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

Review: Blood pressure in haemodialysis patients: The importance of the relationship between the renin-angiotensin-aldosterone system, salt intake and extracellular volume

This review outlines the major mechanisms for control of blood pressure (BP) in individuals with renal failure on haemodialysis. Dietary salt stimulates thirst and, thereby, greater fluid intake with excessive fluid gain between dialysis sessions and chronic expansion of extracellular volume. At the same time, this volume expansion often fails to suppress the renin-angiotensin system (RAS) appropriately and this inevitably leads to high BP in the majority of individuals on haemodialysis.

A greater understanding of the mechanisms involved leads to more rational treatment and better BP control. This can be achieved by careful measurement of BP before and after dialysis, allowing time for the equilibration of extracellular fluid shifts that occur after dialysis, combined with measurements of plasma renin activity. It is relatively easy to then decide how the high BP should be treated either by removal of excess volume by gradual ultrafiltration combined with restriction of salt intake to help prevent thirst and excessive fluid gain between dialyses, or by inhibition of the RAS, or by a combination of both.

In those individuals who are unable to adequately reduce their dietary salt intake and still continue to gain large amounts of weight between dialysis, and are resistant to reducing their pre-dialysis weight, calcium antagonists may help to lower BP, either alone or in combination with RAS blockade. However, the BP often remains resistant to treatment unless they can be persuaded to reduce their salt intake.

Chronic Kidney Disease As a Potential Indication for Renal Denervation

Renal denervation is being used as a blood pressure lowering therapy for patients with apparent treatment resistant hypertension. However, this population does not represent a distinct disease condition in which benefit is predictable. In fact, the wide range in effectiveness of renal denervation could be a consequence of this heterogeneous pathogenesis of hypertension. Since renal denervation aims at disrupting sympathetic nerves surrounding the renal arteries, it seems obvious to focus on patients with increased afferent and/or efferent renal sympathetic nerve activity. In this review will be argued, from both a pathophysiological and a clinical point of view, that chronic kidney disease is particularly suited to renal denervation.

The Effect of Chronic Kidney Disease on Mortality with Cardiac Resynchronization Therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) improves functional status, reduces heart failure hospitalizations, and decreases mortality. Several comorbidities including renal function affect outcomes with CRT. However, moderate to severe chronic kidney disease (CKD) was an exclusion criterion in the large randomized control trials.

OBJECTIVE

To evaluate the association of renal function on survival following CRT implantation.

METHODS

This was a retrospective analysis of 432 consecutive patients implanted with an implantable cardioverter defibrillator with CRT (CRT-D). The primary end point was defined as death by any cause, and it was determined using hospital records and the U.S. Social Security Death Index. A Kaplan-Meier analysis was performed separating renal dysfunction into renal stage based on glomerular filtration rate. Multivariate analysis was performed to assess the clinical predictors of mortality.

RESULTS

Patients were followed for up to 12 years with a mean follow-up time of 4.3 ± 3.2 years. A total of 164 patients (39.3%) died over the course of the study. Patients with normal and mild renal diseases (Stages 1 and 2) had improved survival compared with those with moderate-, severe-, or end-stage (Stages 3-5) renal disease. This effect remained statistically significant after multivariate analysis. The estimated 5-year mortality was 36.3% for stage 1, 33.4% for stage 2, 40.6% for stage 3, and 62.1% for stage 4/5 kidney disease (P = 0.004 by log-rank test).

CONCLUSION

CKD is a strong and an independent predictor of long-term mortality among patients undergoing CRT-D implantation.

Sympathomodulatory Effects of Antihypertensive Drug Treatment

BACKGROUND

An activation of sympathetic neural influences to the heart and peripheral circulation has been shown to represent a hallmark of the essential hypertensive state, adrenergic neural factors participating together with other variables at the development and progression of the high blood pressure state as well as of the hypertension-related target organ damage. This represents the rationale for employing in hypertension treatment drugs which combine the blood pressure-lowering properties with the modulatory effects on the sympathetic neural function.

