Specific Afferent Renal Denervation Prevents Reduction in Neuronal Nitric Oxide Synthase Within the Paraventricular Nucleus in Rats With Chronic Heart Failure

A kidney-brain neural circuit drives progressive kidney damage and heart failure

Chronic kidney disease (CKD) and heart failure (HF) are highly prevalent, aggravate each other, and account for substantial mortality. However, the mechanisms underlying cardiorenal interaction and the role of kidney afferent nerves and their precise central pathway remain limited. Here, we combined virus tracing techniques with optogenetic techniques to map a polysynaptic central pathway linking kidney afferent nerves to subfornical organ (SFO) and thereby to paraventricular nucleus (PVN) and rostral ventrolateral medulla that modulates sympathetic outflow. This kidney-brain neural circuit was overactivated in mouse models of CKD or HF and subsequently enhanced the sympathetic discharge to both the kidney and the heart in each model. Interruption of the pathway by kidney deafferentation, selective deletion of angiotensin II type 1a receptor (AT1a) in SFO, or optogenetic silence of the kidney-SFO or SFO-PVN projection decreased the sympathetic discharge and lessened structural damage and dysfunction of both kidney and heart in models of CKD and HF. Thus, kidney afferent nerves activate a kidney-brain neural circuit in CKD and HF that drives the sympathetic nervous system to accelerate disease progression in both organs. These results demonstrate the crucial role of kidney afferent nerves and their central connections in engaging cardiorenal interactions under both physiological and disease conditions. This suggests novel therapies for CKD or HF targeting this kidney-brain neural circuit.

Potential Neuromodulation of the Cardio-Renal Syndrome

The cardio-renal syndrome (CRS) type 2 is defined as a progressive loss of renal function following a primary insult to the myocardium that may be either acute or chronic but is accompanied by a decline in myocardial pump performance. The treatment of patients with CRS is difficult, and the disease often progresses to end-stage renal disease that is refractory to conventional therapy. While a good deal of information is known concerning renal injury in the CRS, less is understood about how reflex control of renal sympathetic nerve activity affects this syndrome. In this review, we provide insight into the role of the renal nerves, both from the afferent or sensory side and from the efferent side, in mediating renal dysfunction in CRS. We discuss how interventions such as renal denervation and abrogation of systemic reflexes may be used to alleviate renal dysfunction in the setting of chronic heart failure. We specifically focus on a novel cardiac sensory reflex that is sensitized in heart failure and activates the sympathetic nervous system, especially outflow to the kidney. This so-called Cardiac Sympathetic Afferent Reflex (CSAR) can be ablated using the potent neurotoxin resinferitoxin due to the high expression of Transient Receptor Potential Vanilloid 1 (TRPV1) receptors. Following ablation of the CSAR, several markers of renal dysfunction are reversed in the post-myocardial infarction heart failure state. This review puts forth the novel idea of neuromodulation at the cardiac level in the treatment of CRS Type 2.

Contribution of afferent renal nerve signals to acute and chronic blood pressure regulation in stroke-prone spontaneously hypertensive rats

The activation of sympathetic nervous system plays a critical role in the development of hypertension. The input from afferent renal nerves may affect central sympathetic outflow; however, its contribution to the development of hypertension remains unclear. We investigated the role of afferent renal nerves in acute and chronic blood pressure regulation using normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Acute chemical stimulation of afferent renal nerves elicited larger increases in blood pressure and renal sympathetic nerve activity in young 9-week-old SHRSP compared to WKY. Selective afferent renal denervation (ARDN) and conventional total renal denervation (TRDN) ablating both afferent and efferent nerves in young SHRSP revealed that only TRDN, but not ARDN, chronically attenuated blood pressure elevation. ARDN did not affect plasma renin activity or plasma angiotensin II levels, whereas TRDN decreased both. Neither TRDN nor ARDN affected central sympathetic outflow and systemic sympathetic activity determined by neuronal activity in the parvocellular region of hypothalamic paraventricular nucleus and rostral ventrolateral medulla and by plasma and urinary norepinephrine levels, respectively. Renal injury was not apparent in young SHRSP compared with WKY, suggesting that renal afferent input might not be activated in young SHRSP. In conclusion, the chronic input from afferent renal nerves does not contribute to the development of hypertension in SHRSP despite the increased blood pressure response to the acute stimulation of afferent renal nerves. Efferent renal nerves may be involved in the development of hypertension via activation of the renin-angiotensin system in SHRSP.

