Afferent Renal Nerve Activity Response Research Articles

Deletion of the Transient Receptor Potential Vanilloid 1 Channel Attenuates Sympathoexcitation and Hypertension and Improves Glomerular Filtration Rate in 2-Kidney-1-Clip Rats.

Renal denervation lowers arterial blood pressure in both clinical populations and multiple experimental models of hypertension. This therapeutic effect is partly attributed to the removal of overactive renal sensory nerves. The TRPV1 (transient receptor potential vanilloid 1) channel is highly expressed in renal sensory nerves and detects changes in noxious and mechanosensitive stimuli, pH, and chemokines. However, the extent to which TRPV1 channels contribute to 2-kidney-1-clip (2K1C) renovascular hypertension has not been tested. We generated a novel Trpv1-/- (TRPV1 knockout) rat using CRISPR/Cas9 and 26-bp deletion in exon 3 and induced 2K1C hypertension. The majority (85%) of rat renal sensory neurons retrogradely labeled from the kidney were TRPV1-positive. Trpv1-/- rats lacked TRPV1 immunofluorescence in the dorsal root ganglia, had a delayed tail-flick response to hot but not cold water, and lacked an afferent renal nerve activity response to intrarenal infusion of the TRPV1 agonist capsaicin. Interestingly, 2K1C hypertension was significantly attenuated in male Trpv1-/- versus wild-type rats. 2K1C hypertension significantly increased the depressor response to ganglionic blockade, total renal nerve activity (efferent and afferent), and afferent renal nerve activity in wild-type rats, but these responses were attenuated in male Trpv1-/- rats. 2K1C hypertension was attenuated in female rats with no differences between female strains. Finally, glomerular filtration rate was reduced by 2K1C in wild-type rats but improved in Trpv1-/- rats. These findings suggest that renovascular hypertension requires activation of the TRPV1 channel to elevate renal afferent and sympathetic nerve activity, reduce glomerular filtration rate, and increase arterial blood pressure.

Afferent renal nerve activity response to IL-6 and IL-1ß antagonism in the DOCA-salt rat model of hypertension

Hypertension is the highest risk factor for cardiovascular disease, which remains the leading cause of death worldwide. Though hypertension is a multifaceted disease, there is an increasingly clear role for renal nerves in hypertension progression – both sympathetic and afferent. Moreover, afferent renal nerve activity (ARNA) is reportedly elevated in several models of hypertension and hypothesized to be a major contributor to the disease etiology. Yet, the underlying stimulus for this increased activity is unknown. Previous studies from our lab highlighted a direct correlation between ARNA and renal proinflammatory cytokine content in hypertensive rats, specifically IL-6 and IL-1ß. Therefore, we aimed to acutely disrupt IL-6 and IL-1ß activity to elucidate the direct effects on ARNA in hypertension. We hypothesized that antagonism of IL-6 and IL-1ß will decrease ARNA in hypertensive rats. To address this hypothesis, we employed the deoxycorticosterone acetate (DOCA)-salt model of hypertension. Briefly, uninephrectomized male Sprague Dawley rats (275-325g, n=3) were administered DOCA (100 mg, s.c) and saline drinking water (0.9% NaCl) for three weeks. Next, rats were surgically prepared for renal nerve activity measurement and administration of cytokine antagonists. Under anesthesia (Urethane, 1800 mg/kg/h, IV), a renal nerve bundle of the left kidney was hooked with a bipolar electrode. Renal sympathetic nerve activity (RSNA) was rectified and integrated to identify burst rate. To isolate the ARNA, the proximal end of the nerve bundle was cut and nerve activity was rectified and integrated over 50 ms. Basal ARNA was normalized to peak ARNA response to 5 μl capsaicin (10 μg/μl). To suppress IL-6 and IL-1ß intrarenally, 10 μl of IL-6 antibody (0.1 μg/μl) and 10 μl of IL-1ß antibody (0.1 μg/μl) were injected into the renal artery. Vehicle (saline) injections were used as control. ARNA was recorded for 10 mins after injections and expressed as percentage of baseline (%ARNABase). Data were analyzed by repeated measures one-way ANOVA with Dunnett post hoc test vs. vehicle (*p<.05) and presented as mean±SEM. At time of acute surgical preparation, mean arterial blood pressure was 152±1mmHg. Basal RSNA was 5.4±0.6bursts/s and 1.5±0.26bursts/beat. Resting ARNA was 9.5±2.8%ARNAMAX. Compared to the response to vehicle administration (84.4±8.0 %ARNABase), IL-6 antibody decreased ARNA to *49.8±6.9 %ARNABase. No difference in IL-1ß antibody response (53.6±15.4 %ARNABase, P>.05) was detected compared to vehicle. These preliminary results partially support our hypothesis that antibody-mediated suppression of renal IL-6 acutely lowers ARNA in hypertensive DOCA-salt rats. This highlights that increased ARNA in the hypertension may be driven in part by direct stimulation from proinflammatory cytokines such as IL-6. Further studies are underway to increase sample size, include female cohorts, and measure the effects of antibody treatment in normotensive controls. R00HL141650 (CTB), Doris Duke Charitable Foundation (CTB) This is the full abstract presented at the American Physiology Summit 2023 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.

Sympathoexcitatory responses to renal chemosensitive stimuli are exaggerated at nighttime in rats.

