Afferent Renal Nerve Research Articles

Renal nerves in physiology, pathophysiology and interoception.

Sympathetic efferent renal nerves have key roles in the regulation of kidney function and blood pressure. Increased renal sympathetic nerve activity is thought to contribute to hypertension by promoting renal sodium retention, renin release and renal vasoconstriction. This hypothesis led to the development of catheter-based renal denervation (RDN) for the treatment of hypertension. Two RDN devices that ablate both efferent and afferent renal nerves received FDA approval for this indication in 2023. However, in animal models, selective ablation of afferent renal nerves resulted in comparable anti-hypertensive effects to ablation of efferent and afferent renal nerves and was associated with a reduction in sympathetic nerve activity. Selective afferent RDN also improved kidney function in a chronic kidney disease model. Notably, the beneficial effects of RDN extend beyond hypertension and chronic kidney disease to other clinical conditions that are associated with elevated sympathetic nerve activity, including heart failure and arrhythmia. These findings suggest that the kidney is an interoceptive organ, as increased renal sensory nerve activity modulates sympathetic activity to other organs. Future studies are needed to translate this knowledge into novel therapies for the treatment of hypertension and other cardiorenal diseases.

Increased Blood Pressure in Mice with Impaired Function of Afferent Renal Nerves Due to Lack of Sodium Nav1.8 Channels

Increased Blood Pressure in Mice with Impaired Function of Afferent Renal Nerves Due to Lack of Sodium Nav1.8 Channels

Abstract P383: Increased renal afferent nerve activity and peak response to pro-inflammatory cytokine interleukin 6 in isolated dorsal root ganglion neurons from hypertensive rats

Renal afferent nerves are reported to mediate the progression of hypertension in preclinical models, putatively via an aberrant increase in activation. The underlying source of this nerve activation is unknown but we hypothesized renal inflammatory cytokines are a primary driver. We previously reported interleukin 6 (IL-6) is increased in the kidneys of hypertensive rats, and intrarenal administration of IL-6 can activate renal afferent nerves. Though these data are promising, the direct effects of IL-6 on afferent renal nerves remain unclear. We hypothesized that isolated renal afferent neurons from hypertensive rats will have increased activity and responsiveness to inflammatory cytokine IL-6 compared to normotensive controls. To test our hypothesis, we tested the direct effects of interleukin-6 (IL-6) on renal afferent nerve action potentials (AP) generated in freshly isolated dorsal root ganglion (DRG) neurons. To model salt-sensitive hypertension, uninephrectomized rats (n=6) were administered deoxycorticosterone acetate (DOCA; 100mg, sc) and 0.9% saline for drinking water for 21 days. Control rats (n=6) were uninephrectomized. To label renal afferent nerves, neuronal tracer DiI was introduced by intrarenal injection 6 days prior to DRG collection. DRGs from T10-L1 were isolated, enzymatically digested and dissociated, and cultured overnight for whole-cell patch-clamp the following day. DiI-positive neurons from both control and DOCA rats generated AP during the delivery of 100, 200, and 300 pA current steps. Data were analyzed by two-way, repeat-measures ANOVA (α=.05). At baseline, DOCA neurons had a higher (p<0.05) mean AP frequency compared to controls (no difference in AP mean peak amplitude or AP duration). In both groups, increasing concentrations of IL-6 (0. 4, 4, and 40 ng/ml) elicited a dose-dependent increase in AP peak amplitude compared to baseline. No difference was detected in IL-6 responses between DOCA and controls. Overall, these data supported our original hypothesis that pro-inflammatory cytokine IL-6 would increase renal afferent nerve activity, and that said activity is increased in hypertensive DOCA-salt rats. IL-6 accumulation triggered by end organ damage due to hypertension might lead to increased afferent renal nerve activity, which exacerbates the hypertensive phenotype through a sympatho-excitatory response. Additional measurements of isolated DRG responses to pro-inflammatory mediators are underway for direct comparison.