Consensus and inconsistency between different consensus documents on renal denervation worldwide: the way forward

ABSTRACT

Given the unsatisfactory hypertension control rates and high rates of non-adherence to antihypertensive medications worldwide, device therapy which can safely provide durable blood pressure-lowering effects can fulfill the unmet need. A series of second-generation randomized sham-controlled renal denervation (RDN) trials have demonstrated the efficacy and safety of RDN in a wide range of hypertensive patients. The four representative consensus documents on RDN (from the Chinese Taiwan Hypertension Society and Taiwan Society of Cardiology [THS/TSOC 2019], Asia Renal Denervation Consortium 2019, European Society of Hypertension [ESH 2021], and Society for Cardiovascular Angiography & Intervention and National Kidney Foundation [SCAI/NKF 2021]) consistently recommend RDN as an alternative or complementary treatment strategy for patients with uncontrolled hypertension. In addition, both documents from Asia further recommend that RDN can be considered as an initial treatment strategy for drug-naïve hypertensive patients. There is still inconsistency regarding whether ambulatory blood pressure monitoring should be used routinely both before and after RDN, and whether patients with a secondary cause of hypertension could be treated with RDN if their blood pressure remains uncontrolled after definitive treatment (treatment-resistant secondary hypertension). The THS/TSOC consensus provides acronyms to summarize key aspects of patient selection (RDNi2) and pre-RDN assessments (RAS). The ESH and SCAI/NKF documents recommend establishing structured pathways for clinical practice and issues regarding reimbursement. All documents identify knowledge gaps in RDN, from identifying predictors of super-responders to demonstrating effects on cardiovascular events. These gaps should be urgently filled to facilitate the wider application of this device therapy for patients with hypertension.

Effects and mechanism of renal denervation on ventricular arrhythmia after acute myocardial infarction in rats

BACKGROUND

Renal denervation (RDN) can reduce ventricular arrhythmia after acute myocardial infarction (AMI), but the mechanism is not clear. The purpose of this study is to study its mechanism.

METHODS

Thirty-two Sprague-Dawley rats were divided into four groups: control group, AMI group, RDN-1d + AMI group, RDN-2w + AMI group. The AMI model was established 1 day after RDN in the RDN-1d + AMI group and 2 weeks after RDN in the RDN-2w + AMI group. At the same time, 8 normal rats were subjected to AMI modelling (the AMI group). The control group consisted of 8 rats without RDN intervention or AMI modelling.

RESULTS

The study confirmed that RDN can reduce the occurrence of ventricular tachycardia in AMI rats, reduce renal sympathetic nerve discharge, and inhibit the activity of local sympathetic nerves and cell growth factor (NGF) protein expression in the heart after AMI. In addition, RDN decreased the expression of norepinephrine (NE) and glutamate in the hypothalamus,and NE in cerebrospinal fluid, and increased the expression level of γ aminobutyric acid (GABA) in the hypothalamus after AMI.

CONCLUSION

RDN can effectively reduce the occurrence of ventricular arrhythmia after AMI, and its main mechanism may be via the inhibition of central sympathetic nerve discharge.

Update on Hypertension Research in 2021

In 2021, 217 excellent manuscripts were published in Hypertension Research. Editorial teams greatly appreciate the authors' contribution to hypertension research progress. Here, our editorial members have summarized twelve topics from published work and discussed current topics in depth. We hope you enjoy our special feature, "Update on Hypertension Research in 2021".

Cardiorenal Syndrome: The Role of Neural Connections Between the Heart and the Kidneys

The maintenance of cardiovascular homeostasis is highly dependent on tightly controlled interactions between the heart and the kidneys. Therefore, it is not surprising that a dysfunction in one organ affects the other. This interlinking relationship is aptly demonstrated in the cardiorenal syndrome. The characteristics of the cardiorenal syndrome state include alterations in neurohumoral drive, autonomic reflexes, and fluid balance. The evidence suggests that several factors contribute to these alterations. These may include peripheral and central nervous system abnormalities. However, accumulating evidence from animals with experimental models of congestive heart failure and renal dysfunction as well as humans with the cardiorenal syndrome suggests that alterations in neural pathways, from and to the kidneys and the heart, including the central nervous system are involved in regulating sympathetic outflow and may be critically important in the alterations in neurohumoral drive, autonomic reflexes, and fluid balance commonly observed in the cardiorenal syndrome. This review focuses on studies implicating neural pathways, particularly the afferent and efferent signals from the heart and the kidneys integrating at the level of the paraventricular nucleus in the hypothalamus to alter neurohumoral drive, autonomic pathways, and fluid balance. Further, it explores the potential mechanisms of action for the known beneficial use of various medications or potential novel therapeutic manipulations for the treatment of the cardiorenal syndrome. A comprehensive understanding of these mechanisms will enhance our ability to treat cardiorenal conditions and their cardiovascular complications more efficaciously and thoroughly.