The circadian cycle impacts sympathetic nerve activity (SNA), cardiovascular hemodynamics, and renal function. Activation of renal sensory nerves by chemosensory and mechanosensory stimuli reflexively changes efferent SNA and arterial blood pressure (ABP) to maintain homeostasis. However, it is unclear to what extent circadian cycle influences reflex SNA and ABP responses to renal sensory stimuli. Renal, splanchnic, and lumbar SNA and ABP responses to intrarenal arterial infusion of bradykinin or capsaicin and elevated renal pelvic pressure were measured in male and female Sprague-Dawley rats during nighttime (wakeful/active phase) and daytime (inactive phase). Intrarenal arterial bradykinin infusion significantly increased efferent renal SNA, splanchnic SNA, and ABP but not lumbar SNA. Responses were greater during nighttime versus daytime. Similarly, intrarenal arterial capsaicin infusion significantly increased renal SNA and splanchnic SNA, and responses were again greater during nighttime. Elevated renal pelvic pressure increased renal SNA and splanchnic SNA; however, responses did not differ between daytime and nighttime. Finally, afferent renal nerve activity responses to bradykinin were not different between daytime and nighttime. Thus, renal chemokines elicit greater sympathoexcitatory responses at nighttime that cannot be attributed to differences in afferent renal nerve activity. Collectively, these data suggest that the circadian cycle alters the excitability of central autonomic networks to alter baseline SNA and ABP as well as the magnitude of visceral reflexes.NEW & NOTEWORTHY The current study discovers that the circadian cycle influences sympathetic and hemodynamic responses to activation of renal chemosensitive sensory fibers. Sympathetic responses to intrarenal bradykinin or capsaicin infusion were exaggerated during nighttime (active period), but mechanosensitive responses to elevated renal pelvic pressure were not. Importantly, renal afferent nerve responses were not different between nighttime and daytime. These data suggest that the circadian cycle modulates sympathetic responses to visceral afferent activation.

Renal Afferent Nerve Activation and Arterial Pressure Control: Role of Inflammatory Cytokines in Hypertension

Neural control of the kidney as well as aberrant renal nerve signaling remain a primary focus of research in cardiovascular and renal disease, including hypertension. Recent preclinical reports employing targeted afferent renal nerve ablation have confirmed the central role for afferent renal nerves in the development of hypertension, including studies in the DOCA‐salt rat. Moreover, direct measurement of afferent renal nerve activity (ARNA) in DOCA‐salt rats revealed elevated tonic ARNA; however, the mechanisms contributing to the increased ARNA, and in turn hypertension, remain unaddressed. Renal inflammation is postulated to be a primary contributor to the aberrant ARNA in this model, due to the elevated pro‐inflammatory cytokines (IL‐1β, IL‐6, TNFα, MCP‐1, GRO/KC) present in the DOCA‐salt kidneys. Therefore, we aimed to directly test the role of these cytokines in modulating ARNA and concomitant cardiovascular responses in normotensive and DOCA‐salt rats. We hypothesized intrarenal inflammatory cytokine administration would increase ARNA and arterial pressure (AP) in both treatment groups.To interrogate this hypothesis, unilateral nephrectomized male Sprague Dawley rats (300–350g; n=16) were administered 100mg DOCA (s.c.) or silicone vehicle (n=8/group), followed by 3vweeks of high salt diet administered through drinking water (0.9% NaCl). Each animal then underwent an acute surgical preparation under isoflurane anesthesia (2%) to record AP, heart rate (HR), and ARNA responses to randomized intrarenal injection (10μL; 0.1 μg/μL) of the following cytokines: IL‐1β, IL‐6, TNFα, MCP‐1, GRO/KC, and 0.9% saline (VEH). ARNA responses were normalized to maximal afferent activation (%Amax) achieved by TRPV1‐agonist (capsaicin; 50μM) injection at end of protocol. Responses between and within treatment groups were analyzed by a repeated‐measures two‐way ANOVA (α=.05). Data presented as mean ± SEM. * p<.05 vs. Vehicle; # p<.05 vs. Saline.Prior to stimulation, baseline ARNA (4.9 ± 1.3 vs. 13.8 ± 2.1 %Amax) and AP (106 ± 2 vs. *151 ± 5 mmHg) were elevated in DOCA rats vs. vehicle controls. Compared to VEH responses, no changes from baseline ARNA, AP or HR responses were detected following IL‐1β, TNFα, MCP‐1, or GRO/KC injection. Compared to saline vehicle, IL‐6 injection produced an increase in ARNA in both VEH (5.9 ± 1.8 vs. #24.1 ± 5.4 %Amax) and DOCA rats (14.7 ± 2.2 vs. #24.1 ± 5.4 %Amax). Interestingly, AP decreased following IL‐6 injection in parallel to ARNA stimulation in VEH (1 ± 1 vs. −6 ± 2mmHg) and DOCA (0 ± 1 vs. −11 ± 4mmHg) compared to saline. No differences in responses between DOCA and VEH were detected.To summarize, IL‐6 injection increased ARNA in both VEH and DOCA supported our hypothesis; however, the corresponding depressor responses did not. Together, we conclude IL‐6 is a direct activator of ARNA independent of DOCA. Several studies have previously reported a depressor response following ARNA activation under anesthesia, so the central processing of ARNA may be altered under anesthesia compared to the conscious state, which is a limitation of this study. Current dose‐response studies and conscious preparations are underway to elucidate this important cardio‐renal‐neural axis in blood pressure homeostasis.Support or Funding InformationNIH R00HL141650 (CTB); R01HL116476 (JWO)

