Peter Friberg

Cardiac Sympathetic Nerve Function in Congestive Heart Failure

BACKGROUND Increased availability of norepinephrine (NE) for activation of cardiac adrenoceptors (increased cardiac adrenergic drive) and depletion of myocardial NE stores may contribute to the pathophysiology and progression of congestive heart failure. This study used a comprehensive neurochemical approach to examine the mechanisms responsible for these abnormalities. METHODS AND RESULTS Subjects with and without congestive heart failure received intravenous infusions of [(3)H]NE. Cardiac spillover, reuptake, vesicular-axoplasmic exchange, and tissue stores of NE were assessed from arterial and coronary venous plasma concentrations of endogenous and [(3)H]-labeled NE and dihydroxyphenylglycol. Tyrosine hydroxylase activity was assessed from plasma dopa, and NE turnover was assessed from measurements of NE metabolites. NE release and reuptake were both increased in the failing heart; however, the efficiency of NE reuptake was reduced such that cardiac spillover of NE was increased disproportionately more than neuronal release of NE. Cardiac NE stores were 47% lower and the rate of vesicular leakage of NE was 42% lower in the failing than in the normal heart. Cardiac spillover of dopa and NE turnover were increased similarly in congestive heart failure. CONCLUSIONS Increased neuronal release of NE and decreased efficiency of NE reuptake both contribute to increased cardiac adrenergic drive in congestive heart failure. Decreased vesicular leakage of NE, secondary to decreased myocardial stores of NE, limits the increase in cardiac NE turnover in CHF. Decreased NE store size in the failing heart appears to result not from insufficient tyrosine hydroxylation but from chronically increased NE turnover and reduced efficiency of NE reuptake and storage.

Increased Cardiac Adrenergic Drive Precedes Generalized Sympathetic Activation in Human Heart Failure

BACKGROUND Previous studies with radiotracer methods have indicated increases in cardiac norepinephrine (NE) and renal NE spillover in patients with severe congestive heart failure (CHF). However, data on the regional sympathetic profile in early stages of CHF are limited. In this study, sympathetic function in the heart, kidneys, and skeletal muscle was evaluated in patients with mild-to-moderate CHF and compared with that in patients with severe CHF and healthy subjects. METHODS AND RESULTS Total body and regional NE spillover from the heart and kidney was assessed with isotope dilution with steady state infusions of [3H]NE. Sympathetic nerve traffic to the skeletal muscle vascular bed (MSA) was recorded intraneurally. Cardiac NE spillover in patients with mild-to-moderate CHF (n = 21) was increased threefold versus that in healthy subjects (n = 12, P < .05), whereas total body and renal NE spillover and MSA did not differ from those in healthy subjects. In the severe CHF group (n = 12), cardiac NE spillover was increased fourfold (P < .05), and total body and renal NE spillover and MSA were high compared with both mild-to-moderate CHF subjects and healthy subjects (P < .05 for both). Fractional extraction of [3H]NE across the heart was reduced by approximately 40% in both CHF groups versus control subjects (P < .05). CONCLUSIONS These results indicate a selective increase in cardiac adrenergic drive (increased amounts of transmitter available at neuroeffector junctions) in patients with mild-to-moderate CHF. This increase appears to precede the augmented sympathetic outflow to the kidneys and skeletal muscle found in advanced CHF.

Increased Sympathetic Nervous Activity in Patients With Nontraumatic Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE Activation of the sympathetic nervous system, which leads to elevation of circulating catecholamines, is implicated in the genesis of cerebral vasospasm and cardiac aberrations after subarachnoid hemorrhage. To this juncture, sympathetic nervous testing has relied on indirect methods only. METHODS We used an isotope dilution technique to estimate the magnitude and time course of sympathoadrenal activation in 18 subarachnoid patients. RESULTS Compared with 2 different control groups, the patients with subarachnoid hemorrhage exhibited an approximately 3-fold increase in total-body norepinephrine spillover into plasma within 48 hours after insult (3.2+/-0.3 and 4.2+/-0.7 versus 10.2+/-1.4 nmol/L; P<0.05 versus both). This sympathetic activation persisted throughout the 7- to 10-day examination period and was normalized at the 6-month follow-up visit. CONCLUSIONS The present study has established that massive sympathetic nervous activation occurs in patients after subarachnoid hemorrhage. This overactivation may relate to the well-known cardiac complications described in subarachnoid hemorrhage.

