Afferent renal nerve-dependent hypertension following acute renal artery stenosis in the conscious rat

Neurocardiology: translational advancements and potential

In our original white paper published in the The Journal of Physiology in 2016, we set out our knowledge of the structural and functional organization of cardiac autonomic control, how it remodels during disease, and approaches to exploit such knowledge for autonomic regulation therapy. The aim of this update is to build on this original blueprint, highlighting the significant progress which has been made in the field since and major challenges and opportunities that exist with regard to translation. Imbalances in autonomic responses, while beneficial in the short term, ultimately contribute to the evolution of cardiac pathology. As our understanding emerges of where and how to target in terms of actuators (including the heart and intracardiac nervous system (ICNS), stellate ganglia, dorsal root ganglia (DRG), vagus nerve, brainstem, and even higher centres), there is also a need to develop sensor technology to respond to appropriate biomarkers (electrophysiological, mechanical, and molecular) such that closed-loop autonomic regulation therapies can evolve. The goal is to work with endogenous control systems, rather than in opposition to them, to improve outcomes.

Periglomerular afferent innervation of the mouse renal cortex

Recent studies using a novel method for targeted ablation of afferent renal nerves have demonstrated their importance in the development and maintenance of some animal models of hypertension. However, relatively little is known about the anatomy of renal afferent nerves distal to the renal pelvis. Here, we investigated the anatomical relationship between renal glomeruli and afferent axons identified based on transient receptor potential vanilloid 1 channel (TRPV1) lineage or calcitonin gene related peptide (CGRP) immunolabeling. Analysis of over 6,000 (10,000 was accurate prior to the removal of the TH data during the review process) glomeruli from wildtype C57BL/6J mice and transgenic mice expressing tdTomato in TRPV1 lineage cells indicated that approximately half of all glomeruli sampled were closely apposed to tdTomato+ or CGRP+ afferent axons. Glomeruli were categorized as superficial, midcortical, or juxtamedullary based on their depth within the cortex. Juxtamedullary glomeruli were more likely to be closely apposed by afferent axon subtypes than more superficial glomeruli. High-resolution imaging of thick, cleared renal slices and subsequent distance transformations revealed that CGRP+ axons closely apposed to glomeruli were often found within 2 microns of nephrin+ labeling of glomerular podocytes. Furthermore, imaging of thick slices suggested that CGRP+ axon bundles can closely appose multiple glomeruli that share the same interlobular artery. Based on their expression of CGRP or tdTomato, prevalence near glomeruli, proximity to glomerular structures, and close apposition to multiple glomeruli within a module, we hypothesize that periglomerular afferent axons may function as mechanoreceptors monitoring glomerular pressure. These anatomical findings highlight the importance of further studies investigating the physiological role of periglomerular afferent axons in neural control of renal function in health and disease.

The potential protective effects of estradiol and 2-methoxyestradiol in ischemia reperfusion-induced kidney injury in ovariectomized female rats

AIMS

Investigating the impact of 17β estradiol (E2) and its endogenous non-hormonal metabolite 2-methoxyestradiol (2ME) on renal ischemia-reperfusion (RIR) induced kidney injury in ovariectomized (OVX) rats and the role of catechol-O-methyltransferase (COMT) in their effects.

MAIN METHODS

Eighty female rats were allocated into eight groups. Control group, Sham group, OVX group, OVX and RIR group, OVX + RIR + E2 group, OVX + RIR + 2ME group, OVX + RIR + E2 + Entacapone group and OVX + RIR + 2ME + Entacapone group, respectively. Twenty-four hours post RIR, creatinine (Cr) and blood urea nitrogen (BUN) were determined in serum, while malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), Glutathione (GSH), myeloperoxidase (MPO), as well as the expressions of COMT, hypoxia inducible factor-1α (HIF-1α) and tyrosine hydroxylase (TH) were assessed in the kidney tissues.

KEY FINDINGS

Serum Cr, BUN, MPO, as well as HIF-1α and TH expressions were significantly higher with concomitant decrease in COMT expression, SOD and CAT activities and GSH content observed in OVX and RIR group compared to sham group. E2 and 2ME treatment significantly ameliorated all parameters measured in OVX and RIR rats. On the other hand, Entacapone significantly decreased the effect of E2, with no effect on 2ME treatment.

SIGNIFICANCE

E2 ameliorates RIR-induced kidney injury and this effect is mediated, at least in part, via its COMT-mediated conversion to 2ME. Thus, 2ME by the virtue of its pleiotropic pharmacological effects can be used as a safe and effective treatment of RIR injury.

Epididymal Fat-Derived Sympathoexcitatory Signals Exacerbate Neurogenic Hypertension in Obese Male Mice Exposed to Early Life Stress

[Figure: see text].

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.

Sensory signals mediating high blood pressure via sympathetic activation: role of adipose afferent reflex

Blood pressure regulation in health and disease involves a balance between afferent and efferent signals from multiple organs and tissues. Although there are numerous reviews focused on the role of sympathetic nerves in different models of hypertension, few have revised the contribution of afferent nerves innervating adipose tissue and their role in the development of obesity-induced hypertension. Both clinical and basic research support the beneficial effects of bilateral renal denervation in lowering blood pressure. However, recent studies revealed that afferent signals from adipose tissue, in an adipose-brain-peripheral pathway, could contribute to the increased sympathetic activation and blood pressure during obesity. This review focuses on the role of adipose tissue afferent reflexes and briefly describes a number of other afferent reflexes modulating blood pressure. A comprehensive understanding of how multiple afferent reflexes contribute to the pathophysiology of essential and/or obesity-induced hypertension may provide significant insights into improving antihypertensive therapeutic approaches.

Renal Nerves and Long-Term Control of Arterial Pressure

The objective of this review is to provide an in-depth evaluation of how renal nerves regulate renal and cardiovascular function with a focus on long-term control of arterial pressure. We begin by reviewing the anatomy of renal nerves and then briefly discuss how the activity of renal nerves affects renal function. Current methods for measurement and quantification of efferent renal-nerve activity (ERNA) in animals and humans are discussed. Acute regulation of ERNA by classical neural reflexes as well and hormonal inputs to the brain is reviewed. The role of renal nerves in long-term control of arterial pressure in normotensive and hypertensive animals (and humans) is then reviewed with a focus on studies utilizing continuous long-term monitoring of arterial pressure. This includes a review of the effect of renal-nerve ablation on long-term control of arterial pressure in experimental animals as well as humans with drug-resistant hypertension. The extent to which changes in arterial pressure are due to ablation of renal afferent or efferent nerves are reviewed. We conclude by discussing the importance of renal nerves, relative to sympathetic activity to other vascular beds, in long-term control of arterial pressure and hypertension and propose directions for future research in this field. © 2017 American Physiological Society. Compr Physiol 7:263-320, 2017.

