Roles of central renin-angiotensin system and afferent renal nerve in the control of systemic hemodynamics in rats

Renal autonomic dynamics in hypertension: how can we evaluate sympathetic activity for renal denervation?

This review explores the various pathophysiological factors influencing antihypertensive effects, involving the regulation of vascular resistance, plasma volume, cardiac function, and the autonomic nervous system, emphasizing the interconnected processes regulating blood pressure (BP). The kidney's pivotal role in BP control and its potential contribution to hypertension is complicated but important to understand the effective mechanisms of renal denervation (RDN), which may be a promising treatment for resistant hypertension. Excessive stimulation of the sympathetic nervous system or the renin-angiotensin-aldosterone system (RAAS) can elevate BP through various physiological changes, contributing to chronic hypertension. Renal sympathetic efferent nerve activation leads to elevated norepinephrine levels and subsequent cascading effects on vasoconstriction, renin release, and sodium reabsorption. RDN reduces BP in resistant hypertension by potentially disrupting sensory afferent nerves, decreasing feedback activation to the central nervous system, and reducing efferent sympathetic nerve activity in the heart and other structures. RDN may also modulate central sympathetic outflow and inhibit renal renin-angiotensin system overactivation. While evidence for RDN efficacy in hypertension is increasing, accurate patient selection becomes crucial, considering complex interactions that vary among patients. This review also discusses methods to evaluate autonomic nerve activity from the golden standard to new potential examination for finding out optimization in stimulation parameters or rigorous patient selection based on appropriate biomarkers.

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.

Afferent Renal Denervation Attenuates Sympathetic Overactivation From the Paraventricular Nucleus in Spontaneously Hypertensive Rats

BACKGROUND

The effectiveness of renal denervation (RDN) in reducing blood pressure and systemic sympathetic activity in hypertensive patients has been established. However, the underlying central mechanism remains unknown. This study aimed to investigate the role of RDN in regulating cardiovascular function via the central renin-angiotensin system (RAS) pathway.

METHODS

Ten-week-old spontaneously hypertensive rats (SHR) were subjected to selective afferent renal denervation (ADN) using capsaicin solution. We hypothesized that ADN would effectively reduce blood pressure and rebalance the RAS component of the paraventricular nucleus (PVN) in SHR.

RESULTS

The experimental results show that the ADN group exhibited significantly lower blood pressure, reduced systemic sympathetic activity, decreased chronic neuronal activation marker C-FOS expression in the PVN, and improved arterial baroreflex function, compared with the Sham group. Furthermore, ACE and AT1 protein expression was reduced while ACE2 and MAS protein expression was increased in the PVN of SHR after ADN.

CONCLUSIONS

These findings suggest that RDN may exert these beneficial effects through modulating the central RAS pathway.

Comprehensive mapping of sensory and sympathetic innervation of the developing kidney

The kidney functions as a finely tuned sensor to balance body fluid composition and filter out waste through complex coordinated mechanisms. This versatility requires tight neural control, with innervating efferent nerves playing a crucial role in regulating blood flow, glomerular filtration rate, water and sodium reabsorption, and renin release. In turn sensory afferents provide feedback to the central nervous system for the modulation of cardiovascular function. However, the cells targeted by sensory afferents and the physiological sensing mechanisms remain poorly characterized. Moreover, how the kidney is innervated during development to establish these functions remains elusive. Here, we utilized a combination of light-sheet and confocal microscopy to generate anatomical maps of kidney sensory and sympathetic nerves throughout development and resolve the establishment of functional crosstalk. Our analyses revealed that kidney innervation initiates at embryonic day (E)13.5 as the nerves associate with vascular smooth muscle cells and follow arterial differentiation. By E17.5 axonal projections associate with kidney structures such as glomeruli and tubules and the network continues to expand postnatally. These nerves are synapsin I-positive, highlighting ongoing axonogenesis and the potential for functional crosstalk. We show that sensory and sympathetic nerves innervate the kidney concomitantly and classify the sensory fibers as calcitonin gene related peptide (CGRP)+, substance P+, TRPV1+, and PIEZO2+, establishing the presence of PIEZO2 mechanosensory fibers in the kidney. Using retrograde tracing, we identified the primary dorsal root ganglia, T10-L2, from which PIEZO2+ sensory afferents project to the kidney. Taken together our findings elucidate the temporality of kidney innervation and resolve the identity of kidney sympathetic and sensory nerves.