New Insights Into the Role of Inflammation in the Brain in Heart Failure

Heart failure is a growing medical problem. Although the underlying aetiology of heart failure differs according to the phenotype, there are some common characteristics observed in patients with heart failure. These include an increased sympathetic nerve activity, an activated renin–angiotensin system, and inflammation. The mechanisms mediating the increased sympathetic activity are not completely understood but the central nervous system plays a major role. Activation of the renin–angiotensin system plays an active role in the remodelling of the heart and in fluid and electrolyte imbalance. The presence of a central renin–angiotensin system means that locally produced angiotensin in the brain may also play a key role in autonomic dysfunction seen in heart failure. Markers of inflammation in the heart and in the circulation are observed in patients diagnosed with heart failure. Circulating pro-inflammatory cytokines can also influence cardiac function further afield than just locally in the heart including actions within the brain to activate the sympathetic nervous system. Preclinical evidence suggests that targeting the pro-inflammatory cytokines would be a useful therapy to treat heart failure. Most clinical studies have been disappointing. This mini-review suggests that pro-inflammatory cytokines in the brain play a key role and there is a problem associated with access of effective doses of the drugs to the site of action in the brain. The recent advances in nanotechnology delivery techniques may provide exciting future technology to investigate the role of specific pro-inflammatory mediators as novel targets within the brain in the treatment of heart failure.

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.

Renal denervation reduces atrial remodeling in hypertensive rats with metabolic syndrome

Atrial fibrillation (AF) is highly prevalent in hypertensive patients with metabolic syndrome and is related to inflammation and activation of the sympathoadrenergic system. The multi-ligand Receptor-for-Advanced-Glycation-End-products (RAGE) activates inflammation-associated tissue remodeling and is regulated by the sympathetic nervous system. Its counterpart, soluble RAGE (sRAGE), serves as anti-inflammatory decoy receptor with protective properties. We investigated the effect of sympathetic modulation by renal denervation (RDN) on atrial remodeling, RAGE/sRAGE and RAGE ligands in metabolic syndrome. RDN was performed in spontaneously hypertensive obese rats (SHRob) with metabolic syndrome compared with lean spontaneously hypertensive rats (SHR) and with normotensive non-obese control rats. Blood pressure and heart rate were measured by telemetry. The animals were killed 12 weeks after RDN. Left atrial (LA) and right atrial (RA) remodeling was assessed by histological analysis and collagen types. Sympathetic innervation was measured by tyrosine hydroxylase staining of atrial nerve fibers, RAGE/sRAGE, RAGE ligands, cytokine expressions and inflammatory infiltrates were analyzed by Western blot and immunofluorescence staining. LA sympathetic nerve fiber density was higher in SHRob (+44%) versus controls and reduced after RDN (-64% versus SHRob). RAGE was increased (+718%) and sRAGE decreased (- 62%) in SHRob as compared with controls. RDN reduced RAGE expression (- 61% versus SHRob), significantly increased sRAGE levels (+162%) and induced a significant decrease in RAGE ligand levels in SHRob (- 57% CML and - 51% HMGB1) with reduced pro-inflammatory NFkB activation (- 96%), IL-6 production (- 55%) and reduced inflammatory infiltrates. This led to a reduction in atrial fibrosis (- 33%), collagen type I content (- 72%), accompanied by reduced LA myocyte hypertrophy (- 21%). Transfection experiments on H9C2 cardiomyoblasts demonstrated that RAGE is directly involved in fibrosis formation by influencing cellular production of collagen type I. In conclusion, suppression of renal sympathetic nerve activity by RDN prevents atrial remodeling in metabolic syndrome by reducing atrial sympathetic innervation and by modulating RAGE/sRAGE balance and reducing pro-inflammatory and pro-fibrotic RAGE ligands, which provides a potential therapeutic mechanism to reduce the development of AF.

