Selective afferent renal denervation mitigates renal and splanchnic sympathetic nerve overactivity and renal function in chronic kidney disease-induced hypertension

Renal denervation: a key approach to hypertension and cardiovascular disease

Sympathetic activation plays a critical role in the development of hypertension and cardiovascular disease, including heart failure and arrhythmias. Renal nerves contribute to the regulation of blood pressure and fluid volume through renal sympathetic efferent nerves, and to the modulation of sympathetic outflow through renal sensory afferent nerves. Previous studies including ours suggest that selective afferent renal denervation with preservation of efferent renal nerves can significantly decrease central sympathetic outflow in animal models of hypertension with renal damage. In Dahl salt-sensitive rats fed high salt diet from an early age, a model of hypertensive heart failure, this central sympathoinhibition by afferent renal denervation may attenuate the development of heart failure without significant blood pressure reduction. Accumulating clinical evidence supports the efficacy of renal denervation as an antihypertensive treatment. However, it remains important to clarify the appropriate indications and predictors of responders to renal denervation in the treatment of hypertension. Several clinical studies suggest beneficial effects of renal denervation in patients with heart disease, with or without hypertension, although most were not sham-controlled. In particular, some clinical studies have demonstrated that renal denervation reduces the incidence of atrial fibrillation or cardiovascular events even without a significant antihypertensive effect. It is essential to accumulate more insightful data in patients undergoing renal denervation, to establish the efficacy of renal denervation in patients with cardiovascular disease in the clinical setting, and to elucidate the therapeutic mechanisms of renal denervation and the renal nerves-linked pathophysiology of cardiovascular disease in basic research. This review outlines the effects of renal denervation on sympathetic activity and organ damage in animal models of hypertension and hypertensive heart failure, including our own data. Beyond the antihypertensive effects, the beneficial effects of renal denervation on cardiovascular disease are also discussed based on clinical studies. Several animal and clinical studies suggest the cardioprotective effects of renal denervation even in the absence of significant blood pressure reduction, probably due to its sympathoinhibitory effects.

Renal denervation for hypertensive heart disease and atrial fibrillation

Accumulating evidence supports the efficacy of renal denervation (RDN) as an antihypertensive treatment. Additionally, several RDN clinical studies, including meta-analyses, have suggested that RDN may potentially have beneficial effects on left ventricular hypertrophy, diastolic function, and new-onset/recurrence of atrial fibrillation (AF), although most studies were not randomized sham-controlled. In particular, the effects of RDN on left ventricular hypertrophy and AF recurrence appear to be relatively evident. Sympathetic activation plays a critical role in the development of hypertension, hypertensive heart disease, and AF. Notably, several studies suggest the cardioprotective effects of RDN even in the absence of significant blood pressure reduction, probably due to its sympathoinhibitory effects. It is imperative to establish the efficacy of RDN in patients with hypertensive heart disease and/or AF, focusing on parameters of sympathetic activity in the clinical setting, including randomized sham-controlled trials. Moreover, further basic research is essential to elucidate the therapeutic mechanisms of RDN beyond blood pressure lowering and the renal nerves-linked pathophysiologies of hypertensive heart disease and AF. This review outlines the effects of renal denervation on hypertensive heart disease, particularly on left ventricular hypertrophy and diastolic function, and on atrial fibrillation. The sympathoinhibitory effect of renal denervation, an important potential mechanism of its beneficial effects on heart disease, is also discussed.

Sympathetic Pathophysiology in Hypertension Origins: The Path to Renal Denervation

The importance of the sympathetic nervous system in essential hypertension has been recognized in 2 eras. The first was in early decades of the 20th century, through to the 1960s. Here, the sympathetic nervous system was identified as a target for the treatment of hypertension, and an extensive range of antiadrenergic therapies were developed. Then, after a period of lapsed interest, in a second era from 1985 on, the development of precise measures of human sympathetic nerve firing and transmitter release allowed demonstration of the importance of neural mechanisms in the initiation and maintenance of the arterial blood pressure elevation in hypertension. This led to the development of a device treatment of hypertension, catheter-based renal denervation, which we will discuss.