P180 CONTRIBUTION OF AFFERENT RENAL NERVES TO HYPERTENSION AND HYPERTENSIVE HEART FAILURE

Background and Objective: Renal nerves contain efferent and afferent fibers. This study aimed to investigate the contribution of afferent renal nerves to the development of hypertension and hypertensive heart failure in several rat models of hypertension. Methods: Selective afferent renal nerve denervation (ARDN) or sham operation was performed in the following models: (1) SHRSP at 9 weeks; (2) 4% high-salt diet (HS)-fed SHRSP at 8 weeks (HS from 8 weeks); and (3) 8% HS-fed Dahl salt-sensitive rats at 9 weeks (HS from 6 weeks). Dahl rats fed 0.3% low-salt diet were controls for (3). Blood pressure (BP) was measured by telemetry in (1) and (2), and by tail-cuff method in (3). Results: (1) Mean BP was elevated from 9 weeks to 11 weeks in sham-SHRSP (155.2±2.0 vs 144.0±1.9 mmHg, n=10, p<0.05). Mean BP in ARDN-SHRSP (157.8±2.7 mmHg, n=10) did not differ from sham-SHRSP at 11 weeks. (2) Mean BP increased from 8 weeks to 11 weeks in HS-sham-SHRSP (191.5±8.1 vs 126.5±4.0 mmHg, n=6, p<0.05). Mean BP in HS-ARDN-SHRSP (186.0±7.1 mmHg, n=6) did not differ from HS-sham-SHRSP at 11 weeks. (3) Systolic BP increased (243.6±7.0 vs 140.0±2.7 mmHg, n=9 each, p<0.05) and echocardiographic left ventricular (LV) fractional shortening decreased (25.9±1.7 vs 48.8±0.4%, p<0.05) in HS-sham-Dahl rats compared to low-salt controls at 16 weeks (“HFrEF” phase). LV weight, lung weight, and LV fibrosis were significantly increased in HS-sham-Dahl rats compared to controls. ARDN attenuated these changes except for BP. At 12 weeks (pre-HFrEF phase), plasma norepinephrine levels increased in HS-sham-Dahl rats compared to controls and were attenuated by ARDN (controls 188.7±16.5, HS-sham 563.8±82.7, HS-ARDN 327.4±50.2 pg/ml; n=15, 12, 14; p<0.05). Conclusions: Signals from afferent renal nerves contribute to sympathoexcitation and the development of HFrEF without affecting BP in Dahl salt-sensitive hypertensive rats, but not to the development of hypertension in SHRSP and HS-fed SHRSP.

Abstract 54: The kidney-OVLT axis in renovascular hypertension: Individual and combined effects of afferent renal denervation and OVLT lesion in 2K1C rats.

We have recently reported that afferent renal denervation (ARDN) markedly attenuates the pathogenesis of hypertension in the 2 kidney 1 clip (2K1C) model in the rat. This was associated with a reduction in neurogenic pressor activity (NPA). We have also recently shown that lesion of the organum vasculosum of the lamina terminalis (OVLT), a forebrain circumventricular organ, had nearly identical effects in 2K1C rats as ARDN. Together these findings suggest that a neural pathway from the kidney to the OVLT plays an important role in 2K1C hypertension. Based on these findings we hypothesized that the combined effect of ARDN and lesion of the OVLT (OVLTx) on arterial pressure in 2K1C rats would not be greater than the individual treatments. Male Sprague-Dawley rats were randomly selected to receive either OVLT lesion (x) or sham-OVLTx. One week later, rats were instrumented with telemeters to measure mean arterial pressure (MAP). One week later, renal artery stenosis was created by placing a clip on the left renal artery and then, rats were subjected to ARDN by periaxonal capsaicin or sham treatment of the clipped kidney creating 4 experimental groups: sham+sham (n=6), sham+ARDN (n=6), OVLTx+sham (n=5), OVLTx+ARDN (n=5). MAP was measured daily for 28 days, and at the end of the protocol, NPA was assessed by measuring the peak MAP response to ganglionic blockade. MAP was similar in all 4 groups at the beginning of the study averaging 108±3 mmHg. MAP increased to 180±10 mmHg in the sham+sham group compared to 130±13mmHg in sham+ARDN, 142±18mmHg in OVLTx+sham rats and 158±14mmHg in OVLTx+ARDN rats (p<0.001). NPA in Sham+sham rats was significantly higher (-44 ± 8 mmHg) compared to sham+ARDN (-18 ± 3 mmHg), OVLTx+sham (-21 ± 2 mmHg) and OVLTx+ARDN (-19 ± 4 mmHg) rats (p<0.05). Notably, the combined effects of OVLTx+ARDN on MAP and NPA were not significantly different from either OVLTx (p=1.00 and p=0.819) or ARDN (p=0.113 and p= 0.878) alone. In summary, ARDN and OVLTx attenuated hypertension and NPA similarly in 2K1C-HTN rats but the combination of these treatments did not produce any additional effect on MAP or NPA. These findings are consistent with the hypothesis that afferent renal nerves and the OVLT are linked in a common neural pathway required for the development of hypertension following renal artery stenosis.

