Efferent Renal Sympathetic Nerve Research Articles

JS-HR-10: ADVANCES IN RENAL DENERVATION FOR TREATING HYPERTENSION

Excessive activation of sympathetic nervous system is closely related to the onset and progression of hypertension. Renal nerves are composed of sympathetic efferent and sensory afferent nerves. Activation of the efferent renal sympathetic nerves induces renin secretion, sodium absorption, and increased renal vascular resistance, which lead to increased blood pressure (BP) and fluid retention. Afferent renal sensory nerves, which are densely innervated in the renal pelvic wall, project to the cardiovascular center in the brain to modulate sympathetic outflow to the periphery, including the heart, kidneys, and arterioles. Renal denervation (RDN) is a neuromodulation therapy that partially interrupts both the efferent outputs from the brain to the kidney and the afferent inputs from the kidney to the brain and has attracted attention as a novel device therapy for hypertension. In clinical practice, denervation is performed through the lumen of the renal artery using a catheter. Radiofrequency, ultrasound, and alcohol-based RDN devices are being developed as new second-generation devices. A randomized sham-controlled trials using 24-hour ambulatory BP measurement is required for approval of clinical use of RDN. The SPYRAL HTN OFF-MED pivotal trial showed the superiority of RDN using radiofrequency-based catheter compared with a sham procedure to safely lower 24-hour systolic BP in the absence of antihypertensive medications. The RADIANCE-HTN TRIO trials showed the superiority of RDN using ultrasound-based catheter compared with a sham procedure to safely lower daytime BP in patients with resistant hypertension. The REQUIRE trial is the first trial of ultrasound RDN in Asian patients from Japan and South Korea with resistant hypertension. The study findings were neutral for the primary endpoint, with similar reductions in 24-hour systolic BP in the RDN and sham control groups. Although BP reduction after RDN was similar to other sham-controlled studies, the sham group in this study showed much greater reduction. Japanese Society of Hypertension performed the meta-analysis of nine randomized sham-controlled trials of RDN including these three trials mentioned above. The results showed that RDN significantly reduced a range of office, home and 24-hour BP parameters in patients with resistant, uncontrolled, and drug-naïve hypertension. There were no significant differences in magnitude of BP reduction between radiofrequency-based and ultrasound-based devices. Recently, the efficacy and safety of RDN in the SPYRAL HTN OFF-MED pivotal trial up to 36 months have been reported. In this session, the latest basic and clinical evidence/aspects of RDN will be summarized and discussed, which is about to be introduced into the clinical practice.

Renal denervation: basic and clinical evidence.

Renal nerves have critical roles in regulating blood pressure and fluid volume, and their dysfunction is closely related with cardiovascular diseases. Renal nerves are composed of sympathetic efferent and sensory afferent nerves. Activation of the efferent renal sympathetic nerves induces renin secretion, sodium absorption, and increased renal vascular resistance, which lead to increased blood pressure and fluid retention. Afferent renal sensory nerves, which are densely innervated in the renal pelvic wall, project to the hypothalamic paraventricular nucleus in the brain to modulate sympathetic outflow to the periphery, including the heart, kidneys, and arterioles. The effects of renal denervation on the cardiovascular system are mediated by both efferent denervation and afferent denervation. The first half of this review focuses on basic research using animal models of hypertension and heart failure, and addresses the therapeutic effects of renal denervation for hypertension and heart failure, including underlying mechanisms. The second half of this review focuses on clinical research related to catheter-based renal denervation in patients with hypertension. Randomized sham-controlled trials using second-generation devices, endovascular radiofrequency-based devices and ultrasound-based devices are reviewed and their results are assessed. This review summarizes the basic and clinical evidence of renal denervation to date, and discusses future prospects and potential developments in renal denervation therapy for cardiovascular diseases.

GLP-1 mediated diuresis and natriuresis are blunted in heart failure and restored by selective afferent renal denervation