An intact renin-angiotensin system is a prerequisite for normal renal development

All components of the renin–angiotensin system (RAS) are highly expressed in the developing kidney in a pattern that suggests a role for angiotensin II in renal development. In support of this notion, pharmacological interruption of angiotensin II type-1 (AT1) receptor-mediated effects in animals with an ongoing nephrogenesis produces specific renal abnormalities characterized by papillary atrophy, abnormal wall thickening of intrarenal arterioles, tubular atrophy associated with expansion of the interstitium, and a marked impairment in urinary concentrating ability. Similar changes in renal morphology and function also develop in mice with targeted inactivation of the genes that encode angiotensinogen, angiotensin converting enzyme, or both AT1 receptor isoforms simultaneously. Taken together, these results clearly indicate that an intact signalling through AT1 receptors is a prerequisite for normal renal development. In a recent study, an increased incidence of congenital anomalies of the kidney and urinary tract was detected in mice deficient in the angiotensin II type-2 receptor, suggesting that this receptor subtype is also involved in the development of the genitourinary tract. The present report mainly reviews the renal abnormalities that have been induced by blocking the RAS pharmacologically or by gene targeting in experimental animal models. In addition, pathogenetic mechanisms and clinical implications are discussed.

Ghrelin directly targets the ventral tegmental area to increase food motivation.

Ghrelin, a circulating orexigenic stomach-derived hormone, has recently been implicated in extra-homeostatic feeding, increasing food reward and food-motivated behavior. The precise target site(s) for ghrelins effects on food reward have yet to be elucidated. The neurocircuitry underpinning food-motivated behavior involves, in particular, the dopamine cells of the ventral tegmental area (VTA) that project to the nucleus accumbens (NAcc). Ghrelin stimulation in both of these mesolimbic reward areas increases chow intake. Here we sought to determine if ghrelin acts directly within these mesolimbic reward areas to increase food reward/motivation in studies that combine feeding behavior, pharmacology, and neuroanatomy. We found that motivated behavior for a sucrose reward, assessed in an operant conditioning paradigm in rats, was increased when ghrelin was microinjected directly into the VTA but not into the NAcc. By contrast, ghrelin administration to both areas increased the free feeding of chow. Importantly, in a state of overnight food restriction, where endogenous levels of ghrelin are increased, ghrelin receptor (GHS-R1A) blockade in the VTA was sufficient to decrease the motivation to work for a sugar reward. Blockade of the GHS-R1A in VTA or NAcc was not sufficient to reduce fasting-induced chow hyperphagia. Taken together our data identify the VTA but not the NAcc as a direct, necessary, and sufficient target site for ghrelins action on food motivation.

Cohort Profile: Updating the cohort profile for the MRC National Survey of Health and Development: a new clinic-based data collection for ageing research

MRC Unit for Lifelong Health and Ageing, Research Department of Epidemiology and Public Health, University College London, London, UK, Clinical Radiology, Manchester Royal Infirmary, Oxford Road, Manchester, UK, Vascular Physiology Unit, Institute of Child Health, University College London, London, UK, MRC Epidemiology Unit, Cambridge, UK, Cardiovacular Institute, Sahlgrenska University Hospital, Göteborg, Sweden, Wellcome Trust Clinical Research Facility Manchester, Manchester, UK, International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, London, UK, Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK, Department of Echocardiography, The Heart Hospital, London, UK and MRC Human Nutrition Research, Cambridge, UK

Plasma metanephrines in the diagnosis of pheochromocytoma.