IL-1R Mediated Activation of Renal Sensory Nerves in DOCA-Salt Hypertension.

Clinical trials of renal denervation for the treatment of hypertension have shown a variety of off-target improvements in conditions associated with sympathetic overactivity. This may be due to the ablation of sympathoexcitatory afferent renal nerves, which are overactive under conditions of renal inflammation. Renal IL (interleukin)-1β is elevated in the deoxycorticosterone acetate-salt model of hypertension, and its activity may be responsible for the elevation in afferent renal nerve activity and arterial pressure. Continuous blood pressure recording of deoxycorticosterone acetate-salt mice with IL-1R (IL-1 receptor) knockout or antagonism was used individually and combined with afferent renal denervation (ARDN) to assess mechanistic overlap. Protein quantification and histological analysis of kidneys were performed to characterize renal inflammation. ARDN attenuated deoxycorticosterone acetate-salt hypertension (-20±2-Δmm Hg mean arterial pressure [MAP] relative to control at study end) to a similar degree as total renal denervation (-21±2-Δmm Hg MAP), IL-1R knockout (-16±4-Δmm Hg MAP), or IL-1R antagonism (-20±3-Δmm Hg MAP). The combination of ARDN with knockout (-18±2-Δmm Hg MAP) or antagonism (-19±4-Δmm Hg MAP) did not attenuate hypertension any further than ARDN alone. IL-1R antagonism was found to have an acute depressor effect (-15±3-Δmm Hg MAP, day 10) in animals with intact renal nerves but not those with ARDN. These findings suggest that IL-1R signaling is partially responsible for the elevated afferent renal nerve activity, which stimulates central sympathetic outflow to drive deoxycorticosterone acetate-salt hypertension.

TRPV1 signaling of perirenal adipose tissue promotes DOCA-Salt-induced hypertension and kidney injury.

Denervation of renal or perirenal adipose tissue (PRAT) can reduce arterial blood pressure in various hypertensive experimental models. Trpv1 (transient receptor potential vanillin 1) channel is highly expressed in the renal sensory nerves and the dorsal root ganglias (DRGs) projected by PRAT. However, it is currently unclear whether Trpv1 in DRGs projected from PRAT can regulate renal hypertension. We used resintoxin (RTX) to block the afferent sensory nerves of rat PRAT. We also constructed Trpv1 -/- mice and Trpv1 +/- mice or used the injection of AAV2-retro-shTrpv1 to detect the effects of Trpv1 knockout or knockdown of PRAT-projected DRGs on deoxycorticosterone acetate (DOCA)-Salt-induced hypertension and kidney injury. Blocking the afferent sensory nerves of PRAT with RTX can alleviate DOCA-Salt-induced hypertension and renal injury in rats. And this blockade reduces the expression of Trpv1 in the DRGs projected by PRAT. Injecting AAV2-retro-shTrpv1 into the PRAT of DOCA-Salt mice also achieved the same therapeutic effect. However, DOCA-Salt-induced hypertension and renal injury can be treated in Trpv1 +/- mice but not alleviated or even worsened in Trpv1 -/- mice, possibly because of compensatory increase of Trpv5 in DRG of Trpv1 -/- mice. Reducing, rather than eliminating, Trpv1 in DRG from PRAT-projection can reduce blood pressure and kidney damage in DOCA-Salt in rats or mice. Trpv1 in PRAT-DRGs may serve as a therapeutic target for salt-sensitive hypertension and its renal complications.

