The rat renal nerves during development

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

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

Innervation of the developing kidney in vivo and in vitro

Within the adult kidney, renal neurites can be observed alongside the arteries where they play a role in regulating blood flow. However, their role and localization during development has so far not been described in detail. In other tissues, such as the skin of developing limb buds, neurons play an important role during arterial differentiation. Here, we aim to investigate whether renal nerves could potentially carry out a similar role during arterial development in the mouse kidney. In order to do so, we used whole-mount immunofluorescence staining to identify whether the timing of neuronal innervation correlates with the recruitment of arterial smooth muscle cells. Our results show that neurites innervate the kidney between day 13.5 and 14.5 of development, arriving after the recruitment of smooth muscle actin-positive cells to the renal arteries.

Function of Renal Nerves in Kidney Physiology and Pathophysiology

Renal sympathetic (efferent) nerves play an important role in the regulation of renal function, including glomerular filtration, sodium reabsorption, and renin release. The kidney is also innervated by sensory (afferent) nerves that relay information to the brain to modulate sympathetic outflow. Hypertension and other cardiometabolic diseases are linked to overactivity of renal sympathetic and sensory nerves, but our mechanistic understanding of these relationships is limited. Clinical trials of catheter-based renal nerve ablation to treat hypertension have yielded promising results. Therefore, a greater understanding of how renal nerves control the kidney under physiological and pathophysiological conditions is needed. In this review, we provide an overview of the current knowledge of the anatomy of efferent and afferent renal nerves and their functions in normal and pathophysiological conditions. We also suggest further avenues of research for development of novel therapies targeting the renal nerves.

The morphogenesis of the renal plexus: Renal artery and sympathetic fibers

To examine the origin and development of the renal plexus and its relationship to the renal vessels in embryos and early human fetuses. Serial sections of 34 human embryos (stages 16 to 23 of Carnegie, 4 or 5-8 weeks) and 38 fetuses (9-19 weeks) were analyzed. Throughout the embryonic period, the kidney was not innervated by the renal plexus. Those nerves appeared at the beginning of the early fetal period (9 weeks) as branches given off by the immature autonomic abdominal plexus. The renal nerves started to approach to the kidney during the early fetal period at 9-10 weeks of development. They were distributed in close proximity to the renal arteries and their branches. They were observed first with the settlement of the renal veins. The renal artery is present as a branch of the abdominal aorta at stage 19 (between 6 and 7 weeks) prior to development of the renal plexus. The renal veins were not present during the embryonic period but appeared at the start of the fetal period, along with the renal nerves that emerged from segmented sympathetic para-aortic bodies (SPBs). Clin. Anat. 32:272-276, 2019. © 2018 Wiley Periodicals, Inc.

Differential Distribution of Renal Nerves in the Sympathetic Ganglia of the Rat

The renal nerve plexus comprises efferent and afferent fibers. It controls urine production and bodily fluid homeostasis. Efferent fibers to the kidney include sympathetic nerve fibers from their main ganglia, the prevertebral suprarenal ganglia (SrG), and the paravertebral sympathetic chain ganglia (ChG). In the present study, we examined topological innervation from these ganglia to the renal parenchymal segments of the left kidney of the rat. Fluoro-Gold was injected into the rostral or caudal poles of the left kidney. Approximately 50% of the cells in the SrG of rats injected in the rostral pole were labeled, while 60% of the cells in the ChG T13 of rats injected in the caudal pole were labeled. In addition, we performed dual-probe retrograde tracing of the nerves using two kinds of fluorescent-conjugated cholera toxins (f-CTbs) injected into the rostral and caudal poles of the left kidney. The cells labeled with each f-CTb were distributed differently in the left SrG and the lower ChGs; no dual-labeled cells were found in these ganglia. Anterograde tracing with pCAGGS-tdTomato vector transfected into the left SrG showed that tdTomato-labeled nerve varicosities extended to the cortical arterioles and urinary tubules. Immunohistochemistry revealed that they were positive to tyrosine hydroxylase and synaptophysin, suggesting that they possessed sympathetic nerve endings. Our results show that renal efferent nerves in the SrG may control the rostral part of the kidney and innervate the multiple effectors in the cortex. Anat Rec, 300:2263-2272, 2017. © 2017 Wiley Periodicals, Inc.

Renal sodium handling and blood pressure changes in gestational protein-restricted offspring: Role of renal nerves and ganglia neurokinin expression

Background

Considering long-term changes in renal sodium handling and blood pressure in maternal protein-restricted (LP) offspring, we assumed that the development of LP hypertension results from abnormal dorsal root ganglia (DRG) neurokinin expression associated with impaired responsiveness of renal sensory receptors, promoting a reduced urinary excretion of sodium. The present study investigates whether increased blood pressure in protein-restricted offspring would be associated with changes in the DRG cells and in renal pelvic wall expression of NK1R, SP and CGRP when compared to NP offspring. In addition, we assessed the tubular sodium handling, estimated by creatinine and lithium clearances before and after bilateral renal denervation in conscious LP offspring relative to age-matched NP counterparts.

Methods

Dams received a normal (NP) or low-protein diet (LP) during their entire pregnancy period. Male NP or LP offspring underwent bilateral surgical renal denervation before the 8-week renal functional test and blood pressure measurements. Immunofluorescence staining in DRG cells was assessed in optical sections by confocal laser scanning microscope.

Results

The current data demonstrated a sustained rise in blood pressure associated with a decrease in fractional excretion of sodium (FENa) by reducing post-proximal tubule sodium rejection in 16-wk old LP rats relative to age-matched NP counterparts. According to this study, bilateral renal denervation attenuated blood pressure and increased FENa in LP offspring. Furthermore, an immunohistochemical analysis showed a reduced expression of SP and CGRP in DRGs of LP when compared with NP rats. Renal pelvis of LP rats did not show a strong CGRP expression related to NP rats, whereas there was no change in SP immunostaining.

Conclusions

These observations raise the possibility that impaired DRG and pelvic neurokinin expression associated with responsiveness of renal sensory receptors in 16-wk old LP offspring are conducive to excess renal reabsorption of sodium and development of hypertension in this programmed model.

Developmental Origins of Chronic Kidney Disease: Should We Focus on Early Life?