METHODS AND RESULTS

Several studies published during the past 40 years have investigated the impact of antihypertensive drugs on the sympathetic target as assessed by indirect and direct approaches. In the present paper, the effects of different monotherapies or combination drug treatment used in hypertension to lower elevated blood pressure values on various adrenergic markers will be examined. This will be followed by a discussion of the (i) hemodynamic and nonhemodynamic consequences of employing antihypertensive drugs with sympathomodulatory or sympathoexcitatory properties and (ii) mechanisms potentially responsible for the adrenergic responses to a given antihypertensive drug. The final part of this review will address the questions still open related to the impact of antihypertensive drug treatment on sympathetic function. Two questions in particular will be examined, i.e., whether antihypertensive drugs with sympathomodulatory properties may be capable to fully restore a "normal" adrenergic drive and how far sympathetic activity should be reduced in hypertensive patients.

CONCLUSION

Future investigations aimed at answering these questions will be needed in order to improve cardiovascular protection in treated hypertensive patients.

Tetrahydrobiopterin ameliorates the exaggerated exercise pressor response in patients with chronic kidney disease: a randomized controlled trial

Chronic kidney disease (CKD) patients have an exaggerated increase in blood pressure (BP) during rhythmic handgrip exercise (RHG 20%) and static handgrip exercise (SHG 30%). Nitric oxide levels increase during exercise and help prevent excessive hypertension by both increasing vasodilation and reducing sympathetic nerve activity (SNA). Therefore, we hypothesized that tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthase, would ameliorate the exaggerated exercise pressor response in CKD patients. In a randomized, double-blinded, placebo-controlled trial, we tested the effects of 12 wk of sapropterin dihydrochloride (6R-BH4; n = 18) versus placebo (n = 14) treatement on BP and muscle SNA (MSNA) responses during RHG 20% and SHG 30% in CKD patients. The 6R-BH4-treated group had a significantly lower systolic BP (+6 ± 1 vs. +13 ± 2 mmHg, P = 0.002) and mean arterial pressure response (+5 ± 1 vs. +10 ± 2 mmHg, P = 0.020) during RHG 20% and a significantly lower systolic BP response (+19 ± 3 vs. +28 ± 3 mmHg, P = 0.043) during SHG 30%. Under baseline conditions, there was no significant difference in MSNA responses between the groups; however, when the BP response during exercise was equalized between the groups using nitroprusside, the 6R-BH4-treated group had a significantly lower MSNA response during RHG 20% (6R-BH4 vs. placebo, +12 ± 1 vs. +21 ± 2 bursts/min, P = 0.004) but not during SHG 30%. These findings suggest that 6R-BH4 ameliorates the augmented BP response during RHG 20% and SHG 30% in CKD patients. A reduction in reflex activation of SNA may contribute to the decreased exercise pressor response during RHG 20% but not during SHG 30% in CKD patients.

Cardiovascular Autonomic Dysfunction in Chronic Kidney Disease: a Comprehensive Review

Cardiovascular autonomic dysfunction is a major complication of chronic kidney disease (CKD), likely contributing to the high incidence of cardiovascular mortality in this patient population. In addition to adrenergic overdrive in affected individuals, clinical and experimental evidence now strongly indicates the presence of impaired reflex control of both sympathetic and parasympathetic outflow to the heart and vasculature. Although the principal underlying mechanisms are not completely understood, potential involvements of altered baroreceptor, cardiopulmonary, and chemoreceptor reflex function, along with factors including but not limited to increased renin-angiotensin-aldosterone system activity, activation of the renal afferents and cardiovascular structural remodeling have been suggested. This review therefore analyzes potential mechanisms underpinning autonomic imbalance in CKD, covers results accumulated thus far on cardiovascular autonomic function studies in clinical and experimental renal failure, discusses the role of current interventional and therapeutic strategies in ameliorating autonomic deficits associated with chronic renal dysfunction, and identifies gaps in our knowledge of neural mechanisms driving cardiovascular disease in CKD.

Obsessive Compulsive Inventory-Child Version (OCV-CI) to Evaluate Obsessive Compulsive Disorder in Children With Early Stages of Chronic Kidney Disease: A Case Control Study

Background:

Chronic kidney disease (CKD) is a common medical condition among children and obsessive-compulsive disorder (OCD) is a frequent, chronic, costly, and disabling disorder among them.

Objectives:

The aim of this study was to investigate obsessive-compulsive disorder (OCD) in children with early stages of CKD, and to compare it with the occurrence of OCD in healthy children.