BackgroundGlucagon-like peptide-1 (GLP-1) induces diuresis and natriuresis. Previously we have shown that GLP-1 activates afferent renal nerve to increase efferent renal sympathetic nerve activity that negates the diuresis and natriuresis as a negative feedback mechanism in normal rats. However, renal effects of GLP-1 in heart failure (HF) has not been elucidated. The present study was designed to assess GLP-1-induced diuresis and natriuresis in rats with HF and its interactions with renal nerve activity.MethodsHF was induced in rats by coronary artery ligation. The direct recording of afferent renal nerve activity (ARNA) with intrapelvic injection of GLP-1 and total renal sympathetic nerve activity (RSNA) with intravenous infusion of GLP-1 were performed. GLP-1 receptor expression in renal pelvis, densely innervated by afferent renal nerve, was assessed by real-time PCR and western blot analysis. In separate group of rats after coronary artery ligation selective afferent renal denervation (A-RDN) was performed by periaxonal application of capsaicin, then intravenous infusion of GLP-1-induced diuresis and natriuresis were evaluated.ResultsIn HF, compared to sham-operated control; (1) response of increase in ARNA to intrapelvic injection of GLP-1 was enhanced (3.7 ± 0.4 vs. 2.0 ± 0.4 µV s), (2) GLP-1 receptor expression was increased in renal pelvis, (3) response of increase in RSNA to intravenous infusion of GLP-1 was enhanced (132 ± 30% vs. 70 ± 16% of the baseline level), and (4) diuretic and natriuretic responses to intravenous infusion of GLP-1 were blunted (urine flow 53.4 ± 4.3 vs. 78.6 ± 4.4 µl/min/gkw, sodium excretion 7.4 ± 0.8 vs. 10.9 ± 1.0 µEq/min/gkw). A-RDN induced significant increases in diuretic and natriuretic responses to GLP-1 in HF (urine flow 96.0 ± 1.9 vs. 53.4 ± 4.3 µl/min/gkw, sodium excretion 13.6 ± 1.4 vs. 7.4 ± 0.8 µEq/min/gkw).ConclusionsThe excessive activation of neural circuitry involving afferent and efferent renal nerves suppresses diuretic and natriuretic responses to GLP-1 in HF. These pathophysiological responses to GLP-1 might be involved in the interaction between incretin-based medicines and established HF condition. RDN restores diuretic and natriuretic effects of GLP-1 and thus has potential beneficial therapeutic implication for diabetic HF patients.

Glucagon‐like peptide‐1 mediated renal sympathetic activation in obese rats: role of intrarenal mechanisms

Accumulated evidence indicates that obesity is associated with enhanced sympathetic activation. Chronic sympathetic activation increases the risk of cardiovascular complications and subsequent mortality. The mechanisms linking obesity with sympathetic activation are complex and not completely understood. Gut produced hormone glucagon‐like peptide‐1 (GLP‐1) affects cardiovascular function via regulating blood pressure and sympathetic nerve activity. The aim of the study was to determine the role of intrarenal GLP‐1 mediated renal sympathetic activation in obese rats. In anesthetic Sprague Dawley rats, renal intra‐pelvic infusion of GLP‐1 receptor agonist exendin‐4 increased afferent renal sympathetic nerve activity (A‐RSNA), efferent renal sympathetic nerve activity (T‐RSNA), arterial pressure and heart rate. All the sympathetic and hemodynamic responses to the exendin‐4 infusion were significantly enhanced in high fat diet (HFD, 42% of calories from fat for 12 weeks) induced obese rats. The natriuretic and diuretic effects mediated by intrarenal exendin‐4 infusion was significantly blunted in the obese rats. Furthermore, ablation of renal sympathetic nerves significantly improved the diuretic and natriuretic responses to exendin‐4 infusion in obese rats. We also found significant altered GLP‐1 level and GLP‐1 receptor expression in the kidney of obese rats. The results suggest that altered intrarenal GLP‐1 mediated mechanisms may contribute to the development of obesity‐related high sympathetic activation and obesity hypertension.Support or Funding InformationThe study was supported by the author’s faculty start‐up fund from Sanford School of Medicine of the University of South Dakota Department of Basic Biomedical Sciences.

A selective impairment in the mechanosensitive afferent renal nerve‐mediated sympathoinhibitory reno‐renal reflex contributes to age‐related hypertension

