major contribution to systemic plasma neuropeptide Y levels in humans. Sympathetic activation by exercise produced a modest increase in cardiac neuropeptide Y overflow but to only approximately 25% of the resting input from the gut and without a change in arterial neuropeptide Y concentration. Plasma neuropeptide Y measurements are less sensitive than those of plasma norepinephrine concentrations as an index for quantifying sympathetic neural responses regulating the systemic circulation.

Cerebral metabolism and its relationship with sympathetic nervous activity in essential hypertension: evaluation of the Dickinson hypothesis

OBJECTIVE

To examine Dickinson's hypothesis in mild essential hypertension, in which neurogenic mechanisms are believed to be particularly relevant, by combining measures of cerebral oxygen consumption with the concurrent assessment of sympathetic nervous activity.

DESIGN AND METHODS

Twenty-five untreated essential hypertensive subjects and 28 healthy age-matched volunteers underwent direct blood sampling using percutaneously inserted catheters advanced into the internal jugular vein, with cerebral blood flow scans to differentiate between cortical and subcortical venous drainage of the brain. Venoarterial blood gas measurements and internal jugular vein blood flows were used to calculate cerebral respiratory quotients and cerebral oxygen utilization. The total body rate of noradrenaline spillover into plasma was measured to assess relationships between cerebral oxidative metabolism and sympathetic nervous activity.

RESULTS

Compared with controls, the hypertensive subjects exhibited reductions in internal jugular vein blood flow (482 +/- 29 versus 410 +/- 15 ml/min), cerebral oxygen consumption (27 +/- 2 versus 23 +/- 1 ml/min) and cerebral oxygen supply (93 +/- 6 versus 78 +/- 3 ml/min). The cerebral respiratory quotients were identical (1.00 +/- 0.04 in normotensives and 0.98 +/- 0.03 in hypertensives). Technetium blood flow scans revealed that the reductions in internal jugular blood flow and cerebral oxygen consumption in the hypertensive patients were confined to cortical brain regions. Cortical blood flow was quantitatively linked to the matching respiratory quotient and oxygen consumption, neither of which bore any relation to the level of sympathetic nervous activity. The spillover of noradrenaline into the plasma for the body as a whole did not differ between the two groups.

CONCLUSIONS

In accord with Dickinson's hypothesis, we have established a reduction in internal jugular vein blood flow and cerebral oxygen utilization in hypertension. These reductions were confined to cortical brain regions. However, cerebral respiratory quotients in our hypertensive study group were no different from those in our controls, suggesting that glucose remained as the major cerebral metabolic substrate in hypertension. We were not able to establish a link between cerebral metabolism and blood pressure or sympathetic nervous activity in mildly hypertensive patients.

Total norepinephrine spillover, muscle sympathetic nerve activity and heart-rate spectral analysis in a patient with dopamine beta-hydroxylase deficiency

Dopamine-beta-hydroxylase (D beta H) is the enzyme responsible for intraneural conversion of dopamine to norepinephrine. Its deficiency results in failure of norepinephrine synthesis, excessive dopamine release and orthostatic hypotension. We studied a young patient with this deficiency using the currently available methods to assess sympathetic function namely measurement of norepinephrine kinetics, microneurography to assess muscle sympathetic nerve activity (MSNA), and heart-rate spectral analysis. We compared these findings with those in 24 young healthy controls, and 4 patients with peripheral autonomic failure (PAF). Recordings were made in our subject before and after 5 months of treatment with L-threo-3,4-dihydroxyphenylserine (DOPS) (which is converted directly into L-norepinephrine bypassing the D beta H enzymatic step); measurements were made at rest in the supine position and after 15 min of 30 degrees head-up tilt. Our subject with D beta H deficiency had a high resting nerve firing rate (40.3 bursts/min) compared with the mean value in normal controls (19.3 bursts/min), and an appropriate increase in nerve firing rate during tilt. Total body norepinephrine spillover at rest was very low, 38 ng/min, compared with age-matched normals (519 +/- 43.3 ng/min, mean +/- SEM), and epinephrine secretion was undetectable. Conversely, the plasma concentrations of dopamine, DOPAC, HVA and DOPA were raised. At rest, low-frequency heart-rate variability (0.1 Hz) was absent with preservation of the respiratory-related high-frequency peak. In contrast, the PAF subjects had no detectable muscle sympathetic nerve activity, very low levels of norepinephrine spillover and epinephrine secretion and a reduction in heart rate variability at all frequencies. After 5 months treatment with L-threo-3,4-dihydroxyphenylserine (DOPS) in the D beta H deficiency patient there was a dramatic clinical improvement with resolution of the orthostatic symptoms, dramatic reduction in MSNA activity at rest, and return of plasma norepinephrine, norepinephrine spillover, DHPG and MHPG to within the normal range, indicating intraneuronal production of norepinephrine.