Pheochromocytoma is a tumor of chromaffin cells that usually presents as hypertension. The tumor has potentially life-threatening consequences if it is not promptly diagnosed, located, and removed. Evidence of excessive production of catecholamines is essential for diagnosis of the tumor. Traditional tests have relied on measurements of the 24-hour urinary excretion of catecholamines (norepinephrine and epinephrine) or of the products of catecholamine metabolism [1-4]. Because of the common problems of incompleteness and inconvenience associated with 24-hour urine collections, clinicians have long sought a diagnostic test based on sampling of antecubital venous blood. Measurements of plasma catecholamines are useful in this respect [4, 5]. However, patients with a pheochromocytoma can have plasma concentrations of catecholamines that fall within the range of those in patients with essential hypertension [4, 6] (that is, false-negative results). In addition, emotional distress or pathologic conditions other than pheochromocytoma (such as heart failure) can produce abnormally high catecholamine concentrations [7, 8] (that is, false-positive results). Glucagon stimulation and clonidine suppression testing can enhance the accuracy of plasma catecholamine determinations in the diagnosis of pheochromocytoma [9, 10]. These tests, however, can still yield false-negative or false-positive results [9-11]; they also require considerable time and effort. The search has continued for a single simple, highly sensitive and specific blood test with which to confirm the presence of the tumor in patients with pheochromocytoma. We studied the diagnostic accuracy of tests for specific catecholamine metabolites for this purpose, notably the metanephrinesnormetanephrine and metanephrine. An understanding of why plasma metanephrines may be particularly useful for diagnosis of pheochromocytoma requires an understanding of catecholamine metabolism. Norepinephrine and epinephrine are first metabolized intraneuronally by deamination to dihydroxyphenylglycol or extraneuronally by o-methylation to the metanephrines [12]. Because most dihydroxyphenylglycol is formed from norepinephrine leaking from neuronal stores and little is formed from circulating catecholamines [13, 14], plasma levels of this metabolite are relatively insensitive to the release of catecholamines into the circulation from a pheochromocytoma [6, 15]. The formation of most methoxyhydroxyphenylglycol from dihydroxyphenylglycol [14] and the formation of most vanillylmandelic acid from methoxyhydroxyphenylglycol within the liver [16] explains why a test for vanillylmandelic acid is also a poorer marker for pheochromocytoma than other tests [17]. In contrast, preferential metabolism of circulating catecholamines compared with neuronal catecholamines by extraneuronal pathways [14] suggests that the metanephrinesas extraneuronal metabolitesmay provide good markers for release of catecholamines from a pheochromocytoma. Furthermore, substantial production of metanephrines within adrenal tissue [18] suggests that metanephrines may be produced within the tumor itself. In humans, metanephrines are extensively sulfate-conjugated [18, 19]. Assays of metanephrines in urine depend on measurements after deconjugation to free metanephrines [19] so that measurements represent the sum of free and conjugated metabolites (total metanephrines). In contrast, good sensitivity of the assay for plasma metanephrines [20] enables measurements of both free and total metanephrines. We compared the sensitivity, specificity, and positive and negative predictive values of tests for plasma free and total metanephrines with those of tests for plasma catecholamines and urinary total metanephrines. Study participants included a relatively large sample of patients with pheochromocytoma, patients with essential hypertension or secondary hypertension from causes other than pheochromocytoma, and patients with either heart failure or angina pectoris in whom sympathetically mediated catecholamine release would be expected to be increased. Methods Patients Fifty-two patients with a histologically proven pheochromocytoma were studied. Thirty patients were studied retrospectively, and 22 were studied before the final diagnosis was made. The pheochromocytoma was benign in 39 patients and malignant in 13. Sixty-seven healthy, normotensive persons and 51 patients with essential hypertension served as a reference group. Blood samples were obtained from 23 patients with secondary hypertension (12 patients with renal artery stenosis, 2 with kidney disease, 1 with Cushing disease, 1 with primary hyperaldosteronism, and 7 with cyclosporine-induced hypertension) and from 50 patients with either heart failure or angina pectoris. The age, sex, and specialty center where the patients were studied for each of the five groups are shown in Table 1. Except for the few patients who were being treated with phenoxybenzamine, no