AimThe afferent renal nerves (ARN) mediate reno‐renal reflexes that influence efferent renal sympathetic nerve activity, sodium homeostasis, and blood pressure. These studies tested the hypothesis that impairments in the sympathoinhibitory reno‐renal reflex contribute to age‐related hypertension (HTN).MethodsThree‐month (mo), 8mo, and 16mo male (M) Sprague Dawley (SD) rats on a normal salt (NS; 0.6% NaCl) diet underwent an acute isotonic saline volume expansion (VE; 5% body weight – mechanoreceptor stimulus) or an acute isovolumetric 1M NaCl infusion (20μL/min, 2hr – chemoreceptor stimulus) and mean arterial pressure (MAP), natriuresis (UNaV), and paraventricular nucleus (PVN) neuronal activation (c‐Fos expression) were assessed. Three and 8mo female SD rats also underwent acute VE. N=6/gp.In 3mo, 8mo and 16mo M SD rats, 1) sympathetic tone (plasma and renal norepinephrine [NE] content) or 2) ex vivo ARN activity (substance P [SP] release in response to 1250pM NE [general stimulus] or 450mM NaCl [chemoreceptor stimulus]) were assessed on day 21 of NS or high salt (HS; 4% NaCl) diet. N=6/gp.In 3mo and 16mo M SD rats on a NS diet, MAP and sodium balance were assessed on day 10 after selective ARN ablation (33mM capsaicin) or total bilateral renal denervation (RDNX; 10% phenol). N=6/gp.ResultsAged rats develop HTN (MAP [mmHg] 3mo 124 ± 2 vs 8mo 135 ± 4 vs 16mo 150 ± 3, p<0.05) and exhibit blunted natriuretic and PVN sympathoinhibitory parvocellular neuronal responses to an acute VE (% sodium load excreted 3mo 78 ± 6 vs 8mo 60 ± 7 vs 16mo 22 ± 9, p<0.05; medial parvocellular neuronal activation [c‐fos+ cell count] 3mo 59 ± 4 vs 8mo 42 ± 7 vs 16mo 13 ± 5, p<0.05). There are no sex differences in VE responses in 3 or 8mo rats. The natriuretic and PVN neuronal responses to a 1M NaCl infusion are intact in aged rats.Aged rats exhibit reduced NE‐evoked ARN activity during NS intake and fail to increase NE‐evoked ARN activity during HS intake (SP release [pg/min] 3mo NS 14 ± 2 vs HS 23 ± 4, p<0.05; 8mo NS 8 ± 2 vs HS 6 ± 3, ns; 16mo NS 2 ± 7 vs HS 2 ± 6, ns). Age and diet did not alter 450mM NaCl‐evoked ARN activity.Aged rats exhibit elevated basal plasma and renal sympathetic tone and impaired HS‐evoked suppression of sympathetic tone (renal NE content [pg/mg] 3mo NS 612 ± 36 vs HS 368 ± 32; 8mo NS 835 ± 48 vs HS 722 ± 44, p<0.05; 16mo HS 974 ± 13 vs NS 1019 ± 34, ns).Bilateral RDNX attenuates MAP and improves sodium balance in aged rats (MAP [mmHg] 15mo intact 150 ± 3 vs RDNX 140 ± 2, p<0.05; 24hr sodium balance [mEq] 15mo intact 0.51 ± 0.13 vs RDNX 0.08 ± 0.13, p<0.05). Selective ARN ablation has no impact on MAP or sodium balance.ConclusionsAge‐related HTN is characterized by a selective impairment in the mechanosensitive ARN. We speculate that a decrease in ARN‐mediated sympathoinhibitory reno‐renal reflex activity promotes sympathoexcitation, perhaps due to reduced PVN parvocellular neuronal activity, driving sodium retention and HTN. Critically, RDNX attenuates age‐related HTN and may do so via an improvement in sodium balance.Support or Funding InformationThis work was supported by NIH R56 AG057687, R01 HL139867, R01 HL141406 and 17GRNT33670023 to RDW and NIH F31 DK116501 to AAF.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Peripherally Administered Proinflammatory Cytokines Increase Afferent Renal Nerve Activity in Rat

Inflammation plays an important role in sympathetic activation in cardiovascular diseases. Systemic administration of the proinflammatory cytokines (PICs) tumor necrosis factor‐α (TNF‐α) and interleukin‐1β (IL‐1β) increases mean blood pressure (MBP), heart rate (HR) and efferent renal sympathetic nerve activity. However, the renal nerve contains both afferent and efferent fibers. The afferent renal nerve is composed of chemoreceptor and mechanoreceptor fibers, and delivers peripheral signals to the brain that have been reported to increase sympathetic outflow in hypertension and heart failure. The effect of circulating PICs on afferent renal nerve activity (ARNA) has not previously been investigated. The present study sought to determine whether peripherally administered PICs TNF‐α and IL‐1β increase ARNA. Urethane anesthetized male Sprague Dawley rats (300–350 g) underwent an intravenous (IV) or a renal artery injection of TNF‐α or IL‐1β. MBP (mmHg), HR (beats/min) and ARNA (% change from baseline) were continuously recorded for 4–5 hours. IV injection of TNF‐α (500 ng/kg) or IL‐1β (500 ng/kg) significantly (* p<0.01 vs. baseline) increased MBP (20.1 ± 2.2* and 23.4 ± 2.1*, respectively), HR (51.5 ± 6.7* and 58.8 ± 7.1*, respectively) and ARNA (37.2 ± 3.5* and 42.1 ± 3.5*, respectively) with peak responses 20–30 mins after injection. Similarly, renal artery injection of the same doses of TNF‐α or IL‐1β induced increases (*p<0.01 vs. baseline) in MBP (17.0 ± 2.1* and 19.9 ± 2.2*, respectively), HR (45.5 ± 5.6* and 49.3 ± 4.6*, respectively) and ARNA (30.7 ± 3.5* and 38.4 ± 4.5*, respectively) that began within 5–10 mins and peaked at 20–30 mins after the injection. Quantitative real‐time PCR showed high mRNA levels of TNF‐α receptor 1 and IL‐1β receptor in renal cortex and medulla. These data indicate that circulating TNF‐α and IL‐1β can act at the kidney to augment afferent renal nerve activity, suggesting that circulating PICs may activate ARN fibers to elicit a sympathetically mediated pressor response. PIC activation of renal afferent nerves may be an important mechanism contributing to inflammation‐driven sympathetic activation in heart failure and hypertension. These findings provide support for the potential therapeutic benefit of renal afferent denervation.Support or Funding InformationSupported by NIH grant R01 HL139521 (S.G. Wei)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A6532 Partial reinnervation of efferent renal sympathetic nerves 30 months after radiofrequency catheter-based renal denervation in sheep with hypertensive chronic kidney disease