Neuroimmune interplay in kidney health and disease: Role of renal nerves

Renal nerves and their role in physiology and disease have been a topic of increasing interest in the past few decades. Renal inflammation contributes to many cardiorenal disease conditions, including hypertension, chronic kidney disease, and polycystic kidney disease. Much is known about the role of renal sympathetic nerves in physiology - they contribute to the regulation of sodium reabsorption, renin release, and renal vascular resistance. In contrast, far less is known about afferent, or "sensory," renal nerves, which convey signals from the kidney to the brain. While much remains unknown about these nerves in the context of normal physiology, even less is known about their contribution to disease states. Furthermore, it has become apparent that the crosstalk between renal nerves and the immune system may augment or modulate disease. Research from other fields, especially pain research, has provided critical insight into neuroimmune crosstalk. Sympathetic renal nerve activity may increase immune cell recruitment, but far less work has been done investigating the interplay between afferent renal nerves and the immune system. Evidence from other fields suggests that inflammation may augment afferent renal nerve activity. Furthermore, these nerves may exacerbate renal inflammation through the release of afferent-specific neurotransmitters.

[Five-year dynamics adrenergic reactivity of erythrocytes after radio-frequency sympathic denervation of renal arteries in patients with resistant arterial hypertension]

AIM

To study the initial state of adrenergic reactivity and the five-year dynamics of the beta-adrenergic reactivity index of erythrocyte membranes and the manifestation of the antihypertensive effect of the procedure for radiofrequency destruction of sympathetic structures of the renal artery in patients with resistant arterial hypertension.

SUBJECTS AND METHODS

The analysis included 42 patients with resistant arterial hypertension (RH). The renal denervation (RD) procedure of the kidneys was performed by endovascular bilateral transcatheter radiofrequency ablation of the renal arteries. The study of 24-hour blood pressure monitoring (BPM) and the determination of β-adrenoreactivity of erythrocytes (β-ARM) by changes in the osmoresistance of erythrocyte membranes were performed initially, 1 week, 6 months, 1, 2, 3 and 5 years after RD. Patients retrospectively, at a follow-up period of 6 months after RD, were divided into responders (decrease in blood pressure by 10 or more mm Hg) and non-responders (decrease in blood pressure less than 10 mm Hg).

RESULTS

6 months after the RD, the number of responders was 28 people (66.7%), after 5 years - 31 people (73.8%). At the time of inclusion in the study, the median β-ARM in the group of non-responders was not significantly higher than in the group of responders. After 6 months after the RD procedure, the β-ARM indicator in the non-responder group was significantly lower than in the responder group (p = 0.043). With further follow-up in the group of responders, an increase in the median β-ARM was noted, which reached significant differences relative to the baseline values in the group at follow-up periods of 1 year (p = 0.036) and 5 years (p = 0.004) after RD. The change in the β-ARM indicator in the non-responder group was wavy in nature, the changes did not reach the significance criteria.

CONCLUSION

Renal denervation in 73.8% of cases is accompanied by a stable antihypertensive response for 5 years of observation and an increase in β-ARM, which may indicate the implementation of compensatory mechanisms in conditions of increasing activity of the sympathoadrenal system in response to a decrease in blood pressure.

Renal nerve stimulation identifies renal innervation and optimizes the strategy for renal denervation in canine

BACKGROUND

Renal denervation (RDN) was still performed without any intra-procedural method for nerve mapping. Whether renal nerve stimulation (RNS) is an efficient way to identify renal autonomic innervation and optimize the strategy for RDN remain to be worthy for further exploration.

METHODS

The characteristics of renal autonomic innervation at the sites with different blood pressure (BP) responses to RNS were explored. Then, dogs anatomically eligible for RDN were randomly assigned into elevated BP response ablation group, reduced BP response ablation group, and RNS-control group. The postoperative outcomes were measured at baseline and after 4 weeks follow-up.

RESULTS

The proportion of afferent sensory nerve was higher at elevated BP response sites (ERS) than reduced BP response sites (RRS) and non-response sites (NRS) (P = 0.012 and P = 0.004). Conversely, the proportion of parasympathetic nerve at RRS was the highest (RRS vs. ERS, P = 0.017; RRS vs. NRS, P = 0.023). More importantly, there was a significant correlation between systolic blood pressure changes and the area ratios of afferent sensory and parasympathetic nerve (R = 0.859; P < 0.001). In addition, ablation at BP-elevation sites can result in a significant decrease in BP and plasma norepinephrine (NE) after 4 weeks (P = 0.002; P = 0.008), while ablation at BP-reduction sites can lead to significant increases in BP and plasma NE (P = 0.016; P = 0.033).

CONCLUSIONS

RNS is an effective method to identify renal autonomic innervation. It could not only help to identify optimal target sites, but also avoid ablation of sympathetic-inhibitory areas during RDN.

