Xpert MTB/RIF versus sputum microscopy as the initial diagnostic test for tuberculosis: a cluster-randomised trial embedded in South African roll-out of Xpert MTB/RIF

BACKGROUND

In South Africa, sputum smear microscopy has been replaced with Xpert MTB/RIF as the initial diagnostic test for tuberculosis. In a pragmatic parallel cluster-randomised trial, we evaluated the effect on patient and programme outcomes.

METHODS

We randomly allocated 20 laboratories (clusters) in medium-burden districts of South Africa to either an Xpert (immediate Xpert) or microscopy (Xpert deferred) group (1:1), stratified by province. At two primary care clinics per laboratory, a systematic sample of adults giving sputum for tuberculosis investigation was assessed for eligibility. The primary outcome was mortality at 6 months from enrolment. Masking of participants' group allocation was not possible because of the pragmatic trial design. The trial is registered with the ISRCTN registry (ISRCTN68905568) and the South African Clinical Trial Register (DOH-27-1011-3849).

FINDINGS

Between June and November, 2012, 4972 people were screened, and 4656 (93·6%) enrolled (median age 36 years; 2891 [62%] female; 2212 [62%] reported being HIV-positive). There was no difference between the Xpert and microscopy groups with respect to mortality at 6 months (91/2324 [3·9%] vs 116/2332 [5·0%], respectively; adjusted risk ratio [aRR] 1·10, 95% CI 0·75-1·62]).

INTERPRETATION

Xpert did not reduce mortality at 6 months compared with sputum microscopy. Improving outcomes in drug-sensitive tuberculosis programmes might require not only better diagnostic tests but also better linkage to care.

FUNDING

Bill & Melinda Gates Foundation.

The need to accelerate access to new drugs for multidrug-resistant tuberculosis

Approximately half a million people are thought to develop multidrug-resistant tuberculosis annually. Barely 20% of these people currently receive recommended treatment and only about 10% are successfully treated. Poor access to treatment is probably driving the current epidemic, via ongoing transmission. Treatment scale-up is hampered by current treatment regimens, which are lengthy, expensive, poorly tolerated and difficult to administer in the settings where most patients reside. Although new drugs provide an opportunity to improve treatment regimens, current and planned clinical trials hold little promise for developing regimens that will facilitate prompt treatment scale-up. In this article we argue that clinical trials, while necessary, should be complemented by timely, large-scale, operational research that will provide programmatic data on the use of new drugs and regimens while simultaneously improving access to life-saving treatment. Perceived risks – such as the rapid development of resistance to new drugs – need to be balanced against the high levels of mortality and transmission that will otherwise persist. Doubling access to treatment and increasing treatment success could save approximately a million lives over the next decade.

Loss from treatment for drug resistant tuberculosis: risk factors and patient outcomes in a community-based program in Khayelitsha, South Africa

Background

A community based drug resistant tuberculosis (DR-TB) program has been incrementally implemented in Khayelitsha, a high HIV and TB burden community in South Africa. We investigated loss from treatment (LFT), and post treatment outcomes of DR-TB patients in this setting.

Methodology

LFT, defined as interruption of treatment for ≥2 consecutive months was assessed among patients initiating DR-TB treatment for the first time between January 2009 and July 2011. Patients were traced through routine data sources to identify those who subsequently restarted treatment and those who died. Additional information on patient status and survival after LTF was obtained from community DR-TB counselors and from the national death registry. Post treatment outcomes were observed until July 2013.

Results

Among 452 patients initiating treatment for the first time within the given period, 30% (136) were LFT, with 67% retention at 18 months. Treatment was restarted in 27 (20%) patients, with additional resistance recorded in 2/25 (8%), excluding two with presumed DR-TB. Overall, 34 (25%) patients died, including 11 who restarted treatment. Males and those in the age category 15-25 years had a greater hazard of LFT; HR 1.93 (95% CI 1.35-2.75), and 2.43 (95% CI 1.52-3.88) respectively. Older age (>35 years) was associated with a greater hazard of death; HR 3.74 (1.13- 12.37) post treatment. Overall two-year survival was 62%. It was lower (45%) in older patients, and was 92% among those who received >12 months treatment.

Conclusion

LFT was high, occurred throughout the treatment period and was particularly high among males and those aged 15-25 years. Overall long term survival was poor. High rates of LFT should however not preclude scale up of community based care given its impact in increasing access to treatment. Further research is needed to support retention of DR-TB patients on treatment, even within community based treatment programs.

Impact of Decentralized Care and the Xpert MTB/RIF Test on Rifampicin-Resistant Tuberculosis Treatment Initiation in Khayelitsha, South Africa

Decentralization of treatment for rifampicin-resistant tuberculosis was associated with high treatment initiation and resulted in reduced time to treatment initiation. Xpert for TB diagnosis resulted in a significant further reduction in time to treatment.

Background. Globally, case detection and treatment access are poor for rifampicin-resistant tuberculosis (RR-TB). The Xpert MTB/RIF test has the potential to increase detection and reduce time to treatment (TTT). However, these benefits are dependent on health system capacity to provide treatment.