Objectives: Radiofrequency catheter-based renal denervation (RDN) maybe effective in reducing blood pressure (BP) in resistant hypertension. Regrowth of renal nerves and restoration of function occurs from 5.5 months after RDN in normotensive sheep with regrowth and function of nerves restored to levels of intact by 11 months. Our studies in sheep with hypertensive CKD show BP is reduced at 2 and 5 months after RDN. In the present study we examined 1) if the reduction in BP was sustained and 2) the extent of regrowth of renal nerves at 30 months after RDN in the same cohort of sheep. Methods: At 10 months sheep underwent RDN using the Symplicity Flex catheter (control-RDN, n = 8; CKD-RDN, n = 7) or sham procedure (control-intact, n = 6; CKD-intact, n = 7). BP was measured in conscious sheep via carotid arterial catheter. Kidneys underwent immunohistochemical staining of renal efferent nerves (tyrosine hydroxlylase) at 30 months after RDN. Results: BP was higher in CKD-intact compared with control-intact but was less in CKD-RDN than CKD-intact (BP (mmHg); control-intact; 86 ± 1, control-RDN; 87 ± 4, CKD-intact; 95 ± 6, CKD-RDN; 83 ± 4). TH (percentage of kidney section volume) was 60% greater in CKD-intact compared with control-intact but was 2-fold less in CKD-RDN than CKD-intact (Fig 1). There was no difference in BP and TH staining between control-intact and control-RDN sheep. Conclusion: There is increased sympathetic innervation in this model of hypertensive-CKD, which may be driving elevated BP. Reinnervation occurred in both normotensive and hypertensive sheep after RDN. However, restoration to levels of intact animals was only observed in normotensive sheep, with only partial restoration observed in CKD sheep at 30 months post-RDN. This may account for the sustained reduction in BP observed following RDN.

Renal Sympathetic Denervation Reverses Diastolic Dysfunction in a Rodent Model of Heart Failure with Preserved Ejection Fraction (HFpEF)

Background: Heart failure with preserved ejection fraction (HFpEF) accounts for 50% of heart failure and has generally poor prognosis. However, there are no approved therapies available for reducing mortality or hospitalization rates in these patients. Renal sympathetic denervation (RDN) is under investigation for the treatment of resistant hypertension and primarily acts primarily by modulating afferent and efferent renal sympathetic nerves activity. We have previously reported the cardioprotective effects of RDN in myocardial ischemia-reperfusion injury. The aim of this study is to investigate the therapeutic potential of RF-RDN in a rodent model of HFpEF. Methods: 4-week-old male Sprague-Dawley rats were subjected to supracoronary aortic banding (SAB) for 14 weeks followed by administration of L-NAME (2.6mg/kg/24h) for 8 weeks to develop HFpEF. At 22-weeks after SAB, bilateral radiofrequency (RF)-RDN was performed in combination with the application of phenol on the renal arteries. Echocardiography was performed to assess systolic and diastolic function at 4 week intervals throughout the experimental protocol. Results: Twenty-two weeks following SAB and L-NAME, echocardiography revealed left ventricular (LV) hypertrophy with preserved EF and diastolic dysfunction [attenuated E/A ratio and prolonged deceleration time (DcT)]. Following RF-RDN, E/A significantly increased (1.10 ± 0.05 vs. 1.63 ± 0.06, p < 0.01) and DcT significantly shortened (38.7 ± 0.9 ms vs. 31.8 ± 0.8 ms, p < 0.01) compared to those of prior to RF-RDN. There were no significant changes in LV ejection fraction throughout the study. Conclusion: RF-RDN reversed diastolic dysfunction in a rodent model of HFpEF without affecting LV systolic function. Our preliminary results suggest that RF-RDN may have therapeutic potential in the setting of HFpEF.

Renal denervation in the treatment of resistant hypertension: Dead, alive or surviving?

Hypertension is one of the most common chronic clinical problems encountered by physicians. The prevalence of resistant hypertension is estimated at 9% in the US. Patients with resistant hypertension have been shown to be at higher risk for adverse cardiovascular events, hence the need for greater efforts in improving the treatment of hypertension. The renal sympathetic nerves play an important role in the development of hypertension, mediated via sodium and water retention, increased renin release and alterations in renal blood flow. The proximity of the afferent and efferent renal sympathetic nerves to the adventitia of the renal arteries suggested the feasibility of an endovascular, selective, minimally invasive approach to renal denervation; a potential treatment option for resistant hypertension. While the RAPID, Reduce-HTN, EnligHTN, DENERHTN and Symplicity HTN-1 and -2 studies showed significant benefit of renal denervation in the treatment of resistant hypertension, the results of Oslo RDN, Prague-15 and Symplicity HTN-3 were not so favorable. Future well-designed clinical trials are needed to ascertain the benefits or otherwise of renal denervation in treatment-resistant hypertension.