patients with pheochromocytoma had been receiving medication for at least 2 weeks at the time of blood sampling. No patients with essential hypertension had been receiving medication for at least 2 weeks at the time of blood sampling. Medications taken by the other patient groups included digoxin, calcium channel blockers, diuretics, acetylsalicylic acid, dipyridamole, and cyclosporine. Procedures used in our study were approved by the hospital ethics committee or intramural research board of each of the three centers where patients were studied. Table 1. Patient Characteristics* Blood and Urine Samples All patients refrained from ingesting methylxanthine-containing food products and from smoking after midnight on the day before blood sampling. Blood was collected from an indwelling catheter in an antecubital vein after the patients had rested supine for 20 minutes. In 39 patients with heart failure and 15 with secondary hypertension, arterial blood was obtained through an indwelling arm arterial catheter. Blood samples were collected into precooled tubes containing heparin or EGTA and glutathione and were centrifuged within 30 minutes to separate the plasma, which was stored frozen until assayed. All plasma catecholamine and urinary metanephrine assays were done within 2 weeks of sample collection. Seven of the 52 pheochromocytoma samples were assayed for plasma metanephrines after being stored at 80C for more than 2 years (range, 2 to 8 years), whereas the remaining 45 samples were assayed within 2 years of collection (22 samples within 4 weeks). In 46 of the 52 patients with pheochromocytoma, a 24-hour urine collection was obtained, with 30 mL of 6-M hydrochloric acid used as a preservative. Analytic Methods Plasma metanephrines were assayed at the National Institutes of Health (NIH) using liquid chromatography with electrochemical detection [20]. Concentrations of total metanephrines (the sum of concentrations of free and sulfoconjugated metanephrines) were measured after incubation of 0.25 mL of plasma with 0.1 units of sulfatase (Sigma Chemical Company, St. Louis, Missouri) at 37 C for 30 minutes. The detection limits were 0.013 nmol/L for normetanephrine and 0.019 nmol/L for metanephrine. At a plasma normetanephrine concentration of 0.31 nmol/L and a metanephrine concentration of 0.21 nmol/L, the interassay coefficients of variation were 12.2% for normetanephrine and 11.2% for metanephrine. As previously reported [20], the presence of acetaminophen in samples of plasma can substantially interfere with measurements of plasma normetanephrine concentrations. Therefore, this analgesic must not be used by patients for several days before blood samples are collected. No analytic interference of various other drugs with this assay has been shown [20]. Plasma catecholamines were assayed using liquid chromatography. Electrochemical detection was used for quantification at the NIH [21], and fluorometric detection was used at St. Radboud University Hospital, Nijmegen, the Netherlands [22]. At the NIH, the detection limits were 0.006 nmol/L for norepinephrine and 0.010 nmol/L for epinephrine. At a plasma norepinephrine concentration of 2.4 nmol/L and an epinephrine concentration of 0.39 nmol/L, the interassay coefficients of variation were 6.5% for norepinephrine and 11.4% for epinephrine. At St. Radboud University Hospital, the detection limits for norepinephrine and epinephrine were 0.002 nmol/L and 0.003 nmol/L, respectively. At plasma concentrations of 1.02 nmol/L for norepinephrine and 0.15 nmol/L for epinephrine, interassay coefficients of variation were 8.5% for norepinephrine and 7.2% for epinephrine. Urinary concentrations of metanephrines were measured according to a previously described method [23]; the upper reference limit of the normal range for the 24-hour urinary output of metanephrines was 6.8 mol/d. Data Analysis Because plasma concentrations of catecholamines and metanephrines were not normally distributed, only medians and ranges are presented for these concentrations. Differences in plasma concentrations of metanephrines and catecholamines among patients with pheochromocytoma and other groups were tested using the Kruskal-Wallis test. We assessed relations among variables using the Spearman rank correlation coefficient. Normal distributions of plasma concentrations of catecholamines and metanephrines were obtained after logarithmic transformation of the data. Thus, upper reference limits, defined as the 97.5th percentile, were determined after logarithmic transformation of individual values for the combined data from normotensive persons and those with essential hypertension (118 persons). The 97.5th percentiles were calculated from the antilogarithm of the mean plus 2 standard deviations of the transformed data. A false-negative result of a test for plasma metanephrines in a patient with pheochromocytoma was defined as plasma concentrations of both normetanephrines and metanephrines that were