Abstract P231: High Fat Diet-induced Er Stress and Inflammation in the Kidney: Role of Trpv1-positive Afferent Renal Nerves

Chronic high fat diet (HFD) intake may lead to enhancement in endoplasmic reticulum (ER) stress, reactive oxygen species (ROS) production, and inflammation in the kidney, but the mechanisms of HD effects are largely unknown. This study tests the hypothesis that HFD impairs afferent renal nerves expressing the transient receptor potential vanilloid 1 (TRPV1) channels, and that stimulating/preserving TRPV1-positive afferent renal nerves prevents against HFD-induced increases in ER stress, ROS production, and inflammation in the kidney. HFD decreased levels of TRPV1 in the kidney, levels of urinary calcitonin-gene related peptide (CGRP) and substance P (SP), and responses of afferent renal nerve activity (ARNA) to capsaicin, a TRPV1 agonist, perfused into the renal pelvis. HFD increased ER stress (XBP-1, CREB2, GRP78, p-JNK), ROS production (urinary 8-isoprostane), and inflammation (TNF-α, IL-1β) in the kidney. N-oleoyldopamine (OLDA, a TRPV1 agonist, 1 ng/kg, daily) or vehicle was given intrathecally (i.t.) via indwelled catheters to segments (T8-L3) supplying the kidneys of rats fed a HFD or normal fat diet (Con) for 8 weeks. OLDA prevented HFD-induced decreases in the levels of renal TRPV1, urinary CGRP and SP, and ARNA responses to capsaicin, as well as HFD-induced increases in renal ER stress, ROS production, and inflammation. OLDA-induced protection during HFD was abolished by degeneration of TRPV1-positive afferent renal nerves by topical application of resiniferatoxin (RTX, 2 μg/ml x 2 times), a potent TRPV1 agonist, on renal nerves (TNF-α, Con: 0.17±0.02, HFD: 0.41±0.03, HFD+OLDA: 0.21±0.02, HFD+OLDA+RTX: 0.46±0.04, p<0.05; 8-isoprostane, Con: 8.8±1.2, HFD: 17±2, HFD+OLDA: 11±1, HFD+OLDA+RTX: 22±3 ng/day, p<0.05). Thus, our data show that HFD impairs TRPV1-positive afferent renal nerves, and chronic stimulation of TRPV1 via intrathecal injection of OLDA to T8-L3 segments preserves TRPV1-positive afferent renal nerves to against HFD-induced ER stress, ROS production, and inflammation in the kidney given that impairment of this population of afferent renal nerves abolishes OLDA effects. These data indicate that TRPV1-positive afferent renal nerves play a counteractive role against HFD-induced renal injury.

Norepinephrine (NE)‐mediated activation of renal sensory nerves is controlled by a crosstalk between the PLC/PKC and adenylyl cyclase/cAMP/PKA transduction pathways

NE increases and decreases afferent renal nerve activity (ARNA) by activating α1-adrenoceptors (AR) and α2-AR, respectively, on renal sensory nerves. Stimulation of α1-AR activates PLC and PKC leading to increased PGE2 release which in turn activates the adenylyl cyclase (AC)/cAMP/PKA transduction cascade resulting in increases in substance P release and ARNA. Activation of α2-AR results in decreased substance P release in association with decreased PGE2 release. To examine the mechanisms involved in the α2-mediated reduction in substance P and PGE2 release, renal pelvises were pretreated with pertussis toxin (PTX), deactivator of Gi proteins. PTX enhanced the NE-induced activation of the renal sensory nerves to a similar extent as an α2-AR antagonist. These data suggest that NE-mediated activation of α2-AR, coupled to Gi proteins, leads to reduction in AC activity. In isolated renal pelvises, NE 2 pM failed to increase substance P and PGE2 release. However in the presence of the AC activator forskolin, 2 pM NE increased renal pelvic release of PGE2 from 97±8 to 274±30 pg/min and substance P from 5±1 to 10±1 pg/min (P<0.01, n=8). The forskolin-induced enhancement of the NE-induced increases in PGE2 and substance P release were abolished by indomethacin (P<0.01, n=6), the AC inhibitor dideoxyadenosine (n=4) and the PLC inhibitor U73122 (P<0.01, n=9). Likewise, in vivo studies showed that renal pelvic perfusion with forskolin resulted in enhanced ARNA responses to 2 pM NE that were reduced by U73122. Conclusion NE-mediated activation of renal sensory nerves involves a positive feedback loop consisting of AC facilitating the α1-AR-stimulation of PLC/PKC which in turn leads to increased PGE2 release with subsequent release of substance P and increased ARNA. This is counter regulated by α2-AR mediated inhibition of AC.