Patients and Methods:

In this case-control study, we evaluated 160 children aged 7 to 17 years old who were visited in the pediatric clinics of Amir-Kabir hospital, Arak, Iran. The control group consisted of 80 healthy children and the case group included 80 children with Stage 1 to 3 CKD. The ages and sex of the children in the two groups were matched. OCD in children was evaluated using the obsessive compulsive inventory-child version (OCI-CV).

Results:

The mean scores of doubting/checking (case: 3.52 ± 2.54, control: 2.5 ± 2.32, P = 0.007) and ordering (case: 2.59 ± 1.81, control: 1.5 ± 2.56, P = 0.005) in the children with CKD was significantly higher than in the healthy ones. Moreover, the mean total scores for the OCI-CV of the children with CKD at 15.32 ± 7.69 was significantly higher than the scores of the healthy ones at 11.12 ± 2.54 (P = 0.021). There was a significant correlation between the CKD duration and doubting/checking (P = 0.004, correlation coefficient (CC): 0.4), obsessing (P = 0.06, CC: 0.02), washing (P = 0.031, CC: 0.8), ordering (P = 0.001, CC: 0.2), and the total scores of the OCI-CV questionnaire (P = 0.04, CC: 0.4).

Conclusions:

The risk of OCD in children with CKD is significantly higher than that in healthy children. Although the results seem to suggest that psychiatric intervention can be helpful in treating OCD in children with CKD, further investigation into the medical condition is required so as to obtain more definitive conclusions.

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.

The role of the kidney and the sympathetic nervous system in hypertension

Nearly one-third of the world's population has hypertension. The human and societal impact of hypertension is enormous. Primary hypertension accounts for 95 % of cases of hypertension in adults. The pathogenesis of primary hypertension is complex. The kidney and the sympathetic nervous system play important roles in the development and maintenance of hypertension. This review discusses their respective roles, the interaction between the two, implications of sympathetic overactivity in kidney disease and therapeutic interventions that have been developed on the basis of this knowledge, especially modulation of the sympathetic nervous system.

The baroreflex as a long-term controller of arterial pressure

Because of resetting, a role for baroreflexes in long-term control of arterial pressure has been commonly dismissed in the past. However, in recent years, this perspective has changed. Novel approaches for determining chronic neurohormonal and cardiovascular responses to natural variations in baroreceptor activity and to electrical stimulation of the carotid baroreflex indicate incomplete resetting and sustained responses that lead to long-term alterations in sympathetic activity and arterial pressure.

[Pathophysiology of hypertension : What are our current concepts?]

In the year 2015, many questions regarding the pathophysiology of essential arterial hypertension remain unresolved. Substantial scientific progress has been made in various medical areas aided by novel molecular"omics" techniques. The findings could then be implemented in diagnostic and therapeutic procedures. In the field of hypertension research such methods have been applied in very large cohorts but have contributed less to pathophysiological understanding and clinical management than expected. The findings on the pathophysiological importance of baroreflex mechanisms, natriuretic peptides and osmotically inactive sodium storage discussed in this article all have something in common: all are based on small, carefully conducted human physiological investigations and often challenge current textbook knowledge. Nevertheless, these findings have opened up new research fields and are likely to affect clinical care.

The effects of single hemodialysis session on arterial stiffness in hemodialysis patients

Increased arterial stiffness in hemodialysis patients is a strong predictor of cardiovascular morbidity and mortality. Pulse wave velocity (PWV) and augmentation index (AIx), which are markers of arterial stiffness, were used to determine the severity of vascular damage noninvasively. This study aimed to investigate the effects of solute volume removal and hemodynamic changes on PWV and AIx of a single hemodialysis session. Thirty hemodialysis patients were enrolled in the study. Before initiation of hemodialysis, every 15 minutes during hemodialysis, and 30 minutes after the completion of the session, measurements of PWV and AIx@75 (normalized with heart rate 75 bpm) were obtained from each patient. Body composition was analyzed by bioimpedance spectroscopy device before and 30 minutes after completion of the hemodialysis session. During the hemodialysis, no significant change was observed in AIx@75. However, PWV decreased steadily during the session reaching statistically significant level at 135th minute (P = 0.026), with a maximal drop at 210th minute (P < 0.001). At 210th minute, decrease in PWV correlated positively with the decrease in central systolic blood pressure, central diastolic blood pressure, central pulse pressure, augmentation pressure, and AIx@75. Multiple regression analysis showed that decrease in PWV at 210th minute was associated with decrease in central systolic blood pressure and central pulse pressure. Ultrafiltration during hemodialysis had no significant effect on PWV and AIx@75. Delta urea correlated positively with delta PWV at 240th minute. A significant decrease in PWV was observed during hemodialysis and correlated with urea reduction; however, we were unable to document any effect of volume removal on arterial stiffness.