Renal denervation based on experimental rationale

Excessive activation of the sympathetic nervous system is one of the pathophysiological hallmarks of hypertension and heart failure. Within the central nervous system, the paraventricular nucleus (PVN) of the hypothalamus and the rostral ventrolateral medulla in the brain stem play critical roles in the regulation of sympathetic outflow to peripheral organs. Information from the peripheral circulation, including serum concentrations of sodium and angiotensin II, is conveyed to the PVN via adjacent structures with a weak blood-brain barrier. In addition, signals from baroreceptors, chemoreceptors and cardiopulmonary receptors as well as afferent input via the renal nerves are all integrated at the level of the PVN. The brain renin-angiotensin system and the balance between nitric oxide and reactive oxygen species in these brain areas also determine the final sympathetic outflow. Additionally, brain inflammatory responses have been shown to modulate these processes. Renal denervation interrupts both the afferent inputs from the kidney to the PVN and the efferent outputs from the PVN to the kidney, resulting in the suppression of sympathetic outflow and eliciting beneficial effects on both hypertension and heart failure.

Effects of salt intake on sympathetic neural and pressor responses to cold pressor test in premenopausal women with a history of normal pregnancy

Excessive salt intake is considered a risk factor for the development of hypertension. Additionally, aberrant neurocirculatory responses to a cold stimulus are associated with an increased risk of hypertension. This study aimed to determine whether salt loading versus salt reduction would impact hemodynamic and sympathetic neural responses during the cold pressor test (CPT) in premenopausal women with a history of normal pregnancy. Nine healthy premenopausal women [42 ± 3 (SD) yr] were given a standardized isocaloric high-salt (HS; 250 mEq sodium/day) or low-salt (LS; 50 mEq sodium/day) diet for 1-wk each (∼2 mo apart with the order randomized), while water intake was ad libitum. Laboratory testing was performed following each HS and LS period in the mid-luteal phase of the menstrual cycle. Subjects were in the supine position and beat-by-beat blood pressure (BP), heart rate (HR), and muscle sympathetic nerve activity (MSNA) were continuously measured during 1-min baseline followed by 2-min CPT, and 3-min recovery. BP and HR increased during the CPT (both P < 0.001); the responses were similar between HS and LS. MSNA increased during the CPT, but the increment (Δ) was greater during HS than LS (29 ± 6 vs. 15 ± 4 bursts/min; P < 0.001). The transduction of MSNA for vasoconstriction during the CPT was lower in HS (P < 0.05). Thus, salt loading augments sympathetic neural reactivity to the cold stimulus with similar pressor responses compared with salt reduction, which may be attributed to the blunted neurovascular transduction-a compensatory mechanism for hemodynamic homeostasis in premenopausal women with a history of normal pregnancy.

The involvement of renal afferents in the maintenance of cardiorenal diseases

Elevated sympathetic vasomotor activity is a common feature of cardiorenal diseases. Therefore, the sympathetic nervous system is an important therapeutic target, particularly the fibers innervating the kidneys. In fact, renal denervation has been applied clinically and shown promising results in patients with hypertension and chronic kidney disease. However, the underlying mechanisms involved in the cardiorenal protection induced by renal denervation have not yet been fully clarified. This mini-review highlights historical and recent aspects related to the role of renal sensory fibers in the control of cardiorenal function under normal conditions and in experimental models of cardiovascular disease. Results have demonstrated that alterations in renal sensory function participate in the maintenance of elevated sympathetic vasomotor activity and cardiorenal changes; as such, renal sensory fibers may be a potential therapeutic target for the treatment of cardiorenal diseases. Although it has not yet been applied in clinical practice, selective afferent renal denervation may be promising, since such an approach maintains efferent activity and can provide more refined control of renal function compared with total renal denervation. However, more studies are needed to understand the mechanisms by which renal afferents partially contribute to such changes, in addition to the need to evaluate the safety and advantages of the approach for application in the clinical practice.