Methods. We retrospectively assessed the impact of Xpert on treatment initiation and TTT in the context of decentralized RR-TB care in Khayelitsha, Cape Town, using routine programmatic data. Community-based treatment was introduced progressively from 2008. Before 2007, diagnosis relied on phenotypic resistance (culture). During 2007–2008, the line probe assay (LPA) was introduced, followed by Xpert in 2012.

Results. Before decentralization (2003–2006), median TTT was 71 days (interquartile range [IQR], 49–134; n = 158). The LPA introduction during 2007–2008 was associated with reduced median TTT from 76 to 50 days (P < .0001, n = 257). Between January 2009 and June 2013, 938 RR-TB cases were diagnosed (74% human immunodeficiency virus [HIV]-infected). Decentralization during 2008–2011 was associated with declining TTT (P < .0001, test for trend), a decline to 28 days in 2011 (IQR, 16–40; n = 173). Xpert was associated with a further reduction to 8 days in 2013 (IQR, 5–25; n = 89; P < .0001). Treatment initiation remained unchanged with Xpert and was lower among HIV-infected (2010–2013); 87.9% (445 of 506) compared with 96.9% (188 of 194) for HIV-uninfected (P < .0001) patients.

Conclusions. Improved case detection and rapid treatment initiation are required to interrupt transmission and reduce mortality. In this setting, decentralization was associated with high treatment initiation and reduced TTT. Xpert implementation significantly enhanced the reduction in TTT and has the potential to reduce transmission.

Impact of Xpert MTB/RIF for TB diagnosis in a primary care clinic with high TB and HIV prevalence in South Africa: a pragmatic randomised trial

BACKGROUND

Xpert MTB/RIF is approved for use in tuberculosis (TB) and rifampicin-resistance diagnosis. However, data are limited on the impact of Xpert under routine conditions in settings with high TB burden.

METHODS AND FINDINGS

A pragmatic prospective cluster-randomised trial of Xpert for all individuals with presumptive (symptomatic) TB compared to the routine diagnostic algorithm of sputum microscopy and limited use of culture was conducted in a large TB/HIV primary care clinic. The primary outcome was the proportion of bacteriologically confirmed TB cases not initiating TB treatment by 3 mo after presentation. Secondary outcomes included time to TB treatment and mortality. Unblinded randomisation occurred on a weekly basis. Xpert and smear microscopy were performed on site. Analysis was both by intention to treat (ITT) and per protocol. Between 7 September 2010 and 28 October 2011, 1,985 participants were assigned to the Xpert (n = 982) and routine (n = 1,003) diagnostic algorithms (ITT analysis); 882 received Xpert and 1,063 routine (per protocol analysis). 13% (32/257) of individuals with bacteriologically confirmed TB (smear, culture, or Xpert) did not initiate treatment by 3 mo after presentation in the Xpert arm, compared to 25% (41/167) in the routine arm (ITT analysis, risk ratio 0.51, 95% CI 0.33-0.77, p = 0.0052). The yield of bacteriologically confirmed TB cases among patients with presumptive TB was 17% (167/1,003) with routine diagnosis and 26% (257/982) with Xpert diagnosis (ITT analysis, risk ratio 1.57, 95% CI 1.32-1.87, p<0.001). This difference in diagnosis rates resulted in a higher rate of treatment initiation in the Xpert arm: 23% (229/1,003) and 28% (277/982) in the routine and Xpert arms, respectively (ITT analysis, risk ratio 1.24, 95% CI 1.06-1.44, p = 0.013). Time to treatment initiation was improved overall (ITT analysis, hazard ratio 0.76, 95% CI 0.63-0.92, p = 0.005) and among HIV-infected participants (ITT analysis, hazard ratio 0.67, 95% CI 0.53-0.85, p = 0.001). There was no difference in 6-mo mortality with Xpert versus routine diagnosis. Study limitations included incorrect intervention allocation for a high proportion of participants and that the study was conducted in a single clinic.

CONCLUSIONS

These data suggest that in this routine primary care setting, use of Xpert to diagnose TB increased the number of individuals with bacteriologically confirmed TB who were treated by 3 mo and reduced time to treatment initiation, particularly among HIV-infected participants.

TRIAL REGISTRATION

Pan African Clinical Trials Registry PACTR201010000255244. Please see later in the article for the Editors' Summary.

Resistance to fluoroquinolones and second-line injectable drugs: impact on multidrug-resistant TB outcomes

A meta-analysis for response to treatment was undertaken using individual data of multidrug-resistant tuberculosis (MDR-TB) (resistance to isoniazid and rifampicin) patients from 26 centres. The analysis assessed the impact of additional resistance to fluoroquinolones and/or second-line injectable drugs on treatment outcome. Compared with treatment failure, relapse and death, treatment success was higher in MDR-TB patients infected with strains without additional resistance (n=4763; 64%, 95% CI 57-72%) or with resistance to second-line injectable drugs only (n=1130; 56%, 95% CI 45-66%), than in those having resistance to fluoroquinolones alone (n=426; 48%, 95% CI 36-60%) or to fluoroquinolones plus second-line injectable drugs (extensively drug resistant (XDR)-TB) (n=405; 40%, 95% CI 27-53%). In XDR-TB patients, treatment success was highest if at least six drugs were used in the intensive phase (adjusted OR 4.9, 95% CI 1.4-16.6; reference fewer than three drugs) and four in the continuation phase (OR 6.1, 95% CI 1.4-26.3). The odds of success in XDR-TB patients was maximised when the intensive phase reached 6.6-9.0 months duration and the total duration of treatment 20.1-25.0 months. In XDR-TB patients, regimens containing more drugs than those recommended in MDR-TB but given for a similar duration were associated with the highest odds of success. All data were from observational studies and methodologies varied between centres, therefore, the bias may be substantial. Better quality evidence is needed to optimise regimens.