Chronic kidney disease (CKD) is becoming a global burden, despite recent advances in management. CKD can begin in early life by so-called "developmental programming" or "developmental origins of health and disease" (DOHaD). Early-life insults cause structural and functional changes in the developing kidney, which is called renal programming. Epidemiological and experimental evidence supports the proposition that early-life adverse events lead to renal programming and make subjects vulnerable to developing CKD and its comorbidities in later life. In addition to low nephron endowment, several mechanisms have been proposed for renal programming. The DOHaD concept opens a new window to offset the programming process in early life to prevent the development of adult kidney disease, namely reprogramming. Here, we review the key themes on the developmental origins of CKD. We have particularly focused on the following areas: evidence from human studies support fetal programming of kidney disease; insight from animal models of renal programming; hypothetical mechanisms of renal programming; alterations of renal transcriptome in response to early-life insults; and the application of reprogramming interventions to prevent the programming of kidney disease.

Clinical neurocardiology defining the value of neuroscience-based cardiovascular therapeutics

The autonomic nervous system regulates all aspects of normal cardiac function, and is recognized to play a critical role in the pathophysiology of many cardiovascular diseases. As such, the value of neuroscience-based cardiovascular therapeutics is increasingly evident. This White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology, pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Complex reinnervation pattern after unilateral renal denervation in rats

Renal denervation (DNX) is a treatment for resistant arterial hypertension. Efferent sympathetic nerves regrow, but reinnervation by renal afferent nerves has only recently been shown in the renal pelvis of rats after unilateral DNX. We examined intrarenal perivascular afferent and sympathetic efferent nerves after unilateral surgical DNX. Tyrosine hydroxylase (TH), CGRP, and smooth muscle actin were identified in kidney sections from 12 Sprague-Dawley rats, to distinguish afferents, efferents, and vasculature. DNX kidneys and nondenervated kidneys were examined 1, 4, and 12 wk after DNX. Tissue levels of CGRP and norepinephrine (NE) were measured with ELISA and mass spectrometry, respectively. DNX decreased TH and CGRP labeling by 90% and 95%, respectively (P < 0.05) within 1 wk. After 12 wk TH and CGRP labeling returned to baseline with a shift toward afferent innervation (P < 0.05). Nondenervated kidneys showed a doubling of both labels within 12 wk (P < 0.05). CGRP content decreased by 72% [3.2 ± 0.3 vs. 0.9 ± 0.2 ng/gkidney; P < 0.05] and NA by 78% [1.1 ± 0.1 vs. 0.2 ± 0.1 pmol/mgkidney; P < 0.05] 1 wk after DNX. After 12 wk, CGRP, but not NE, content in DNX kidneys was fully recovered, with no changes in the nondenervated kidneys. The use of phenol in the DNX procedure did not influence this result. We found morphological reinnervation and transmitter recovery of afferents within 12 wk after DNX. Despite morphological evidence of sympathetic regrowth, NE content did not fully recover. These results suggest a long-term net surplus of afferent influence on the DNX kidney may be contributing to the blood pressure lowering effect of DNX.

Effects of renal denervation on renal pelvic contractions and connexin expression in rats

AIMS

The renal pelvis shows spontaneous rhythmic contractile activity. We assessed to what extent this activity depends on renal innervation and studied the role of connexins in pelvic contractions.

METHODS

Rats underwent unilateral renal denervation or renal transplantation. Renal pelvic pressure and diuresis were measured in vivo. Spontaneous and agonist-induced contractions of isolated renal pelves were investigated by wire myography. Rat and human renal pelvic connexin mRNA abundances and connexin localization were studied by real-time PCR and immunofluorescence respectively.

RESULTS

Renal denervation or transplantation increased renal pelvic pressure in vivo by about 60 and 150%, respectively, but did not significantly affect pelvic contraction frequency. Under in vitro conditions, isolated pelvic preparations from innervated or denervated kidneys showed spontaneous contractions. Pelves from denervated kidneys showed about 50% higher contraction frequencies than pelves from innervated kidneys, whereas contraction force was similar in pelves from denervated and innervated kidneys. There was no denervation-induced supersensitivity to noradrenaline or endothelin-1. Renal denervation did not increase pelvic connexin37, 40, 43 or 45 mRNA abundances. Gap junction blockade had no effect on spontaneous pelvic contractile activity.

CONCLUSIONS

The denervation-induced effect on pelvic pressure may be the consequence of the enhanced diuresis. The mechanisms underlying the denervation-induced effects on pelvic contraction frequency remain unknown. Our data rule out a major role for two important candidates, by showing that renal denervation neither induced supersensitivity to contractile agonists nor increased connexin mRNA abundance in the pelvic wall.

Role of renal sensory nerves in physiological and pathophysiological conditions

Whether activation of afferent renal nerves contributes to the regulation of arterial pressure and sodium balance has been long overlooked. In normotensive rats, activating renal mechanosensory nerves decrease efferent renal sympathetic nerve activity (ERSNA) and increase urinary sodium excretion, an inhibitory renorenal reflex. There is an interaction between efferent and afferent renal nerves, whereby increases in ERSNA increase afferent renal nerve activity (ARNA), leading to decreases in ERSNA by activation of the renorenal reflexes to maintain low ERSNA to minimize sodium retention. High-sodium diet enhances the responsiveness of the renal sensory nerves, while low dietary sodium reduces the responsiveness of the renal sensory nerves, thus producing physiologically appropriate responses to maintain sodium balance. Increased renal ANG II reduces the responsiveness of the renal sensory nerves in physiological and pathophysiological conditions, including hypertension, congestive heart failure, and ischemia-induced acute renal failure. Impairment of inhibitory renorenal reflexes in these pathological states would contribute to the hypertension and sodium retention. When the inhibitory renorenal reflexes are suppressed, excitatory reflexes may prevail. Renal denervation reduces arterial pressure in experimental hypertension and in treatment-resistant hypertensive patients. The fall in arterial pressure is associated with a fall in muscle sympathetic nerve activity, suggesting that increased ARNA contributes to increased arterial pressure in these patients. Although removal of both renal sympathetic and afferent renal sensory nerves most likely contributes to the arterial pressure reduction initially, additional mechanisms may be involved in long-term arterial pressure reduction since sympathetic and sensory nerves reinnervate renal tissue in a similar time-dependent fashion following renal denervation.