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.

Mixed circuit training acutely reduces arterial stiffness in patients with chronic stroke: a crossover randomized controlled trial

PURPOSE

Investigate whether a single bout of mixed circuit training (MCT) can elicit changes in arterial stiffness in patients with chronic stroke. Second, to assess the between-day reproducibility of post-MCT arterial stiffness measurements.

METHODS

Seven participants (58 ± 12 years) performed a non-exercise control session (CTL) and two bouts of MCT on separate days in a randomized counterbalanced order. The MCT involved 3 sets of 15 repetition maximum for 10 exercises, with each set separated by 45-s of walking. Brachial-radial pulse wave velocity (br-PWV), radial artery compliance (AC) and reflection index (RI_1,2) were assessed 10 min before and 60 min after CTL and MCT. Ambulatory arterial stiffness index (AASI) was calculated from 24-h recovery ambulatory blood pressure monitoring.

RESULTS

Compared to CTL, after 60 min of recovery from the 1st and 2nd bouts of MCT, lower values were observed for br-PWV (mean diff = - 3.9 and - 3.7 m/s, respectively, P < 0.01; ICC_2,1 = 0.75) and RI_1,2 (mean diff = - 16.1 and - 16.0%, respectively, P < 0.05; ICC_2,1 = 0.83) concomitant with higher AC (mean diff = 1.2 and 1.0 × 10^-6 cm⁵/dyna, respectively, P < 0.01; ICC_2,1 = 0.40). The 24-h AASI was reduced after bouts of MCT vs. CTL (1st and 2nd bouts of MCT vs. CTL: mean diff = - 0.32 and - 0.29 units, respectively, P < 0.001; ICC_2,1 = 0.64).

CONCLUSION

A single bout of MCT reduces arterial stiffness during laboratory (60 min) and ambulatory (24 h) recovery phases in patients with chronic stroke with moderate-to-high reproducibility.

TRIAL REGISTRATION

Ensaiosclinicos.gov.br identifier RBR-5dn5zd.

Insight on Efficacy of Renal Artery Denervation for Refractory Hypertension with Chronic Kidney Diseases: A Long-Term Follow-Up of 24-Hour Ambulatory Blood Pressure

Aims

To explore the long-term efficacy and safety of renal denervation in patients with RHT and CKD, a post hoc analysis of eGFR subgroups was completed.

Methods

Fifty-four patients with refractory hypertension with chronic kidney disease were treated with RDN and enrolled in the study. Patients were divided into three groups according to eGFR: eGFR 46–90 ml/min group, eGFR 15–45 ml/min group, and eGFR <15 ml/min group. The planned follow-up period was 48 months to assess 24 h ambulatory blood pressure, renal function, type of antihypertensive medication, and RDN complications.

Results

The ablation sites of the GFR 46–90 ml/min group and GFR 15–45 ml/min group were 32.57 ± 2.99 and 29.53 ± 5.47, respectively. No complications occurred in the GFR 46–90 ml/min group. The GFR<15 ml/min group was treated with 27.07 ± 5.59  ablation. Renal artery dissection occurred in each group of GFR 15–45 ml/min and GFR <15 ml/min. And renal stent implantation artery was performed on these two patients. No severe renal artery stenosis occurred. There were no significant differences in Scr and eGFR between the three groups at each follow-up point. Compared with baseline, SBP was significantly of each group decreased to varying degrees at each follow-up time point. SBP decreased most in the GFR 46–90 ml/min group. Compared with baseline, the type of antihypertensive drugs used in the GFR46-90 ml/min group decreased significantly except for 36 and 48 months. At 48 months' postadmission, there was a significant decrease in the type of antihypertensive medication used in the GFR15-45 ml/min group, and there was no significant decrease in the type of antihypertensive medication used in the GFR<15 ml/min group.

Conclusions

RDN can safely reduce SBP in CKD patients combined with RHT for 48 months, with the most pronounced reduction in the GFR15-45 ml/min group. The variety of antihypertensive drugs was significantly reduced after RDN. This was particularly evident in patients with GFR 15–45 ml/min.