Impaired Interaction Between Efferent and Afferent Renal Nerve Activity in SHR Involves Increased Activation of α 2 -Adrenoceptors

Activation of efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), leading to decreases in ERSNA by activation of the renorenal reflexes in the overall goal of maintaining low ERSNA. The renorenal reflex responses to various stimuli are impaired in spontaneously hypertensive rats (SHR). Because renal tissue density of α(2)-adrenoceptors (ARs) is increased in SHR, we examined whether the ERSNA-induced increases in ARNA are impaired in SHR and, if so, the role of α(2)-ARs. The ARNA responses to increases in ERSNA were impaired in SHR, 2390 ± 460%·seconds, versus in Wistar-Kyoto rats, 6620 ± 1690%·seconds. Renal pelvic release of substance P was not altered by 6250 pmol/L norepinephrine (NE) in SHR but was increased by 250 pmol/L NE in Wistar-Kyoto rats, from 5.7 ± 0.7 to 12.5±1.3 pg/min. Renal pelvic administration of the α(2)-AR antagonist rauwolscine enhanced the ERSNA-induced increases in ARNA, 4170 ± 900%·seconds, in SHR but not in Wistar-Kyoto rats. In the presence of rauwolscine, 250 pmol/L NE increased substance P release, from 5.2 ± 0.3 to 11.2 ± 0.8 pg/min, in pelvises from SHR. Because angiotensin II suppresses the activation of renal mechanosensory nerves in SHR, we examined whether losartan improved the ERSNA-induced ARNA responses. Losartan had no effect on the ARNA responses or the NE-induced increases in substance P in SHR. However, losartan+rauwolscine resulted in further enhancement of the responsiveness of the renal sensory nerves to increases in ERSNA and NE in SHR but not in WKY. We conclude that increased activation of renal α(2)-ARs and angiotensin II type 1 receptors contributes to the impaired interaction between ERSNA and ARNA in SHR.

Dietary sodium modulates the interaction between efferent and afferent renal nerve activity by altering activation of α2-adrenoceptors on renal sensory nerves

Activation of efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), which then reflexively decreases ERSNA via activation of the renorenal reflexes to maintain low ERSNA. The ERSNA-ARNA interaction is mediated by norepinephrine (NE) that increases and decreases ARNA by activation of renal α(1)-and α(2)-adrenoceptors (AR), respectively. The ERSNA-induced increases in ARNA are suppressed during a low-sodium (2,470 ± 770% s) and enhanced during a high-sodium diet (5,670 ± 1,260% s). We examined the role of α(2)-AR in modulating the responsiveness of renal sensory nerves during low- and high-sodium diets. Immunohistochemical analysis suggested the presence of α(2A)-AR and α(2C)-AR subtypes on renal sensory nerves. During the low-sodium diet, renal pelvic administration of the α(2)-AR antagonist rauwolscine or the AT1 receptor antagonist losartan alone failed to alter the ARNA responses to reflex increases in ERSNA. Likewise, renal pelvic release of substance P produced by 250 pM NE (from 8.0 ± 1.3 to 8.5 ± 1.6 pg/min) was not affected by rauwolscine or losartan alone. However, rauwolscine+losartan enhanced the ARNA responses to reflex increases in ERSNA (4,680 ± 1,240%·s), and renal pelvic release of substance P by 250 pM NE, from 8.3 ± 0.6 to 14.2 ± 0.8 pg/min. During a high-sodium diet, rauwolscine had no effect on the ARNA response to reflex increases in ERSNA or renal pelvic release of substance P produced by NE. Losartan was not examined because of low endogenous ANG II levels in renal pelvic tissue during a high-sodium diet. Increased activation of α(2)-AR contributes to the reduced interaction between ERSNA and ARNA during low-sodium intake, whereas no/minimal activation of α(2)-AR contributes to the enhanced ERSNA-ARNA interaction under conditions of high sodium intake.

Activation of endothelin A receptors contributes to impaired responsiveness of renal mechanosensory nerves in congestive heart failureThis article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research.

Increasing renal pelvic pressure results in PGE2-mediated release of substance P, leading to increases in afferent renal nerve activity (ARNA) and natriuresis, that is, a renorenal reflex response. The renorenal reflexes are impaired in congestive heart failure (CHF). Impairment of the renorenal reflexes may contribute to the increased renal sympathetic nerve activity and sodium retention in CHF. Endothelin (ET)-1 contributes to the pathological changes in cardiac and renal function in CHF. Therefore, we examined whether the ETA receptor antagonist BQ123 altered the responsiveness of renal mechanosensory nerves in CHF. The ARNA responses to increasing renal pelvic pressure were suppressed in CHF but not in sham-CHF rats. In CHF, increasing renal pelvic pressure by 7.5 mm Hg before and during renal pelvic perfusion with BQ123 increased ARNA 12% +/- 3% and 21% +/- 3% (p < 0.05 vs. vehicle). In isolated renal pelvises from CHF rats, PGE2 increased substance P release from 5 +/- 0 to 7 +/- 1 pg/min without BQ123 and from 4 +/- 1 to 9 +/- 1 pg/min with BQ123 in the bath (p < 0.01 vs. vehicle). BQ123 had no effect on the ARNA responses or substance P release in sham-CHF. In conclusion, activation of ETA receptors contributes to the impaired responsiveness of renal mechanosensory nerves in CHF rats by a mechanism(s) at the renal sensory nerve endings.