Regional origins of 3-methoxy-4-hydroxyphenylglycol in plasma: effects of chronic sympathetic nervous activation and denervation, and acute reflex sympathetic stimulation

The plasma level and urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG), the principal metabolite of noradrenaline in the brain, are often used as indicators of central nervous system noradrenergic activity. Using percutaneously placed catheters, we studied the regional inputs into the plasma MHPG pool in 62 healthy volunteers. Veno-arterial plasma concentration differences and regional organ blood flows were used to quantify the relative amounts of MHPG contributed by various sites into plasma. Positive veno-arterial concentration gradients were found across the forearm, cardiac and jugular vessels in the healthy subjects. By far the majority of MHPG in plasma was derived from skeletal muscle, 5.3 +/- 1.8 nmol/min, with only minimal contribution (0.9 +/- 0.2 nmol/min) from the brain. Thus, to obtain an accurate indication of central nervous system noradrenergic activity the confounding influences of regional MHPG production must be excluded. 34 patients with chronic congestive heart failure, 6 patients with pure autonomic failure and 9 recent heart transplant recipients were used to investigate the possible effects of chronic sympathetic nervous system overactivity and sympathetic underactivity and denervation on peripheral MHPG production and plasma MHPG concentration. To examine the utility of plasma MHPG determinations as an indicator of acute alterations in sympathetic nervous activity we examined the influence of a variety of laboratory stressors on the arterial level and cardiac production of MHPG. The resting arterial plasma MHPG concentration mirrored sympathetic function in the patients with cardiac failure (sympathetic activation) and pure autonomic failure (sympathetic denervation), with mean MHPG plasma concentrations being 180 and 40% of those in healthy subjects. Cardiac MHPG production was increased in heart failure patients, and near zero with the cardiac sympathetic denervation accompanying transplantation and pure autonomic failure. In contrast, acute reflex stimulation of sympathetic nervous activity was not associated with parallel changes in the arterial level or cardiac production of MHPG. Measurements of peripheral plasma MHPG levels provide an index of prevailing sympathetic nervous function in clinical models of sympathetic overactivity and denervation, but are insensitive to acute sympathetic nervous system responses.

Increased central nervous system monoamine neurotransmitter turnover and its association with sympathetic nervous activity in treated heart failure patients

BACKGROUND

Congestive heart failure is a debilitating disease characterized by impaired cardiac function with accompanying activation of a variety of neural and hormonal counter-regulatory systems. Abnormal activity of the sympathetic nervous system and renin-angiotensin-aldosterone axis and a predisposition to the generation of fatal ventricular arrhythmias are often associated with the development of the disease. Although the underlying cause of sudden death in these patients remains to be unequivocally elucidated, abnormally increased cardiac sympathetic nervous activity may be involved.

METHODS AND RESULTS

Twenty-two patients with severe congestive heart failure (New York Heart Association functional class III or IV with left ventricular ejection fraction of 18 +/- 1%) and 29 healthy male volunteers participated in this study. By combining direct sampling of internal jugular venous blood via a percutaneously placed catheter with a norepinephrine and epinephrine isotope dilution method for examining neuronal transmitter release, we were able to quantify the release of central nervous system monoamine and indoleamine neurotransmitters and investigate their association with the increased efferent sympathetic outflow that is variably present in treated patients with this condition. Mean cardiac norepinephrine spillover was 145% higher in treated heart failure patients than in healthy subjects (P < .05), with norepinephrine release from the heart in 6 of 22 patients being more than the highest control value. Raised internal jugular venous spillover of epinephrine (26 +/- 12 versus 2 +/- 4 pmol/min, P < .05) and of norepinephrine and its metabolites (2740 +/- 480 versus 875 +/- 338 pmol/min, P < .05), indicative of increased central nervous system turnover of both catecholamines, occurred in cardiac failure and was quantitatively linked to the degree of activation of the cardiac sympathetic nervous outflow, as was the jugular overflow of the principal serotonin metabolite, 5-hydroxyindoleacetic acid.