Adverse events among HIV/MDR-TB co-infected patients receiving antiretroviral and second line anti-TB treatment in Mumbai, India

Background

Significant adverse events (AE) have been reported in patients receiving medications for multidrug- and extensively-drug-resistant tuberculosis (MDR-TB & XDR-TB). However, there is little prospective data on AE in MDR- or XDR-TB/HIV co-infected patients on antituberculosis and antiretroviral therapy (ART) in programmatic settings.

Methods

Médecins Sans Frontières (MSF) is supporting a community-based treatment program for drug-resistant tuberculosis in HIV-infected patients in a slum setting in Mumbai, India since 2007. Patients are being treated for both diseases and the management of AE is done on an outpatient basis whenever possible. Prospective data were analysed to determine the occurrence and nature of AE.

Results

Between May 2007 and September 2011, 67 HIV/MDR-TB co-infected patients were being treated with anti-TB treatment and ART; 43.3% were female, median age was 35.5 years (Interquartile Range: 30.5–42) and the median duration of anti-TB treatment was 10 months (range 0.5–30). Overall, AE were common in this cohort: 71%, 63% and 40% of patients experienced one or more mild, moderate or severe AE, respectively. However, they were rarely life-threatening or debilitating. AE occurring most frequently included gastrointestinal symptoms (45% of patients), peripheral neuropathy (38%), hypothyroidism (32%), psychiatric symptoms (29%) and hypokalaemia (23%). Eleven patients were hospitalized for AE and one or more suspect drugs had to be permanently discontinued in 27 (40%). No AE led to indefinite suspension of an entire MDR-TB or ART regimen.

Conclusions

AE occurred frequently in this Mumbai HIV/MDR-TB cohort but not more frequently than in non-HIV patients on similar anti-TB treatment. Most AE can be successfully managed on an outpatient basis through a community-based treatment program, even in a resource-limited setting. Concerns about severe AE in the management of co-infected patients are justified, however, they should not cause delays in the urgently needed rapid scale-up of antiretroviral therapy and second-line anti-TB treatment.

embCAB sequence variation among ethambutol-resistant Mycobacterium tuberculosis isolates without embB306 mutation

OBJECTIVES

Mechanisms of resistance to ethambutol in Mycobacterium tuberculosis remain inadequately described. Although there is mounting evidence that mutations of codon 306 in embB play a key role, a significant number of phenotypically ethambutol-resistant strains do not carry mutations in this codon. Here, other mutations in the embCAB operon are suggested to be involved in resistance development.

METHODS

The entire embCAB operon ( approximately 10 kb) was analysed in 34 phenotypically ethambutol-resistant M. tuberculosis strains without mutations in embB306 and in 12 ethambutol-susceptible strains. Furthermore, 106 control strains were investigated for the presence of particular mutations only.

RESULTS

Overall, 18 non-synonymous mutations in 15 distinct codons of the embCAB operon were identified in ethambutol-resistant strains but not in ethambutol-susceptible isolates. The majority occurred in the embB gene (10 distinct codons), in a 570 bp region also encompassing embB306. Mutations in embC and embA were found rarely and in most cases in combination with polymorphisms in embB. One synonymous mutation (embA 228 bp) and two non-synonymous mutations (embCVal981Leu and embCArg738Gln) were found in ethambutol-susceptible strains as well as resistant strains and were confirmed to represent phylogenetic markers for strains of the Beijing, Haarlem and Delhi/CAS genotypes, respectively.

CONCLUSIONS

Besides mutations in embB306, mutations in embB406 and embB497 were confirmed as hot spots for genomic variation in ethambutol-resistant clinical isolates. Of all resistant strains 70.6% carry a mutation in a relatively short region in embB, which therefore represents a promising target for inclusion in molecular assays for rapid detection of ethambutol resistance.

Genomic diversity among drug sensitive and multidrug resistant isolates of Mycobacterium tuberculosis with identical DNA fingerprints

Background

Mycobacterium tuberculosis complex (MTBC), the causative agent of tuberculosis (TB), is characterized by low sequence diversity making this bacterium one of the classical examples of a genetically monomorphic pathogen. Because of this limited DNA sequence variation, routine genotyping of clinical MTBC isolates for epidemiological purposes relies on highly discriminatory DNA fingerprinting methods based on mobile and repetitive genetic elements. According to the standard view, isolates exhibiting the same fingerprinting pattern are considered direct progeny of the same bacterial clone, and most likely reflect ongoing transmission or disease relapse within individual patients.

Methodology/Principal Findings

Here we further investigated this assumption and used massively parallel whole-genome sequencing to compare one drug-susceptible (K-1) and one multidrug resistant (MDR) isolate (K-2) of a rapidly spreading M. tuberculosis Beijing genotype clone from a high incidence region (Karakalpakstan, Uzbekistan). Both isolates shared the same IS6110 RFLP pattern and the same allele at 23 out of 24 MIRU-VNTR loci.