Dietary sodium modulates the interaction between efferent renal sympathetic nerve activity and afferent renal nerve activity: role of endothelin

Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), which in turn decreases ERSNA via activation of the renorenal reflexes in the overall goal of maintaining low ERSNA. We now examined whether the ERSNA-induced increases in ARNA are modulated by dietary sodium and the role of endothelin (ET). The ARNA response to reflex increases in ERSNA was enhanced in high (HNa)- vs. low-sodium (LNa) diet rats, 7,560 +/- 1,470 vs. 900 +/- 390%.s. The norepinephrine (NE) concentration required to increase PGE(2) and substance P release from isolated renal pelvises was 10 pM in HNa and 6,250 pM in LNa diet rats. In HNa diet pelvises 10 pM NE increased PGE(2) release from 67 +/- 6 to 150 +/- 13 pg/min and substance P release from 6.7 +/- 0.8 to 12.3 +/- 1.8 pg/min. In LNa diet pelvises 6,250 pM NE increased PGE(2) release from 64 +/- 5 to 129 +/- 22 pg/min and substance P release from 4.5 +/- 0.4 to 6.6 +/- 0.7 pg/min. In the renal pelvic wall, ETB-R are present on unmyelinated Schwann cells close to the afferent nerves and ETA-R on smooth muscle cells. ETA-receptor (R) protein expression in the renal pelvic wall is increased in LNa diet. In HNa diet, renal pelvic administration of the ETB-R antagonist BQ788 reduced ERSNA-induced increases in ARNA and NE-induced release of PGE(2) and substance P. In LNa diet, the ETA-R antagonist BQ123 enhanced ERSNA-induced increases in ARNA and NE-induced release of substance P without altering PGE(2) release. In conclusion, activation of ETB-R and ETA-R contributes to the enhanced and suppressed interaction between ERSNA and ARNA in conditions of HNa and LNa diet, respectively, suggesting a role for ET in the renal control of ERSNA that is dependent on dietary sodium.

Salt sensitive modulation of the interaction between efferent and afferent renal nerve activity mediated by PGE2 and endothelin (ET)

Increases in efferent renal sympathetic nerve activity (ERSNA) increase afferent renal nerve activity (ARNA) which in turn decreases ERSNA via activation of the renorenal reflexes in the overall goal of maintaining low ERSNA to limit sodium retention. We examined if dietary sodium modulates the interaction between ERSNA and ARNA and the norepinephrine (NE)‐induced activation of renal sensory nerves. Thermal cutaneous stimulation (HOT) to increase ERSNA was produced by placing the rat's tail in 47 and 49°C water in rats fed high sodium (HNa) and low sodium (LNa) diet (lower heat activation threshold in HNa vs LNa rats). HOT increased ERSNA and ARNA 100120 ± 1830 and 7660±1380 % sec (AUC) in HNa rats and 4370 ± 1290 and 970 ± 420% sec in LNa rats. In isolated renal pelvises from HNa rats, NE 10 pM increased the release of substance P from 7 ± 1 to 12 ± 2 pg/min and PGE2 from 67 ± 1 to 150 ± 13 pg/min. In pelvises from LNa rats, NE 10‐6250 pM had no effect. Renal pelvic administration of the ET B receptor (ETB‐R) antagonist BQ788 blocked the ARNA response to HOT by 76 ± 6% in vivo and the NE‐induced increases in substance P and PGE2 by 65 ± 16 and 34 ± 15% in vitro. Conversely in LNa rats, the ETA‐R antagonist BQ123 enhanced the ARNA response to HOT from 970 to 7360 ± 2124 % sec and the renal pelvic release of substance P produced by NE 6250 pM. NE increased substance P release from 5 ± 0 to 7 ± 1 pg/min (NS) before and from 5 ± 1 to 9 ± 1 pg/min (P&lt;0.01) during BQ123. BQ123 had no effect on the NE‐induced release of PGE2. BQ788 and BQ123 have no effect in normal sodium diet rats.Conclusion: Activation of ETB‐R contributes to the increased PGE2 synthesis and increased interaction between ERSNA and ARNA in HNa rats. Activation of ETA‐R contributes to the decreased interaction between ERSNA and ARNA in LNa rats by a mechanism distal to PGE2 synthesis.

Renal sympathetic nerve activity modulates afferent renal nerve activity by PGE2-dependent activation of α1- and α2-adrenoceptors on renal sensory nerve fibers

Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA). To test whether the ERSNA-induced increases in ARNA involved norepinephrine activating alpha-adrenoceptors on the renal sensory nerves, we examined the effects of renal pelvic administration of the alpha(1)- and alpha(2)-adrenoceptor antagonists prazosin and rauwolscine on the ARNA responses to reflex increases in ERSNA (placing the rat's tail in 49 degrees C water) and renal pelvic perfusion with norepinephrine in anesthetized rats. Hot tail increased ERSNA and ARNA, 6,930 +/- 900 and 4,870 +/- 670%.s (area under the curve ARNA vs. time). Renal pelvic perfusion with norepinephrine increased ARNA 1,870 +/- 210%.s. Immunohistochemical studies showed that the sympathetic and sensory nerves were closely related in the pelvic wall. Renal pelvic perfusion with prazosin blocked and rauwolscine enhanced the ARNA responses to reflex increases in ERSNA and norepinephrine. Studies in a denervated renal pelvic wall preparation showed that norepinephrine increased substance P release, from 8 +/- 1 to 16 +/- 1 pg/min, and PGE(2) release, from 77 +/- 11 to 161 +/- 23 pg/min, suggesting a role for PGE(2) in the norepinephrine-induced activation of renal sensory nerves. Prazosin and indomethacin reduced and rauwolscine enhanced the norepinephrine-induced increases in substance P and PGE(2). PGE(2) enhanced the norepinephrine-induced activation of renal sensory nerves by stimulation of EP4 receptors. Interaction between ERSNA and ARNA is modulated by norepinephrine, which increases and decreases the activation of the renal sensory nerves by stimulating alpha(1)- and alpha(2)-adrenoceptors, respectively, on the renal pelvic sensory nerve fibers. Norepinephrine-induced activation of the sensory nerves is dependent on renal pelvic synthesis/release of PGE(2).