Renal denervation in the treatment of resistant hypertension: Dead, alive or surviving?

Hypertension is one of the most common chronic clinical problems encountered by physicians. The prevalence of resistant hypertension is estimated at 9% in the US. Patients with resistant hypertension have been shown to be at higher risk for adverse cardiovascular events, hence the need for greater efforts in improving the treatment of hypertension. The renal sympathetic nerves play an important role in the development of hypertension, mediated via sodium and water retention, increased renin release and alterations in renal blood flow. The proximity of the afferent and efferent renal sympathetic nerves to the adventitia of the renal arteries suggested the feasibility of an endovascular, selective, minimally invasive approach to renal denervation; a potential treatment option for resistant hypertension. While the RAPID, Reduce-HTN, EnligHTN, DENERHTN and Symplicity HTN-1 and -2 studies showed significant benefit of renal denervation in the treatment of resistant hypertension, the results of Oslo RDN, Prague-15 and Symplicity HTN-3 were not so favorable. Future well-designed clinical trials are needed to ascertain the benefits or otherwise of renal denervation in treatment-resistant hypertension.

Chronic Kidney Disease As a Potential Indication for Renal Denervation.

Renal denervation is being used as a blood pressure lowering therapy for patients with apparent treatment resistant hypertension. However, this population does not represent a distinct disease condition in which benefit is predictable. In fact, the wide range in effectiveness of renal denervation could be a consequence of this heterogeneous pathogenesis of hypertension. Since renal denervation aims at disrupting sympathetic nerves surrounding the renal arteries, it seems obvious to focus on patients with increased afferent and/or efferent renal sympathetic nerve activity. In this review will be argued, from both a pathophysiological and a clinical point of view, that chronic kidney disease is particularly suited to renal denervation.

The Potential Role of Catheter-Based Renal Sympathetic Denervation in Chronic and End-Stage Kidney Disease.

Sympathetic activation is a hallmark of chronic and end-stage renal disease and adversely affects cardiovascular prognosis. Hypertension is present in the vast majority of these patients and plays a key role in the progressive deterioration of renal function and the high rate of cardiovascular events in this patient cohort. Augmentation of renin release, tubular sodium reabsorption, and renal vascular resistance are direct consequences of efferent renal sympathetic nerve stimulation and the major components of neural regulation of renal function. Renal afferent nerve activity directly influences sympathetic outflow to the kidneys and other highly innervated organs involved in blood pressure control via hypothalamic integration. Renal denervation of the kidney has been shown to reduce blood pressure in many experimental models of hypertension. Targeting the renal nerves directly may therefore be specifically useful in patients with chronic and end-stage renal disease. In this review, we will discuss the potential role of catheter-based renal denervation in patients with impaired kidney function and also reflect on the potential impact on other cardiovascular conditions commonly associated with chronic kidney disease such as heart failure and arrhythmias.

Autonomic modulation for the management of patients with chronic heart failure.

Dysregulation of the autonomic nervous system in heart failure (HF) has received considerable attention during the past 3 decades, largely because of the well-recognized association between increased sympathetic activity and the elaboration of biologically active molecules, collectively referred to as neurohormones, that help to maintain cardiovascular homeostasis through increased volume expansion, peripheral arterial vasoconstriction, and increased myocardial contractility. However, high and sustained levels of these biologically active molecules (eg, norepinephrine, angiotensin II, aldosterone) are overtly toxic to the heart and circulation.1 These and other insights have led to the clinical use of neurohormonal antagonists, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, aldosterone antagonists, and β-blockers to treat patients with HF with a reduced left ventricular ejection fraction (LVEF).1 The effectiveness of these pharmacological agents is predominantly because of their ability to directly antagonize the deleterious effects of excessive sympathetic and renin–angiotensin activation. However, the current guideline-directed medical therapy (GDMT) in patients with HF fails to completely restore normal autonomic balance disrupted as a part of HF pathophysiology. During the last decade, a novel approach has generated widespread interest: modulation of the autonomic nervous system as a result of either a one-time intervention (eg, denervation) or of ongoing active therapy (eg, electric stimulation) as a means of further diminishing the sympathovagal imbalance that develops in HF.2,3 Of note, therapeutic neuromodulation with device-based therapies, either with spinal cord stimulation (SCS) or vagal stimulation (VS), has been used safely in patients with chronic pain, epilepsy, and depression, since the 1980s. As noted above, HF with a reduced LVEF is associated with sustained activation of the sympathetic nervous system that is accompanied by a withdrawal of parasympathetic tone. Impaired arterial baroreflexes have been proposed as an important mechanism that contributes to the sympathovagal imbalance present in HF4 …

Effects of anesthetics on the renal sympathetic response to anaphylactic hypotension in rats.