CONCLUSIONS

An association between the degree of activation of central monoaminergic neurons and the level of sympathetic nervous tone in the heart was identified in treated patients with heart failure. Epinephrine neurons in the brain may contribute to the sympathoexcitation that is seen in this condition, with the activation of sympathoexcitatory noradrenergic neurons, most likely those of the forebrain, playing an accessory role.

Regional 5-hydroxyindoleacetic acid production in humans

Veno-arterial plasma concentration differences and regional organ plasma flows were used to quantify the relative amounts of 5-hydroxyindoleacetic acid (5-HIAA) contributed by various sites into the peripheral circulation. Positive venoarterial concentration gradients were found in the hepatosplanchnic, forearm, cardiac and jugular vessels in the healthy subjects. The renal circulation was determined to be the principal site of 5-HIAA clearance, extracting 18 +/- 2 nmol/min. The gut was the greatest contributor to the total 5-HIAA plasma pool with the relative contributions of the various organs being as follows: hepatosplanchnic organs 58%, skeletal muscle 26%, brain 6% and the heart 3%. The source of 5-HIAA stemming from these regional beds remains unknown, it may derive from serotonin taken up by and deaminated in ubiquitous endothelial cells, enterochromaffin cells of the gut, peripheral serotonergic nerves, serotonin turnover in platelets or perhaps the metabolism of serotonin taken up by sympathetic nerves. To test the latter hypothesis we examined 23 patients with chronic congestive heart failure and 9 patients with pure autonomic failure to investigate the possible effects of sympathetic nervous system overactivity and underactivity on peripheral 5-HIAA production and plasma 5-HIAA concentration. The resting arterial plasma 5-HIAA concentration in the heart failure patients was increased three-fold. This elevated plasma 5-HIAA concentration was attributable to an increased rate of whole body 5-HIAA production. The arterial 5-HIAA plasma concentration in the autonomic failure patients was paradoxically elevated, being 70% greater than that of the healthy subjects. The increased 5-HIAA plasma concentration in these patients was accounted for by a reduction in 5-HIAA plasma clearance. In all subjects studied there was a weak relationship only between total body norepinephrine spillover to plasma and the arterial 5-HIAA plasma concentration. We found that in healthy subjects the overflow of 5-HIAA into the hepatic vein was significantly related to the underlying degree of sympathetic activity. It can be concluded that 5-HIAA is produced at a number of sites throughout the body with the arterial plasma concentration being dependent on both the level of production and plasma clearance. By far the majority of 5-HIAA in plasma is derived from the gut with only minimal contribution from the brain.

Central nervous system noradrenergic and dopaminergic turnover in response to acute neuroleptic challenge

The objective of this study was to obtain direct neurochemical measures of the central nervous system's response to a typical neuroleptic, haloperidol, in human subjects. Nine healthy volunteers participated in this study. Central nervous system neuronal activity was assessed by measuring the plasma concentration and overflow from the brain of dopamine, norepinephrine, and their lipophilic and acidic metabolites after acute intravenous administration of haloperidol. By combining bilateral internal jugular vein blood sampling with cerebral blood flow scans we were able to differentiate between cortical and subcortical responses to haloperidol. The central nervous system response to haloperidol administration displayed a degree of regional specificity. Dopamine release, estimated from the overflow of homovanillic and dihydroxyphenylacetic acids, was reduced in cortical but not subcortical brain regions. Norepinephrine turnover was increased in cortical and subcortical brain regions. The overflow of homovanillic acid from the brain into the internal jugular veins was not related quantitatively to the arterial plasma concentrations of the catecholamines examined, homovanillic and dihydroxyphenylacetic acids or prolactin. Measurements of catecholamines and their metabolites in arterial plasma gave little indication as to monoaminergic neuronal activity in the brain.

Effects of aging on the responsiveness of the human cardiac sympathetic nerves to stressors

BACKGROUND

Aging increases human sympathetic nervous activity at rest. Beause of the probable importance of neural stress responses in the heart as triggers for clinical end points of coronary artery disease, it is pertinent to investigate whether sympathetic nervous responses to stresses are increased by aging.