We generated 23.9 million (K-1) and 33.0 million (K-2) paired 50 bp purity filtered reads corresponding to a mean coverage of 483.5 fold and 656.1 fold respectively. Compared with the laboratory strain H37Rv both Beijing isolates shared 1,209 SNPs. The two Beijing isolates differed by 130 SNPs and one large deletion. The susceptible isolate had 55 specific SNPs, while the MDR variant had 75 specific SNPs, including the five known resistance-conferring mutations.

Conclusions

Our results suggest that M. tuberculosis isolates exhibiting identical DNA fingerprinting patterns can harbour substantial genomic diversity. Because this heterogeneity is not captured by traditional genotyping of MTBC, some aspects of the transmission dynamics of tuberculosis could be missed or misinterpreted. Furthermore, a valid differentiation between disease relapse and exogenous reinfection might be impossible using standard genotyping tools if the overall diversity of circulating clones is limited. These findings have important implications for clinical trials of new anti-tuberculosis drugs.

Long term efficacy of DOTS regimens for tuberculosis: systematic review

OBJECTIVE

To identify published studies assessing tuberculosis recurrence after successful treatment with standard short course regimens for six months to determine the strength and sufficiency of evidence to support current guidelines.

DESIGN

Systematic review.

DATA SOURCES

Medline, Embase, Cochrane clinical trials register, specialist tuberculosis journals, and reference lists. Only English language publications were eligible.

REVIEW METHODS

Studies were included irrespective of methodology or quality. Abstracted information included inclusion and exclusion criteria for participants, duration of follow-up, and definitions of treatment success and disease recurrence. The primary outcome was the proportion of successfully treated patients recorded with recurrent tuberculosis during the follow-up period.

RESULTS

17 study arms from 16 studies met the inclusion criteria; 10 were controlled clinical trials and six were either studies done under programmatic conditions or observational studies from functioning tuberculosis programmes. Although several clinical trials supported the use of daily treatment regimens, studies reporting tuberculosis recurrence after intermittent regimens were limited. Few studies carried out under routine programmatic conditions reported disease recurrence. Overall there was wide variation in recurrence after successful treatment, ranging from 0% to 14%. Considerable heterogeneity across studies precluded the systematic assessment of factors contributing to tuberculosis recurrence.

CONCLUSIONS

Despite DOTS (directly observed treatment, short course) being implemented for more than 10 years and millions of patients treated for tuberculosis, few studies have assessed the ability of standard DOTS regimens to result in lasting cure for patients treated under routine programmatic conditions.

Multidrug-resistant tuberculosis treatment outcomes in Karakalpakstan, Uzbekistan: treatment complexity and XDR-TB among treatment failures

Background

A pilot programme to treat multidrug-resistant TB (MDR-TB) was implemented in Karakalpakstan, Uzbekistan in 2003. This region has particularly high levels of MDR-TB, with 13% and 40% among new and previously treated cases, respectively.

Methodology

This study describes the treatment process and outcomes for the first cohort of patients enrolled in the programme, between October 2003 and January 2005. Confirmed MDR-TB cases were treated with an individualised, second-line drug regimen based on drug susceptibility test results, while suspected MDR-TB cases were treated with a standardised regimen pending susceptibility results.

Principal Findings

Of 108 MDR-TB patients, 87 were started on treatment during the study period. Of these, 33 (38%) were infected with strains resistant to at least one second-line drug at baseline, but none had initial ofloxacin resistance. Treatment was successful for 54 (62%) patients, with 13 (15%) dying during treatment, 12 (14%) defaulting and 8 (8%) failing treatment. Poor clinical condition and baseline second-line resistance contributed to treatment failure or death. Treatment regimens were changed in 71 (82%) patients due to severe adverse events or drug resistance. Adverse events were most commonly attributed to cycloserine, ethionamide and p-aminosalicylic acid. Extensively drug resistant TB (XDR-TB) was found among 4 of the 6 patients who failed treatment and were still alive in November 2006.

Conclusions

While acceptable treatment success was achieved, the complexity of treatment and the development of XDR-TB among treatment failures are important issues to be addressed when considering scaling up MDR-TB treatment.

Risk of Acquired Drug Resistance during Short-Course Directly Observed Treatment of Tuberculosis in an Area with High Levels of Drug Resistance

BACKGROUND

Data on the performance of standardized short-course directly observed treatment (DOTS) of tuberculosis (TB) in areas with high levels of drug resistance and on the potential impact of DOTS on amplification of resistance are limited. Therefore, we analyzed treatment results from a cross-sectional sample of patients with TB enrolled in a DOTS program in an area with high levels of drug resistance in Uzbekistan and Turkmenistan in Central Asia.