Abnormal neurocirculatory control during exercise in humans with chronic renal failure

Abnormal neurocirculatory control during exercise is one important mechanism leading to exercise intolerance in patients with both end-stage renal disease (ESRD) and earlier stages of chronic kidney disease (CKD). This review will provide an overview of mechanisms underlying abnormal neurocirculatory and hemodynamic responses to exercise in patients with kidney disease. Recent studies have shown that ESRD and CKD patients have an exaggerated increase in blood pressure (BP) during both isometric and rhythmic exercise. Subsequent studies examining the role of the exercise pressor reflex in the augmented pressor response revealed that muscle sympathetic nerve activity (MSNA) was not augmented during exercise in these patients, and metaboreflex-mediated increases in MSNA were blunted, while mechanoreflex-mediated increases were preserved under basal conditions. However, normalizing the augmented BP response during exercise via infusion of nitroprusside (NTP), and thereby equalizing baroreflex-mediated suppression of MSNA, an important modulator of the final hemodynamic response to exercise, revealed that CKD patients had an exaggerated increase in MSNA during isometric and rhythmic exercise. In addition, mechanoreflex-mediated control was augmented, and metaboreceptor blunting was no longer apparent in CKD patients with baroreflex normalization. Factors leading to mechanoreceptor sensitization, and other mechanisms underlying the exaggerated exercise pressor response, such as impaired functional sympatholysis, should be investigated in future studies.

Chronic kidney disease (CKD) as a systemic disease: whole body autoregulation and inter-organ cross-talk

The inter-organ cross-talk and the functional integration of organ systems is an exceedingly complex process which until now has been investigated with a reductionist approach. CKD perturbs the inter-organ cross-talk and demands central resetting of autonomic (nervous) control of organ systems. Due to limitations inherent to the reductionist approach, we currently identify CKD-related pseudo-syndromes and largely fail at describing the complex systemic inter-relationships set into motion by renal damage and renal dysfunction. A mature technology for a system-analysis approach to physiology and pathophysiology of CKD now exists. System biology will allow in depth understanding of complex diseases like CKD and will set the stage for predictive, preventive and personalized medicine, a long-standing dream of doctors and patients alike.

The effect of percutaneous renal denervation on muscle sympathetic nerve activity in hypertensive patients

OBJECTIVE

The rationale of percutaneous renal denervation (RDN) is based on extensive studies suggesting that renal nerves contribute to hypertension and that they comprise a sensible treatment target. Muscle sympathetic nerve activity (MSNA) is considered to be one of the few reliable methods to quantify central sympathetic activity. The aim of this current study is to determine the effect of RDN on MSNA in a standardized fashion.

METHODS

MSNA was determined in 13 patients before and 6months after RDN. Anti-hypertensive medication was stopped before MSNA. If cessation of medication was considered unsafe, a patient was instructed to use the exact same medication on both occasions.

RESULTS

Ten sets of MSNA recordings were of good quality for analysis. Mean age was 57 ± 3 years and mean eGFR was 85 ± 18 mL/min/1.73 m(2). MSNA was determined twice during a medication free interval in 5 patients; 1 patient used the exact same medication twice, and 4 patients used different drugs. Mean BP changed from 206 ± 7 over 116 ± 4 mmHg, to 186 ± 6 over 106 ± 3 mmHg, 6 months after RDN (p=0.06 for systolic BP, p=0.04 for diastolic BP). Mean resting heart rate did not change (p=0.44). MSNA did not change after RDN: 37 ± 4 bursts/min and 43 ± 4 bursts/min (p=0.11) at baseline and after RDN, respectively. In the 6 patients with standardized medication use during the MSNA sessions, results were comparable.