METHODS AND RESULTS

We applied kinetic methods for measuring the fluxes to plasma of neurochemicals relevant to sympathetic neurotransmission in younger (aged 20 to 30 years) and older (aged 60 to 75 years) healthy men during mental stress (difficult mental arithmetic), isometric exercise (sustained handgrip), and dynamic exercise (supine cycling). The increase in total norepinephrine spillover to plasma with mental stress was unaffected by age. In contrast, the increase in cardiac norepinephrine spillover was two to three times higher in the older subjects (P < .05). The probable mechanism of this higher cardiac norepinephrine spillover was reduced neuronal reuptake of the transmitter, because age had no influence on the overflow of the norepinephrine precursor, dihydroxyphenylalanine, or intraneuronal metabolite, dihydroxyphenylglycol (levels of these two substances reflect rates of cardiac norepinephrine synthesis and intraneuronal metabolism), and the transcardiac extraction of plasma radiolabeled norepinephrine was lower in the older subjects (P < .05). An almost identical pattern of neurochemical response was seen with isometric exercise. During cycling, total norepinephrine spillover was 16% lower in the older men, but cardiac norepinephrine spillover was 53% higher.

CONCLUSIONS

Reduced norepinephrine reuptake increases the overflow of the neurotransmitter to plasma from the aging heart during stimulation of the cardiac sympathetic outflow. Failure of transmitter inactivation at postjunctional receptors with aging would amplify the neural signal, and in the presence of myocardial disease could trigger adverse stress-induced cardiovascular events, particularly when accompanied by an age-dependent reduction in vagal tone. Reduction of postsynaptic adrenergic responsiveness with aging, however, might protect against this, as indicated by our finding that in no case was the heart rate increase during stress greater in older men, despite their having larger increases in cardiac norepinephrine spillover.

Aging effects on human sympathetic neuronal function

To study the effect of aging on human sympathetic nervous function, we applied kinetic methods for measuring the fluxes to plasma of neurochemicals relevant to sympathetic neurotransmission in younger (aged 20-30 yr) and older (aged 60-75 yr) healthy men. Mean plasma norepinephrine concentration was 66% higher in older men, attributable to 22% lower norepinephrine plasma clearance (P < 0.05) and 29% higher norepinephrine spillover to plasma (difference not statistically significant). Regional venous sampling disclosed that sympathetic outflow to all organs was not activated by aging. Renal norepinephrine spillover was normal in older men. Although spillover of norepinephrine from the heart was increased in older men, 21.1 +/- 11.4 ng/min compared with 11.4 +/- 8.6 ng/min (P < 0.05), diminished norepinephrine reuptake rather than increased cardiac sympathetic nerve firing was the most likely cause, although somewhat reduced intracardiac methylation of norepinephrine with aging also possibly contributed. The extraction of tritiated norepinephrine from plasma during transit through the heart was reduced, suggesting neuronal norepinephrine reuptake was lowered and overflow of the norepinephrine precursor dihydroxyphenylalanine and metabolites dihydroxyphenylglycol and 3-methoxy-4-hydroxy phenylglycol was normal, indicating that norepinephrine synthesis and release were not increased.

Central nervous system noradrenergic control of sympathetic outflow in normotensive and hypertensive humans

We applied transmitter washout methodology, sampling internal jugular venous plasma via a percutaneously placed catheter, to study CNS norepinephrine release in humans and its relation to peripheral sympathetic activity. Norepinephrine overflows into the venous drainage of the brain, as do its precursor, DOPA, and metabolites DHPG and MHPG, indicating that the blood-brain barrier provides an incomplete impediment to their outward flux from the brain. Pharmacological testing with two drugs which altered CNS norepinephrine turnover, the tricyclic antidepressant desipramine and the ganglionic blocker, trimethaphan, demonstrated a direct relation existed between CNS norepinephrine release and sympathetic nerve firing rates. In essential hypertension, the sympathetic activation commonly present was associated with, and possibly caused by increased CNS release of norepinephrine, manifested in elevated overflow of norepinephrine, MHPG and DHPG from the brain. Bilateral jugular sampling, coupled with a cerebral venous sinus scan to delineate the drainage pattern, demonstrated that this increased norepinephrine release was confined to subcortical forebrain regions.

Monoaminergic neuronal activity in subcortical brain regions in essential hypertension