The autonomic nervous system plays an important role in rat anaphylactic hypotension. It is well known that sympathetic nerve activity and cardiovascular function are affected by anesthetics. However, the effects of different types of anesthesia on the efferent renal sympathetic nerve activity (RSNA) during anaphylactic hypotension remain unknown. Therefore, we determined the renal sympathetic responses to anaphylactic hypotension in anesthetized and conscious rats and the roles of baroreceptors in these responses. Sprague-Dawley rats were randomly allocated to anesthetic groups that were given pentobarbital, urethane, or ketamine-xylazine and to a conscious group. The rats were sensitized using subcutaneously injected ovalbumin. The systemic arterial pressure (SAP), RSNA and heart rate (HR) were measured. The effects of sinoaortic baroreceptor denervation on RSNA during anaphylaxis were determined in pentobarbital-anesthetized and conscious rats. In all of the sensitized rats, the RSNA increased and SAP decreased after antigen injection. At the early phase within 35 min of the antigen injection, the antigen-induced sympathoexcitation in the conscious rats was significantly greater than that in the anesthetized rats. Anaphylactic hypotension was attenuated in the conscious rats compared to the anesthetized rats. The anesthetic-induced suppression of SAP and RSNA was greater in the order ketamine-xylazine >urethane = pentobarbital. Indeed, in the rats treated with ketamine-xylazine, RSNA did not increase until 40 min, and SAP remained at low levels after the antigen injection. The baroreceptor reflex, as evaluated by increases in RSNA and HR in response to the decrease in SAP induced by sodium nitroprusside (SNP), was suppressed in the anesthetized rats compared with the conscious rats. Consistent with this finding, baroreceptor denervation attenuated the excitatory responses of RSNA to anaphylaxis in the conscious rats but not in the pentobarbital-anesthetized rats. RSNA was increased markedly in conscious rats during anaphylactic hypotension. Anesthetics attenuated this antigen-induced renal sympathoexcitation through the suppression of baroreceptor function.

Role of renal sensory nerves in physiological and pathophysiological conditions.

Whether activation of afferent renal nerves contributes to the regulation of arterial pressure and sodium balance has been long overlooked. In normotensive rats, activating renal mechanosensory nerves decrease efferent renal sympathetic nerve activity (ERSNA) and increase urinary sodium excretion, an inhibitory renorenal reflex. There is an interaction between efferent and afferent renal nerves, whereby increases in ERSNA increase afferent renal nerve activity (ARNA), leading to decreases in ERSNA by activation of the renorenal reflexes to maintain low ERSNA to minimize sodium retention. High-sodium diet enhances the responsiveness of the renal sensory nerves, while low dietary sodium reduces the responsiveness of the renal sensory nerves, thus producing physiologically appropriate responses to maintain sodium balance. Increased renal ANG II reduces the responsiveness of the renal sensory nerves in physiological and pathophysiological conditions, including hypertension, congestive heart failure, and ischemia-induced acute renal failure. Impairment of inhibitory renorenal reflexes in these pathological states would contribute to the hypertension and sodium retention. When the inhibitory renorenal reflexes are suppressed, excitatory reflexes may prevail. Renal denervation reduces arterial pressure in experimental hypertension and in treatment-resistant hypertensive patients. The fall in arterial pressure is associated with a fall in muscle sympathetic nerve activity, suggesting that increased ARNA contributes to increased arterial pressure in these patients. Although removal of both renal sympathetic and afferent renal sensory nerves most likely contributes to the arterial pressure reduction initially, additional mechanisms may be involved in long-term arterial pressure reduction since sympathetic and sensory nerves reinnervate renal tissue in a similar time-dependent fashion following renal denervation.

Rebuttal from Markus P. Schlaich, Yusuke Sata and Murray D. Esler.