Impact of Selective Renal Afferent Denervation on Oxidative Stress and Vascular Remodeling in Spontaneously Hypertensive Rats

Oxidative stress and sustained sympathetic over-activity contribute to the pathogenesis of hypertension. Catheter-based renal denervation has been used as a strategy for treatment of resistant hypertension, which interrupts both afferent and efferent renal fibers. However, it is unknown whether selective renal afferent denervation (RAD) may play beneficial roles in attenuating oxidative stress and sympathetic activity in hypertension. This study investigated the impact of selective RAD on hypertension and vascular remodeling. Nine-week-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were subjected to selective renal afferent denervation (RAD) with 33 mM of capsaicin for 15 min. Treatment with the vehicle of capsaicin was used as a control. The selective denervation was confirmed by the reduced calcitonin gene-related peptide expression and the undamaged renal sympathetic nerve activity response to the stimulation of adipose white tissue. Selective RAD reduced plasma norepinephrine levels, improved heart rate variability (HRV) and attenuated hypertension in SHR.It reduced NADPH oxidase (NOX) expression and activity, and superoxide production in the hypothalamic paraventricular nucleus (PVN), aorta and mesenteric artery of SHR. Moreover, the selective RAD attenuated the vascular remodeling of the aorta and mesenteric artery of SHR. These results indicate that selective removal of renal afferents attenuates sympathetic activity, oxidative stress, vascular remodeling and hypertension in SHR. The attenuated superoxide signaling in the PVN is involved in the attenuation of sympathetic activity in SHR, and the reduced sympathetic activity at least partially contributes to the attenuation of vascular oxidative stress and remodeling in the arteries of hypertensive rats.

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.

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 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.

Renal Deafferentation Prevents Progression of Hypertension and Changes to Sympathetic Reflexes in a Rabbit Model of Chronic Kidney Disease

[Figure: see text].

Mapping Renal Innervations by Renal Nerve Stimulation and Characterizations of Blood Pressure Response Patterns

Increased sympathetic nervous activity is one of main contributors to pathogenesis and progression of hypertension. Renal denervation (RDN) has been demonstrated as a potential therapy for treatment of hypertension; however, lack of indicators of intra-/post-procedure results in inconsistent clinical outcomes. Renal nerve stimulation (RNS), a simple and promising method, could evoke elevated blood pressure as an intraoperative indicator for RDN. But related researches on patterns of blood pressure responses to RNS are still incomplete. To investigate and categorize the phenotypes of blood pressure response to RNS and heart rate alteration before and after RNS, 24 Chinese Kunming dogs were used to perform RNS from bifurcation to ostium of renal arteries after angiography, and a total of 483 stimulated sites were complete. We identified five different patterns of blood pressure response to RNS in 483 stimulated sites, (1) continuous ascending and finally keeping steady above baseline (26.9%), (2) declining and then rising over baseline (11.8%), (3) declining and then rising but below baseline (14.5%), (4) fluctuating in the vicinity of baseline (39.5%), and (5) continuous declining and finally keeping steady below baseline (7.2%), and found no difference in RR intervals among five blood pressure responses before and after renal nerve stimulation. Renal nerve stimulation could elicit different patterns of blood pressure response, which could potentially assist in distinguishing sympathetic-excitatory sites and sympathetic-inhibitory sites from mixed nerve components, which might help to improve the efficacy of RDN.

Whole-Mount Kidney Clearing and Visualization Reveal Renal Sympathetic Hyperinnervation in Heart Failure Mice

Developing a three-dimensional (3D) visualization of the kidney at the whole-mount scale is challenging. In the present study, we optimized mouse whole-mount kidney clearing, which improved the transparency ratio to over 90% based on organ-specific perfusion (OSP)-clear, unobstructed brain imaging cocktails and computational analysis (CUBIC). The optimized OSP-CUBIC-compatible 3D immunostaining and imaging simultaneously visualized the high-resolution 3D structure of the whole-mount renal microvascular, glomerulus, and accompanying wrapped traveling sympathetic nerves in mice. A mouse model of pressure overload-induced heart failure (HF) was then established by minimally invasive transverse aortic constriction (MTAC). Further 3D quantification revealed renal sympathetic hyperinnervation (6.80 ± 1.04% vs. 3.73 ± 0.60%, P < 0.05) in mice with HF. In conclusion, this newly developed whole-organ tissue clearing and imaging system provides comprehensive information at the whole-mount scale and has great potential for kidney research. Our data suggest that renal sympathetic hyperinnervation is involved in HF associated with renal dysfunction.