METHODS

Sputum samples for testing for susceptibility to 5 first-line drugs and for molecular typing were obtained from patients starting treatment in 8 districts. Patients with sputum smear results positive for TB at the end of the intensive phase of treatment and/or at 2 months into the continuation phase were tested again. RESULTS. Among 382 patients with diagnoses of TB, 62 did not respond well to treatment and were found to be infected with an identical Mycobacterium tuberculosis strain when tested again; 19 of these patients had strains that developed new or additional drug resistance. Amplification occurred in only 1.2% of patients with initially susceptible or monoresistant TB strains, but it occurred in 17% of those with polyresistant strains (but not multidrug-resistant strains, defined as strains with resistance to at least isoniazid and rifampicin) and in 7% of those with multidrug-resistant strains at diagnosis. Overall, 3.5% of the patients not initially infected with multidrug-resistant TB strains developed such strains during treatment. Amplification of resistance, however, was found only in polyresistant Beijing genotype strains.

CONCLUSIONS

High levels of amplification of drug resistance demonstrated under well-established DOTS program conditions reinforce the need for implementation of DOTS-Plus for multidrug-resistant TB in areas with high levels of drug resistance. The strong association of Beijing genotype and amplification in situations of preexisting resistance is striking and may underlie the strong association between this genotype and drug resistance.

Decreasing prevalence of cigarette smoking in the middle income country of Mauritius: questionnaire survey

OBJECTIVES

To describe changes in the prevalence of cigarette smoking in the middle income country of Mauritius from 1987 to 1998, and to relate these changes to legislative and health promotion efforts over the same period.

DESIGN

Questionnaire survey.

SETTING

Mauritius, an island in the Indian Ocean with a population of about 1.2 million (about 70% south Asian, 2% Chinese, and 28% Creole).

PARTICIPANTS

Data were obtained from 5072 participants in 1987, 6573 in 1992, and 6281 in 1998.

MAIN OUTCOME MEASURES

Prevalence of current smoking in 1987, 1992, and 1998, sales of cigarettes in Mauritius, and information on activities for control of tobacco.

RESULTS

Self reported cigarette smoking has been decreasing in Mauritius since 1987, with the largest decrease between 1987 and 1992. From 1987 to 1998 smoking prevalence decreased by 23% in men and 61% in women. Smoking decreased across all age and ethnic groups and across different levels of income and education. Sales of cigarettes also decreased in line with smoking prevalence.

CONCLUSIONS

The introduction of cigarette taxes, a limited health promotion programme, and the absence of massive promotional campaigns by the sole tobacco company on Mauritius have led to a striking and continued decrease in smoking prevalence and cigarette consumption on the island.

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.

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.

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.

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.

Pulmonary clearance and release of norepinephrine and epinephrine in newborn lambs

To examine the pulmonary kinetics of the catecholamines norepinephrine and epinephrine immediately after birth, eight fetal lambs were instrumented with vascular catheters under general anesthesia at 133-134 days gestation (term = 147 days) and were delivered by cesarean section 1 wk later. Pulmonary norepinephrine and epinephrine kinetics were then studied 1 and 4 h after birth using radiotracer dilution methodology. The pulmonary fractional extraction of norepinephrine was similar in 1-h (0.111 +/- 0.021) and 4-h (0.117 +/- 0.023) lambs and constituted 24 +/- 5 and 32 +/- 9% of total body norepinephrine clearance, respectively. Pulmonary removal of epinephrine was less pronounced with a fractional extraction of 0.035 +/- 0.017 in 1-h and 0.036 +/- 0.013 in 4-h lambs, which corresponded to 8 +/- 4 and 9 +/- 3% of total body epinephrine clearance, respectively. Pulmonary spillover of norepinephrine into the circulation was similar in 1-h (79 +/- 26 ng.min-1.kg-1) and 4-h (82 +/- 18 ng.min-1.kg-1) lambs, and this comprised 27 +/- 8 and 42 +/- 8% of total body norepinephrine spillover, respectively. Pulmonary epinephrine spillover was not detectable at 1 h, but it occurred in all 4-h lambs, averaging 4.7 +/- 0.8 ng.min-1.kg-1 or 20 +/- 6% of epinephrine total body spillover. These findings indicate that the lungs of newborn lambs 1) are a major site for removal of norepinephrine and epinephrine from the circulation; 2) release a substantial quantity of norepinephrine into the circulation, consistent with the presence of tonic pulmonary sympathetic nerve activity; and 3) constitute a significant extra-adrenal source of plasma epinephrine.

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.

Oxygen consumption in the heart, hepatomesenteric bed, and brain in young and elderly human subjects, and accompanying sympathetic nervous activity

Although the reduction in whole-body energy expenditure with aging has been well documented, there is little information about the changes that individual organs undergo. We therefore measured oxygen consumption in the heart, hepatomesenteric bed, and brain in elderly subjects and young controls, using central venous catheter techniques and the application of Fick's principle. We also measured whole-body, cardiac, and hepatomesenteric sympathetic nervous activity using isotope dilution methodology. Cardiac, hepatomesenteric, and cerebral oxygen consumption was similar in both groups. Whole-body and hepatomesenteric sympathetic nervous activity was also similar in the study groups, whereas cardiac norepinephrine (NE) spillover was significantly higher in the elderly. In contrast to the young, cardiac sympathetic nervous activity as assessed from NE spillover was not related to either cardiac oxygen consumption or cardiac work in the elderly. The data suggest that although oxygen consumption in the heart, hepatomesenteric bed, and brain are not different between young and elderly individuals, the relationship between sympathetic nervous activity and oxygen consumption in individual organs may alter with aging.

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.