Extreme positions are rarely useful and almost invariably hinder rather than facilitate progress in clinical science. Dr Jordan (Jordan, 2014) and Dr Paton (Ratcliffe et al. 2014) and their colleagues seem to share this view and, while making a strong case for each of their points, have provided a reasonably balanced appraisal of the evidence surrounding the interventional approaches for resistant hypertension under debate. Importantly, we seem to share common ground in the view that resistant hypertension is a relevant clinical problem, that non-adherence to prescribed medication is common, that alternative and perhaps device-based therapeutic approaches are needed, and that sympathetic overactivity is a major contributor to the pathophysiology of resistant hypertension thereby providing a logical therapeutic target. Our views differ in how this is best achieved. Dr Jordan elegantly reviews the role of baroreflex circuits in long-term blood pressure (BP) control and how electrical carotid sinus stimulation (CCS) may ameliorate resistant hypertension. While highlighting potential advantages of CCS such as the ability of stimulation adjustment, it becomes clear from his pathophysiological considerations that sympathetic inhibition, specifically suppression of efferent renal sympathetic nerve activity, is an important mediator of CCS-induced depressor responses (Iliescu et al. 2012). Why not target the renal nerves directly when this can be achieved safely with catheter-based approaches (Esler et al. 2010; Bhatt et al. 2014)? Carotid body (CB) denervation is the least developed and investigated approach, which does not negate the physiological relevance of chemoreceptor activation and its role in modulation of both sympathetic nerve activity and blood pressure. Dr Paton promotes the concept of CB tonicity driving sympathetic vasomotor activity chronically, particularly in the scenario of hypertension (Paton et al. 2013). Surgical resection of the CB has been performed to alleviate dyspnoea in patients with obstructive airway disease and coincidentally, a BP reduction was observed in a subgroup of hypertensive patients (Nakayama, 1961). Clearly, recent experimental data is more convincing (McBryde et al. 2013). Nevertheless, evidence for a pivotal role of CB-related mechanisms in human resistant hypertension is weak and the concept far from proven. Major concerns that need to be addressed relate to the potential attenuation or loss of hypoxic ventilatory drive and the potentially serious procedural complications. In keeping with the hypothetical ideals for an interventional approach brought forward by Dr Paton, we would argue that renal denervation remains the most promising therapeutic approach despite the recent setback from a suboptimally conducted clinical trial (Bhatt et al. 2014).

Effects of renal denervation on the development of post-myocardial infarction heart failure and cardiac autonomic nervous system in rats

Prior studies indicated that radiofrequency renal denervation (RD)had beneficial effects on post-myocardial infarction (MI) heart failure(HF) in rats[1–3]. In this studywe aimedtoassessits effects on cardiacautonomic nervous system (CANS) which might be one of the mostimportant mechanisms of RD's therapeutic effect on post-MI HF anddetermine the best timing for RD.One hundred Wistar rats were randomly assigned intofiveexperimental groups: MI group (n = 20), RD group (n = 20),MI-1d + RD group (RD performed one day post-MI, n = 20),MI-4w + RD group (RD performed four weeks post-MI, n = 20),andNgroup(controlgroup, n = 20).MIwasproducedthroughligationof the anterior descending artery. RD was performed through strippingof the renal nerves. The experimental design and implementation wereconducted in accordance with animal welfare guidelines.Eight weeks post-MI, significant improvements were observed inboth MI-1d + RD and MI-4w + RD groups compared to the MIgroup, that include (1) improved left ventricular (LV) function andhemodynamics with increased water and sodium excretion;(2) decreased plasma and renal tissue norepinephrine levelswhile tissue norepinephrine content increased in myocardium;(3) increased β1-receptor in myocardium and improved heartratevariability;and(4)decreasedplasmarenin,angiotensinII,aldoste-rone,BNPandendothelinlevels.Moretherapeuticeffectswerefoundinthe MI-1d + RD group than the MI-4w + RD group (see Table 1 andFig. 1).Firstly, our study showed that RD attenuated the remodeling ofCANS and modulated its activities. RD leads to preservation of β1receptors content along with the β1 mRNA expression in non-infarcted cardiac tissue in this HF model (Fig. 1). This correlated withan improvement in heart function and cardiac remodeling. HRV is asensitive marker for the CANS [4]. RD led to a slower HR and higherSDNN in both intervention groups (See Table 1). The increase in SDNNindicates that cardiac sympathetic over-activation was suppressed andvagal activity was enhanced with the result of stabilizing cardiacelectrical activity, decreasing malignant arrhythmias, thereby reducingthe incidence of sudden death.Secondly, we found that RD blocked both peripheral and centralRAAS and sympathetic nervous system (SNS) at the same time. Andthis may answer the question how RD exerted effect on CANS. In ourstudy RD restores renin, angiotensin II, and aldosterone to near-normal levels. This not only explains the increase in sodium and waterexcretion, but also confirms that RD blocks renal RAAS via blockage ofthe efferent renal sympathetic nerves which is consistent with ourprevious study [2]. Studies have shown that angiotensin II not onlyactivates the central and peripheral SNS, function as part of a positivefeedback cycle between RAAS and the SNS, but also activates the localRAAS of other organs, notably the heart [5]. Our study also showedthat the plasma NE level in MI-1d + RD and MI-4w + RD groupsdecreased significantly, which reflects an overall reduction ofsympathetic activity, and especially represents reduction of centralsympathetic activity. This result maybe in part due to blockade of therenal sympathetic afferent pathway by RD. Furthermore, previousstudies have shown that during HF, the tissue NE levels of both theheart and kidney are decreased due to depletion, decreased reuptakeand increased spillover. The decrease of the tissue NE level causedfeedback activation of the central sympathetic system [6].Thus,increased tissue NE level may alleviate the activation of the centralsympathetic system, which was reflected by our data (Fig. 1).Many studies have shown that central RAAS stimulates the central

Abstract 538: Prolonged Functional Sympathetic Efferent Denervation Following Ablation of the Renal Nerves in SHR