Autonomic control of ventricular function in health and disease: current state of the art

PURPOSE

Cardiac autonomic dysfunction is one of the main pillars of cardiovascular pathophysiology. The purpose of this review is to provide an overview of the current state of the art on the pathological remodeling that occurs within the autonomic nervous system with cardiac injury and available neuromodulatory therapies for autonomic dysfunction in heart failure.

METHODS

Data from peer-reviewed publications on autonomic function in health and after cardiac injury are reviewed. The role of and evidence behind various neuromodulatory therapies both in preclinical investigation and in-use in clinical practice are summarized.

RESULTS

A harmonic interplay between the heart and the autonomic nervous system exists at multiple levels of the neuraxis. This interplay becomes disrupted in the setting of cardiovascular disease, resulting in pathological changes at multiple levels, from subcellular cardiac signaling of neurotransmitters to extra-cardiac, extra-thoracic remodeling. The subsequent detrimental cycle of sympathovagal imbalance, characterized by sympathoexcitation and parasympathetic withdrawal, predisposes to ventricular arrhythmias, progression of heart failure, and cardiac mortality. Knowledge on the etiology and pathophysiology of this condition has increased exponentially over the past few decades, resulting in a number of different neuromodulatory approaches. However, significant knowledge gaps in both sympathetic and parasympathetic interactions and causal factors that mediate progressive sympathoexcitation and parasympathetic dysfunction remain.

CONCLUSIONS

Although our understanding of autonomic imbalance in cardiovascular diseases has significantly increased, specific, pivotal mediators of this imbalance and the recognition and implementation of available autonomic parameters and neuromodulatory therapies are still lagging.

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.

The role of renal nerve stimulation in percutaneous renal denervation for hypertension: A mini-review

Recent trials have demonstrated the efficacy and safety of percutaneous renal sympathetic denervation (RDN) for blood pressure (BP)-lowering in patients with uncontrolled hypertension. Nevertheless, major challenges exist, such as the wide variation of BP-lowering responses following RDN (from strong response to no response) and lack of feasible and reproducible peri-procedural predictors for patient response. Both animal and human studies have demonstrated different patterns of BP responses following renal nerve stimulation (RNS), possibly related to varied regional proportions of sympathetic and parasympathetic nerve tissues along the renal arteries. Animal studies of RNS have shown that rapid electrical stimulation of the renal arteries caused renal artery vasoconstriction and increased norepinephrine secretion with a concomitant increase in BP, and the responses were attenuated after RDN. Moreover, selective RDN at sites with strong RNS-induced BP increases led to a more efficient BP-lowering effect. In human, when RNS was performed before and after RDN, blunted changes in RNS-induced BP responses were noted after RDN. The systolic BP response induced by RNS before RDN and blunted systolic BP response to RNS after RDN, at the site with maximal RNS-induced systolic BP response before RDN, both correlated with the 24-h ambulatory BP reductions 3-12 months following RDN. In summary, RNS-induced BP changes, before and after RDN, could be used to assess the immediate effect of RDN and predict BP reductions months following RDN. More comprehensive, large-scale and long term trials are needed to verify these findings.

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.

Selective Renal Denervation Guided by Renal Nerve Stimulation in Canine

Renal nerve stimulation (RNS) can result in substantial blood pressure (BP) elevation, and the change was significantly blunted when repeated stimulation after ablation. However, whether RNS could provide a meaningful renal nerve mapping for identification of optimal ablation targets in renal denervation (RDN) is not fully clear. Here, we compared the antihypertensive effects of selective RDN guided by two different BP responses to RNS and explored the nerve innervations at these sites in Kunming dogs. Our data indicated that ablation at strong-response sites showed a more systolic BP-lowering effect than at weak-response sites ( P =0.002), as well as lower levels of tyrosine hydroxylase and norepinephrine in kidney and a greater reduction in plasma norepinephrine ( P =0.004 for tyrosine hydroxylase, P =0.002 for both renal and plasma norepinephrine). Strong-response sites showed a greater total area and mean number of renal nerves than weak-response sites ( P =0.012 for total area and P <0.001 for mean number). Systolic BP-elevation response to RNS before RDN and blunted systolic BP-elevation to RNS after RDN were correlated with systolic BP changes at 4 weeks follow-up ( R =0.649; P =0.012 and R =0.643; P =0.013). Changes of plasma norepinephrine and renal norepinephrine levels at 4 weeks were also correlated with systolic BP changes at 4 weeks ( R =0.837, P <0.001 and R =0.927, P <0.001). These data suggest that selective RDN at sites with strong BP-elevation response to RNS could lead to a more efficient RDN. RNS is an effective method to identify the nerve-enriched area during RDN procedure and improve the efficacy of RDN.