Renal Denervation Improves the Baroreflex and GABA System in Chronic Kidney Disease-induced Hypertension

Hypertensive rats with chronic kidney disease (CKD) exhibit enhanced gamma-aminobutyric acid (GABA)_B receptor function and regulation within the nucleus tractus solitarii (NTS). For CKD with hypertension, renal denervation (RD) interrupts the afferent renal sympathetic nerves, which are connecting to the NTS. The objective of the present study was to investigate how RD improves CKD-induced hypertension. Rats underwent 5/6 nephrectomy for 8 weeks, which induced CKD and hypertension. RD was induced by applying phenol to surround the renal artery in CKD. RD improved blood pressure (BP) by lowering sympathetic nerve activity and markedly restored the baroreflex response in CKD. The GABA_B receptor expression was increased in the NTS of CKD; moreover, the central GABA levels were reduced in the cerebrospinal fluid, and the peripheral GABA levels were increased in the serum. RD restored the glutamic acid decarboxylase activity in the NTS in CKD, similar to the effect observed for central treatment with baclofen, and the systemic administration of gabapentin reduced BP. RD slightly improved renal function and cardiac load in CKD. RD may improve CKD-induced hypertension by modulating the baroreflex response, improving GABA system dysfunction and preventing the development and reducing the severity of cardiorenal syndrome type 4 in CKD rats.

Evaluation and Treatment of Hypertension in End-Stage Renal Disease Patients on Hemodialysis

Hypertension is one of the most common cardiovascular comorbidities in end-stage renal disease patients on hemodialysis. Its complex pathophysiology is related to extracellular volume overload, increased vascular resistance stemming from factors related to uremia or abnormal signaling from the failing kidneys, as well as the unique blood pressure changes that take place during and between hemodialysis treatments. Despite the changing nature of blood pressure over time in hemodialysis patients, hypertension diagnosed in or out of the hemodialysis unit is associated with increased cardiovascular morbidity and mortality. This review details the causes of hypertension in hemodialysis patients and provides an updated review of the clinical consequences and management of hypertension.

Pathophysiology of resistant hypertension in chronic kidney disease

Hypertension associated with chronic kidney diseases often is resistant to drug treatment. This review deals with two main aspects of the management of CKD patients with hypertension: the role of sodium/volume and the need for dietary salt restriction, as well as appropriate use of diuretics and what currently is called sequential nephron blockade; the second aspect that is addressed extensively in this review is the role of the sympathetic nervous system and the possible clinical use of renal denervation.

Pressure natriuresis and the renal control of arterial blood pressure

The regulation of extracellular fluid volume by renal sodium excretion lies at the centre of blood pressure homeostasis. Renal perfusion pressure can directly regulate sodium reabsorption in the proximal tubule. This acute pressure natriuresis response is a uniquely powerful means of stabilizing long-term blood pressure around a set point. By logical extension, deviation from the set point can only be sustained if the pressure natriuresis mechanism is impaired, suggesting that hypertension is caused or sustained by a defect in the relationship between renal perfusion pressure and sodium excretion. Here we describe the role of pressure natriuresis in blood pressure control and outline the cascade of biophysical and paracrine events in the renal medulla that integrate the vascular and tubular response to altered perfusion pressure. Pressure natriuresis is impaired in hypertension and mechanistic insight into dysfunction comes from genetic analysis of blood pressure disorders. Transplantation studies in rats show that blood pressure is determined by the genotype of the kidney and Mendelian hypertension indicates that the distal nephron influences the overall natriuretic efficiency. These approaches and the outcomes of genome-wide-association studies broaden our view of blood pressure control, suggesting that renal sympathetic nerve activity and local inflammation can impair pressure natriuresis to cause hypertension. Understanding how these systems interact is necessary to tackle the global burden of hypertension.

Review article: advances in the management of patients with cirrhosis and portal hypertension-related renal dysfunction

BACKGROUND

In cirrhosis, portal hypertension is associated with a spectrum of renal dysfunction that has significant implications for morbidity and mortality.

AIM

To discuss recent progress in the patho-physiological mechanisms and therapeutic options for portal hypertension-related renal dysfunction.

METHODS

A literature search using Pubmed was performed.

RESULTS

Portal hypertension-related renal dysfunction occurs in the setting of marked neuro-humoral and circulatory derangement. A systemic inflammatory response is a pathogenetic factor in advanced disease. Such physiological changes render the individual vulnerable to further deterioration of renal function. Patients are primed to develop acute kidney injury when exposed to additional 'hits', such as sepsis. Recent progress has been made regarding our understanding of the aetiopathogenesis. However, treatment options once hepatorenal syndrome develops are limited, and prognosis remains poor. Various strategies to prevent acute kidney injury are suggested.

CONCLUSION

Prevention of acute kidney injury in high risk patients with cirrhosis and portal hypertension-related renal dysfunction should be a clinical priority.

Endovascular renal denervation: a novel sympatholytic with relevance to chronic kidney disease

Endovascular renal denervation (sympathectomy) is a novel procedure developed for the treatment of resistant hypertension. Evidence suggests that it reduces both afferent and efferent sympathetic nerve activity, which may offer clinical benefit over and above any blood pressure-lowering effect. Studies have shown objective improvements in left ventricular mass, ventricular function, central arterial stiffness, central haemodynamics, baroreflex sensitivity and arrhythmia frequency. Benefits have also been seen in insulin resistance, microalbuminuria and glomerular filtration rate. In chronic kidney disease, elevated sympathetic activity has been causally linked to disease progression and cardiovascular sequelae. Effecting a marked reduction in sympathetic hyperactivity may herald a significant step in the management of this and other conditions. In this in-depth review, the pathophysiology and clinical significance of the sympatholytic effects of endovascular renal denervation are discussed.

Evidence and consequences of the central role of the kidneys in the pathophysiology of sympathetic hyperactivity

Chronic elevation of the sympathetic nervous system has been identified as a major contributor to the complex pathophysiology of hypertension, states of volume overload – such as heart failure – and progressive kidney disease. It is also a strong determinant for clinical outcome. This review focuses on the central role of the kidneys in the pathogenesis of sympathetic hyperactivity. As a consequence, renal denervation may be an attractive option to treat sympathetic hyperactivity. The review will also focus on first results and the still remaining questions of this new treatment option.