Increased spillover and reduced clearance both contribute to rise in plasma catecholamines after birth in lambs

We studied the relationship between changes in norepinephrine (NE) and epinephrine (Epi) levels, total body spillover, and total body clearance at birth. Near-term fetal lambs were chronically instrumented under general anesthesia with arterial, venous, and left atrial catheters. One week later, NE and Epi kinetics (isotope dilution methodology) and systemic blood flows (radioactive microspheres) were measured in fetuses and then in the same animals 1 and 4 h after cesarean section delivery. Comparing fetal and 1-h lambs 1) systemic output fell by 33% (P < 0.005); 2) systemic plasma NE increased by 144% (P < 0.005), and plasma Epi increased sevenfold (P < 0.005); 3) total body NE spillover rose by 63% (P < 0.01) and Epi spillover by fivefold (P < 0.005); and 4) total body NE clearance decreased by 34% (P < 0.005) and Epi clearance by 37% (P < 0.005). Systemic blood flow and kinetic data were similar in 1- and 4-h lambs and were therefore pooled to define the interrelationship among perinatal changes in NE and Epi plasma levels, spillover, and clearance. Between fetal and newborn lambs, plasma NE rose by 1,375 +/- 207 pg/ml, of which 604 +/- 119 pg/ml (approximately 44%) resulted from increased NE total body spillover and 771 +/- 160 pg/ml from reduced NE total body clearance. In the same interval, plasma Epi rose by 292 +/- 30 pg/ml, of which 123 +/- 18 pg/ml (approximately 42%) was due to Epi total body spillover and 169 +/- 19 pg/ml to reduced Epi total body clearance. These findings indicate that 1) sympathoadrenal activity increases with birth, and 2) increased total body spillover and reduced total body clearance contribute a similar portion of the plasma NE and Epi surge at birth.

Fallibility of plasma noradrenaline measurements in studying postprandial sympathetic nervous responses

The use of the plasma noradrenaline (NA) concentration as an index of sympathetic nervous system (SNS) activity in the postprandial state is associated with several problems: (i) It does not take into account the contribution of alterations in clearance to the plasma NA level, (ii) when antecubital venous blood is sampled, it reflects regional forearm rather than whole body SNS activity and (iii) no insight is gained into the regional pattern of SNS activation. These potential confounders were addressed in this study performed in 17 healthy young men. The validity of plasma NA measurements in assessing postprandial changes in sympathetic nervous activation was evaluated in relation to that of whole body and regional plasma NA spillover, derived using isotope dilution methodology. Plasma clearance of NA is significantly altered following a meal, with a transient elevation in the early postprandial phase which may lead to an underestimation of SNS activation when assessed from arterial plasma NA levels. Forearm plasma NA spillover increases postprandially, such that despite significant postprandial elevations in arterial plasma NA, the plasma arterial contribution to antecubital venous plasma NA levels is maintained at less than 40%, the rest being derived locally from the forearm. This makes venous plasma samples unsuitable for the assessment of SNS activation in organs and vascular sites distant from the sampling site. The kidneys and skeletal muscle are the major regional sites of postprandial sympathetic nervous activation, while cardiac plasma NE spillover is unaltered postprandially. This regional pattern of SNS activation postprandially must be taken into account when relating increments in plasma NA levels to specific physiological events.

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 sympathetic nervous activation after a large meal in humans

1. To investigate the link between post-prandial thermogenesis and sympathetic nervous activation we have studied the effects of a single large meal on regional sympathetic nervous activity in healthy, lean subjects. 2. In nine male subjects, noradrenaline spillover was measured from the heart, kidney and liver using isotope dilution, both while fasting and after consumption of a high-energy liquid meal of composition 53% carbohydrate, 32% fat and 15% protein (energy value 2.64-3.51 MJ). Regional oxygen consumption, whole-body oxygen consumption and, in a subset of subjects, muscle sympathetic nerve firing (microneurography) were also measured. 3. Both whole-body oxygen consumption (P < 0.03) and total body spillover of noradrenaline (P < 0.01) rose after the meal, with peak increases of 24% and 56% respectively. Spillover of noradrenaline from the heart was unchanged, that from the hepatosplanchnic circulation increased marginally (0.377 nmol/min to 0.480 nmol/min, P = 0.09), while renal noradrenaline spillover more than doubled (0.440 nmol/min to 0.937 nmol/min, P < 0.05). Skeletal muscle sympathetic nerve activity (peroneal nerve) increased from 7.7 bursts/min at rest to peak at 17.9 bursts/min 60 min after the meal in the three subjects in whom stable recordings were obtained. 4. The meal increased oxygen consumption in the kidneys and liver significantly, from 11.5 +/- 1.6 ml/min to 14.5 +/- 1.1 ml/min and from 46 +/- 7 ml/min to 57 +/- 6 ml/min respectively (P < 0.05), but not in the heart. 5. Consumption of a large meal produces a substantial and relatively selective increase in sympathetic outflow to the kidneys and skeletal muscle. While resting regional oxygen consumptions and noradrenaline spillovers were related, the changes that occurred in each were unrelated, so that no direct relationship could be demonstrated between postprandial thermogenesis and sympathetic activity.

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.

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.