Relationship Between Patterns in Antihypertensive Drugs Medication and Mortality in Incident Dialysis Patients: A Multicenter Prospective Cohort Study

Hypertension is common in patients with chronic kidney disease. Whether blood pressure management before dialysis initiation influences prognosis during maintenance dialysis remains unclear. Hence, we surveyed the status of antihypertensive drug use in incident dialysis patients. Moreover, we examined the association between antihypertensive drug use patterns at the time of dialysis initiation and mortality. We used a database derived from the multicenter prospective Aichi Cohort Study of Prognosis in Patients Newly Initiated into Dialysis, which included 1520 incident dialysis patients in Aichi prefecture, Japan. The baseline in the present study was set as the time of dialysis initiation. We examined antihypertensive drug prescription patterns at baseline, as well as the association between use of antihypertensive drugs and mortality after dialysis initiation. Among all participants, 1440 were taking at least one antihypertensive drug. The rate of calcium channel blocker (CCB) use was highest, accounting for 74.3%. CCB use was significantly associated with lower all-cause and cardiovascular-related mortality (hazard ratio [HR]: 0.62 and 0.57, 95% confidence interval [CI]: 0.46-0.85 and [0.35-0.91], respectively). Compared with no use of either drug, combination therapy with a renin angiotensin system blocker (RASB) and CCB was significantly associated with lower mortality (HR: 0.51, 95% CI: 0.34-0.76). The present study demonstrated that antihypertensive drugs were used in 95% of incident dialysis patients. In addition, use of a CCB and combination therapy with a CCB and RASB at the time of dialysis initiation was associated with lower mortality during maintenance dialysis.

Effect of dipeptidyl peptidase-4 inhibition on circadian blood pressure during the development of salt-dependent hypertension in rats

A growing body of evidence has indicated that dipeptidyl peptidase-4 (DPP-4) inhibitors have antihypertensive effects. Here, we aim to examine the effect of vildagliptin, a DPP-4-specific inhibitor, on blood pressure and its circadian-dipping pattern during the development of salt-dependent hypertension in Dahl salt-sensitive (DSS) rats. DSS rats were treated with a high-salt diet (8% NaCl) plus vehicle or vildagliptin (3 or 10 mg kg(-1) twice daily by oral gavage) for 7 days. Blood pressure was measured by the telemetry system. High-salt diet for 7 days significantly increased the mean arterial pressure (MAP), systolic blood pressure (SBP) and were also associated with an extreme dipping pattern of blood pressure in DSS rats. Treatment with vildagliptin dose-dependently decreased plasma DPP-4 activity, increased plasma glucagon-like peptide 1 (GLP-1) levels and attenuated the development of salt-induced hypertension. Furthermore, vildagliptin significantly increased urine sodium excretion and normalized the dipping pattern of blood pressure. In contrast, intracerebroventricular infusion of vildagliptin (50, 500 or 2500 μg) did not alter MAP and heart rate in DSS rats. These data suggest that salt-dependent hypertension initially develops with an extreme blood pressure dipping pattern. The DPP-4 inhibitor, vildagliptin, may elicit beneficial antihypertensive effects, including the improvement of abnormal circadian blood pressure pattern, by enhancing urinary sodium excretion.

Angiotensin II-induced activation of central AT1 receptors exerts endocannabinoid-mediated gastroprotective effect in rats

The aim of the present study was to analyze whether angiotensin II via the endocannabinoid system can induce gastric mucosal protection, since transactivation of cannabinoid CB1 receptors by angiotensin AT1 receptor in CHO cells was described. Experimental ulcer was induced by acidified ethanol given orally in male Wistar rats, CB1(+/+) wild type and CB1(-/-) knockout mice. The compounds were administered intracerebroventricularly. It was found, that 1. Angiotensin II inhibited the ethanol-induced gastric lesions (11.9-191pmol); the effect of angiotensin II (191pmol) was inhibited by the CB1 receptor inverse agonist AM 251 (1.8nmol) and the inhibitor of diacylglycerol lipase (DAGL), tetrahydrolipstatin (0.2nmol). 2. Angiotensin II exerted gastroprotection in wild type, but not in CB1(-/-) mice. 3. The gastroprotective effect of angiotensin II (191pmol) was reduced by atropine (1mg/kg i.v.) and bilateral cervical vagotomy. In conclusion, stimulation of central angiotensin AT1 receptors via activation of cannabinoid CB1 receptors induces gastroprotection in a DAGL-dependent and vagus-mediated mechanism.