Sympathetic renal innervation and resistant hypertension

Hypertension in chronic renal disease and renovascular disease is often resistant to therapy. Understanding the pathogenic mechanisms responsible for hypertension in these conditions may lead to improved and more targeted therapeutic interventions. Several factors have been implicated in the pathogenesis of hypertension associated with renal disease and/or renal failure. Although the role of sodium retention, total body volume expansion, and hyperactivity of the renin-angiotensin-aldosterone system (RAAS) are well recognized, increasing evidence suggests that afferent impulses from the injured kidney may increase sympathetic nervous system activity in areas of the brain involved in noradrenergic regulation of blood pressure and contribute to the development and maintenance of hypertension associated with kidney disease. Recognition of this important pathogenic factor suggests that antiadrenergic drugs should be an essential component to the management of hypertension in patients with kidney disease, particularly those who are resistant to other modalities of therapy.

Differential effects of acute and sustained cyclosporine and tacrolimus on sympathetic nerve activity

BACKGROUND

We studied the effect of acute and sustained cyclosporine and tacrolimus on muscle sympathetic nerve activity (MSNA) in groups of healthy male volunteers.

METHODS AND RESULTS

Acute cyclosporine in normal dose (2.5 mg/kg) increased MSNA from 11 +/- 6 to 19 +/- 8 bursts/min (P < 0.05). Acute cyclosporine in high dose (10 mg/kg) increased MSNA from 13 +/- 6 to 25 +/- 4 bursts/min (P < 0.05) and increased heart rate and mean arterial pressure (heart rate from 64 +/- 8 to 74 +/- 6 b.p.m., MAP from 92 +/- 10 to 105 +/- 8 mmHg; both P < 0.05). Sustained cyclosporine (2.5 mg/kg b.i.d. for 2 weeks) suppressed MSNA from 14 +/- 6 to 8 +/- 7 bursts/min (P < 0.05). Blood pressure increased from 89 +/- 6 to 98 +/- 6 mmHg (P < 0.05). Body weight increased and plasma renin activity was suppressed. Acute tacrolimus in regular dose (0.05 mg/kg) and high dose (0.20 mg/kg) had no effect on MSNA and blood pressure. Sustained tacrolimus (0.05 mg/kg b.i.d. for 2 weeks) had no effect on blood pressure, body weight and plasma renin activity, but decreased MSNA from 14 +/- 6 to 8 +/- 5 bursts/min (P < 0.05).

CONCLUSION

Sympathetic overactivity plays a role in the acute hypertensive action of cyclosporine. Cyclosporine given during 2 weeks increases blood pressure and suppresses MSNA, possibly by volume retention. Tacrolimus, in the presently applied dosages, does not cause hypertension or sympathetic overactivity. However, sustained tacrolimus also suppresses sympathetic activity, the reason of which is unclear.

Renal insufficiency coexisting with heart failure is related to elevated sympathetic nerve activity

We investigated whether coexisting renal insufficiency (RI) is associated with elevated sympathetic activity in patients with heart failure (HF). Resting muscle sympathetic nerve activity (MSNA) was determined in 101 patients with HF (ejection fraction<0.45) and 8 patients with RI but without HF (RI group). Diagnosis of RI was made of glomerular filtration rates <60ml/min/1.73m(2) estimated using the simplified Modification of Diet in Renal Disease equation. Of 101 patients, 45 had RI (HFRI group) and 56 did not (HF group). HFRI group was older (p<0.05) and given loop diuretics more frequently (p<0.05), and had a lower specific activity scale (p<0.05) than HF group. HFRI group exhibited significantly greater MSNA indices than either HF group or RI group (burst rate, p<0.05; burst incidence, p<0.01). Univariate analysis showed that RI, age, specific activity scale level and dose of furosemide were significant predictors of increased burst incidence of MSNA in patients with HF. Notably, multivariate analysis revealed that RI was the only independent factor for increased MSNA indices. These findings suggest that coexisting RI is associated with elevated sympathetic activity in patients with HF.

Severe hypertension in children and adolescents: pathophysiology and treatment

Severe, symptomatic hypertension occurs uncommonly in children, usually only in those with underlying congenital or acquired renal disease. If such hypertension has been long-standing, then rapid blood pressure reduction may be risky due to altered cerebral hemodynamics. While many drugs are available for the treatment of severe hypertension in adults, few have been studied in children. Despite the lack of scientific studies, some agents, particularly continuous intravenous infusions of nicardipine and labetalol, are preferred in many centers. These agents generally provide the ability to control the magnitude and rapidity of blood pressure reduction and should--in conjunction with careful patient monitoring--allow the safe reduction of blood pressure and the avoidance of complications. This review provides a summary of the underlying causes and pathophysiology of acute severe hypertension in childhood as well as a detailed discussion of drug treatment and the optimal clinical approach to managing children and adolescents with acute severe hypertension.

Regional expression of NAD(P)H oxidase and superoxide dismutase in the brain of rats with neurogenic hypertension

BACKGROUND

Single injection of small quantities of phenol into the kidney cortex causes hypertension which is mediated by renal afferent sympathetic pathway activation. This phenomenon can be prevented by superoxide dismutase (SOD) infusion in the lateral ventricle, suggesting the role of superoxide (O(2)(-).) in noradrenergic control of arterial pressure. Since NAD(P)H oxidase is a major source of O(2)(-)., we tested the hypothesis that hypertension in this model may be associated with upregulation of NAD(P)H oxidase in relevant regions of brain.

METHODS

NAD(P)H oxidase subunits, mitochondrial (MnSOD) and cytoplasmic (CuZnSOD) SOD were measured in rats 4 weeks after injection of phenol or saline in the left kidney cortex.

RESULTS

Phenol-injected rats exhibited hypertension, upregulation of gp91(phox), p22(phox), p47(phox) and p67(phox) in the medulla, gp91(phox) and p22(phox) in pons and gp91(phox) in hypothalamus. This was associated with upregulation of MnSOD with little change in CuZnSOD.

CONCLUSIONS

Chronic hypertension in phenol-injected rats is associated with upregulation of NAD(P)H oxidase and hence increased O(2)(-). production capacity in the key regions of the brain involved in regulation of blood pressure. Since reactive oxygen species can intensify central noradrenergic activity, the observed maladaptive changes may contribute to the genesis and maintenance of the associated hypertension.