A kidney-hypothalamus axis promotes compensatory glucose production in response to glycosuria

The kidneys facilitate energy conservation through reabsorption of nutrients including glucose. Almost all the filtered blood glucose is reabsorbed by the kidneys. Loss of glucose in urine (glycosuria) is offset by an increase in endogenous glucose production to maintain normal energy supply in the body. How the body senses this glucose loss and consequently enhances glucose production is unclear. Using renal Slc2a2 (also known as Glut2) knockout mice, we demonstrate that elevated glycosuria activates the hypothalamic-pituitary-adrenal axis, which in turn drives endogenous glucose production. This phenotype was attenuated by selective afferent renal denervation, indicating the involvement of the afferent nerves in promoting the compensatory increase in glucose production. In addition, through plasma proteomics analyses we observed that acute phase proteins - which are usually involved in the body’s defense mechanisms against a threat – were the top candidates which were either upregulated or downregulated in renal Slc2a2 KO mice. Overall, afferent renal nerves contribute to promoting endogenous glucose production in response to elevated glycosuria and loss of glucose in urine is sensed as a biological threat in mice. These findings may be useful in improving the efficiency of drugs like SGLT2 inhibitors that are intended to treat hyperglycemia by enhancing glycosuria but are met with a compensatory increase in endogenous glucose production.

A kidney-hypothalamus axis promotes compensatory glucose production in response to glycosuria.

The kidneys facilitate energy conservation through reabsorption of nutrients including glucose. Almost all the filtered blood glucose is reabsorbed by the kidneys. Loss of glucose in urine (glycosuria) is offset by an increase in endogenous glucose production to maintain normal energy supply in the body. How the body senses this glucose loss and consequently enhances glucose production is unclear. Using renal Slc2a2 (also known as Glut2) knockout mice, we demonstrate that elevated glycosuria activates the hypothalamic-pituitary-adrenal axis, which in turn drives endogenous glucose production. This phenotype was attenuated by selective afferent renal denervation, indicating the involvement of the afferent nerves in promoting the compensatory increase in glucose production. In addition, through plasma proteomics analyses we observed that acute phase proteins - which are usually involved in the body's defense mechanisms against a threat - were the top candidates which were either upregulated or downregulated in renal Slc2a2 KO mice. Overall, afferent renal nerves contribute to promoting endogenous glucose production in response to elevated glycosuria and loss of glucose in urine is sensed as a biological threat in mice. These findings may be useful in improving the efficiency of drugs like SGLT2 inhibitors that are intended to treat hyperglycemia by enhancing glycosuria but are met with a compensatory increase in endogenous glucose production.

Integrated renal and sympathetic mechanisms underlying the development of sex- and age-dependent hypertension and the salt sensitivity of blood pressure

Aging is a non-modifiable understudied risk factor for hypertension. We hypothesized that sympathetically mediated activation of renal sodium reabsorption drives age-dependent hypertension and the salt sensitivity of blood pressure (BP). Using 3-, 8-, and 16-month-old male and female Sprague–Dawley rats as a model of normal aging, we assessed BP, indices of sympathetic tone, and the physiological responses to acute and chronic sodium challenge including sodium chloride cotransporter (NCC) regulation. The effects of renal nerve ablation and NCC antagonism were assessed in hypertensive male rats. We observed sex-dependent impaired renal sodium handling (24 h sodium balance (meq), male 3-month 0.36 ± 0.1 vs. 16-month 0.84 ± 0.2; sodium load excreted during 5% bodyweight isotonic saline volume expansion (%) male 3-month 77 ± 5 vs. 16-month 22 ± 8), hypertension (MAP (mmHg) male 3-month 123 ± 4 vs. 16-month 148 ± 6), and the salt sensitivity of BP in aged male, but not female, rats. Attenuated sympathoinhibitory afferent renal nerve (ARN) responses contributed to increased sympathetic tone and hypertension in male rats. Increased sympathetic tone contributes to renal sodium retention, in part through increased NCC activity via a dysfunctional with-no-lysine kinase-(WNK) STE20/SPS1-related proline/alanine-rich kinase signaling pathway, to drive hypertension and the salt sensitivity of BP in aged male rats. NCC antagonism and renal nerve ablation, which reduced WNK dysfunction and decreased NCC activity, attenuated age-dependent hypertension in male Sprague–Dawley rats. The contribution of an impaired sympathoinhibitory ARN reflex to sex- and age-dependent hypertension in an NCC-dependent manner, via an impaired WNK1/WNK4 dynamic, suggests this pathway as a mechanism-based target for the treatment of age-dependent hypertension.