Methodological standardization for the pre-clinical evaluation of renal sympathetic denervation

Transcatheter ablation of renal autonomic nerves is a viable option for the treatment of resistant arterial hypertension; however, structured pre-clinical evaluation with standardization of analytical procedures remains a clear gap in this field. Here we discuss the topics relevant to the pre-clinical model for the evaluation of renal denervation (RDN) devices and report methodologies and criteria toward standardization of the safety and efficacy assessment, including histopathological evaluations of the renal artery, periarterial nerves, and associated periadventitial tissues. The pre-clinical swine renal artery model can be used effectively to assess both the safety and efficacy of RDN technologies. Assessment of the efficacy of RDN modalities primarily focuses on the determination of the depth of penetration of treatment-related injury (e.g., necrosis) of the periarterial tissues and its relationship (i.e., location and distance) and the effect on the associated renal nerves and the correlation thereof with proxy biomarkers including renal norepinephrine concentrations and nerve-specific immunohistochemical stains (e.g., tyrosine hydroxylase). The safety evaluation of RDN technologies involves assessing for adverse effects on tissues local to the site of treatment (i.e., on the arterial wall) as well as tissues at a distance (e.g., soft tissue, veins, arterial branches, skeletal muscle, adrenal gland, ureters). Increasing experience will help to create a standardized means of examining all arterial beds subject to ablative energy and in doing so enable us to proceed to optimize the development and assessment of these emerging technologies.

Renal nerves in blood pressure regulation

PURPOSE

This review highlights the physiological mechanisms underlying the neural regulation of the kidney, normally to maintain cardiovascular homeostasis, and in pathophysiological states of hypertension and renal disease. It is relevant because of the demonstration that bilateral renal denervation in different hypertensive groups causes a sustained reduction in blood pressure.

RECENT FINDINGS

There are patients groups in whom their hypertension is resistant to antihypertensive drugs or with renal diseases in which they are contraindicated. Recently, medical devices have been developed to manipulate the sympathetic nervous system, for example, implantation of carotid sinus nerve stimulating electrodes and ablation of the renal innervation. These approaches have been relatively successful but there remains a lack of understanding of the neural mechanisms impinging on the kidney that regulate long-term control of blood pressure.

SUMMARY

The observation that bilateral renal nerve ablation can reduce blood pressure represents an important therapeutic milestone. Nonetheless, questions arise as to the underlying mechanisms, the long-term consequences, whether there may be re-innervation over a number of years, or whether some unknown consequence to the denervation may arise. This may point to the development of novel compounds targeted to the innervation of the kidney.

Renal denervation: current implications and future perspectives

SNS (sympathetic nervous system) activation is a common feature of arterial hypertension and has been demonstrated to contribute to the development and progression of the hypertensive state. Persuasive evidence suggests a strong association between SNS overactivity and variety of disease states, including chronic renal failure, insulin resistance, congestive heart failure, sleep apnoea, ventricular arrhythmias and others. Although sympatholytic agents are available to target SNS overactivity pharmacologically, they are not widely used in clinical practice, leaving the SNS unopposed in many patients. The recent introduction of catheter-based renal denervation as an alternative approach to target the SNS therapeutically has been demonstrated to result in a clinically relevant blood pressure reduction in patients with resistant hypertension, presumably through its effects on both efferent and afferent renal nerve traffic. Available data on this interventional procedure demonstrate a favourable vascular and renal safety profile. Preliminary data obtained primarily from small and mostly uncontrolled studies in related disease states often characterized by overactivity of the SNS are promising, but require confirmation in appropriately designed clinical trials. In the present paper, we briefly review the physiology of the renal nerves and their role in hypertension and other relevant disease states, summarize the data currently available from clinical studies pertaining to the safety and efficacy of renal denervation in resistant hypertension, discuss potential future implications and the available data supporting such a role for renal denervation, and describe some of the newer devices currently under investigation to achieve improved blood pressure control via renal denervation.

Renal sympathetic denervation for the treatment of systemic hypertension

Systemic hypertension is a common cardiovascular problem that often cannot be fully treated with existing nonpharmacologic and pharmacologic measures. A catheter-based strategy which denervates the renal afferent and efferent autonomic nervous system has been developed for the treatment of drug-resistant hypertension. In early clinical trials, this procedure was shown to be both feasible and safe in reducing blood pressure in patients with uncontrolled hypertension receiving treatment with a minimum of 3 antihypertensive drugs. In addition, this procedure has been associated with decreased renin secretion, preservation of renal function, improved glucose tolerance, and a reduction in left ventricular hypertrophy. The long-term effects of this procedure (beyond 3 years) still need to be determined. A large 530-patient sham-controlled trial is now in progress.

Renal sensory and sympathetic nerves reinnervate the kidney in a similar time-dependent fashion after renal denervation in rats

Efferent renal sympathetic nerves reinnervate the kidney after renal denervation in animals and humans. Therefore, the long-term reduction in arterial pressure following renal denervation in drug-resistant hypertensive patients has been attributed to lack of afferent renal sensory reinnervation. However, afferent sensory reinnervation of any organ, including the kidney, is an understudied question. Therefore, we analyzed the time course of sympathetic and sensory reinnervation at multiple time points (1, 4, and 5 days and 1, 2, 3, 4, 6, 9, and 12 wk) after renal denervation in normal Sprague-Dawley rats. Sympathetic and sensory innervation in the innervated and contralateral denervated kidney was determined as optical density (ImageJ) of the sympathetic and sensory nerves identified by immunohistochemistry using antibodies against markers for sympathetic nerves [neuropeptide Y (NPY) and tyrosine hydroxylase (TH)] and sensory nerves [substance P and calcitonin gene-related peptide (CGRP)]. In denervated kidneys, the optical density of NPY-immunoreactive (ir) fibers in the renal cortex and substance P-ir fibers in the pelvic wall was 6, 39, and 100% and 8, 47, and 100%, respectively, of that in the contralateral innervated kidney at 4 days, 4 wk, and 12 wk after denervation. Linear regression analysis of the optical density of the ratio of the denervated/innervated kidney versus time yielded similar intercept and slope values for NPY-ir, TH-ir, substance P-ir, and CGRP-ir fibers (all R(2) > 0.76). In conclusion, in normotensive rats, reinnervation of the renal sensory nerves occurs over the same time course as reinnervation of the renal sympathetic nerves, both being complete at 9 to 12 wk following renal denervation.