Hypertension in children with chronic kidney disease: pathophysiology and management

Arterial hypertension is very common in children with all stages of chronic kidney disease (CKD). While fluid overload and activation of the renin-angiotensin system have long been recognized as crucial pathophysiological pathways, sympathetic hyperactivation, endothelial dysfunction and chronic hyperparathyroidism have more recently been identified as important factors contributing to CKD-associated hypertension. Moreover, several drugs commonly administered in CKD, such as erythropoietin, glucocorticoids and cyclosporine A, independently raise blood pressure in a dose-dependent fashion. Because of the deleterious consequences of hypertension on the progression of renal disease and cardiovascular outcomes, an active screening approach should be adapted in patients with all stages of CKD. Before one starts antihypertensive treatment, non-pharmacological options should be explored. In hemodialysis patients a low salt diet, low dialysate sodium and stricter dialysis towards dry weight can often achieve adequate blood pressure control. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers are first-line therapy for patients with proteinuria, due to their additional anti-proteinuric properties. Diuretics are a useful alternative for non-proteinuric patients or as an add-on to renin-angiotensin system blockade. Multiple drug therapy is often needed to maintain blood pressure below the 90th percentile target, but adequate blood pressure control is essential for better renal and cardiovascular long-term outcomes.

Renal denervation attenuates long-term hypertensive effects of Angiotensin ii in the rat

1. It is well accepted that some of the long-term effects of angiotensin (Ang) II are mediated via the central nervous system. Some of these actions that are mediated by the circumventricular organs and the baroreceptor reflex are thought to then alter sympathetic nervous system activity. In particular, there is some debate as to the role of renal nerves in the chronic effects of AngII. The aim of the present study was to assess the contribution of the renal nerves in a long-term model of progressive AngII-induced hypertension. 2. Male Sprague-Dawley rats were subjected to either bilateral renal denervation (RDX; n = 7) or sham surgery (SHAM; n = 8). Rats were instrumented with radiotelemetric transducers and venous catheters for the measurement of blood pressure and AngII infusion, respectively. A 4.0% NaCl diet and distilled water were provided ad libitum. The first 3 days served as the control period (7 mL/day, 0.9% NaCl, i.v.). This was followed by an infusion of AngII for 16 days (10 ng/kg per min, i.v.) and a 3 day recovery period identical to control. 3. Baseline arterial pressure between RDX and SHAM rats did not differ. Following AngII treatment, the arterial pressure of SHAM rats increased more rapidly than that of RDX rats. By Day 10 of treatment, the mean arterial pressure was significantly different between groups, having increased to 166 +/- 4 mmHg in SHAM rats and 135 +/- 11 mmHg in RDX rats. This trend continued for the remainder of AngII treatment. 4. The present results indicate that the renal nerves are necessary for the full expression of AngII-induced hypertension.

Hypertension in renal parenchymal disease: why is it so resistant to treatment?

The association between hypertension and chronic renal disease is well known. The pathogenesis of hypertension in patients with chronic kidney disease (CKD) is complex and multifactorial, which may explain why it is resistant to treatment. The traditional paradigm is that hypertension in CKD is due either to an excess of intravascular volume (volume dependent) or to excessive activation of the renin-angiotensin system in relation to the state of sodium/volume balance (renin-dependent hypertension). This review focuses on the importance of less established mechanisms, such as increased activity of the sympathetic nervous system, increased endothelin production, decreased availability of endothelium-derived vasodilators and structural changes of the arteries, renal ischemia, and sleep apnea.

Two cases of renovascular hypertension and ischemic renal dysfunction: reliable choice of examinations and treatments

We experienced two aged patients with atherosclerotic renovascular stenosis associated with hypertension and ischemic nephropathy. Both patients exhibited sudden rise in blood pressure (BP) and progressive aggravation of renal dysfunction. In these patients, the use of contrast medium to screen for renal artery stenosis (RAS) ran the risk of further deterioration of renal function. We therefore used magnetic resonance angiography (MRA), which is less conducive to renal damage, to screen for RAS. One-sided RAS was treated by percutaneous transluminal angioplasty of the renal artery (PTRA) and stenting. As a result, BP decreased in both patients. Serum creatinine (Cr) decreased slightly in one patient, whereas, in the other, serum Cr increased transiently and then decreased and stabilized to pre-treatment levels. Thus, although it is unclear whether the combination of PTRA and stenting is among the best treatments for patients with RAS and moderate-to-severe renal dysfunction, PTRA and stenting are clearly of benefit in selected patients. In addition, recent progress in characterizing the pathophysiology of ischemic nephropathy associated with renovascular hypertension has created interest in the therapeutic potential of angiotensin II receptor antagonists, sympatholytic agents, and antioxidants. Therefore, we discuss the therapeutic utility of PTRA and stenting and the above-mentioned medications in patients with RAS and renal dysfunction.

Sympathetic hyperactivity in chronic kidney disease: pathogenesis, clinical relevance, and treatment

Cardiovascular morbidity and mortality importantly influence live expectancy of patients with chronic renal disease (CKD). Traditional risk factors are usually present, but several other factors have recently been identified. There is now evidence that CKD is often characterized by an activated sympathetic nervous system. This may contribute to the pathogenesis of renal hypertension, but it may also adversely affect prognosis independently of its effect on blood pressure. The purpose of this review is to summarize available knowledge on the role of the sympathetic nervous system in the pathogenesis of renal hypertension, its clinical relevance, and the consequences of this knowledge for the choice of treatment.

Sympathetic nerve activity is inappropriately increased in chronic renal disease

The hypothesis that in hypertensive patients with renal parenchymal disease sympathetic activity is "inappropriately" elevated and that this overactivity is a feature of renal disease and not of a reduced number of nephrons per se is addressed. Fifty seven patients with renal disease (various causes, no diabetes, all on antihypertensive medication) were studied, age range 18 to 62, creatinine clearance 10 to 114 ml/min per 1.73 m(2). Antihypertensives were stopped, but diuretics were allowed, to prevent overhydration. Matched control subjects were also studied. The effect of changes in fluid status was examined in seven patients while on and after stopping diuretics and in eight control subjects while on low- and high-sodium diet. Seven kidney donors were studied before and after unilateral nephrectomy. Sympathetic activity was quantified as muscle sympathetic nerve activity (MSNA) in the peroneal nerve. Mean arterial pressure, MSNA, and plasma renin activity were higher in patients than in control subjects, respectively (115 +/- 12 and 88 +/- 11 mmHg, 31 +/- 15 and 18 +/- 10 bursts/min, and 500 [20 to 6940] and 220 [40 to 980] fmol/L per s; P < 0.01 for all items). Extracellular fluid volume (bromide distribution) did not differ. Seven patients were studied again after stopping diuretics. MSNA decreased from 34 +/- 18 to 19 +/- 18 bursts/min (P < 0.01). Eight healthy subjects were studied during low- and high-sodium diet. MSNA was 26 +/- 12 and 13 +/- 7 bursts/min (P < 0.01). The curves relating extracellular fluid volume to MSNA were parallel in the two groups but shifted to a higher level of MSNA in the patients. In the kidney donors, creatinine clearance reduced by 25%, but MSNA was identical before and after donation. It is concluded that in hypertensive patients with renal parenchymal disease, sympathetic activity is inappropriately high for the volume status and that reduction of nephron number in itself does not influence sympathetic activity.