Prenatal LPS leads to increases in RAS expression within the PVN and overactivation of sympathetic outflow in offspring rats

The renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) are two major blood pressure-regulating systems. The link between the renal and cerebral RAS axes was provided by reflex activation of renal afferents and efferent sympathetic nerves. There is a self-sustaining enhancement of the brain and the intrarenal RAS. In this study, prenatal exposure to lipopolysaccharide (LPS) led to increased RAS activity in the paraventricular nucleus (PVN) and overactivation of sympathetic outflow, accompanied by increased production of reactive oxygen species (ROS) and disturbances between inhibitory and excitatory neurons in PVN. The AT1 receptor blocker losartan and α2 adrenergic receptor agonist clonidine in the PVN significantly decreased renal sympathetic nerve activity (RSNA) and synchronously reduced systolic blood pressure. Prenatal LPS stimulation caused H3 acetylation at H3K9 and H3K14 in the PVN, which suggested that epigenetic changes are involved in transmitting the prenatal adverse stimulative information to the next generation. Additionally, melatonin treatment during pregnancy reduced RAS activity and ROS levels in the PVN; balanced the activity of inhibitory and excitatory neurons in the PVN; increased urine sodium secretion; reduced RSNA and blood pressure. In conclusion, prenatal LPS leads to increased RAS expression within the PVN and overactivation of the sympathetic outflow, thereby contributing to hypertension in offspring rats. Melatonin is expected to be a promising agent for preventing prenatal LPS exposure-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.

The role of afferent renal nerves in regulating sympathetic outflow via central nervous system mechanisms.

The role of afferent renal nerves in regulating sympathetic outflow via central nervous system mechanisms.

Renal Afferent Nerve Activity and Association with Neurohumoral Dysregulation in a Model of Autosomal Recessive Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a rare, genetic kidney disease characterized by cyst growth that leads to kidney failure. Renal nerves play an important role in the development and maintenance of hypertension and other renal diseases. Afferent (sensory) nerves convey information to the central nervous system in response to intrarenal stimuli. Our laboratory demonstrated that afferent renal nerve activity (ARNA) is elevated in 10-week-old PCK rats compared to non-cystic, age-matched Sprague-Dawley (SD) controls. Furthermore, ARNA positively correlated with cystic index (CI; a measure of cyst growth). To further elucidate the relationship between renal nerve activity, age, and cyst progression, we aimed to quantify both ARNA and renal sympathetic nerve activity (RSNA) in PCK and SD rats. We hypothesized that ARNA and RSNA would be greater in PCK than SD. Furthermore, arginine vasopressin (AVP) is elevated in PKD and increases cyst growth. There is evidence that activation of the afferent renal nerves can contribute to secretion of AVP. Thus, we propose that elevated ARNA increases AVP secretion, thereby increasing cyst growth. We also hypothesized that ARNA would positively correlate with age, CI, and copeptin (an indirect marker of AVP) in young PCK rats. To test our first hypothesis, we conducted direct renal nerve recordings in 10- to 12-week-old PCK (n=16;11M/5F) and 10-week-old SD (n=9;7M/2F) rats. For our second hypothesis, we conducted nerve recordings in 4- to 10-week-old PCK rats to evaluate the correlation of nerve activity with age, cystic index, and copeptin in animals ages 4- to 12-weeks-old (n=28;21M/7F). Multiunit nerve recording was performed under inactin anesthesia. As we previously published, a renal nerve bundle is isolated, placed on an iridium bipolar electrode, and encased in silicone. Resting RSNA was recorded following 10-minute stabilization period, then the nerve bundle was severed proximal to the electrode to isolate ARNA. ARNA recordings were normalized to maximal ARNA evoked by intrarenal 50 μM capsaicin. Comparisons between PCK and SD were analyzed by Student’s t-test (p<.05). Linear regression analyses were used to assess variable correlation (p<.05). Data presented as mean ± SEM. In contrast to our first hypothesis, RSNA did not differ between 10- to 12-week-old SD and PCK rats, whether measured via burst frequency (SD 6.92 ± 0.82; PCK *6.97 ± 0.34 Hz) or bursts/heart beat (SD 1.36±0.16; PCK 1.28 ± 0.06). ARNA was calculated as a percentage of maximal ARNA using either integrated ARNA (ARNAInt) or spikes/s (ARNASpikes). Baseline ARNAInt was greater in PCK rats (29.14±3.35%) than SD (13.46±2.08%, n=4), whereas PCK ARNASpikes trended (p=.06) higher than SD controls (SD 5.57±2.21; PCK 13.90±2.21%). In correlative analysis, RSNA trended (p=.05) to correlate with age in the PCK rat. However, there was no relationship between RSNA and (1) CI (p=0.29) or (2) copeptin (p=0.15). Similarly, there was no correlation detected between ARNA and age (ARNAInt: p=0.41; ARNASpikes: p=0.16) or serum copeptin (ARNAInt: p=0.96; ARNASpikes: p=0.20). ARNAInt trended (p=.07) to correlate with CI, but ARNASpikes did not correlate with CI (p=0.48). Overall, these data partially support our hypotheses. RSNA did not differ between SD and PCK rats, but ARNAInt was increased in PCK rats vs. SD. We failed to detect a correlation between either ARNA or RSNA and age, CI, or copeptin in PCK rats though, ARNAInt trended to correlate with CI. As ARNA does not appear to be correlated with serum copeptin, further studies are required to uncover the relationship between afferent renal nerves and cystogenesis in this model of PKD. PKD Foundation Research Award 1022534 (CB) NIDDK/PKD RRC Pilot and Feasibility Award U24DK126110 (CB) AHA 21PRE0000216068 (MG). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Analysis of Brain Regions Activated by Afferent Renal Nerves in DOCA-Salt Hypertensive Mice