In this study we aimed to elucidate the role of central noradrenergic, dopaminergic, adrenergic and serotonergic neuronal systems in the development of essential hypertension. Fifteen untreated essential hypertensive subjects (aged 44 +/- 3 years) and 32 healthy volunteers (aged 38 +/- 3 years) participated in this study. By combining direct blood sampling techniques with cerebral blood flow scans we were able to differentiate between cortical and subcortical venous drainage of the brain. Veno-arterial MHPG, HVA and 5-HIAA plasma concentration gradients combined with internal jugular vein plasma flows were used, according to the Fick Principle, to derive metabolite spillovers which in turn were used as indicators of central noradrenergic, dopaminergic and serotonergic neuronal activity, respectively. These amine systems, in both the brainstem and forebrain, have been implicated in the regulation of sympathetic outflow and blood pressure. Total body noradrenaline spillover to plasma was concurrently measured to assess the relationship between central monoamine turnover and sympathetic activity. Compared to their healthy counterparts the hypertensive subjects had an elevated release of MHPG from subcortical brain regions (1.4 +/- 0.3 v 0.5 +/- 0.2 nmol/min, p < 0.05). An inverse relationship between blood pressure and subcortical HVA overflow existed, with the HVA overflow being significantly lower in the hypertensives (0.5 +/- 0.2 v 2.1 +/- 0.5 nmol/min, p < 0.05). Subcortical 5-HUAA overflow did not differ between the two groups, and adrenaline spillover from the brain was not detected in either group. Subcortical MHPG overflow was significantly correlated with total body NA spillover to plasma (p < 0.05). These results indicate that reciprocal aberrations in subcortical noradrenaline and dopamine turnover exist in essential hypertension. Although the physiological significance of this remains to be unequivocally elucidated we postulate that elevated subcortical noradrenergic activity, presumably in the forebrain where noradrenergic neurons are pressor, may cause sympathoexcitation and play a role in the development of essential hypertension.

Neurochemical evidence of cardiac sympathetic activation and increased central nervous system norepinephrine turnover in severe congestive heart failure

OBJECTIVES

The aim of this study was to characterize cardiac sympathetic nervous function in patients with severe heart failure and to investigate the influence of the cause of heart failure, hemodynamic variables and central nervous system catecholamine release on cardiac sympathetic tone.

BACKGROUND

Although heart failure is generally accompanied by sympathoexcitation, the integrity of cardiac sympathetic nerve function in heart failure remains controversial, particularly in relation to nerve firing activity and to the capacity of sympathetic nerves to recapture norepinephrine. Additionally, the location of the afferent and central neural pathways implicated in heart failure-induced sympathoexcitation remains unclear.

METHODS

Radiotracer techniques were applied in 41 patients with severe heart failure and 15 healthy control subjects to study the biochemical aspects of whole body and cardiac sympathetic activity. Hemodynamic indexes of cardiac performance were measured in the heart failure group, and their association with sympathetic activity was studied. Jugular venous catechol spillover was measured to study the central noradrenergic control of sympathetic outflow.

RESULTS

Sympathoexcitation was evident in the heart failure group, reflected by a 62% increase (p < 0.001) in total body and a 277% increase (p < 0.001) in cardiac norepinephrine spillover rates. These changes were accompanied by significant increases in the cardiac spillover of the norepinephrine precursor dihydroxyphenylalanine, the sympathetic cotransmitter neuropeptide Y and the extraneuronal metabolite 3-methoxy-4-hydroxyphenylglycol. The level of cardiac sympathetic activity was significantly correlated (r = 0.59, p < 0.001) with the mean pulmonary artery pressure. An increase in the spillover of dihydroxyphenylalanine and 3-methoxy-4-hydroxyphenylglycol from the brain was present, suggesting activation of central noradrenergic neurons.

CONCLUSIONS

Cardiac sympathetic activation is present in severe heart failure, bearing a close relation with pulmonary artery pressures, independent of heart failure etiology. Activation of noradrenergic neurons in the brain is also present and may be the underlying central nervous mechanism of the sympathoexcitation observed in heart failure.

The influence of aging on the plasma concentration and renal clearance of homovanillic acid

Using percutaneously placed arterial and venous catheters, we examined the influence of aging on the plasma concentration, whole body production rate, and renal clearance of homovanillic acid (HVA) in 60 healthy adult volunteers. The arterio-renal fractional extraction of HVA combined with the renal plasma flow (Fick Principle) were used to estimate the whole body HVA production rate and the renal plasma HVA clearance. The arterial HVA plasma concentration, whole body rate of HVA production, and HVA plasma clearance were determined to be 54 +/- 3 nmol/l, 27 +/- 2 nmol/min and 502 +/- 32 ml/min, respectively. The resting arterial HVA plasma concentration was positively correlated with aging, with the increased HVA concentrations in the older subjects being due to a diminished renal HVA plasma clearance. The diminished clearance of HVA occurred in response to a decreased renal plasma flow; the fractional extraction of HVA across the kidney remained unchanged with aging. This study emphasises the need for using age-matched control groups in neurochemical and neuropsychiatric studies, and demonstrates that increases in the arterial level of HVA do not necessarily reflect an increased rate of HVA production but may arise due to a diminished excretion rate of HVA from the body.