Renal Sensory Activity Regulates the γ-Aminobutyric Acidergic Inputs to the Paraventricular Nucleus of the Hypothalamus in Goldblatt Hypertension

Renal sensory activity is centrally integrated within brain nuclei involved in the control of cardiovascular function, suggesting that renal afferents regulate basal and reflex sympathetic vasomotor activity. Evidence has shown that renal deafferentation (DAx) evokes a hypotensive and sympathoinhibitory effect in experimental models of cardiovascular diseases; however, the underlying mechanisms involved in this phenomenon need to be clarified, especially those related to central aspects. We aimed to investigate the role of renal afferents in the control of γ-aminobutyric acid (GABA)ergic inputs to the paraventricular nucleus (PVN) of the hypothalamus in renovascular hypertensive (2K1C) rats and their influence in the regulation of cardiovascular function. Hypertension was induced by clipping the left renal artery. After 4 weeks, renal DAx was performed by exposing the left renal nerve to a 33 mM capsaicin solution for 15 min. After 2 weeks of DAx, microinjection of muscimol into the PVN was performed in order to evaluate the influence of GABAergic activity in the PVN and its contribution to the control of renal sympathetic nerve activity (rSNA) and blood pressure (BP). Muscimol microinjected into the PVN triggered a higher drop in BP and rSNA in the 2K1C rats and renal DAx mitigated these responses. These results suggest that renal afferents are involved in the GABAergic changes found in the PVN of 2K1C rats. Although the functional significance of this phenomenon needs to be clarified, it is reasonable to speculate that GABAergic alterations occur to mitigate microglia activation-induced sympathoexcitation in the PVN of 2K1C rats.

Sympathoexcitatory input from hypothalamic paraventricular nucleus neurons projecting to rostral ventrolateral medulla is enhanced after myocardial infarction

Elevated sympathetic vasomotor tone seen in heart failure (HF) may involve dysfunction of the hypothalamic paraventricular nucleus neurons that project to the rostral ventrolateral medulla (PVN-RVLM neurons). This study aimed to elucidate the role of PVN-RVLM neurons in the maintenance of resting renal sympathetic nerve activity (RSNA) after myocardial infarction (MI). In male rats, the left coronary artery was chronically ligated to induce MI. The rats received PVN microinjections of an adeno-associated viral (AAV) vector encoding archaerhodopsin T (ArchT) with the reporter yellow fluorescence protein (eYFP). The ArchT rats had abundant distributions of eYFP-labeled, PVN-derived axons in the RVLM. In anesthetized ArchT rats with MI (n = 12), optogenetic inhibition of the PVN-RVLM pathway achieved by 532-nm-wavelength laser illumination to the RVLM significantly decreased RSNA. This effect was not found in sham-operated ArchT rats (n = 6). Other rat groups received RVLM microinjections of a retrograde AAV vector encoding the red light-drivable halorhodopsin Jaws (Jaws) with the reporter green fluorescence protein (GFP) and showed expression of GFP-labeled cell bodies and dendrites in the PVN. Laser illumination of the PVN at a 635 nm wavelength elicited significant renal sympathoinhibition in Jaws rats with MI (n = 9) but not in sham-operated Jaws rats (n = 8). These results indicate that sympathoexcitatory input from PVN-RVLM neurons is enhanced after MI, suggesting that this monosynaptic pathway is part of the central nervous system circuitry that plays a critical role in generating an elevated sympathetic vasomotor tone commonly seen with HF.NEW & NOTEWORTHY Using optogenetics in rats, we report that sympathoexcitatory input from hypothalamic paraventricular nucleus neurons that project to the rostral ventrolateral medulla is enhanced after myocardial infarction. It is suggested that this monosynaptic pathway makes up a key part of central nervous system circuitry underlying sympathetic hyperactivation commonly seen in heart failure.