We have reported that the neurogenic component of DOCA-salt HTN is dependent on afferent renal nerves (ARNs) that modulate central autonomic networks, however, the central pathways are poorly understood. Targeted recombination in active populations (TRAP2) mice provide a model for global visualization and quantification of neuronal activity via the expression of the fluorescent reporter protein tdTomato which is expressed under the immediate-early gene, c-Fos, a neuronal activation marker, via tamoxifen-inducible Cre. In combination with the deoxycorticosterone-acetate (DOCA)-salt model of hypertension (HTN), neuronal activation in central autonomic centers can be evaluated in TRAP2 mice during DOCA-salt-induced HTN to identify the role of ARNs in the control of blood pressure. We evaluated the expression of tdTomato in TRAP2 mice as a measure of c-Fos activation following 7 days of DOCA-salt HTN and compared it to immunolabeled c-Fos at day 21 of DOCA-salt HTN in brain regions known to be involved in blood pressure regulation. We hypothesized that DOCA will increase the expression of tdTomato and c-Fos in mice with intact renal nerves and that afferent renal denervation (ARDN) will attenuate this DOCA-induced neuronal activity. Three groups of TRAP2-DOCA mice were studied: normotensive (Vehicle-Sham), hypertensive (DOCA-Sham), hypertensive with ARDN (DOCA-ARDN). Mice received a nephrectomy, sham or ARDN, implant of 50mg DOCA and 0.9% saline drinking water for the length of the study (drug-free pellet and diH2O for vehicle). TRAP2-DOCA-salt mice received an injection of 5mg/mL 4-hydroxytamoxifen (4-OHT), a short acting tamoxifen metabolite, on day 7 to induce Cre recombination and expression of tdTomato during the development of HTN. On day 21, mice were anesthetized and perfused with 4% paraformaldehyde. Brains were immunolabeled for c-Fos expression indicating day 21 neuronal activation and compared to endogenous Cre-induced tdTomato expression from day 7 4-OHT. Preliminary data indicate increased neuronal activity in TRAP2 DOCA-Sham mice compared to Vehicle-Sham in the paraventricular nucleus of the hypothalamus, lateral parabrachial nucleus, and nucleus of the solitary tract. This activation pattern was reduced in TRAP2 DOCA-ARDN compared to TRAP2 DOCA-Sham mice. A future study will evaluate c-Fos expression in wild-type DOCA-salt mice at day 7 and 21 of DOCA-salt HTN development to validate the observations in the TRAP2-DOCA model. This experiment will also validate TRAPing as a method for measuring neuronal activation at two time points within the same animal. These preliminary results establish an anatomical foundation for future investigations into the physiological role of ARN input to central autonomic control centers that regulate blood pressure in a salt-induced hypertensive model. NIH R01 HL116476. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sex differences in the regulation of salt appetite in Spontaneously Hypertensive Rats after loss of interoceptive input from the kidney