CONCLUSIONS

Treatment with RDN did not result in a change in MSNA. Changes in BP did not correlate with changes in MSNA.

Impact of chronic kidney disease on myocardial blood flow regulation in dogs

BACKGROUND/AIMS

Chronic kidney disease (CKD) increases cardiovascular risk possibly due to coronary microvessel dysfunction and impaired myocardial flow reserve. This study investigated the effects of CKD on the regulation and transmural distribution of myocardial blood flow along with oxygen demand during intravenous dobutamine-induced increases in cardiac work.

METHODS

CKD was produced in dogs by a two-stage subtotal nephrectomy (kidney ablation-infarction model). Serum creatinine and blood urea nitrogen were evaluated during the development of CKD along with systemic blood pressure (tail-cuff plethysmography). After 5 weeks, the CKD dogs were staged according to the International Renal Interest Society staging system; all dogs were anesthetized and surgically prepared for blood flow studies. Data analyses were performed between sham control (CTR) and stage 1 and 2 CKD dogs.

RESULTS

At baseline, myocardial blood flow and diastolic aortic pressure were similar for all groups. During intravenous dobutamine, myocardial blood flow was markedly higher than CTR even though hematocrit levels declined with the severity of CKD. In the CTR dogs, myocardial blood flow increased in direct relation to cardiac work. However, in the CKD dogs (stage 1 and 2), maximum blood flow was achieved with low-dose dobutamine, indicating that coronary autoregulation is more readily exhausted with minimal increases in cardiac work during CKD.

CONCLUSION

We report that CKD markedly impairs coronary vascular reserve and myocardial blood flow regulation which could contribute to greater cardiovascular risk and poor clinical outcomes in CKD patients.

Angiotensin receptor blockers regulate the synchronization of circadian rhythms in heart rate and blood pressure

OBJECTIVE

The sympathetic nervous system plays an important role in blood pressure regulation even in the early stages of chronic kidney disease (CKD).

METHODS

To understand the role of the sympathetic system, we examined the relationship between day/night ratios of both heart rate (HR) and mean arterial pressure (MAP) as well as HR variability (HRV, SD) before and during an 8-week treatment with the angiotensin II receptor blocker (ARB), olmesartan, in 45 patients with CKD.

RESULTS

The day/night HR ratio strongly correlated with the day/night MAP ratio before and during ARB treatment. The ratio of [day/night HR ratio] over [day/night MAP ratio] was increased as renal function deteriorated at baseline (r = -0.31, P = 0.04), and it was attenuated (1.10 ± 0.10 to 1.06 ± 0.10; P = 0.04) and became independent of renal function during ARB treatment (r = -0.04, P = 0.8). ARB increased both the day/night HR ratio (1.17 ± 0.09 to 1.21 ± 0.13; P = 0.04) and HRV (10.6 ± 2.9 to 11.7 ± 4.2; P = 0.04), which were lower when baseline renal function deteriorated.

CONCLUSION

The present study indicates that there exists a close correlation in circadian rhythms between HR and MAP in CKD. Synchronization between the two rhythms was progressively lost as renal function deteriorated, and ARB partly restored the synchronization. These findings suggest that the sympathetic nervous system is activated as renal function deteriorates, and ARB may suppress its activation.

Differential contribution of afferent and central pathways to the development of baroreflex dysfunction in chronic kidney disease