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

OBJECTIVE

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

Increased norepinephrine spillover into the jugular veins in essential hypertension

In essential hypertension sympathetic nerve firing is commonly increased. A central nervous system origin has been presumed but not tested directly. To estimate cerebral norepinephrine release in essential hypertension, spillover of norepinephrine into the cerebrovascular circulation was measured by isotope dilution, with high internal jugular venous sampling. Norepinephrine was released into the cerebrovascular circulation in both hypertensive patients and healthy volunteers and was present after administration of the ganglion blocker trimethaphan and in patients with sympathetic nervous failure, indicating that brain neurons and not cerebrovascular sympathetic nerves were the probable source. Although differing among hypertensive patients, norepinephrine spillover on average was higher in the hypertensive patients (153 +/- 41 pmol/min) than in healthy subjects (59 +/- 12 pmol/min; p less than 0.05), and was elevated in six of 17 patients, in whom the accompanying whole body norepinephrine spillover rate was higher than in the remaining 11 patients (p less than 0.01). To test for a possible link between brain norepinephrine release and human sympathetic nervous function, the effect of the tricyclic antidepressant desipramine (0.3 mg/kg i.v.) on both brain and whole body norepinephrine spillover was measured in healthy volunteers. Desipramine lowered the cerebrovascular spillover of norepinephrine, its precursor dihydroxyphenylalanine, and its metabolite dihydroxyphenylglycol by 50-80% and produced a mean fall of 35% in whole body norepinephrine spillover. One interpretation of these results is that human sympathetic nerve firing is dependent on norepinephrine release within the brain and that increased cerebral norepinephrine release may possibly be present in some patients with essential hypertension, underlying their higher sympathetic nerve firing rates.

Neuronal reuptake of norepinephrine and production of dihydroxyphenylglycol by cardiac sympathetic nerves in the anesthetized dog

BACKGROUND

Reuptake of norepinephrine by cardiac sympathetic nerves before and during two levels of electrical stimulation of the left ansa subclavia was estimated in anesthetized dogs from the cardiac production of dihydroxyphenylglycol (DHPG), the intraneuronal metabolite of norepinephrine.

METHODS AND RESULTS

The method depended on the effects of neuronal uptake blockade with desipramine on the cardiac production of [3H]DHPG from intravenously infused [3H]norepinephrine. The ratio of the desipramine-induced decrease in the cardiac extraction of [3H]norepinephrine to the production of [3H]DHPG was used to transform the cardiac production of DHPG from recaptured norepinephrine into a rate for norepinephrine reuptake. Cardiac spillover of norepinephrine into plasma increased from 49 +/- 12 to 205 +/- 40 and 451 +/- 118 pmol/min during sympathetic activation. Cardiac DHPG production increased from 108 +/- 18 to 166 +/- 34 and 240 +/- 47 pmol/min. Desipramine decreased resting cardiac DHPG production by 20% and completely blocked the stimulation-induced increase. Thus, most (80%) cardiac DHPG produced at rest was derived from norepinephrine leaking from storage vesicles. This amount remained constant, and that derived from recaptured norepinephrine increased during sympathetic activation. The cardiac extraction of [3H]norepinephrine (126,000 dpm/min) and production of [3H]DHPG (3,790 dpm/min) were decreased by 55-57% after desipramine. Thus, only 3% of the norepinephrine recaptured by cardiac sympathetic nerves appeared in plasma as DHPG. The remainder was sequestered into storage vesicles (more than 94%) or ultimately formed metabolites other than DHPG (less than 3%). Reuptake of norepinephrine by cardiac sympathetic nerves was 1,188 +/- 476 pmol/min and increased in parallel with cardiac norepinephrine spillover to 4,182 +/- 1,982 and 6,594 +/- 2,241 pmol/min during sympathetic stimulation.

CONCLUSIONS

Of the norepinephrine released by cardiac sympathetic nerves, 16-fold more was recaptured than entered plasma. Combined estimation of norepinephrine reuptake and spillover offers an approach to assess the efficiency of neuronal reuptake in disorders of cardiac function.

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.

Increased plasma dihydroxyphenylalanine during sympathetic activation in humans is related to increased norepinephrine turnover

Plasma concentrations of dihydroxyphenylalanine (DOPA) were measured before and during isometric handgrip exercise or mental stress and after coffee drinking or intravenous infusion of desipramine to examine the influence of sympathetic nervous activity on DOPA formation. Sympathetic activity was assessed by the spillover of norepinephrine into plasma. Turnover of norepinephrine was assessed by the plasma concentration of its intraneuronal metabolite, dihydroxyphenylglycol (DHPG). In normal subjects the resting plasma concentration of DOPA was 6.05 +/- 0.16 nmol/L (n = 42). Plasma DOPA level was increased by stimulation of the sympathetic nervous system; handgrip exercise caused a 0.49 +/- 0.07 nmol/L increase (n = 15), mental stress a 0.25 +/- 0.10 nmol/L increase (n = 34), and coffee drinking a 0.85 +/- 0.19 nmol/L increase (n = 9). Desipramine decreased plasma DOPA level by 0.25 +/- 0.06 nmol/L (n = 23). The small but consistent changes in plasma DOPA level during manipulations of sympathetic activity were positively correlated with changes in norepinephrine spillover (r = 0.55, n = 81) and plasma DHPG level (r = 0.66, n = 81). Percentage increases in plasma DOPA level during sympathetic activation were similar to those in plasma DHPG but were a sixth of the percentage increases in norepinephrine spillover. The similar increases in plasma DOPA and DHPG levels indicated that production of DOPA was related to the turnover of norepinephrine in sympathetic nerves. The smaller percentage increases in plasma DOPA (smaller than those in norepinephrine spillover) were consistent with the partial contribution of exocytotic neurotransmitter release to the turnover of norepinephrine in sympathetic nerves.