Activation of Endothelin-A Receptors Contributes to Angiotensin-Induced Suppression of Renal Sensory Nerve Activation

Activation of renal mechanosensory nerves is enhanced by a high-sodium diet and suppressed by a low-sodium diet. Angiotensin (Ang) II and endothelin (ET)-1 each contributes to the impaired responsiveness of renal mechanosensory nerves in a low-sodium diet. We examined whether stimulation of ETA receptors (Rs) contributes to Ang II-induced suppression of the responsiveness of renal mechanosensory nerves. In anesthetized rats fed a low-sodium diet, renal pelvic administration of the Ang type I receptor (AT1-R) antagonist losartan enhanced the afferent renal nerve activity (ARNA) response to increasing renal pelvic pressure 7.5 mm Hg from 7+/-2% to 15+/-2% and the prostaglandin (PG) E(2)-mediated substance P release from 0+/-1 to 8+/-1 pg/min. Adding the ETA-R antagonist BQ123 to the renal pelvic perfusate containing losartan did not produce any further enhancement of the ARNA response or PGE(2)-mediated release of substance P (17+/-3% and 8+/-1 pg/min). Likewise, renal pelvic administration of BQ123 and BQ123+losartan resulted in similar enhancements of the ARNA responses to increased renal pelvic pressure and PGE(2)-mediated substance P release. In high-sodium-diet rats, pelvic administration of Ang II reduced the ARNA response to increased renal pelvic pressure from 27+/-4% to 8+/-3% and the PGE(2)-mediated substance P release from 9+/-0 to 1+/-1 pg/min. Adding BQ123 to the renal pelvic perfusate containing Ang II restored the increases in ARNA and the PGE(2)-mediated substance P release toward control (27+/-6% and 7+/-1 pg/min). In conclusion, stimulation of ETA-R plays an important contributory role to the Ang II-mediated suppression of the activation of renal mechanosensory nerves in conditions of low-sodium diet.

Differential effects of endothelin on activation of renal mechanosensory nerves: stimulatory in high-sodium diet and inhibitory in low-sodium diet

Activation of renal mechanosensory nerves is enhanced by high and suppressed by low sodium dietary intake. Afferent renal denervation results in salt-sensitive hypertension, suggesting that activation of the afferent renal nerves contributes to water and sodium balance. Another model of salt-sensitive hypertension is the endothelin B receptor (ETBR)-deficient rat. ET and its receptors are present in sensory nerves. Therefore, we examined whether ET receptor blockade altered the responsiveness of the renal sensory nerves. In anesthetized rats fed high-sodium diet, renal pelvic administration of the ETBR antagonist BQ-788 reduced the afferent renal nerve activity (ARNA) response to increasing renal pelvic pressure 7.5 mmHg from 26+/-3 to 9+/-3% and the PGE2-mediated renal pelvic release of substance P from 9+/-1 to 3+/-1 pg/min. Conversely, in rats fed low-sodium diet, renal pelvic administration of the ETAR antagonist BQ-123 enhanced the ARNA response to increased renal pelvic pressure from 9+/-2 to 23+/-6% and the PGE2-mediated renal pelvic release of substance P from 0+/-0 to 6+/-1 pg/min. Adding the ETAR antagonist to ETBR-blocked renal pelvises restored the responsiveness of renal sensory nerves in rats fed a high-sodium diet. Adding the ETBR antagonist to ETAR-blocked pelvises suppressed the responsiveness of the renal sensory nerves in rats fed a low-sodium diet. In conclusion, activation of ETBR and ETAR contributes to the enhanced and suppressed responsiveness of renal sensory nerves in conditions of high- and low-sodium dietary intake, respectively. Impaired renorenal reflexes may contribute to the salt-sensitive hypertension in the ETBR-deficient rat.

Interaction between endothelin and angiotensin in the activation of renal sensory nerves