Renal Sympathetic Denervation for the Treatment of Difficult-to-Control or Resistant Hypertension

Hypertension represents a major health problem with an appalling annual toll. Despite the plethora of antihypertensive drugs, hypertension remains resistant in a considerable number of patients, thus creating the need for alternative strategies, including interventional approaches. Recently, catheter-based renal sympathetic denervation has been shown to be fairly safe and effective in patients with resistant hypertension. Pathophysiology of kidney function, interaction and crosstalk between the kidney and the brain, justifies the use of renal sympathetic denervation in the treatment of hypertension. Data from older studies have shown that sympathectomy has effectively lowered blood pressure and prolonged life expectancy of hypertensive patients, but at considerable cost. Renal sympathetic denervation is devoid of the adverse effects of surgical sympathectomy, due to its localized nature, is minimally invasive, and provides short procedural and recovery times. This paper outlines the pathophysiological background for renal sympathetic denervation, describes the past and the present of this interventional approach, and considers several future potential applications.

Activation of endothelin A receptors contributes to impaired responsiveness of renal mechanosensory nerves in congestive heart failure

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 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.

Renal sympathetic denervation and systemic hypertension

Hypertension represents a major health problem, with an appalling annual toll. Despite the plethora of antihypertensive drugs, hypertension remains resistant in a considerable number of patients, thus creating the need for alternative strategies, including interventional approaches. Recently, renal sympathetic denervation (RSD) using a very elegant, state-of-the-art technique (percutaneous, catheter-based radiofrequency ablation) was shown to be beneficial in patients with resistant hypertension. The pathophysiology of kidney function justifies the use of RSD in the treatment of hypertension. Data from older studies have shown that sympathectomy has efficiently lowered blood pressure and prolonged the life expectancy of patients with hypertension, but at considerable cost. RSD is devoid of the adverse effects of sympathectomy because of its localized nature, is minimally invasive, and provides short procedural and recovery times. In conclusion, this review outlines the pathophysiologic background of RSD, describes the past and the present of this interventional approach, and considers several future potential applications.

Methods for imaging Renin-synthesizing, -storing, and -secreting cells

Renin-producing cells have been the object of intense research efforts for the past fifty years within the field of hypertension. Two decades ago, research focused on the concept and characterization of the intrarenal renin-angiotensin system. Early morphological studies led to the concept of the juxtaglomerular apparatus, a minute organ that links tubulovascular structures and function at the single nephron level. The kidney, thus, appears as a highly "topological organ" in which anatomy and function are intimately linked. This point is reflected by a concurrent and constant development of functional and structural approaches. After summarizing our current knowledge about renin cells and their distribution along the renal vascular tree, particularly along glomerular afferent arterioles, we reviewed a variety of imaging techniques that permit a fine characterization of renin synthesis, storage, and release at the single-arteriolar, -cell, or -granule level. Powerful tools such as multiphoton microscopy and transgenesis bear the promises of future developments of the field.

Translational medicine: the antihypertensive effect of renal denervation

Translational medicine is concerned with the translation of research discoveries into clinical applications for the prevention, diagnosis, and treatment of human diseases. Here we briefly review the research concerning the role of the renal sympathetic nerves (efferent and afferent) in the control of renal function, with particular reference to hypertension. The accumulated evidence is compelling for a primary role of the renal innervation in the pathogenesis of hypertension. These research discoveries led to the development of a catheter-based procedure for renal denervation in human subjects. A proof-of-principle study in patients with hypertension resistant to conventional therapy has demonstrated that the procedure is safe and produces renal denervation with sustained lowering of arterial pressure.

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.

Afferent renal denervation impairs baroreflex control of efferent renal sympathetic nerve activity

Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), which decreases ERSNA to prevent sodium retention. High-sodium diet enhances ARNA, suggesting an important role for ARNA in suppressing ERSNA during excess sodium intake. Mean arterial pressure (MAP) is elevated in afferent renal denervated by dorsal rhizotomy (DRX) rats fed high-sodium diet. We examined whether the increased MAP in DRX is due to impaired arterial baroreflex function. In DRX and sham DRX rats fed high-sodium diet, arterial baroreflex function was determined in conscious rats by intravenous nitroprusside and phenylephrine or calculation of transfer function gain from arterial pressure to ERSNA (spontaneous baroreflex sensitivity). Increasing MAP did not suppress ERSNA to the same extent in DRX as in sham DRX, -60 +/- 4 vs. -77 +/- 6%. Maximum gain, -4.22 +/- 0.45 vs. -6.04 +/- 0.90% DeltaERSNA/mmHg, and the maximum value of instantaneous gain, -4.19 +/- 0.45 vs. -6.04 +/- 0.81% DeltaERSNA/mmHg, were less in DRX than in sham DRX. Likewise, transfer function gain was lower in DRX than in sham DRX, 3.9 +/- 0.2 vs. 6.1 +/- 0.5 NU/mmHg. Air jet stress produced greater increases in ERSNA in DRX than in sham DRX, 35,000 +/- 4,900 vs. 20,900 +/- 3,410%.s (area under the curve). Likewise, the ERSNA responses to thermal cutaneous stimulation were greater in DRX than in sham DRX. These studies suggest impaired arterial baroreflex suppression of ERSNA in DRX fed high-sodium diet. There were no differences in arterial baroreflex function in DRX and sham DRX fed normal-sodium diet. Impaired arterial baroreflex function contributes to increased ERSNA, which would eventually lead to sodium retention and increased MAP in DRX rats fed high-sodium diet.