Central sympathoinhibition and peripheral neuronal uptake blockade after desipramine in rabbits

Peripheral- and central nervous system (CNS)-mediated effects of desipramine (Des) on sympathetic nerves and the contribution of alpha 2-adrenoceptors to these effects were studied in conscious rabbits. Blood pressure, renal sympathetic nerve activity (SNA), and norepinephrine (NE) reuptake and spillover into plasma were measured before and after intracisternal (ic) or intravenous (i.v.) administration of Des. In other animals, NE spillover responses to i.v. Des were examined before and after alpha 2-adrenoceptor blockade with i.v. idazoxan. Treatment with i.v. Des blocked neuronal reuptake and decreased renal SNA but did not alter blood pressure or NE spillover. Decreased NE release by sympathetic nerves after i.v. Des was reflected by a decrease in the combined rate of NE reuptake and spillover. Treatment with ic Des (at 1.7% of the i.v. dose) decreased blood pressure and renal SNA and produced equivalent falls in NE reuptake and spillover, indicating little peripheral effect of centrally administered Des on the efficiency of neuronal reuptake. Thus Des had two distinct actions: the drug blocked neuronal reuptake by direct actions on nerve endings and reduced SNA by actions within the CNS. After ic Des, decreased SNA produced parallel falls in NE reuptake, spillover, and blood pressure. After i.v. Des, blockade of neurotransmitter reuptake increased NE concentrations at sympathoeffector junctions offsetting the fall in SNA, so that there was little change in NE spillover or blood pressure. However, after alpha 2-adrenoceptor blockade with i.v. idazoxan, NE spillover increased in response to i.v. Des. Thus the Des-induced decrease in NE release was partly mediated by an action of raised intrasynaptic NE concentrations on inhibitory alpha 2-adrenoceptors.

Effects of desipramine on sympathetic nerve firing and norepinephrine spillover to plasma in humans

In isolated organs, or when given in low dose intra-arterially, tricyclic antidepressant drugs are known to block reuptake of norepinephrine into sympathetic nerve varicosities, with a resultant increased norepinephrine washout. On the other hand, systemic administration of such drugs in humans reduces norepinephrine spillover to plasma. To clarify these seemingly contradictory findings, we have measured concurrently muscle sympathetic activity in the peroneal nerve (microneurography) and rates of norepinephrine spillover to plasma for the body as a whole and for the heart, the kidneys, and the forearm (radiotracer technique), both before and after intravenous infusion of desipramine, 0.5 mg/kg. Desipramine lowered the overflow of norepinephrine to plasma for the body as a whole and from the forearm and the kidneys (by 30-50%) but increased cardiac norepinephrine spillover by 25%. Both the number of sympathetic bursts per min in the peroneal nerve and their mean voltage amplitudes were markedly reduced after desipramine; total activity (bursts/min x mean burst amplitude) fell by approximately 90%. The effects of desipramine on norepinephrine spillover are explicable in terms of inhibition of central sympathetic outflow, balanced against the local blockade of transmitter reuptake. In most sites, the predominant effect is a reduction of norepinephrine overflow. For the heart, where reuptake is so important in transmitter disposition, the net effect is increased overflow.

Noradrenaline reuptake and plasma dihydroxyphenylglycol during sustained changes in sympathetic activity in rabbits

The effects of sustained changes in sympathetic activity, produced by intracisternal (i.c.) infusion of yohimbine or clonidine, on the formation of the intraneuronal noradrenaline metabolite, dihydroxyphenylglycol (DHPG), and on the efficiency of noradrenaline reuptake were examined in conscious rabbits. Noradrenaline spillover was estimated by radiotracer dilution analysis of i.v. infused [3H]noradrenaline. Noradrenaline reuptake was estimated from the amount of DHPG derived from recaptured neurotransmitter and the effects of desipramine-induced neuronal uptake blockade on noradrenaline clearance and plasma [3H]DHPG. The efficiency of neuronal reuptake was assessed from relationships between noradrenaline reuptake and spillover. Sustained sympathetic activation with i.c. yohimbine increased the amount of plasma DHPG that was derived from recaptured noradrenaline as well as that derived from other sources. Acute administration of desipramine decreased both components so that the decrease in plasma DHPG overestimated the amount derived from recaptured noradrenaline. Thus, estimation of the component of plasma DHPG that was derived from recaptured noradrenaline was most accurately achieved by examination of relationships between plasma noradrenaline and DHPG. Noradrenaline reuptake and spillover into plasma were decreased by i.c. infusion of clonidine and increased by i.c. infusion of yohimbine. Neither i.c. infusion of clonidine nor yohimbine altered relationships between noradrenaline reuptake and spillover indicating that the efficiency of neuronal reuptake was unaltered by sustained changes in sympathetic activity.