The average American consumes 3,400 mg/day of sodium, 1000mg over the American Heart Association’s recommended maximum daily allowance. Excessive salt intake accelerates the progression of many diseases including hypertension, congestive heart failure, and chronic kidney disease. Reducing sodium intake has beneficial effects on a population level and in at risk patients. In previous studies we have shown that afferent renal nerves are involved in the regulation of sodium intake in DOCA hypertensive rats. Like DOCA hypertensive rats, Spontaneously Hypertensive rats (SHR) are a model with increased salt appetite. Here, we tested the hypothesis that afferent renal nerves regulate sodium intake in SHR. Secondarily, it is well documented that estrogens modulate salt intake. To examine the effect of sex on sodium intake we compared salt-appetite between male and female SHR. Bilateral afferent renal denervation (ARDN) was performed using the periaxonal application of 33mM capsaicin. In sham rats the renal arteries were isolated but not treated. Mean arterial blood pressure (MAP) was assessed using radiotelemetry, with the catheter implanted in the femoral artery. Four groups of rats were studied: male SHR-sham (n=9), female SHR-sham (n=3), male SHR+ARDN (n=8) and female SHR+ARDN (n=4). All rats were given ad libitum access to two bottles, one containing dH2O and the other containing 1.8% NaCl. The bottle position was rotated, and fluid intake was recorded daily for 21-days. ARDN caused a significant reduction in 1.8% intake in female but not male SHR rats (p=0.02, female SHR-sham v female SHR-ARDN, p>0.99 male SHR v male SHR-ARDN). This effect was specific for saline intake, water intake was not altered by ARDN in the female SHR (p=0.3). The female SHR drank more saline than male SHR when normalized to body weight (p=0.04 female SHR-sham v male SHR-sham). MAP was not reduced by ARDN in the male SHR (p=0.39), and ongoing studies are examining MAP in response to ARDN in female SHR. The data presented demonstrate for the first time that ARDN decreases salt appetite in female but not male SHR. We also found that baseline saline intake was higher in female SHR than male SHR. In future studies we will examine the renal mechanisms underlying these sex differences. Together, these data suggest that reduced sodium intake may offer an additional therapeutic benefit of renal denervation in female patients with hypertension and cardiovascular disease. LE is funded by R01HL152166; ACV is funded by FAPESP. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

SIGNIFICANCE OF THE NAV 1.8. VOLTAGE-GATED, TETRODOTOXIN-RESISTANT SODIUM CHANNEL FOR THE RENAL SENSORY INNERVATION IN MICE AND RATS

Objective: Our previous work repeatedly showed that the sensory innervation of the kidney in rats has a peculiarity containing predominantly (more than 50%) highly active tonic neurons to electrical stimulation. In a previous publication demonstrated an increased mRNA expression of the TTX-resistant sodium channel Nav1.8 in renal sensory neurons. Hence, we tested the hypothesis that tonic firing pattern is related to the specific expression of Nav1.8 on the cell surface of neurons with renal sensoric axons in the dorsal root ganglia (DRG Th12-L2). Design and method: Harvested dorsal root ganglion neurons (DRG Th11-L2) from Sprague Dawley (SD) with renal afferents were investigated in neuronal cell culture using current clamp mode to assess action potential generation during current injection and to characterize neurons as tonic highly active and phasic less active neurons using a Nav1.8 blocker (A-803467) before and after stimulation. Further, renal DRG neurons from a Nav1.8 knock out mouse (C57BL6J-Scn10atm1Jwo) were investigated in a current clamp mode. C57BL6 mice were used as controls. Results: At a concentration of 0.3μM the maximum AP firing frequency of tonic neurons was blocked from 13+/- 1.1 APs/600ms to 7.6+/-1.4 APs/600ms under superfusion with a Nav1.8 blocker. No blocker effects were seen at a concentration of 0.1 μM and due to superfusion with the solvent methanol alone. The firing pattern of renal neurons in the C57BL6 mouse was similar to that in the SD rat with a dominance of the tonic highly active neurons. In a Nav1.8 knock out mouse (C57BL6J-Scn10atm1Jwo) in the population of neurons with dendrites from the kidney only a single cell out of 70 showed tonic firing behavior (control vs Nav1.8 KO mouse, z-test, p<0.05). Conclusions: Under physiological conditions, renal sensory neurons exhibit predominantly a firing pattern associated with higher excitability. Our findings in this study support the significance of the TTX-resistant sodium channel Nav1.8 for the specific tonic firing pattern of neurons with renal projections. That might be of importance for pharmacological interventions to influence renal nerve activity, which likely plays a crucial role in the regulation of blood pressure and control of cardiovascular function.