Topology of Schwann cells and sympathetic innervation along preglomerular vessels: a confocal microscopic study in protein S100B/EGFP transgenic mice

Schwann cells (Sc), associated axons, and nearby vascular endothelium constitute a functional trilogy of major importance during the development and regrowth of peripheral vascular nerves. The goal of the present study is to provide a technique of triple fluorescence confocal imaging of these cell types along renal preglomerular vessels. We took advantage of a protein S100B/EGFP transgenic mouse to visualize Sc. The endothelium was labeled with an intravenous injection of fluorescently tagged lectin, and after tissue processing, adrenergic nerves were revealed with an antibody against the marker protein synaptophysin. As a validation step, we found that EGFP-positive perivascular cells with prominent cell bodies and extensive, multidirectional cell processes were protein S100B positive. They were identified as Sc and indirectly assumed to be unmyelinated Sc. By contrast, we found strong EGFP expression in proximal epithelial cells and in the epithelium lining thin limbs of Henle. This epithelial fluorescence was not associated with immunoreactive protein S100B and thus corresponded to ectopic EGFP expressions in this mouse strain. Sc were organized in bundles or as a meshwork surrounding the preglomerular vasculature from arcuate arteries to afferent arterioles. No Sc were detected in the medulla. Although most Sc were closely apposed to adrenergic varicosities, many varicosities were not associated with detectable Sc processes. The present technique, and the capacity of confocal microscopy to yield three-dimensional imaging, allow the study of the microtopology of Sc and related sympathetic axons in the renal perivascular interstitium.

Impaired responsiveness of renal sensory nerves in streptozotocin-treated rats and obese Zucker diabetic fatty rats: role of angiotensin

Increasing afferent renal nerve activity decreases efferent renal nerve activity and increases urinary sodium excretion. Activation of renal pelvic mechanosensory nerves is impaired in streptozotocin (STZ)-treated rats (model of type 1 diabetes). Decreased activation of renal sensory nerves would lead to increased efferent renal nerve activity, sodium retention, and hypertension. We examined whether the reduced activation of renal sensory nerves in STZ rats was due to increased renal angiotensin activity and whether activation of the renal sensory nerves was impaired in obese Zucker diabetic fatty (ZDF) rats (model of type 2 diabetes). In an isolated renal pelvic wall preparation from rats treated with STZ for 2 wk, PGE2failed to increase the release of substance P, from 5 ± 1 to 6 ± 1 pg/min. In pelvises from sham STZ rats, PGE2increased substance P release from 6 ± 1 to 13 ± 2 pg/min. Adding losartan to the incubation bath increased PGE2-mediated release of substance P in STZ rats, from 5 ± 1 to 10 ± 2 pg/min, but had no effect in sham STZ rats. In pelvises from obese ZDF rats (22–46 wk old), PGE2increased substance P release from 12.0 ± 1.2 to 18.3 ± 1.2 pg/min, which was less than that from lean ZDF rats (10.3 ± 1.6 to 22.5 ± 2.4 pg/min). Losartan had no effect on the PGE2-mediated substance P release in obese or lean ZDF rats. We conclude that the mechanisms involved in the decreased responsiveness of the renal sensory nerves in STZ rats involve activation of the renin angiotensin system in STZ but not in obese ZDF rats.

Transient receptor potential vanilloid type 1 channels act as mechanoreceptors and cause substance P release and sensory activation in rat kidneys

Stimulation of capsaicin receptors results in an increase in afferent renal nerve activity (ARNA), but it is unclear how capsaicin contributes to sensory activation intrarenally. Here, we studied the relationships between capsaicin receptor activation, substance P (SP) release, and the sensory response in the rat renal pelvis. Immunoblots showed that one of the capsaicin receptors, transient receptor potential vanilloid type 1 channel (TRPV1), was found in various renal tissues and was especially abundant in the renal pelvis, where most sensory nerve fibers originate. Interestingly, immunolabeling showed colocalization of TRPV1, SP, and the panneuronal marker PGP9.5 in the renal pelvis. Electrophysiological recordings showed that SP and capsaicin activated the same mechanosensitive ARNA in a single-unit preparation. Intrapelvic administration of capsaicin or a specific TRPV1 agonist, resiniferatoxin, resulted in a dose-dependent increase in multi-unit ARNA and SP release, and these effects were blocked by the TRVP1 blocker capsazepine. Inhibition of the SP receptor by L-703,606 largely prevented capsaicin- or resiniferatoxin-induced ARNA. Capsazepine also prevented intrapelvic pressure (IPP)-dependent ARNA activation and contralateral diuresis/natriuresis in the renorenal reflex at an IPP of 20 mmHg, but had no effect at an IPP of 50 mmHg. These data indicate that TRPV1, a low-pressure baroreceptor, is present in the renal pelvis and exclusively regulates neuropeptide release from primary renal afferent C-fibers in response to mechanostimulation.

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 α-adrenoceptors on the renal sensory nerves, we examined the effects of renal pelvic administration of the α1- and α2-adrenoceptor antagonists prazosin and rauwolscine on the ARNA responses to reflex increases in ERSNA (placing the rat's tail in 49°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 PGE2 release, from 77 ± 11 to 161 ± 23 pg/min, suggesting a role for PGE2 in the norepinephrine-induced activation of renal sensory nerves. Prazosin and indomethacin reduced and rauwolscine enhanced the norepinephrine-induced increases in substance P and PGE2. PGE2 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 α1- and α2-adrenoceptors, respectively, on the renal pelvic sensory nerve fibers. Norepinephrine-induced activation of the sensory nerves is dependent on renal pelvic synthesis/release of PGE2.

The role of angiotensin(1-7) in renal vasculature of the rat

OBJECTIVE

Angiotensin(1-7) is an active component of the renin-angiotensin-aldosterone system. Its exact role in renal vascular function is unclear. We therefore studied the effects of angiotensin(1-7) on the renal vasculature in vitro and in vivo.

METHODS

Isolated small renal arteries were studied in an arteriograph system by constructing concentration-response curves to angiotensin II, without and with angiotensin(1-7). In isolated perfused kidneys, the response of angiotensin II on renal vascular resistance was measured without and with angiotensin(1-7). The influence of angiotensin(1-7) on angiotensin II-induced glomerular afferent and efferent constriction was assessed with intravital microscopy in vivo under anaesthesia. In freely moving rats, we studied the effect of angiotensin(1-7) on angiotensin II-induced reduction of renal blood flow with an electromagnetic flow probe.