The effects of chronic kidney disease on baroreflex control of renal sympathetic nerve activity (RSNA) and deficits in afferent and central components of the baroreflex were studied in juvenile and adult male Lewis Polycystic Kidney (LPK) and control Lewis rats under anesthesia (n=35). Blood pressure (BP), heart rate (HR), aortic depressor nerve activity (ADNA), and RSNA were determined after pharmacological manipulation of BP. Responses to ADN stimulation (4.0 V, 2.0 ms, 1-24 Hz) were determined, and the aortic arch was collected for histomorphometry. In juvenile LPK versus age-matched Lewis rats, gain of RSNA (-1.5±0.2 versus -2.8±0.2%/mm Hg; P<0.05) and ADNA (2.5±0.3 versus 5.0±0.6%/mm Hg; P<0.05), but not HR barocurves, were reduced. BP, HR, and RSNA responses to ADN stimulation were normal or enhanced in juvenile LPK. In adult LPK versus age-matched Lewis, the gain and range of RSNA (gain: -1.2±0.1 versus -2.2±0.2%/mm Hg, range: 62±8 versus 98±7%) and HR (gain: -0.7±0.1 versus -3.5±0.7 bpm/mm Hg, range: 44±8 versus 111±19 bpm) barocurves were reduced (P<0.05). The gain and range of the ADNA barocurves were also reduced in adult LPK versus Lewis [1.5±0.4 versus 5.2±1.1 (%/mm Hg) and 133±35 versus 365±61 (%) P<0.05] and correlated with aortic arch vascular remodeling. BP, HR, and RSNA responses to ADN stimulation were significantly reduced in adult LPK. Our data demonstrate a deficit in the afferent component of the baroreflex that precedes the development of impaired central regulation of RSNA and HR in chronic kidney disease, and that progressive impairment of both components is associated with marked dysfunction of the baroreflex pathway.

Essential hypertension: an approach to its etiology and neurogenic pathophysiology

Essential hypertension, a rise in blood pressure of undetermined cause, includes 90% of all hypertensive cases and is a highly important public health challenge that remains, however, a major modifiable cause of morbidity and mortality. This review emphasizes that, from an evolutionary point of view, we are adapted to ingest and excrete <1 g of sodium (2.5 g of salt) per day and that essential hypertension develops when the kidneys become unable to excrete the amount of sodium ingested, unless blood pressure is increased. The renal-mean arterial pressure set-point model is briefly described to explain that a shift of the pressure natriuresis relationship toward abnormally high pressure levels is a pathophysiological characteristic of essential hypertension. Evidence indicating that this anomaly in the pressure natriuresis relationship arises from a sympathetic nervous system dysfunction is briefly formulated, and the most widely accepted pathophysiologic proposal to explain the development of this sympathetic dysfunction is described, with commentaries about novel action mechanisms of some drugs currently used in essential hypertension treatment.

Cardiorenal syndrome--current understanding and future perspectives

Combined cardiac and renal dysfunction has gained considerable attention. Hypotheses about its pathogenesis have been formulated, albeit based on a relatively small body of experimental studies, and a clinical classification system has been proposed. Cardiorenal syndrome, as presently defined, comprises a heterogeneous group of acute and chronic clinical conditions, in which the failure of one organ (heart or kidney) initiates or aggravates failure of the other. This conceptual framework, however, has two major drawbacks: the first is that, despite worldwide interest, universally accepted definitions of cardiorenal syndrome are lacking and characterization of heart and kidney failure is not uniform. This lack of consistency hampers experimental studies on mechanisms of the disease. The second is that, although progress has been made in developing hypotheses for the pathogenesis of cardiorenal syndrome, these initiatives are at an impasse. No hierarchy has been identified in the myriad of haemodynamic and non-haemodynamic factors mediating cardiorenal syndrome. This Review discusses current understanding of cardiorenal syndrome and provides a roadmap for further studies in this field. Ultimately, discussion of the definition and characterization issues and of the lack of organization among pathogenetic factors is hoped to contribute to further advancement of this complex field.

Enalapril attenuates the exaggerated sympathetic response to physical stress in prenatally programmed hypertensive rats

Adulthood hypertension can be prenatally programmed by maternal dietary protein deprivation. We have shown that the sympathetically mediated pressor response to physical stress is exaggerated in prenatally programmed hypertensive (PPH) rats. The mechanisms underlying this abnormal responsiveness remain undetermined. The renin-angiotensin system is known to affect sympathetic nerve activity. Therefore, the purpose of this study was to determine whether inhibition of the renin-angiotensin system attenuates the enhanced sympathetic and pressor responses to physical stress in PPH rats. Changes in renal sympathetic nerve activity and blood pressure in response to hindlimb contraction, hindlimb stretch, and hindlimb intra-arterial capsaicin administration were assessed in control and PPH rats treated (from age 3 weeks) with either vehicle or the angiotensin-converting enzyme inhibitor enalapril. Conscious resting systolic arterial pressure was significantly greater in PPH rats (142±5 mm Hg) than in control (128±2 mm Hg) after vehicle treatment (P<0.05). Resting systolic pressure was reduced by enalapril treatment in PPH rats (125±2 mm Hg) but had no effect in control (128±2 mm Hg). The pressor and renal sympathetic responses to muscle contraction and stretch were significantly higher in decerebrate PPH rats than in decerebrate control in vehicle-treated groups. Responses to capsaicin were variable. Enalapril significantly attenuated the enhanced contraction-induced elevations in mean pressure (vehicle, 45±6 mm Hg; enalapril, 21±3 mm Hg) and renal sympathetic activity (vehicle, 175±22%; enalapril, 89±23%) in PPH rats. Its effects were similar on responses to stretch in PPH rats but were equivocal during capsaicin administration. The results suggest that the renin-angiotensin system contributes to the enhancement of the renal sympathetic and pressor responses to physical stress in PPH rats.