Increased sympathetic nerve activity in renovascular hypertension.

BACKGROUND Increased sympathetic nerve activity may contribute to the progression of renovascular hypertension. Because previous results have been inconclusive, we investigated whether renovascular hypertensives show increased total and regional sympathetic nerve activity. METHODS AND RESULTS Sixty-five patients underwent renal angiography and measurements of plasma renin activity and angiotensin II in conjunction with estimation of sympathetic nerve activity by means of radiotracer dilution and intraneural recordings of muscle sympathetic nerve activity (MSNA). Age-matched healthy subjects (n=15) were examined for comparison. Total body norepinephrine (NE) spillover, an index of overall sympathetic nerve activity, was increased by 100% and MSNA by 60% in the hypertensive patients compared with healthy subjects (P<0.01 for both). A subgroup of 24 patients with well-defined renovascular hypertension (cured or improved hypertension after renal angioplasty) showed similar increases in total body NE spillover compared with the group at large. Patients with arterial plasma renin activity and angiotensin II levels above median had higher values for total body NE spillover than patients below median (P<0.01). CONCLUSIONS This study unequivocally demonstrates elevated sympathetic nerve activity in patients with renovascular hypertension. The adrenergic overactivity may contribute to the blood pressure elevation and perhaps also to the high cardiovascular mortality in renovascular hypertension.

Thoracic Epidural Anesthesia During Coronary Artery Bypass Surgery: Effects on Cardiac Sympathetic Activity, Myocardial Blood Flow and Metabolism, and Central Hemodynamics

The effects of high thoracic epidural anesthesia (TEA) on cardiac sympathetic nerve activity, myocardial blood flow and metabolism, and central hemodynamics were studied in 20 patients undergoing coronary artery bypass grafting (CABG). In 10 of the patients, TEA (T1-5 block) was used as an adjunct to a standardized fentanyl-nitrous oxide anesthesia. Hemodynamic measurements and blood sampling were performed after induction of anesthesia but prior to skin incision and after sternotomy. Assessment of total and cardiac sympathetic activity was performed by means of the norepinephrine kinetic approach. Prior to surgery, mean arterial pressure (MAP), great cardiac vein flow (GCVF), and regional myocardial oxygen consumption (Reg-MVO2) were lower in the TEA group compared to the control group. During sternotomy there was a pronounced increase in cardiac norepinephrine spillover, MAP, systemic vascular resistance index (SVRI), pulmonary capillary wedge pressure (PCWP), GCVF, and Reg-MVO2 in the control group. These changes were clearly attenuated in the TEA group. None of the patients in the TEA group had metabolic (lactate) or electrocardiographic signs of myocardial ischemia. Three patients in the control group had indices of myocardial ischemia prior to and/or during surgery. We conclude that TEA attenuates the surgically mediated sympathetic stress response to sternotomy, thereby preventing the increase in myocardial oxygen demand in the pre-bypass period without jeopardizing myocardial perfusion.

Plasma methoxytyramine: a novel biomarker of metastatic pheochromocytoma and paraganglioma in relation to established risk factors of tumour size, location and SDHB mutation status.

BACKGROUND There are currently no reliable biomarkers for malignant pheochromocytomas and paragangliomas (PPGLs). This study examined whether measurements of catecholamines and their metabolites might offer utility for this purpose. METHODS Subjects included 365 patients with PPGLs, including 105 with metastases, and a reference population of 846 without the tumour. Eighteen catecholamine-related analytes were examined in relation to tumour location, size and mutations of succinate dehydrogenase subunit B (SDHB). RESULTS Receiver-operating characteristic curves indicated that plasma methoxytyramine, the O-methylated metabolite of dopamine, provided the most accurate biomarker for discriminating patients with and without metastases. Plasma methoxytyramine was 4.7-fold higher in patients with than without metastases, a difference independent of tumour burden and the associated 1.6- to 1.8-fold higher concentrations of norepinephrine and normetanephrine. Increased plasma methoxytyramine was associated with SDHB mutations and extra-adrenal disease, but was also present in patients with metastases without SDHB mutations or those with metastases secondary to adrenal tumours. High risk of malignancy associated with SDHB mutations reflected large size and extra-adrenal locations of tumours, both independent predictors of metastatic disease. A plasma methoxytyramine above 0.2nmol/L or a tumour diameter above 5cm indicated increased likelihood of metastatic spread, particularly when associated with an extra-adrenal location. CONCLUSION Plasma methoxytyramine is a novel biomarker for metastatic PPGLs that together with SDHB mutation status, tumour size and location provide useful information to assess the likelihood of malignancy and manage affected patients.