Cardiac sympathetic nervous activity in congestive heart failure. Evidence for increased neuronal norepinephrine release and preserved neuronal uptake

BACKGROUND

Increased concentrations of norepinephrine in coronary sinus plasma reported in congestive heart failure (CHF) could result from increased cardiac sympathetic nerve firing and norepinephrine release or from failure of neuronal uptake mechanisms to recapture released norepinephrine. We have applied neurochemical indexes of cardiac sympathetic nerve function in heart failure patients to delineate the underlying neural pathophysiology.

METHODS AND RESULTS

Cardiac norepinephrine synthesis, assessed from the cardiac overflow of the norepinephrine precursor dihydroxyphenylalanine (DOPA), intraneuronal metabolism estimated from the overflow of the intraneuronal metabolite dihydroxyphenylglycol (DHPG), neuronal norepinephrine reuptake assessed from the fractional extraction of plasma-tritiated norepinephrine and production of tritiated DHPG across the heart, and norepinephrine spillover to plasma were examined in eight patients with CHF caused by coronary artery disease (left ventricular ejection fraction of 26 +/- 5%, mean +/- SEM) and 14 age-matched healthy subjects. Cardiac norepinephrine spillover was increased eightfold in CHF subjects (127 ng/min versus 14 ng/min in healthy subjects; standard error of the difference [SED], 8 ng/min; P < .002), and cardiac DOPA was increased twofold (P < .02). The fractional extraction of tritiated norepinephrine across the heart was marginally less in CHF subjects (0.63 versus 0.73 in normal subjects; SED, 0.02), but the extent to which pharmacological neuronal uptake blockade with desipramine reduced the cardiac extraction of tritiated norepinephrine (by 71% versus 73% in normal subjects) and reduced the production of tritiated DHPG derived from uptake and intraneuronal metabolism of tritiated norepinephrine was similar in CHF patients and healthy subjects.

CONCLUSIONS

The marked increase in norepinephrine spillover from the heart in CHF attributable to coronary artery disease results primarily from an increase in sympathetic nerve firing and neuronal release of norepinephrine, not from faulty neuronal reuptake of norepinephrine.

Dobutamine, but not dopamine, augments the normal chronotropic response to acute hypoxemia

Infusion of exogenous dopamine has been shown to alter both the hypoxic and the hypercapnic ventilatory response, but its effects on the hypoxic and the hypercapnic cardiac response have not been reported. The purpose of this study was to determine if cardiac responses to hypoxemia and hypercapnia are altered by infusion of either dopamine (DOP) or its analog dobutamine (DBT). Baseline mean arterial blood pressure (MAP) and heart rate (HR) were measured in 7 normal male subjects while normal saline was infused intravenously (NS1) for 30 min. Each subject then underwent both a eucapnic hypoxemic challenge (EHC), and a hyperoxic hypercapnic challenge (HHC). In a double-blinded randomized fashion either DOP1 or DBT1 was selected and infused at 5 micrograms/kg/min for 30 min. EHC and HHC were again performed. This sequence was then repeated following a second NS infusion (NS2) and the alternate vasopressor. On a second study day, the dose of dopamine (DOP2) selected was that sufficient to induce a similar rise in MAP as seen with DBT1. Following NS and DOP1 there was a reproducible significant linear increase in HR with progressive hypoxemia seen in all subjects. This response was significantly augmented following infusion of DBT1 (p < 0.03), but no such augmentation was noted with DOP2. No significant change in HR was noted during HHC. The mechanisms responsible for this augmentation of hypoxemic response during dobutamine infusion are unclear, and do not appear to be related to a rise in MAP. We speculate that it is due to an effect of dobutamine on beta 1-receptor activity.