Increasing renal pelvic pressure increases afferent renal nerve activity (ARNA) and urinary sodium excretion. Low sodium (LNA) diet impairs and high Na diet (HNA) enhances the activation of renal sensory nerves. Renal pelvic administration of losartan or the endothelin A receptor (ETA-R) antagonist BQ123 enhances the activation of renal sensory nerves in LNA diet rats. We now examined if angiotensin (ANG) II suppresses ARNA via interaction with ET. ANG II is present in renal pelvis and its levels are higher in LNA than in HNA diet rats. ET-1 is also present in renal pelvis, its levels being similar in LNA and HNA diet, 13∀2 and 13∀2 pg/mg protein. The ET-1 levels in renal pelvis were lower than in papilla but higher than in cortex; 191∀33 and 1.3∀0.1 pg/mg protein. In LNA diet rats, increasing renal pelvic pressure 7.5 mmHg in the presence of renal pelvic perfusion with vehicle, losartan and losartan+BQ123 increased ARNA 7∀2, 14∀2 and 16∀3%. Thus losartan and losartan+BQ123 resulted in similar enhancements of the ARNA response (P<0.01 vs vehicle). Similar results were produced when renal pelvis was perfused with BQ123 before BQ123+losartan. In isolated renal pelvises from LNA diet rats, PGE2 failed to increase substance P (SP) release. Adding losartan or losartan+BQ123 to the incubation bath enhanced the PGE2-mediated SP release to a similar extent, from 7∀1 to 15∀2 and from 9∀1 to 16∀1 pg/min, both P<0.01. Similar results were produced by incubating pelvises in BQ123 or BQ123+losartan. In isolated pelvises from HNA diet rats, PGE2 increased SP, from 5∀2 to 13∀2 pg/min (P<0.01). Adding ANG II to the bath abolished the PGE2-mediated SP release. However, incubating the pelvises with ANG II+BQ123 restored the PGE2-mediated SP release, from 6∀1 to 13∀1 pg/min (P<0.01). Conclusion, ET-1 by activating ETA-R contributes to ANG II-mediated suppression of the activation of renal sensory nerves.

Activation of EP4 receptors contributes to prostaglandin E2-mediated stimulation of renal sensory nerves

Induction of cyclooxygenase-2 (COX-2) in the renal pelvic wall increases prostaglandin E(2) (PGE(2)) leading to stimulation of cAMP production, which results in substance P (SP) release and activation of renal mechanosensory nerves. The subtype of PGE receptors involved, EP2 and/or EP4, was studied by immunohistochemistry and renal pelvic administration of agonists and antagonists of EP2 and EP4 receptors. EP4 receptor-like immunoreactivity (LI) was colocalized with calcitonin gene-related peptide (CGRP)-LI in dorsal root ganglia (DRGs) at Th(9)-L(1) and in nerve terminals in the renal pelvic wall. Th(9)-L(1) DRG neurons also contained EP3 receptor-LI and COX-2-LI, each of which was colocalized with CGRP-LI in some neurons. No renal pelvic nerves contained EP3 receptor-LI and only very few nerves COX-2-LI. The EP1/EP2 receptor antagonist AH-6809 (20 microM) had no effect on SP release produced by PGE(2) (0.14 microM) from an isolated rat renal pelvic wall preparation. However, the EP4 receptor antagonist L-161,982 (10 microM) blocked the SP release produced by the EP2/EP4 receptor agonist butaprost (10 microM) 12 +/- 2 vs. 2 +/- 1 and PGE(2), 9 +/- 1 vs. 1 +/- 0 pg/min. The SP release by butaprost and PGE(2) was similarly blocked by the EP4 receptor antagonist AH-23848 (30 microM). In anesthetized rats, the afferent renal nerve activity (ARNA) responses to butaprost 700 +/- 100 and PGE(2).780 +/- 100%.s (area under the curve of ARNA vs. time) were unaffected by renal pelvic perfusion with AH-6809. However, 1 microM L-161,982 and 10 microM AH-23848 blocked the ARNA responses to butaprost by 94 +/- 5 and 78 +/- 10%, respectively, and to PGE(2) by 74 +/- 16 and 74 +/- 11%, respectively. L-161,982 also blocked the ARNA response to increasing renal pelvic pressure 10 mmHg, 85 +/- 5%. In conclusion, PGE(2) increases renal pelvic release of SP and ARNA by activating EP4 receptors on renal sensory nerve fibers.

Angiotensin blocks substance P release from renal sensory nerves by inhibiting PGE2-mediated activation of cAMP.

Activation of renal sensory nerves involves PGE2-mediated release of substance P (SP) via activation of the cAMP-PKA pathway. The PGE2-mediated SP release is suppressed by a low- and enhanced by a high-sodium (Na+) diet, suggesting an inhibitory effect of ANG. We now examined whether ANG II is present in the pelvic wall and inhibits PGE2-mediated SP release by blocking PGE2-mediated increases in cAMP. ANG II levels in renal pelvic tissue were 710 +/- 95 and 260 +/- 30 fmol/g tissue in rats fed a low- and high-Na+ diet, respectively. In a renal pelvic preparation from high-Na+-diet rats, 0.14 microM PGE2 produced an increase in SP release from 7 +/- 1 to 19 +/- 3 pg/min that was blocked by 15 nM ANG II. Treating pelvises with pertussis toxin (PTX) abolished the effects of ANG II. In pelvises from low-Na+ rats, neither basal nor bradykinin-mediated SP release was altered by PGE2. However, the bradykinin-mediated release of SP was enhanced by the permeable cAMP analog CPT-cAMP, from 4 +/- 1 to 11 +/- 2 pg/min, a response similar to that in normal-Na+-diet rats. In vivo, renal pelvic administration of PGE2 enhanced the afferent renal nerve activity (ARNA) response to bradykinin in normal- but not in low-Na+ diet rats. CPT-cAMP produced similar enhancement of the ARNA responses to bradykinin in normal- and low-Na+-diet rats, 1,670 +/- 490 and 1,760 +/- 400%.s (area under the curve of ARNA vs. time). Similarly, the ARNA responses to increases in renal pelvic pressure were similarly enhanced by CPT-cAMP in normal- and low-Na+-diet rats. In conclusion, renal pelvic ANG II modulates the responsiveness of renal sensory nerves by suppressing PGE2-mediated activation of adenylyl cyclase via a PTX-sensitive mechanism.