RESULTS

Angiotensin(1-7) alone had no effect on the renal vasculature in any of the experiments. In vitro, angiotensin(1-7) antagonized angiotensin-II-induced constriction of isolated renal arteries (9.71 +/- 1.21 and 3.20 +/- 0.57%, for control and angiotensin(1-7) pre-treated arteries, respectively; P < 0.0005). In isolated perfused kidneys, angiotensin(1-7) reduced the angiotensin II response (100 +/- 16.6 versus 72.6 +/- 15.6%, P < 0.05) and shifted the angiotensin II dose-response curve rightward (pEC50, 6.69 +/- 0.19 and 6.26 +/- 0.12 for control and angiotensin(1-7) pre-treated kidneys, respectively; P < 0.05). Angiotensin(1-7), however, was devoid of effects on angiotensin-II-induced constriction of glomerular afferent and efferent arterioles and on angiotensin-II-induced renal blood flow reduction in freely moving rats in vivo.

CONCLUSION

Angiotensin(1-7) antagonizes angiotensin II in renal vessels in vitro, but does not appear to have a major function in normal physiological regulation of renal vascular function in vivo.

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.

Neonatal sympathectomy reduces NADPH oxidase activity and vascular resistance in spontaneously hypertensive rat kidneys

Neonatal sympathectomy reduces arterial pressure in spontaneously hypertensive rats (SHR). In SHR transplanted with a kidney from sympathectomized SHR, arterial pressure was lower and less Na+ sensitive than in SHR transplanted with a kidney from hydralazine-treated SHR. This study was performed to identify underlying renal mechanisms. Tests for differential renal mRNA expression of nine a priori selected genes revealed robust differences for renal medullary expression of the NADPH oxidase subunit p47phox. Therefore, we investigated the effects of neonatal sympathectomy on renal mRNA expression of NADPH oxidase subunits, NADPH oxidase activity, and renal function. In 10-wk-old sympathectomized SHR fed a 0.6% NaCl diet, medullary p47phox and gp91phox expression was 40% less than in hydralazine-treated SHR. Also, after a 1.8% NaCl diet, medullary p47phox mRNA expression was lower in sympathectomized than in hydralazine-treated SHR. We found lower cortical (-30%, P<0.01) and medullary (-30%, P<0.05) NADPH oxidase activities in sympathectomized than in hydralazine-treated or untreated SHR. Glomerular filtration rate, renal blood flow, medullary blood flow, and fractional Na+ excretion in kidney grafts from sympathectomized and hydralazine-treated donors (n=8 per group) were similar at baseline and in response to a 20-mmHg rise in renal perfusion pressure. Renal vascular resistance was lower in kidneys from sympathectomized than hydralazine-treated donors (25+/-2 vs. 32+/-4 mmHg.min.ml-1, P<0.05). The results indicate that the sympathetic nervous system contributes to the level of renal NADPH oxidase activity and to perinatal programming of alterations in renal vascular function that lead to elevated renal vascular resistance in SHR.

Expression and localization of NK(1)R, substance P and CGRP are altered in dorsal root ganglia neurons of spontaneously hypertensive rats (SHR)

The kidneys play a pivotal role in the pathogenesis of essential hypertension because of a primary defect in renal hemodynamics and/or tubule hydro-saline handling that results in the retention of fluid and electrolytes. Previous studies have shown that increasing the renal pelvic pressure increased ipsilateral afferent renal nerve activity (ARNA), the ipsilateral renal pelvic release of substance P (SP) and the contralateral urinary sodium excretion in Wistar--Kyoto rats (WKy). However, spontaneously hypertensive rats (SHR) present an impaired renorenal reflex activity associated, partly, with a peripheral defect at the level of the sensory receptors in the renal pelvis. Furthermore, the renal pelvic administration of SP failed to increase ARNA in most of SHR at concentrations that produced marked increases in WKy. Since we have assessed the expression and localization of NK(1) receptor (NK(1)R), SP and calcitonin gene-related peptide (CGRP) in different dorsal root ganglia (DRG) cell subtypes and renal pelvis of 7- and 14-week-old SHR. The results of this study show increased SP and CGRP expression in the dorsal ganglia root cells of SHR compared to WKy rats. Additionally, there was a progressive, significant, age-dependent, decrease in NK(1)R expression on the membrane surface in SHR DRG cells and in the renal pelvis. In conclusion, the results of the present study suggest that the impaired activation of renal sensory neurons in SHR may be related to changes in the expression of neuropeptides and/or to a decreased presence of NK(1)R in DRG cells. Such abnormalities could contribute to the enhanced sodium retention and elevation of blood pressure seen in SHR.

Ontogeny of intrinsic innervation in the human kidney

We aimed to define, for the first time, the ontogeny of intrarenal innervation and to assess the distribution and nature of parenchymal nerves in the human fetal kidney. Our material consisted of routinely-processed renal tissue sections from 17 human fetuses, six of 20-24 gestational weeks (gw) and 11 of 25-40 gw, and three adults. We used immunohistochemistry with antibodies to the pan-neural markers neuron-specific enolase (NSE), neurofilaments (NF), PGP9.5, S100, and the adrenergic marker tyrosine hydroxylase (TH). NSE-, NF-, S100-, and PGP9.5-positive nerves, associated with arterial and venous vasculature, were identified in the renal cortex from 20 gw onwards, and their density appeared to increase with gestation, reaching adult levels at 28 gw. Most of the intrarenal nerves were TH-positive. Nerve fibers extended from the corticomedullary region to the outer cortex, reaching the renal capsule in the 3rd trimester. In detail, NSE-, NF-, S100-, PGP9.5-, and TH-immunoreactive fibers were observed in close apposition to the renal artery and its branches, occasionally reaching the afferent and efferent arteriole (3rd trimester). Nerve fibers were detected in close apposition to the juxtaglomerular apparatus in the 2nd and 3rd trimesters. In the renal medulla, NSE-, PGP9.5-, S100-, and TH-positive nerve fibers were detected close to tubular cells as early as 20 gw. However, their density gradually decreased during the 3rd trimester, and they were not observed in the medulla of the adult kidney. In conclusion, the human fetal kidney appears richly innervated during the 2nd and 3rd trimesters. There is a progressive increase in the density of parenchymal nerve fibers towards term from the corticomedullary region to the cortex. Most intrarenal nerves are adrenergic and have a predominant perivascular distribution, implying that renal innervation plays an important functional role during intrauterine life.

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.