Regional homovanillic acid production in humans

Peripheral plasma levels of homovanillic acid (HVA), the deaminated and o-methylated metabolite of dopamine, are often used as an indicator of central nervous system dopaminergic activity. Using percutaneously placed catheters, we studied the regional inputs into the plasma HVA pool in 60 healthy volunteers. Veno-arterial differences and organ plasma flows were used to quantify the relative amounts of HVA contributed by various sites into the peripheral circulation. Positive arterio-venous HVA gradients were found in the pulmonary, hepatosplanchnic, skeletal muscle and jugular vessels of the normal volunteers. No HVA increment was found in the coronary sinus. The renal circulation was determined to be the principal site of HVA clearance, extracting 27 nmol/min. The regional contributions of HVA were as follows: lungs 21 nmol/min, hepatosplanchnic organs 3 nmol/min, skeletal muscle 3 nmol/min and the brain 4 nmol/min. The pattern of regional HVA production contrasted with that of the deaminated dopamine metabolite, dihydroxyphenylacetic acid, for which the heart was the principal site of production identified. Sixteen patients with chronic congestive heart failure (CHF) and 6 patients with pure autonomic failure (PAF) were also studied to investigate possible effects of sympathetic nervous system overactivity and underactivity on peripheral HVA production and plasma HVA concentration. The resting arterial plasma HVA concentration in CHF was increased approximately 3-fold. Unexpectedly, this was attributable to reduced HVA plasma clearance, not increased HVA production. Total HVA production in PAF was diminished by 40%. PAF patients had normal resting arterial HVA levels, this being accounted for by a 57% fall in the renal plasma clearance of HVA. Acute sympathetic nervous system activation in response to bicycle riding was accompanied by a 34% increase in the arterial concentration of HVA. It can be concluded that HVA is produced at a number of sites throughout the body not renowned for their dopaminergic innervation. Regional HVA production is associated, in part, with the metabolism of precursor dopamine in sympathetic nerves and at a rate which appears to be influenced by sympathetic nervous activity. To obtain an accurate indication of central dopaminergic activity the confounding influences of HVA plasma clearance and peripheral HVA production must be excluded.

Right middle lobe syndrome caused by Mycobacterium fortuitum in a patient with human immunodeficiency virus infection

We have reported a previously undescribed syndrome of Mycobacterium fortuitum infection manifested as localized pulmonary disease that required lung resection and prolonged combined chemotherapy for clinical response in a patient with HIV infection. M fortuitum infections must be considered in HIV-infected patients with possible infectious pulmonary complications.

Plasma norepinephrine responses to head-up tilt are misleading in autonomic failure

The failure of plasma norepinephrine to rise during upright posture is accepted as a diagnostic sign of autonomic nervous failure in patients with postural hypotension. Our clinical experience has been that this test is misleading, with an increase in plasma norepinephrine commonly occurring. To test whether this might result from absent reflex postural venous constriction lowering cardiac output and plasma norepinephrine clearance, we measured norepinephrine plasma kinetics during recumbency and 30 degrees head-up tilting in six patients with pure autonomic failure and eight healthy subjects. Mean arterial pressure fell by 54 +/- 8 mm Hg with head-up tilt in the patients with pure autonomic failure. The plasma norepinephrine concentration (arterial sampling) increased 73 +/- 29 pg/ml (mean difference +/- SED, p less than 0.02), solely because of a 36% reduction in the clearance of norepinephrine from plasma (0.78 +/- 0.09 l/min, p less than 0.0001). In normal subjects, plasma norepinephrine concentration rose by 112 +/- 20 pg/ml (p less than 0.001), largely because of a 24% increase in norepinephrine spillover to plasma (190 +/- 20 ng/min, p less than 0.005). When the postural fall in blood pressure and cardiac output in the pure autonomic failure patients was prevented by the selective venoconstrictor dihydroergotamine (10 micrograms/kg i.v.), no fall in plasma clearance or rise in plasma concentration of norepinephrine occurred. Measurement of the change in plasma norepinephrine with postural stimulation in patients with orthostatic hypotension is not a reliable diagnostic test for autonomic failure because elevations can occur in the plasma concentration that are entirely attributable to reduced plasma norepinephrine clearance.

Spontaneous splenic rupture associated with thrombolytic therapy and/or concomitant heparin anticoagulation

Two cases of spontaneous splenic rupture in connection with thrombolytic therapy and concomitant heparin anticoagulation are reported. One patient was being treated for peripheral arterial graft occlusion using intraarterial urokinase, the other received intravenous infusion of streptokinase for acute myocardial infarction. Neither patient had a condition predisposing to splenic rupture. Although rare, previous reports of spontaneous splenic rupture associated with thrombolytic therapy and/or anticoagulation have been reported. Splenic rupture as a complication of thrombolytic therapy and/or anticoagulation should be considered when unexplained abdominal symptoms, hypotension, or blood loss is encountered.