MMP9 inhibition increases autophagic flux in chronic heart failure

Increased matrix metalloprotease 9 (MMP9) after myocardial infarction (MI) exacerbates ischemia-induced chronic heart failure (CHF). Autophagy is cardioprotective during CHF; however, whether increased MMP9 suppresses autophagic activity in CHF is unknown. This study aimed to determine whether increased MMP9 suppressed autophagic flux and MMP9 inhibition increased autophagic flux in the heart of rats with post-MI CHF. Sprague-Dawley rats underwent either sham surgery or coronary artery ligation 6-8 wk before being treated with MMP9 inhibitor for 7 days, followed by cardiac autophagic flux measurement with lysosomal inhibitor bafilomycin A1. Furthermore, autophagic flux was measured in vitro by treating H9c2 cardiomyocytes with two independent pharmacological MMP9 inhibitors, salvianolic acid B (SalB) and MMP9 inhibitor-I, and CRISPR/cas9-mediated MMP9 genetic ablation. CHF rats showed cardiac infarct, significantly increased left ventricular end-diastolic pressure (LVEDP), and increased MMP9 activity and fibrosis in the peri-infarct areas of left ventricular myocardium. Measurement of the autophagic markers LC3B-II and p62 with lysosomal inhibition showed decreased autophagic flux in the peri-infarct myocardium. Treatment with SalB for 7 days in CHF rats decreased MMP9 activity and cardiac fibrosis but increased autophagic flux in the peri-infarct myocardium. As an in vitro corollary study, measurement of autophagic flux in H9c2 cardiomyocytes and fibroblasts showed that pharmacological inhibition or genetic ablation of MMP9 upregulates autophagic flux. These data are consistent with our observations that MMP9 inhibition upregulates autophagic flux in the heart of rats with CHF. In conclusion, the results in this study suggest that the beneficial outcome of MMP9 inhibition in pathological cardiac remodeling is in part mediated by improved autophagic flux.NEW & NOTEWORTHY This study elucidates that the improved cardiac extracellular matrix (ECM) remodeling and cardioprotective effect of matrix metalloprotease 9 (MMP9) inhibition in chronic heart failure (CHF) are via increased autophagic flux. Autophagy is cardioprotective; however, the mechanism of autophagy suppression in CHF is unknown. We for the first time demonstrated here that increased MMP9 suppressed cardiac autophagy and ablation of MMP9 increased cardiac autophagic flux in CHF rats. Restoring the physiological level of autophagy in the failing heart is a challenge, and our study addressed this challenge. The novelty and highlights of this report are as follows: 1) MMP9 regulates cardiomyocyte and fibroblast autophagy, 2) MMP9 inhibition protects CHF after myocardial infarction (MI) via increased cardiac autophagic flux, 3) MMP9 inhibition increased cardiac autophagy via activation of AMP-activated protein kinase (AMPK)α, Beclin-1, Atg7 pathway and suppressed mechanistic target of rapamycin (mTOR) pathway.

Salt intake impacts sympathetic neural control but not morning blood pressure surge in premenopausal women with a history of normal pregnancy

Salt intake may alter blood pressure (BP) regulation, but no study has investigated the impact of salt reduction versus salt loading on morning blood pressure surge (MBPS) and sympathetic neural control in premenopausal women with a history of normal pregnancy. Nine healthy women (42 ± 3 yr; mean ± SD) were given a low-salt diet (LS; 50 mEq sodium/day) and high-salt diet (HS; 250 mEq sodium/day) for 1 wk each (~2 mo apart with the order randomized), while water intake was ad libitum. Ambulatory BP at 24 h was measured, and the percent change in blood volume (BV) was calculated following LS and HS. MBPS was defined as the morning systolic BP (averaged for 2 h after wake-up) minus the lowest nocturnal systolic BP. Beat-by-beat BP, heart rate, and muscle sympathetic nerve activity (MSNA) were measured during supine rest. Signal averaging was used to characterize changes in beat-by-beat mean arterial pressure and total vascular conductance following spontaneous MSNA bursts to assess sympathetic vascular transduction. Ambulatory BP and MBPS (32 ± 7 vs. 26 ± 12 mmHg, P = 0.208) did not differ between LS and HS. From LS to HS, BV increased by 4.3 ± 3.7% (P = 0.008). MSNA (30 ± 20 vs. 18 ± 13 bursts/100 heartbeats, P = 0.005) was higher, whereas sympathetic vascular transduction was lower in LS than HS (both, P < 0.01). Changes in MSNA from LS to HS were correlated to percent changes in BV (r = -0.673; P = 0.047). Thus, salt intake affects sympathetic neural control but not MBPS in premenopausal women with a history of normal pregnancy. The underlying mechanisms remain unknown; however, alterations in sympathetic vascular transduction may, in part, contribute.NEW & NOTEWORTHY This is the first study to demonstrate that MBPS and ambulatory BP were not affected by salt intake despite a significant change in sympathetic outflow in healthy premenopausal women with a history of normal pregnancy. This may be due to compensatory adaptations in MSNA and sympathetic vascular transduction during salt reduction versus salt loading.