Renal Denervation in End-Stage Renal Disease: Current Evidence and Perspectives.

In patients with end-stage renal disease (ESRD) undergoing haemodialysis, hypertension is of common detection and frequently inadequately controlled. Multiple pathophysiological mechanisms are involved in the development and progression of the ESRD-related high blood pressure state, which has been implicated in the increased cardiovascular risk reported in this hypertensive clinical phenotype. Renal sympathetic efferent and afferent nerves play a relevant role in the development and progression of elevated blood pressure values in patients with ESRD, often leading to resistant hypertension. Catheter-based bilateral renal nerves ablation has been shown to exert blood pressure lowering effects in resistant hypertensive patients with normal kidney function. Promising data on the procedure in ESRD patients with resistant hypertension have been reported in small scale pilot studies. Denervation of the native non-functioning kidney's neural excitatory influences on central sympathetic drive could reduce the elevated cardiovascular morbidity and mortality seen in ESRD patients. The present review article will focus on the promising results obtained with renal denervation in patients with ESRD, its mechanisms of action and future perspectives in these high risk patients.

Abstract 14951: Input From Renal Afferent Nerves Contributes to Hypertensive Heart Failure With Preserved Systolic Function Through Baroreflex Impairment and Sympathoexcitation

Introduction: Activation of renal afferent nerves, which can be caused by hypertensive renal damage, increases sympathetic output. The nucleus tractus solitarius (NTS) receives the inputs from baroreflex afferent nerves as well as renal afferent nerves. Baroreflex dysfunction leads to increased left ventricular (LV) end-diastolic pressure even in the heart with preserved systolic function. The GABAergic inhibitory system in the NTS blunts the signals from baroreflex afferent nerves, resulting in increased sympathetic output. Hypothesis: Input from renal afferent nerves contributes to hypertensive heart failure with preserved systolic function through baroreflex impairment and sympathoexcitation mediated by increased GABAergic inhibition in the NTS. Methods and Results: Male Dahl salt-sensitive rats with 8% high-salt diet from 7 weeks of age develop hypertensive HFpEF at 19 weeks. These rats underwent sham surgery (Sham), selective afferent renal denervation (ARDN), or additionally dissection of baroreflex afferent nerves (ARDN+BAROX) at 9 weeks. As controls, rats underwent sham surgery with a low-salt diet. The rats were evaluated at 19 weeks. Systolic blood pressure was similarly elevated in the three groups on high-salt diet. Impaired LV diastolic function assessed by echocardiography and pressure-volume loop analysis in Sham was recovered in ARDN group, while systolic function was preserved in all the group. Decreased baroreflex sensitivity and increased sympathetic output in Sham were attenuated in ARDN group. Activity of GABAergic neurons in the NTS evaluated by immunostaining was increased in Sham compared to controls, and was attenuated in ARDN group. All of the changes in ARDN were cancelled in ARDN+BAROX group. Conclusion: Input from renal afferent nerves contributes to hypertensive heart failure with preserved systolic function through baroreflex impairment and sympathoexcitation along with increased GABAergic inhibition in the NTS.

The Positive Effect of Renal Denervation Persists even Through Regrowth of Afferent Axons Improving Renal Afferent Nerve Activity During High Sodium Intake in Rats

The Positive Effect of Renal Denervation Persists even Through Regrowth of Afferent Axons Improving Renal Afferent Nerve Activity During High Sodium Intake in Rats