Renal denervation (RDN) has been shown to be an effective and safe treatment for human resistant hypertension and is considered one of the most promising advances in the field of hypertension. However, the mechanisms mediating the sustained decrease in arterial pressure in response to RDN in humans are unknown. This issue is particularly perplexing, given reports that the depressor effect of RDN in animal models is short lived. The current dogma in the literature is that overtime the efferent sympathetic nerves regrow and so the longevity of the depressor effect of RDN in humans cannot be ascribed to the absence of efferent renal sympathetic nerve activity. We hypothesize that the renal sympathetic nerves regenerate following RDN, and arrive at the target tissues, but the functional response is not fully restored and this contributes to the long-term depressor effect of RDN. Our aim was to examine mean arterial pressure (MAP) and vascular function in spontaneously hypertensive rats (SHR) following RDN. In 10 week old male SHR radiotelemetry probes were implanted to measure MAP. At 12 weeks of age, following 3 days basal MAP recording, sham (n=5) or bilateral RDN (n=5) surgery was performed. MAP was recorded until 24 weeks of age (12 weeks post-RDN). Renal lobar arteries were mounted on a myograph and membrane potential and tension responses to perivascular nerve stimulation assessed. Perivascular nerve stimulation with single pulses at increasing voltage evoked excitatory junction potentials (Ejps) of increasing amplitude in SHR-sham. Ejp amplitude was markedly reduced in arteries from SHR-RDN (P&lt;0.01). Repetitive stimulation (1-8Hz, 5s) evoked slow depolarisation and contraction. At 5Hz 5s, slow depolarisation was 12±2 mV in SHR-shams and 7±2 mV in SHR-RDN (P&lt;0.01), and contractions were smaller than SHR-sham (10 ± 3% vs 22 ± 2% HiK; P&lt;0.01). In conclusion, smaller Ejps suggest that close contacting neuroeffector junctions are not reformed and blunted vasoconstrictor responses indicate neuro-vascular function has only partially returned 12 weeks post-RDN (Fig. 2). Our finding of continued ‘functional’ denervation is compatible with our data that RDN causes a sustained decrease in arterial pressure in SHR.

Renal Sympathetic Denervation and Renal Physiology

The sympathetic nervous system has a profound effect on the kidney's ability to regulate blood pressure and, vice versa, the kidney has an important effect on the overall sympathetic tone. As a result, renal sympathetic nerves are crucial for initiation and the maintenance of systemic hypertension. It is fairly well established that efferent renal sympathetic nerve activity contributes significantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. The afferent nerves from the kidney activate central sympathetic nervous system activity, participate in a reflex control system via reno-renal reflexes and are involved in cardiovascular regulation and pathogenesis of hypertension in CKD patients whose kidney ischemia also seems to play a key role. Sympathetic nerve modulation in hypertension had been considered as a therapeutic strategy long before the advent of modern pharmacological therapies. Renal sympathetic denervation with a percutaneous, catheter-based approach results in significant and sustained blood pressure reduction in patients with resistant hypertension. This procedure has also beneficial effects in multiple organs function. However, renal physiology and the long term observed benefits with the use of renal sympathetic denervation have not completely elucidated.

Mechanisms of cardiovascular actions of urocortins in the hypothalamic arcuate nucleus of the rat

The presence of urocortins (UCNs) and corticotropin-releasing factor (CRF) receptors has been reported in the hypothalamic arcuate nucleus (ARCN). We have previously reported that UCNs are involved in central cardiovascular regulation. Based on this information, we hypothesized that the ARCN may be one of the sites where UCNs exert their central cardiovascular actions. Experiments were done in artificially ventilated, adult male Wistar rats anesthetized with urethane. Unilateral microinjections (30 nl) of UCN1 (0.12-2 mM) elicited decreases in mean arterial pressure (MAP) and heart rate (HR). Maximum cardiovascular responses were elicited by a 1 mM concentration of UCN1. Microinjections of UCN2 and UCN3 (1 mM each) into the ARCN elicited similar decreases in MAP and HR. UCN1 was used as a prototype for the other experiments described below. HR responses elicited by UCN1 were significantly attenuated by bilateral vagotomy. Prior microinjections of NBI-27914 (CRF-1 receptor antagonist) and astressin (CRF-1 receptor and CRF-2 receptor antagonist) (1 mM each) into the ARCN significantly attenuated the cardiovascular responses elicited by UCN1 microinjections at the same site. Microinjections of UCN1 into the ARCN decreased efferent renal sympathetic nerve activity. It was concluded that microinjections of UCN1, UCN2, and UCN3 into the ARCN elicited decreases in MAP and HR. Decreases in MAP, HR, and renal sympathetic nerve activity elicited by UCN1 microinjections into the ARCN were mediated via CRF receptors. Bradycardic responses to UCN1 were mediated via the activation of vagus nerves, and decreases in MAP may be mediated via decreases in sympathetic nerve activity.