Three-dimensional morphometric analysis reveals time-dependent structural changes in microglia and astrocytes in the central amygdala and hypothalamic paraventricular nucleus of heart failure rats

BACKGROUND

Cardiovascular diseases, including heart failure, are the most common cause of death globally. Recent studies support a high degree of comorbidity between heart failure and cognitive and mood disorders resulting in memory loss, depression, and anxiety. While neuroinflammation in the hypothalamic paraventricular nucleus contributes to autonomic and cardiovascular dysregulation in heart failure, mechanisms underlying cognitive and mood disorders in this disease remain elusive. The goal of this study was to quantitatively assess markers of neuroinflammation (glial morphology, cytokines, and A1 astrocyte markers) in the central amygdala, a critical forebrain region involved in emotion and cognition, and to determine its time course and correlation to disease severity during the progression of heart failure.

METHODS

We developed and implemented a comprehensive microglial/astrocyte profiler for precise three-dimensional morphometric analysis of individual microglia and astrocytes in specific brain nuclei at different time points during the progression of heart failure. To this end, we used a well-established ischemic heart failure rat model. Morphometric studies were complemented with quantification of various pro-inflammatory cytokines and A1/A2 astrocyte markers via qPCR.

RESULTS

We report structural remodeling of central amygdala microglia and astrocytes during heart failure that affected cell volume, surface area, filament length, and glial branches, resulting overall in somatic swelling and deramification, indicative of a change in glial state. These changes occurred in a time-dependent manner, correlated with the severity of heart failure, and were delayed compared to changes in the hypothalamic paraventricular nucleus. Morphometric changes correlated with elevated mRNA levels of pro-inflammatory cytokines and markers of reactive A1-type astrocytes in the paraventricular nucleus and central amygdala during heart failure.

CONCLUSION

We provide evidence that in addition to the previously described hypothalamic neuroinflammation implicated in sympathohumoral activation during heart failure, microglia, and astrocytes within the central amygdala also undergo structural remodeling indicative of glial shifts towards pro-inflammatory phenotypes. Thus, our studies suggest that neuroinflammation in the amygdala stands as a novel pathophysiological mechanism and potential therapeutic target that could be associated with emotional and cognitive deficits commonly observed at later stages during the course of heart failure.

Impaired l-arginine-nitric oxide pathway contributes to the pathogenesis of resistant hypertension

The precise mechanisms underlying resistant hypertension remain elusive. Reduced nitric oxide (NO) bioavailability is frequently documented in chronic kidney disease, obesity, diabetes and advanced age, all of which are risk factors for resistant hypertension. Sympathetic overactivity and chronic activation of the renin-angiotensin system are salient features of resistant hypertension. Interestingly, recent data indicate that renal sympathetic overactivity can reduce the expression of neuronal nitric oxide synthase in the paraventricular nucleus. Reduced NO levels in the paraventricular nucleus can increase sympathetic outflow and this can create a vicious cycle contributing to resistant hypertension. Angiotensin II can reduce l-arginine transport and hence NO production. Reduced NO levels may reduce the formation of angiotensin 1-7 dampening the cardio-protective effects of the renin-angiotensin system contributing to resistant hypertension. In addition, interleukin-6 (IL-6) is demonstrated to be independently associated with resistant hypertension, and IL-6 can reduce NO synthesis. Despite this, NO levels have not been quantified in resistant hypertension. Findings from a small proof of concept study indicate that NO donors can reduce blood pressure in patients with resistant hypertension but more studies are required to validate these preliminary findings. In the present paper, we put forward the hypothesis that reduced NO bioavailability contributes substantially to the development of resistant hypertension.

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

Background

Glucagon-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.

Methods

HF 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.

Results

In 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).

Conclusions

The 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.

The Impact of Renal Denervation on the Progression of Heart Failure in a Canine Model Induced by Right Ventricular Rapid Pacing