Impaired substance P release from renal sensory nerves in SHR involves a pertussis toxin-sensitive mechanism

Stretching the renal pelvic wall activates renal mechanosensory nerves by a PGE2-mediated release of substance P via activation of the cAMP-PKA pathway. Renal pelvic ANG II modulates the responsiveness of renal sensory nerves by suppressing the PGE2-mediated activation of adenylyl cyclase via a pertussis toxin (PTX)-sensitive mechanism. In SHR, activation of renal mechanosensory nerves is impaired. This is due to suppressed release of substance P in response to increased pelvic pressure. The present study was performed to investigate whether the PGE2-mediated release of substance P was suppressed in SHR vs. WKY and, if so, whether the impaired PGE2-mediated release of substance P was due to ANG II activating a PTX-sensitive mechanism. In an isolated renal pelvic wall preparation, PGE2, 0.14 μM, increased substance P release from 9 ± 3 to 22 ± 3 pg/min ( P < 0.01) in Wistar-Kyoto rats (WKY), but had no effect in spontaneously hypertensive rats (SHR). A tenfold higher concentration of PGE2, 1.4 μM, was required to increase substance P release in SHR, from 7 ± 1 to 22 ± 3 pg/min ( P < 0.01). In SHR, treating renal pelvises with losartan enhanced the release of substance P produced by subthreshold concentration of PGE2, 0.3 μM, from 16 ± 2 to 26 ± 3 pg/min ( P < 0.01). Likewise, treating renal pelvises with PTX enhanced the PGE2-mediated release of substance P from 10 ± 1 to 33 ± 3 pg/min ( P < 0.01) in SHR. In WKY, neither losartan nor PTX had an effect on the release of substance P produced by subthreshold concentrations of PGE2, 0.03 μM. In conclusion, the impaired responsiveness of renal sensory nerves in SHR involves endogenous ANG II suppressing the PGE2-mediated release of substance P via a PTX-sensitive mechanism.

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.

Nitric oxide modulates renal sensory nerve fibers by mechanisms related to substance P receptor activation

Nerve terminals containing neuronal nitric oxide synthase (nNOS) are localized in the renal pelvic wall where the sensory nerves containing substance P and calcitonin gene-related peptide (CGRP) are found. We examined whether nNOS is colocalized with substance P and CGRP. All renal pelvic nerve fibers that contained nNOS-like immunoreactivity (-LI) also contained substance P-LI and CGRP-LI. In anesthetized rats, renal pelvic perfusion with the nNOS inhibitor S-methyl-L-thiocitrulline (L-SMTC, 20 microM) prolonged the afferent renal nerve activity (ARNA) response to a 3-min period of increased renal pelvic pressure from 5 +/- 0.4 to 21 +/- 2 min (P < 0.01, n = 14). The magnitude of the ARNA response was unaffected by L-SMTC. Similar effects were produced by N(omega)-nitro-L-arginine methyl ester (L-NAME) but not D-NAME. Increasing renal pelvic pressure produced similar increases in renal pelvic release of substance P before and during L-SMTC, from 5.9 +/- 1.4 to 13.6 +/- 4.2 pg/min before and from 4.9 +/- to 12.6 +/- 2.7 pg/min during L-SMTC. L-SMTC also prolonged the ARNA response to renal pelvic perfusion with substance P (3 microM) from 1.2 +/- 0.2 to 5.6 +/- 1.1 min (P < 0.01, n = 9) without affecting the magnitude of the ARNA response.

IN CONCLUSION

activation of NO may function as an inhibitory neurotransmitter regulating the activation of renal mechanosensory nerve fibers by mechanisms related to activation of substance P receptors.

Activation of renal mechanosensitive neurons involves bradykinin, protein kinase C, PGE(2), and substance P

Increased renal pelvic pressure or bradykinin increases afferent renal nerve activity (ARNA) via PGE(2)-induced release of substance P. Protein kinase C (PKC) activation increases ARNA, and PKC inhibition blocks the ARNA response to bradykinin. We now examined whether bradykinin mediates the ARNA response to increased renal pelvic pressure by activating PKC. In anesthetized rats, the ARNA responses to increased renal pelvic pressure were blocked by renal pelvic perfusion with the bradykinin B(2)-receptor antagonist HOE 140 and the PKC inhibitor calphostin C by 76 +/- 8% (P < 0.02) and 81 +/- 5% (P < 0.01), respectively. Renal pelvic perfusion with 4beta-phorbol 12,13-dibutyrate (PDBu) to activate PKC increased ARNA 27 +/- 4% and renal pelvic release of PGE(2) from 500 +/- 59 to 1, 113 +/- 183 pg/min and substance P from 10 +/- 2 to 30 +/- 2 pg/min (all P < 0.01). Indomethacin abolished the increases in substance P release and ARNA. The PDBu-mediated increase in ARNA was also abolished by the substance P-receptor antagonist RP 67580. We conclude that bradykinin contributes to the activation of renal pelvic mechanosensitive neurons by activating PKC. PKC increases ARNA via a PGE(2)-induced release of substance P.

Sympathoadrenal hyperplasia causes renal malformations in Ret(MEN2B)-transgenic mice

The tyrosine kinase receptor Ret is expressed in the ureteric bud and is required for normal renal development. Constitutive loss of Ret, its co-receptor gfralpha-1, or the ligand glial cell line-derived neurotrophic factor results in renal agenesis. Transgenic embryos that express a constitutively active form of Ret (Ret(MEN2B)) under the control of the dopamine-beta-hydroxylase (DbetaH) promoter develop profound neuroglial hyperplasia of their sympathetic ganglia and adrenal medullae. Embryos from two independent DbetaH-Ret(MEN2B)-transgenic lines exhibit renal malformations. In contrast with ret-/- embryos, renal maldevelopment in DbetaH-Ret(MEN2B)-transgenic embryos results from primary changes in sympathoadrenal organs extrinsic to the kidney. The ureteric bud invades the metanephric mesenchyme normally, but subsequent bud branching and nephrogenesis are retarded, resulting in severe renal hypoplasia. Ablation of sympathoadrenal precursors restores normal renal growth in vivo and in vitro. We postulate that disruption of renal development results because Ret(MEN2B) derived from the hyperplastic nervous tissue competes with endogenous renal Ret for gfralpha-1 or other signaling components. This hypothesis is supported by the observation that renal malformations, which do not normally occur in a transgenic line with low levels of DbetaH-Ret(MEN2B) expression, arise in a gdnf+/- background. However, renal maldevelopment was not recapitulated in kidneys that were co-cultured with explanted transgenic ganglia in vitro. Our observations illustrate a novel pathogenic mechanism for renal dysgenesis that may explain how putative activating mutations of the RET gene can produce a phenotype usually associated with RET deficiency.