Impaired responsiveness of renal mechanosensory nerves in heart failure: role of endogenous angiotensin.

Increasing renal pelvic pressure results in PGE(2)-mediated release of substance P. Substance P increases afferent renal nerve activity (ARNA), which leads to a reflex increase in urinary sodium excretion (U(Na)V). Endogenous ANG II modulates the responsiveness of renal mechanosensory nerves. The ARNA and U(Na)V responses are suppressed by low- and enhanced by high-sodium diet. We examined whether the ARNA responses are altered in rats with congestive heart failure (CHF), a condition characterized by increased ANG II and sodium retention. The ARNA responses to increasing renal pelvic pressure </=7.5 mmHg were suppressed in CHF vs. sham-CHF rats fed normal sodium diet. In CHF rats, increasing renal pelvic pressure 2.5 and 7.5 mmHg increased ARNA 0 +/- 1 and 13 +/- 2% (P < 0.01) before and 9 +/- 1 (P < 0.01) and 19 +/- 1% (P < 0.01) during renal pelvic perfusion with losartan. Losartan had no effect on the ARNA responses in sham-CHF rats. In isolated renal pelvises from CHF rats, PGE(2) increased substance P release from 11 +/- 2 to 15 +/- 3 pg/min (not significant) without and from 16 +/- 2 to 30 +/- 4 pg/min (P < 0.01) with losartan in the incubation bath. Losartan had no effect on PGE(2)-mediated substance P release in sham-CHF rats. In conclusion, the responsiveness of renal mechanosensory nerves is impaired in CHF rats due to ANG II inhibiting PGE(2)-mediated release of substance P from renal pelvic nerves.

PGE(2) increases release of substance P from renal sensory nerves by activating the cAMP-PKA transduction cascade.

Increasing renal pelvic pressure increases afferent renal nerve activity (ARNA) by a PGE(2)-mediated release of substance P (SP) from renal pelvic nerves. The role of cAMP activation in the PGE(2)-mediated release of SP was studied by examining the effects of the adenylyl cyclase (AC) activator forskolin and AC inhibitor dideoxyadenosine (DDA). Forskolin enhanced the bradykinin-mediated release of SP from an isolated rat renal pelvic wall preparation, from 7.3 +/- 1.3 to 15.6 +/- 3.0 pg/min. PGE(2) at a subthreshold concentration for SP release mimicked the effects of forskolin. The EP(2) receptor agonist butaprost, 15 microM, and PGE(2), 0.14 microM, produced similar increases in SP release, from 5.8 +/- 0.8 to 17.0 +/- 2.3 pg/min and from 8.0 +/- 1.3 to 21.6 +/- 2.7 pg/min. DDA blocked the SP release produced by butaprost and PGE(2). The PGE(2)-induced release of SP was also blocked by the PKA inhibitors PKI(14-22) and H-89. Studies in anesthetized rats showed that renal pelvic administration of butaprost, 10 microM, and PGE(2), 0.14 microM, resulted in similar ARNA responses, 1,520 +/- 390 and 1,170 +/- 270%. s (area under the curve of ARNA vs. time) that were blocked by DDA. Likewise, the ARNA response to increased renal pelvic pressure, 7,180 +/- 710%. s, was blocked by DDA. In conclusion, PGE(2) activates the cAMP-PKA pathway leading to a release of SP and activation of renal pelvic mechanosensory nerve fibers.

Endogenous angiotensin modulates PGE(2)-mediated release of substance P from renal mechanosensory nerve fibers.

Increasing renal pelvic pressure increases afferent renal nerve activity (ARNA) by a prostaglandin E2 (PGE2)-mediated release of substance P (SP) from renal pelvic sensory nerves. We examined whether the ARNA responses were modulated by high- and low-sodium diets. Increasing renal pelvic pressure resulted in greater ARNA responses in rats fed a high-sodium than in those fed a low-sodium diet. In rats fed a low-sodium diet, increasing renal pelvic pressure 2.5 and 7.5 mmHg increased ARNA 2 +/- 1 and 13 +/- 1% before and 12 +/- 1 and 22 +/- 2% during renal pelvic perfusion with 0.44 mM losartan. In rats fed a high-sodium diet, similar increases in renal pelvic pressure increased ARNA 10 +/- 1 and 23 +/- 3% before and 1 +/- 1 and 11 +/- 2% during pelvic perfusion with 15 nM ANG II. The PGE2-mediated release of SP from renal pelvic nerves in vitro was enhanced in rats fed a high-sodium diet and suppressed in rats fed a low-sodium diet. The PGE2 concentration required for SP release was 0.03, 0.14, and 3.5 microM in rats fed high-, normal-, and low-sodium diets. In rats fed a low-sodium diet, PGE2 increased renal pelvic SP release from 5 +/- 1 to 6 +/- 1 pg/min without and from 12 +/- 1 to 21 +/- 2 pg/min with losartan in the incubation bath. Losartan had no effect on SP release in rats fed normal- and high-sodium diets. ANG II modulates the responsiveness of renal pelvic mechanosensory nerves by inhibiting PGE2-mediated SP release from renal pelvic nerve fibers.