Heart failure (HF) has been proposed as a potential indication of renal denervation (RDN). However, the mechanisms enabling RDN to attenuate HF are not well understood, especially the central effects of RDN. The aim of this study was to decipher the mode of operation of RDN in the treatment of HF using a canine model of right ventricular rapid pacing-induced HF. Accordingly, 24 Chinese Kunming dogs were randomly grouped to receive sham procedure (sham-operated group), bilateral RDN (RDN group), rapid pacing to induce HF (HF-control group), and bilateral RDN plus rapid pacing (RDN + HF group). Echocardiography, plasma brain natriuretic peptide (BNP), and norepinephrine (NE) concentrations of randomized dogs were measured at baseline and 4 weeks after interventions, followed by histological and molecular analyses. Twenty dogs completed the research successfully and were enrolled for data analyses. Results showed that the average optical density of renal efferent and afferent nerves were significantly lower in the RDN and RDN + HF groups than in the sham-operated group, with a significant reduction of renal NE concentration. Rapid pacing in the RDN + HF and HF-control groups, compared with the sham-operated group, induced a significant increase in left ventricular end-diastolic volume and decrease in left ventricular ejection fraction and correspondingly resulted in cardiac fibrosis and dysfunction. Cardiac fibrosis evaluated by Masson’s trichrome staining and the expression of transforming growth factor-β1 (TGF-β1) were significantly higher in the HF-control group than in the sham-operated group, which were remarkably attenuated by the application of the RDN technique in the RDN + HF group. In terms of central renin–angiotensin system (RAS), the expression of angiotensin II (AngII)/angiotensin-converting enzyme (ACE)/AngII type 1 receptor (AT1R) in the hypothalamus of dogs in the HF-control group, compared with the sham-operated group, was upregulated and that of the angiotensin-(1-7) [Ang-(1-7)]/ACE2 was downregulated. Furthermore, both of them were significantly attenuated by the RDN therapy in the RDN + HF group. In conclusion, the RDN technique could damage renal nerves and suppress the cardiac remodeling procedure in canine with HF while concomitantly attenuating the overactivity of central RAS in the hypothalamus.

Afferent innervation of the ischemic kidney contributes to renal dysfunction in renovascular hypertensive rats

The ablation of renal nerves, by destroying both the sympathetic and afferent fibers, has been shown to be effective in lowering blood pressure in resistant hypertensive patients. However, experimental studies have reported that the removal of sympathetic fibers may lead to side effects, such as the impairment of compensatory cardiorenal responses during a hemodynamic challenge. In the present study, we evaluated the effects of the selective removal of renal afferent fibers on arterial hypertension, renal sympathetic nerve activity, and renal changes in a model of renovascular hypertension. After 4 weeks of clipping the left renal artery, afferent renal denervation (ARD) was performed by exposing the left renal nerve to a 33 mM capsaicin solution for 15 min. After 2 weeks of ARD, we found reduced MAP (~ 18%) and sympathoexcitation to both the ischemic and contralateral kidneys in the hypertensive group. Moreover, a reduction in reactive oxygen species was observed in the ischemic (76%) and contralateral (27%) kidneys in the 2K1C group. In addition, ARD normalized renal function markers and proteinuria and podocin in the contralateral kidney. Taken altogether, we show that the selective removal of afferent fibers is an effective method to reduce MAP and improve renal changes without compromising the function of renal sympathetic fibers in the 2K1C model. Renal afferent nerves may be a new target in neurogenic hypertension and renal dysfunction.

Does glucagon-like peptide-1 induce diuresis and natriuresis by modulating afferent renal nerve activity?

Glucagon-like peptide-1 (GLP-1), an incretin hormone, has diuretic and natriuretic effects. The present study was designed to explore the possible underlying mechanisms for the diuretic and natriuretic effects of GLP-1 via renal nerves in rats. Immunohistochemistry revealed that GLP-1 receptors were avidly expressed in the pelvic wall, the wall being adjacent to afferent renal nerves immunoreactive to calcitonin gene-related peptide, which is the dominant neurotransmitter for renal afferents. GLP-1 (3 μM) infused into the left renal pelvis increased ipsilateral afferent renal nerve activity (110.0 ± 15.6% of basal value). Intravenous infusion of GLP-1 (1 µg·kg^-1·min^-1) for 30 min increased renal sympathetic nerve activity (RSNA). After the distal end of the renal nerve was cut to eliminate the afferent signal, the increase in efferent renal nerve activity during intravenous infusion of GLP-1 was diminished compared with the increase in total RSNA (17.0 ± 9.0% vs. 68.1 ± 20.0% of the basal value). Diuretic and natriuretic responses to intravenous infusion of GLP-1 were enhanced by total renal denervation (T-RDN) with acute surgical cutting of the renal nerves. Selective afferent renal nerve denervation (A-RDN) was performed by bilateral perivascular application of capsaicin on the renal nerves. Similar to T-RDN, A-RDN enhanced diuretic and natriuretic responses to GLP-1. Urine flow and Na⁺ excretion responses to GLP-1 were not significantly different between T-RDN and A-RDN groups. These results indicate that the diuretic and natriuretic effects of GLP-1 are partly governed via activation of afferent renal nerves by GLP-1 acting on sensory nerve fibers within the pelvis of the kidney.