[Sympathetic overactivity and the kidney]

Hypertension is present in the majority of patients with chronic renal failure and constitutes a major risk factor for the very high cardiovascular morbidity and mortality in this patient population. Furthermore hypertension is known to be a substantial progression factor in renal disease. In the past, it had been presumed that hypertension in chronic renal failure is due to enhanced sodium retention, chronic hypervolemia and increased activity of the renin-angiotensin-aldosterone-system. Recent studies now provide evidence that sympathetic overactivity plays an additional important role and also promotes progression of renal failure. The treatment goal in renal patients is to delay or even prevent progression of renal failure and to reduce the cardiovascular risk. Recent studies have investigated the respective impact of sympatholytic drugs, e.g. inhibitors of the renin-angiotensin-aldosterone-system, beta-blockers or I1-Imidazolin-receptor-agonists in fulfilling these aims. The present report will review experimental and clinical studies on the role of sympathetic overactivity in hypertension and chronic renal failure and possible new therapeutic options.

Factors influencing acute ischaemia-induced renal hypertension in rats

OBJECTIVE

To verify if the acute hypertension that occurs after reversal of complete renal ischaemia is related to the duration of ischaemia, is different in one-kidney (1K) and two-kidney (2K) rats, and is prevented by angiotensin receptor blockade.

METHODS

Four groups of Sprague-Dawley rats anaesthetized with pentobarbitone were studied before, during and after a reversible, complete renal ischaemia achieved by functional right nephrectomy.

RESULTS

In 1K rats (group 1, n = 21), reopening of right renal hilum after functional right nephrectomy of 180, 60 and 30 min was followed by peak increases in systolic blood pressure of 76.0 10.1 mmHg, 36.5 10.0 mmHg and 18.4 4.4 mmHg, respectively (mean SEM). In 2K rats (group 2, n = 21), functional right nephrectomy of 180, 60 and 30 min was followed by smaller increases in blood pressure of 49.8 7.6 mmHg, 5.9 3.3 mmHg and 8.3 2.1 mmHg, respectively. Plasma renin activity was directly related to the duration of functional right nephrectomy, and was greater in 1K rats. In group 3, irbesartan administered to 1K rats (n = 8) during functional right nephrectomy almost completely prevented the development of hypertension upon reopening. In group 4, labetalol injected intravenously in 1K rats (n = 3) did not prevent the blood pressure surge at reopening (49.2 8.5 mmHg).

CONCLUSIONS

An experimental acute renal hypertension may be elicited both in 1K and in 2K rats and for functional right nephrectomy of 30, 60 and 180 min duration. The increase in blood pressure is proportional to the duration of functional right nephrectomy and greater in 1K than in 2K rats. The experimental acute renal hypertension is due to acute release of renin and generation of endogenous angiotensin II, and is specifically prevented by the angiotensin II type 1 receptor blocker, irbesartan, but not by labetalol.

Neurogenic factors in renal hypertension

Hypertension is very common in patients with chronic renal failure and contributes to cardiovascular morbidity and mortality. Several mechanisms may contribute to hypertension in these patients, but recently a large body of evidence supports the notion that activation of the sympathetic nervous system (SNS) may play a very important role. In rats with 5/6 nephrectomy, the turnover rate of norepinephrine was increased in brain nuclei involved in the noradrenergic control of blood pressure, and dorsal rhizotomy prevented hypertension. Studies in human subjects with chronic renal failure and hypertension have also shown increased peripheral SNS activity measured my microneurography in the peroneal nerve and normalization with nephrectomy. In all, these studies indicate that renal injuries may activate renal afferent pathways that connect with integrative brain structures in SNS activity and blood pressure. We have also shown that central SNS activity is modulated by local expression of nitric oxide, which, in turn, is regulated by interleukin-1b.

Sympathetic activity is increased in polycystic kidney disease and is associated with hypertension

Hypertension is common in patients with polycystic kidney disease (PKD). This study addresses the hypothesis that sympathetic activity is enhanced in hypertensive PKD patients, not only when renal function is impaired but also when renal function is still normal. Muscle sympathetic nerve activity (MSNA, peroneal nerve), plasma renin activity (PRA), heart rate, and BP were studied in PKD patients with normal and with impaired renal function and in matched controls. In hypertensive patients with normal renal function, MSNA and mean arterial pressure (MAP) were higher than in normotensive patients (23 +/- 5 versus 15 +/- 7 bursts/min; 110 +/- 10 versus 90 +/- 3 mmHg; P < 0.05), whereas PRA and heart rate did not differ. In PKD with chronic renal failure (CRF) (creatinine clearance rate, 39 +/- 19 ml/min), MAP, MSNA and PRA were higher than in controls (resp, 116 +/- 7 versus 89 +/- 9 mmHg; 34 +/- 14 versus 19 +/- 9 bursts/min; 405 [20 to 1640] versus 120 [40 to 730] fmol/L per sec; all P < 0.05). Heart rate in PKD CRF did not differ from controls. MSNA correlated with MAP (r = 0.42; P = 0.01) and age with MSNA (r = 0.45; P < 0.01). Regression line of age and MSNA in patients was steeper than that in controls. This study indicates that MSNA is increased in hypertensive PKD patients regardless of renal function. The data support the idea that sympathetic hyperactivity contributes to the pathogenesis of hypertension in PKD.

Effects of a reversible 'nephrectomy' on renal sympathetic activity and blood pressure in the rat: evidence for an acute angiotensin-mediated hypertension

OBJECTIVE

To verify whether the normal kidney exerts a supportive, facilitatory action on renal sympathetic nerve activity (RSNA), the effects of unilateral and bilateral nephrectomy on RSNA have been studied.