Exercise training lowers resting renal but not cardiac sympathetic activity in humans

Endurance exercise training has previously been shown to reduce the plasma concentration of norepinephrine. Whether reduction in sympathetic activity is responsible for the blood pressure-lowering effects of exercise training is unknown. Using a radiotracer technique, we measured resting total, cardiac, and renal norepinephrine spillover to plasma in eight habitually sedentary healthy normotensive men (aged 36 +/- 3 years, mean +/- SEM) after 1 month of regular exercise and 1 month of sedentary activity, performed in a randomized order. One month of bicycle exercise 3 times/wk (40 minutes at 60-70% maximum work capacity) reduced resting blood pressure by 8/5 mm Hg (p less than 0.01) and increased maximum oxygen consumption by 15% (p less than 0.05). The fall in blood pressure was attributable to a 12.1% increase in total peripheral conductance. Total norepinephrine spillover to plasma was reduced by 24% from a mean of 438.8 ng/min (p less than 0.05). Renal norepinephrine spillover fell by an average of 41% from 169.4 ng/min with bicycle training (p less than 0.05), accounting for the majority (66%) of the fall in total norepinephrine spillover. Renal vascular conductance was increased by 10% (p less than 0.05), but this constituted only 18% of the increase in total peripheral conductance. There was no change in cardiac norepinephrine spillover. The reduction in resting sympathetic activity with regular endurance exercise is largely confined to the kidney. The magnitude of the fall in renal vascular resistance, however, is insufficient to directly account for the blood pressure-lowering effect of exercise, although other effects of inhibition of the renal sympathetic outflow may be important.

Biochemical evidence of sympathetic denervation of the heart in pure autonomic failure

Primary autonomic failure is a heterogenous group of diseases with evidence for lesions in both the central and peripheral elements of the autonomic nervous system. We determined the extent of peripheral sympathetic dysfunction in six patients with primary autonomic failure without clinical evidence of central nervous system involvement (pure autonomic failure) using biochemical methods for studying regional noradrenaline spillover and removal. The results were compared with those from 14 age-matched normal subjects, seven of whom were studied before and after pharmacological neuronal uptake-blockade with desipramine. Total, cardiac and renal noradrenaline spillover to plasma were 78%, 98% and 66% lower respectively in pure autonomic failure than in normal subjects (p less than 0.001). Total noradrenaline plasma clearance was 20% lower in pure autonomic failure (p less than 0.005) than in normal subjects and similar to the level observed in normal subjects following neuronal noradrenaline uptake-blockade with desipramine, mean transcardiac extraction of tritiated noradrenaline was 74% in normal subjects and 20% in pure autonomic failure, identical to the value post-desipramine in normal subjects. Cardiac spillover of the noradrenaline precursor, dihydroxyphenylanine, and the primary intra-neuronal metabolite dihydroxyphenylglycol, were 78% and 94% lower respectively in pure autonomic failure than in normal subjects (p less than 0.001). These data indicate a marked reduction in the apparent release rate and neuronal uptake of noradrenaline in the hearts of patients with pure autonomic failure, and provide biochemical evidence of almost total postganglionic sympathetic denervation in this condition.

Direct determination of homovanillic acid release from the human brain, an indicator of central dopaminergic activity

The plasma concentration of the dopamine (DA) metabolite, homovanillic acid (HVA), is used as an indicator of central nervous system dopaminergic activity. Using percutaneously inserted catheters we were able to obtain blood samples simultaneously from the right and left internal jugular veins. Veno-arterial HVA plasma concentration differences combined with adjusted organ plasma flows were used, according to the Fick Principle, to determine the HVA overflow from the brain. The HVA overflow from the liver was also measured. HVA overflow from the brain represented 12% of the total body HVA production. A similar amount was released from the liver, illustrating the limited validity of peripheral plasma HVA measurements as an indicator of central dopaminergic activity. HVA release from the human brain displayed a degree of asymmetry, the overflow into the left internal jugular vein being 36% greater than that into the right. Cerebral venous blood flow scans indicated that cortical cerebral regions drained preferentially into the right internal jugular; by inference the higher HVA overflow on the left originated from dopamine-rich subcortical brain areas. Since HVA in plasma may arise from the metabolism of DA existing either as a neurotransmitter or a norepinephrine (NE) precursor we measured the internal jugular vein plasma concentrations of NE, and its metabolite dihydroxyphenylglycol (DHPG), to determine whether they displayed a similar pattern of release to HVA. The overflow of both NE and DHPG into the right internal jugular vein was approximately double that on the left. Since the overflow of HVA did not parallel that of NE and DHPG it may be inferred that the origin of much of the subcortically produced HVA is from dopaminergic neurons and not from the metabolism of precursor DA in noradrenergic neurones or cerebrovascular sympathetic nerves.