PGE2 increases substance P release from renal pelvic sensory nerves via activation of N-type calcium channels

Activation of renal pelvic sensory nerves by increased pelvic pressure results in a renal pelvic release of substance P that is dependent on intact prostaglandin synthesis. An isolated renal pelvic wall preparation was used to examine whether PGE2 increases the release of substance P from renal pelvic sensory nerves and by what mechanisms. The validity of the model was tested by examining whether 50 mM KCl increased substance P release from the pelvic wall. Fifty millimolar KCl produced an increase in substance P release, from 9.6 +/- 1.6 to 26.8 +/- 4.0 pg/min, P < 0.01, that was blocked by the L-type calcium blocker verapamil (10 microM). PGE2 (0.14 microM) increased the release of substance P from the pelvic wall from 8.9 +/- 0.9 to 20.6 +/- 3.3 pg/min, P < 0.01. PGE2 failed to increase substance P release in a calcium-free medium. The PGE2-induced substance P release was blocked by the N-type calcium blocker omega-conotoxin (0.1 microM) but was unaffected by verapamil. In conclusion, PGE2 increases the release of substance P from renal pelvic sensory nerves by a calcium-dependent mechanism that requires influx of calcium via N-type calcium channels.

Amiloride-sensitive Na+ channels in pelvic uroepithelium involved in renal sensory receptor activation

Stretching the renal pelvic wall increases ipsilateral afferent renal nerve activity (ARNA). This response is enhanced by inhibiting Na+-K+-ATPase with ouabain, suggesting a modulatory role for intracellular Na+ in the activation of mechanosensitive neurons. The messenger RNA for alpha-, beta-, and gamma-subunits of epithelial Na+ channels (ENaC) is found in collecting duct cells. Because ENaC subunits show homology with genes involved in mechanosensation, we examined whether ENaC mRNA could be found in the pelvic wall and whether the ARNA response to increased renal pelvic pressure was modulated by blockers of the Na+ channel. alpha-, beta-, and gamma-subunits are present in the pelvis. The messenger RNA for the beta- and gamma-subunits is readily detected by in situ hybridization throughout the uroepithelium. The ARNA response to increased renal pelvic pressure was reduced by 53 +/- 10% and 40 +/- 10% (P < 0.01) by renal pelvic perfusion with the inhibitors amiloride and benzamil, respectively. Amiloride inhibited the ouabain-induced enhancement of the ARNA response to increased renal pelvic pressure. The magnitude of this inhibition was inversely correlated with the magnitude of the amiloride-mediated blockade of the ARNA response to increased renal pelvic pressure (P < 0.001). Amiloride also reduced the ARNA response to renal pelvic administration of substance P, a mediator of the ARNA response to increased renal pelvic pressure. We conclude that the ENaC complex in the pelvic uroepithelium participates in the activation of renal pelvic mechanosensitive neurons.

Transforming growth factor alpha-immunoreactivity in neural tissues of the rat stomach

We report TGF alpha immunoreactivity in neurons of the myenteric plexus and in nerve fibers in the muscle and submucosal layers of the rat stomach. Association of TGF alpha staining nerve fibers to vessels and smooth muscle cells gives morphological evidence that EGF/TGF alpha's actions to increase mucosal blood flow and gastric motility may be mediated by TGF alpha derived from neural structures. These data suggest that TGF alpha plays a role in the neural control of the gastric function.

Neural control of renal function

The renal nerves are the communication link between the central nervous system and the kidney. In response to multiple peripheral and central inputs, efferent renal sympathetic nerve activity is altered so as to convey information to the major structural and functional components of the kidney, the vessels, glomeruli, and tubules, each of which is innervated. At the level of each of these individual components, information transfer occurs via interaction of the neurotransmitter released at the sympathetic nerve terminal-neuroeffector junction with specific postjunctional receptors coupled to defined intracellular signaling and effector systems. In response to normal physiological stimuli, changes in efferent renal sympathetic nerve activity contribute importantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. Afferent input from sensory receptors located in the kidney participates in this reflex control system via renorenal reflexes that enable total renal function to be self-regulated and balanced between the two kidneys. In pathophysiological conditions, abnormal regulation of efferent renal sympathetic nerve activity contributes significantly to the associated abnormalities of renal function which, in turn, are of importance in the pathogenesis of the disease.

Distribution of nitric oxide synthase-containing ganglionic neuronal somata and postganglionic fibers in the rat kidney

Nitric oxide synthase (NOS)-immunoreactive neurons were identified in the rat kidney by using an antibody against type Ia NOS and the avidin-biotin complex immunoperoxidase method in whole kidneys examined in 100 microns serial sections. The histochemical method for demonstration of the nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) was also used to characterize NOS-containing neurons. All somata showing NOS immunoreactivity also displayed NADPH-d activity. The greatest number of neuronal somata were observed in groups at the wall of the renal pelvis and in the angular space formed by the pole of the renal parenchyma and renal pelvic wall. They were also seen at the renal hilus close to the renal artery and along the interlobar vasculature. The size of the neuronal somata in the 35-day-old rat ranged from 13.6 to 34.8 microns, with a mean size of 21.52 +/- 4.81 microns. Seventy percent, however, ranged in size from 17.8 to 26.8 microns. The shape of the neuronal somata also varied, with the majority having an ovoid or round shape. The distribution of the postganglionic fibers was investigated by means of the camera lucida. Postganglionic fibers projected into the wall of the renal pelvis and/or to the interlobar arteries extending to the arcuate arteries and to the beginning of the afferent arterioles. The NOS-immunoreactive neurons may have a vasodilator and relaxing function on the renal pelvic wall and vasculature. In addition, the presence of NOS-containing nerve fibers in nerve bundles, which are known to have predominantly vasomotor and sensory fibers, suggest that they may have a possible modulatory role on renal neural function.