METHODS

The RSNA, rectal temperature (T), rate of breathing (RB), arterial blood pressure (BP) and heart rate (HR) were continuously recorded in three groups of pentobarbital anaesthetized, spontaneously breathing Sprague-Dawley rats: group 1 (n = 5): both kidneys intact; group 2 (n = 5): left surgical nephrectomy; group 3 (n = 5): left surgical nephrectomy and functional exclusion of the right kidney (functional right nephrectomy, FRN), produced by a tight ligature of the renal hilum which was maintained for 3 h. In a fourth group (n = 7), in which nerve activity was not recorded, reopening of the right renal hilum was preceded or followed by intravenous administration of captopril (3 mg/kg).

RESULTS

In groups 1 and 2 RSNA increased from 22.3 +/- 2.1 to 122.9 +/- 13.6 and from 26.7 +/- 1.2 to 93.2 +/- 14.0 impulses/s (mean +/- SEM), respectively, without concomitant changes in cardiovascular parameters. In group 3 RSNA decreased from 39.1 +/- 3.1 to 13.7 +/- 2.6 impulses/s during the 3 h of FRN. In group 3 the reopening of the right renal hilum was followed by a marked increase in BP and HR that was prevented or reversed by intravenous captopril in rats of group 4.

CONCLUSIONS

The decrease in RSNA observed in rats during bilateral nephrectomy, in contrast to the increase observed in rats with one or both kidneys intact, suggests that the kidney as a whole exerts a supportive role on sympathetic nerve activity. The hypertension and tachycardia that follows the reopening of the right kidney hilum appears to be caused by the generation of endogenous angiotensin II; this is the first evidence of an acute angiotensin-mediated renal hypertension.

Neurogenic factors and hypertension in renal disease

Hypertension in chronic renal failure (CRF) is very common and contributes to morbidity and mortality and to the progression of renal disease. The pathogenesis of hypertension in CRF has been attributed mostly to sodium retention and to activation of the renin-angiotensin-aldosterone system. More recently an abundance of evidence has accumulated to support a role for increased sympathetic nervous system (SNS) activity in the genesis of hypertension associated with CRF. Evidence from our laboratory has also demonstrated that the rise in central SNS activity is mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NO) production, and that the upregulation of NO production in the brain is mediated by IL-1beta.

Reduction of sympathetic hyperactivity by enalapril in patients with chronic renal failure

BACKGROUND

Inhibition of angiotensin-converting enzyme (ACE) reduces the risk of cardiovascular problems in patients with chronic renal failure. This effect may be due in part to a decrease in sympathetic nervous activity, but no direct evidence of such an action is available.

METHODS

We studied muscle sympathetic-nerve activity in 14 patients with hypertension, chronic renal failure, and increased plasma renin activity before, during, and after administration of the ACE inhibitor enalapril. Ten other patients with similar clinical characteristics were studied before and during treatment with the calcium-channel blocker amlodipine. Normal subjects matched for age and weight were included in both studies.

RESULTS

At base line, mean (+/-SD) muscle sympathetic-nerve activity was higher in the group of patients who received enalapril than in the control subjects (35+/-17 vs. 19+/-9 bursts per minute, P=0.004). The baroreflex curve, which reflects changes in muscle sympathetic-nerve activity caused by manipulations of blood pressure with sodium nitroprusside and phenylephrine, was shifted to the right in the patients, but baroreflex sensitivity was similar to that in the control subjects (-2.1+/-1.9 and -2.7+/-1.3 bursts per minute per mm Hg, respectively; P=0.36). A single dose of the sympatholytic drug clonidine caused a greater fall in blood pressure in the patients than in the control subjects. Treatment with enalapril normalized blood pressure and muscle sympathetic-nerve activity (at 23+/-10 bursts per minute) in the patients and shifted the baroreflex curve to the left, reflecting normal blood-pressure levels, without significantly changing sensitivity (-2.3+/-1.8 bursts per minute per mm Hg, P=0.96). In the patients who received amlodipine, treatment also lowered blood pressure but increased muscle sympathetic-nerve activity, from 41+/-19 to 56+/-14 bursts per minute (P=0.02).

CONCLUSIONS

Increased sympathetic activity contributes to hypertension in patients with chronic renal disease. ACE inhibition controls hypertension and decreases sympathetic hyperactivity.

The renal afferent pathways in the rat: a pseudorabies virus study

Retrograde tract tracing studies have indicated that dorsal root ganglion cells from T8 to L2 innervate the rat's left kidney. Electrophysiology studies have indicated that putative second-order sympathetic afferents are found in the dorsal horn at spinal segments T10 to L1 in laminae V-VII. Here, the spread of pseudorabies virus through renal sensory pathways was examined following 2-5 days post-infection (PI) and the virus was located immunocytochemically using a rabbit polyclonal antibody. Two days PI, dorsal root ganglion neurons (first-order sympathetic afferents) were infected with PRV. An average of 1.2, 0.8, 2.1 and 4.4% of the infected dorsal root ganglion neurons were contralateral to the injected kidney at spinal segments T10, T11, T12 and T13, respectively. Four days PI, infected neurons were detected within laminae I and II of the dorsal horn of the caudal thoracic and upper lumbar spinal cord segments. The labeling patterns in the spinal cord are consistent with previous work indicating the location of renal sympathetic sensory pathways. The nodose ganglia were labeled starting 4 days PI, suggesting the involvement of parasympathetic sensory pathways. Five days PI, infected neurons were found in the nucleus tractus solitarius. In the present study, it was unclear whether the infected neurons in the nucleus tractus solitarius are part of sympathetic or parasympathetic afferent pathways or represent a convergence of sensory information. Renal denervation prevented the spread of the virus into the dorsal root ganglia and spinal cord. Sectioning the dorsal roots from T10-L3 blocked viral spread into the spinal cord dorsal horn, but did not prevent infection of neurons in dorsal root ganglion nor did it prevent infection of putative preganglionic neurons in the intermediolateral cell column. The present results indicated that renal afferent pathways can be identified after pseudorabies virus infection of the kidney. Our results suggest that renal afferents travel in sympathetic and parasympathetic nerves and that this information may converge at the NTS.