Impact of anesthesia, sex, and circadian cycle on renal afferent nerve sensitivity

Elevated renal afferent nerve (ARNA) activity or dysfunctional reno-renal reflexes via altered ARNA sensitivity contribute to hypertension and chronic kidney disease. These nerves contain mechano- and chemosensitive fibers that respond to ischemia, changes in intrarenal pressures, and chemokines. Most studies have utilized various anesthetized preparations and exclusively male animals to characterize ARNA responses. Therefore, this study assessed the impact of anesthesia, sex, and circadian period on ARNA responses and sensitivity. Multifiber ARNA recordings were performed in male and female Sprague-Dawley rats (250-400 g) and compared across decerebrate versus Inactin, isoflurane, and urethane anesthesia groups. Intrarenal artery infusion of capsaicin (0.1-50.0 μM, 0.05 mL) produced concentration-dependent increases in ARNA; however, the ARNA sensitivity was significantly greater in decerebrate versus Inactin, isoflurane, and urethane groups. Increases in renal pelvic pressure (0-30 mmHg, 30 s) produced pressure-dependent increases in ARNA; however, ARNA sensitivity was again greater in decerebrate and Inactin groups versus isoflurane and urethane. Acute renal artery occlusion (30 s) increased ARNA, but responses did not differ across groups. Analysis of ARNA responses to increased pelvic pressure between male and female rats revealed significant sex differences only in isoflurane and urethane groups. ARNA responses to intrarenal capsaicin infusion were significantly blunted at nighttime versus daytime; however, ARNA responses to increased pelvic pressure or renal artery occlusion were not different between daytime and nighttime. These results demonstrate that ARNA sensitivity is greatest in decerebrate and Inactin-anesthetized groups but was not consistently influenced by sex.NEW & NOTEWORTHY We determined the impact of anesthesia, sex, and circadian cycle on renal afferent nerve (ARNA) sensitivity to chemical and mechanical stimuli. ARNA sensitivity to renal capsaicin infusion was greatest in decerebrate > Inactin > urethane or isoflurane groups. Elevated renal pelvic pressure significantly increased ARNA; decerebrate and Inactin groups exhibited the greatest ARNA sensitivity. Sex differences in renal afferent responses were not consistently observed. Circadian cycle altered chemosensory but not mechanosensory responses.

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.

Contribution of the Renal Nerves to Hypertension in a Rabbit Model of Chronic Kidney Disease

Overactivity of the sympathetic nervous system and high blood pressure are implicated in the development and progression of chronic kidney disease (CKD) and independently predict cardiovascular events in end-stage renal disease. To assess the role of renal nerves, we determined whether renal denervation (RDN) altered the hypertension and sympathoexcitation associated with a rabbit model of CKD. The model involves glomerular layer lesioning and uninephrectomy, resulting in renal function reduced by one-third and diuresis. After 3-week CKD, blood pressure was 13±2 mm Hg higher than at baseline (P<0.001), and compared with sham control rabbits, renal sympathetic nerve activity was 1.2±0.5 normalized units greater (P=0.01). The depressor response to ganglion blockade was also +8.0±3 mm Hg greater, but total norepinephrine spillover was 8.7±3.7 ng/min lower (bothP<0.05). RDN CKD rabbits only increased blood pressure by 8.0±1.5 mm Hg. Renal sympathetic activity, the response to ganglion blockade and diuresis were similar to sham denervated rabbits (non-CKD). CKD rabbits had intact renal sympathetic baroreflex gain and range, as well as normal sympathetic responses to airjet stress. However, hypoxia-induced sympathoexcitation was reduced by −9±0.4 normalized units. RDN did not alter the sympathetic response to hypoxia or airjet stress. CKD increased oxidative stress markers Nox5 and MCP-1 (monocyte chemoattractant protein-1) in the kidney, but RDN had no effect on these measures. Thus, RDN is an effective treatment for hypertension in this model of CKD without further impairing renal function or altering the normal sympathetic reflex responses to various environmental stimuli.

Role of spinal neurons in the maintenance of elevated sympathetic activity: a novel therapeutic target?

The control of sympathetic vasomotor activity involves a complex network within the brain and spinal circuits. An extensive range of studies has indicated that sympathoexcitation is a common feature in several cardiovascular diseases and that strategies to reduce sympathetic vasomotor overactivity in such conditions can be beneficial. In the present mini-review, we present evidence supporting the spinal cord as a potential therapeutic target to mitigate sympathetic vasomotor overactivity in cardiovascular diseases, focusing mainly on the actions of spinal angiotensin II on the control of sympathetic preganglionic neuronal activity.