Resetting of renal blood autoregulation during acute blood pressure reduction in hypertensive rats

Decrease in systemic blood pressure, duration of pressure decrease, and change in the activity of the renin or the sympathetic nervous system may represent mechanisms involved in resetting the renal blood flow (RBF) autoregulation found in hypertensive rats. Autoregulation of RBF, plasma renin concentration (PRC), and the time needed for resetting to take place were studied in the nonclipped kidney before and after removal of the clipped kidney of two- kidney, one-clip (2K1C) hypertensive rats and before and after mechanical reduction of the renal arterial pressure (RAP) for 10 min in the spontaneously hypertensive rat (SHR) and in the nonclipped kidney of 2K1C hypertensive rats with and without renal denervation. Mean arterial pressure (MAP) fell from 147 to 107 mmHg 30 min after removal of the clipped kidney, and the lower pressure limit of RBF autoregulation decreased from 113 to 90 mmHg (P < 0.01); PRC fell. Mechanical reductions of RAP from 161 to 120 mmHg in the nonclipped kidney for 10 min did not change RBF, but at 120 mmHg, the lower pressure limit of RBF autoregulation was reduced from 115 mmHg before pressure reduction to 96 mmHg afterwards (P < 0.02). In SHR, similar pressure reduction for 10 min decreased the lower pressure limit of RBF autoregulation from 106 to 86 mmHg (P < 0.01). PRC was unchanged in both models, and denervation did not change RBF autoregulation. When RAP was reduced below the lower pressure limit of RBF autoregulation, RBF decreased approximately 20%; the lower pressure limit of RBF autoregulation remained unchanged. In normotensive Wistar-Kyoto rats, pressure reduction did not change the range of RBF autoregulation. These results indicate that acute normalization of the pressure range of RBF autoregulation in hypertensive rats is dependent on the degree of pressure reduction of RAP, whereas renal innervation and PRC do not play a major role. We propose that the mechanism of resetting is due to afterstretch of noncontractile elements of the vessel wall or is caused by pure myogenic mechanisms. An effect of intrarenal angiotensin cannot be excluded.

Influence of sympathetic blockade on the acute hypertensive response to aortic constriction

The objective of the present study was to determine the contribution of the sympathetic nervous system to the hypertensive response to acute (45-min) aortic coarctation in conscious intact or sinoaortic-denervated (SAD) rats. Rats were treated chronically (5 wk) with guanethidine (50 mg.kg-1.day-1 i.p.) to induce sympathetic nerve degeneration or acutely with the alpha 1-adrenergic receptor antagonist prazosin. (1 mg/kg i.v.). Aortic constriction elicited a prompt and sustained rise in mean carotid pressure that was significantly greater in SAD than in intact rats. The increase in pressure was associated with reflex bradycardia only in the intact rats, whereas the heart rate of SAD rats did not change. Guanethidine treatment did not affect the arterial pressure or heart rate responses to aortic coarctation of intact rats but blunted the hypertensive response of SAD rats to the same values exhibited by intact rats. Prazosin administered 10 min after the beginning of aortic coarctation reduced the hypertensive response of SAD rats to the same level as that of intact rats. In conclusion, the data obtained by means of the association of sinoaortic deafferentation with chronic sympathectomy with guanethidine or acute alpha 1-adrenergic receptor blockade with prazosin indicate that the greater hypertensive response of SAD rats involves a lack of suppression of the sympathetic activity in the maintenance of the rise in pressure elicited by aortic coarctation.

Vasopressor mechanisms in acute aortic coarctation hypertension

Angiotensin II (ANG II) and vasopressin (AVP) act together with the mechanical effect of aortic constriction in the onset of acute aortic coarctation hypertension. Blockade of ANG II and AVP V1 receptors demonstrated that ANG II acts on the prompt (5 min) rise in pressure whereas AVP is responsible for the maintenance (30-45 min) of the arterial pressure elevation during aortic coarctation. Hormone assays carried out on blood collected from conscious rats submitted to aortic constriction supported a role for ANG II in the early stage and a combined role for both ANG II and AVP in the maintenance of proximal hypertension. As expected, a role for catecholamines was ruled out in this model of hypertension, presumably due to the inhibitory effect of the sinoaortic baroreceptors. The lack of afferent feedback from the kidneys for AVP release from the central nervous system in rats with previous renal denervation allowed ANG II to play the major role in the onset of the hypertensive response. Median eminence-lesioned rats exhibited a prompt increase in proximal pressure followed by a progressive decline to lower hypertensive levels, revealing a significant role for the integrity of the neuroaxis in the maintenance of the aortic coarctation hypertension through the release of AVP. In conclusion, the important issue raised by this model of hypertension is the likelihood of a link between some vascular territory-probably renal-below the coarctation triggering the release of AVP, with this vasoconstrictor hormone participating with Ang II and the mechanical effect of aortic constriction in the acute aortic coarctation hypertension.

Sympathetic overactivity and 24-hour blood pressure pattern in hypertensives with chronic renal failure

In order to assess the activity of the sympathetic system and to evaluate the 24-h blood pressure pattern in hypertensives with chronic renal failure (CRF), 12 CRF patients and 16 essential hypertensives (EHs) were studied. In all subjects, plasma samples for catecholamines and renin activity were obtained both in the basal condition and after standing, and 24-h blood pressure monitoring (ABPM) was performed. The 24-h mean blood pressure results were quite similar between CRFs and EHs. In 50% of the CRFs, ABPM showed a nighttime decrease in diastolic BP (DBP) greater than 10%, while in the remaining 50% the ABPM indicated a nondipper blood pressure pattern. Of the 16 EHs, 4 had a nighttime decrease in DBP < 10%, that is, nondippers. The study of circulating catecholamines showed no significant differences in plasma epinephrine between CRFs and EHs, while plasma norepinephrine (NE) was significantly higher in hypertensives with CRF than in EHs, both at rest and after standing (p < 0.05 and 0.02, respectively). Among dipper hypertensives, subjects with CRF showed greater values of basal plasma NE than EHs (535 +/- 67 vs. 412 +/- 24.5 pg/mL, p < 0.05); the comparison between dipper and nondipper CRFs showed no differences in circulating NE levels (535 vs. 516 pg/mL). The present study shows that CRFs are characterized by higher values of plasma NE than EHs, and that there are no differences in sympathetic activity between dipper and nondipper hypertensives with CRF.

Renal afferent denervation prevents the progression of renal disease in the renal ablation model of chronic renal failure in the rat

Rats with 5/6 nephrectomy develop hypertension and progressive deterioration in renal function. Several mechanisms may contribute to hypertension and to progressive renal disease in these rats. We have shown that increased activity of the sympathetic nervous system may contribute to hypertension in rats we chronic renal failure. However, the role of the sympathetic nervous system activity in the progression of renal disease has not been investigated. We have evaluated whether neurogenic factors contribute to the progression of renal disease in the renal ablation model of chronic renal failure in the rat. Sprague-Dawley rats underwent 5/6 nephrectomy and dorsal rhizotomy or sham rhizotomy (CRF). Age-matched normal rats were used as controls. Six weeks after surgery, rats with chronic renal failure and dorsal rhizotomy had lower blood pressure and serum creatinine than rats with sham rhizotomy. In addition, kidneys from rats with 5/6 nephrectomy and rhizotomy manifested less severe glomerulosclerosis than kidneys from rats without dorsal rhizotomy. These studies have demonstrated in rats with renal ablation. Although normalization of blood pressure may definitely play a role, the data raise the possibility that neurogenic impulses to the kidneys may contribute to the progression of renal disease.

Sympathetic overactivity in patients with chronic renal failure

BACKGROUND

Hypertension is a frequent complication of chronic renal failure, but its causes are not fully understood. There is indirect evidence that increased activity of the sympathetic nervous system might contribute to hypertension in patients with end-stage renal disease, but sympathetic-nerve discharge has not been measured directly in patients or animals with chronic renal failure.

METHODS

We recorded the rate of postganglionic sympathetic-nerve discharge to the blood vessels in skeletal muscle by means of microelectrodes inserted into the peroneal nerve in 18 patients with native kidneys who were undergoing long-term treatment with hemodialysis (of whom 14 had hypertension), 5 patients receiving hemodialysis who had undergone bilateral nephrectomy (of whom 1 had hypertension), and 11 normal subjects. RESULTS. The mean (+/- SE) rate of sympathetic-nerve discharge was 2.5 times higher in the patients receiving hemodialysis who had not undergone nephrectomy than in the normal subjects (58 +/- 3 vs. 23 +/- 3 bursts per minute, P < 0.01). In contrast, the rate of sympathetic-nerve discharge was similar in the patients receiving hemodialysis who had undergone bilateral nephrectomy (21 +/- 6 bursts per minute) and the normal subjects. The rate of sympathetic-nerve discharge in the patients receiving hemodialysis who had not undergone nephrectomy was also significantly higher (P < 0.01) than that in the patients with bilateral nephrectomy, and it was accompanied in the former group by higher values for vascular resistance in the calf (45 +/- 4 vs. 22 +/- 4 units, P < 0.05) and mean arterial pressure (106 +/- 4 vs. 76 +/- 14 mm Hg, P < 0.05). The rate of sympathetic-nerve discharge was not correlated with either plasma norepinephrine concentrations or plasma renin activity.

CONCLUSIONS

Chronic renal failure may be accompanied by reversible sympathetic activation, which appears to be mediated by an afferent signal arising in the failing kidneys.

The reflex effect of changes in renal perfusion on hindlimb vascular resistance in anaesthetized rabbits

This study was designed to characterise the response of the hindlimb vasculature to reduced renal perfusion in the anaesthetized rabbit and to elucidate whether the stimulus was dependent upon reduced renal perfusion pressure (RPP) or blood flow (RBF). Acute decreases in renal perfusion resulted in rapid and reversible increases in femoral perfusion (FPP). This vascular response was completely abolished following renal denervation indicating that the afferent components of the reflex is neurally mediated. Acute hindlimb responses to changes in renal perfusion pressure were present whether the limb was perfused with homologous blood or cross-perfused with blood from a donor rabbit, demonstrating that the efferent component of the response is also neurally mediated. There was a 28-s latency for initiation of the hindlimb vasoconstriction, which is consistent with recent evidence for renal autocoid stimulation of the afferent renal nerve receptors. Decreasing RPP indirectly, by altering flow, resulted in a hindlimb vasoconstriction below approximately 55 mm Hg (7.3 kPa) RPP or 15 ml/min RBF. However, decreasing RPP by directly reducing pressure in graded steps resulted in increases in FPP, which reflected the changes in renal flow; thus during the autoregulatory phase, where flow did not change as pressure fell, FPP also remained stable. The results of these protocols suggest that a neurally mediated hindlimb vascular reflex is stimulated by decreased renal flow rather than pressure.

Studies on the afferent and efferent renal nerves following autotransplantation of the canine kidney

The presence of both afferent and efferent renal nerves following renal transplantation was investigated in a canine autotransplant model. The efferent postganglionic sympathetic renal nerves were studied using the glyoxylic acid histofluorescence technique to identify renal tissue adrenergic amines (Grade 0-4). The afferent sensory renal nerves were studied by the systemic blood pressure response to renal arterial injection of capsaicin. In 8 control dogs with native innervated kidneys (Group I), intrarenal injection of capsaicin significantly increased the systemic blood pressure from baseline by 32.4 +/- 6.3 mm. Hg (p less than 0.01). This response was equivalent to the blood pressure increase following injection of capsaicin into the mesenteric artery which was 37.3 +/- 9.8 mm. Hg. The renal tissue histofluorescence grade in this group was 4. Six dogs were studied two to three weeks after autotransplantation of a solitary kidney (Group II). Intrarenal injection of capsaicin did not increase the systemic blood pressure in these animals. Three dogs in this group had no evidence of renal tissue adrenergic amines by histofluorescence (Grade 0); the remaining two animals had renal tissue histofluorescence grades of 1 and 2. Eight dogs were studied 12 to 35 months after autotransplantation of a solitary kidney (Group III). Intrarenal injection of capsaicin in these animals significantly increased the systemic blood pressure from baseline by 10 +/- 1.4 mm. Hg (p less than 0.001). The renal tissue histofluorescence grade in this group ranged from 1 to 3. These data support the presence of both afferent and efferent renal nerves in the kidney at greater than or equal to one year post-transplant.

Tetrodotoxin protects against acute ischemic renal failure in the rat

Tetrodotoxin has been reported to cause prolonged systemic hypotension without resultant ischemic damage. We tested its ability to protect the kidney during 60 minutes of warm ischemia in uninephrectomized rats. Protection was observed when tetrodotoxin was given intravenously at two microgram./kg. and four microgram./kg. as assessed by serial plasma blood urea nitrogen and creatinine measurements over two weeks. Tetrodotoxin was protective when given immediately before or immediately after the ischemic period. The renal protection of tetrodotoxin was not due to its effects on renal nerves as renal denervation did not protect the kidney from the ischemic damage. The renal protective effects of four microgram. tetrodotoxin/kg. were similar to those of four mg. captopril/kg. but the combination of the two was paradoxically without effect. We tested whether tetrodotoxin and captopril chemically antagonized each other, but in the presence of tetrodotoxin, captopril was still a potent inhibitor of the conversion of angiotensin I to angiotensin II. These results indicate that tetrodotoxin could be useful in elucidating the sequence of events associated with ischemic-reperfusion renal injury and in identifying ways of preserving renal function during renal surgery.