Renal denervation prevents stroke and brain injury via attenuation of oxidative stress in hypertensive rats

Background

Although renal denervation (RD) is shown to reduce blood pressure significantly in patients with resistant hypertension, the benefit of RD in prevention of stroke is unknown. We hypothesized that RD can prevent the incidence of stroke and brain injury in hypertensive rats beyond blood pressure lowering.

Methods and Results

High‐salt‐loaded, stroke‐prone, spontaneously hypertensive rats (SHRSP) were divided into 4 groups: (1) control; (2) sham operation; (3) bilateral RD; and (4) hydralazine administration to examine the effect of RD on stroke and brain injury of SHRSP. RD significantly reduced the onset of neurological deficit and death in SHRSP, and this protection against stroke by RD was associated with the increase in cerebral blood flow (CBF), the suppression of blood–brain barrier disruption, the limitation of white matter (WM) lesions, and the attenuation of macrophage infiltration and activated microglia. Furthermore, RD significantly attenuated brain oxidative stress, and NADPH oxidase subunits, P67 and Rac1 in SHRSP. On the other hand, hydralazine, with similar blood pressure lowering to RD, did not significantly suppress the onset of stroke and brain injury in SHRSP. Furthermore, RD prevented cardiac remodeling and vascular endothelial impairment in SHRSP.

Conclusions

Our present work provided the first experimental evidence that RD can prevent hypertensive stroke and brain injury, beyond blood pressure lowering, thereby highlighting RD as a promising therapeutic strategy for stroke as well as hypertension.

Novel Approaches for the Treatment of the Patient with Resistant Hypertension: Renal Nerve Ablation

Sympathetic innervation of the kidneys plays a major role in the pathogenesis of hypertension through modulation of renin secretion, glomerular filtration rate and renal absorption of sodium. Targeted interventions for renal nerve ablation are being developed for treatment of drug resistant hypertension in the USA and rest of the world. Early studies with the use of radiofrequency based renal denervation systems have shown encouraging results with significant reduction of blood pressure in patients inadequately controlled despite nearly maximal drug therapy regimens. Thus far, the renal denervation procedure has been associated with minimal side effects. Long term efficacy and safety beyond 3 years needs to be determined for renal nerve ablation. This review focuses on the physiology of the renal sympathetic system, the rationale for renal nerve ablation and current evidence in support of the available therapeutic renal denervation systems.

Association between blood pressure and target organ damage in patients with chronic kidney disease and hypertension: results of the APrODiTe study

Blood pressure control is the most established practice for preventing the progression of chronic kidney disease. Evidence addressing blood pressure control status or nocturnal blood pressure dipping in Korean hypertensive patients with chronic kidney disease is scarce. We recruited 1317 hypertensive patients (chronic kidney disease stages 2-4, median age 58) from 21 centers in Korea. These patients underwent office and ambulatory blood pressure monitoring. High office and ambulatory blood pressure were defined as >140/90 mm Hg and >135/85 mm Hg (daytime)/ >120/70 mm Hg (nighttime), respectively. The blood pressure control status was as follows: true controlled (19%), white-coat (4.3%), masked (33.9%) and sustained uncontrolled (42.3%) hypertension. The dipping status was as follows: extreme-dipping (14.9%), dipping (33.3%), non-dipping (34.5%) and reverse-dipping (17.3%). Masked and sustained hypertension as well as non-dipping/reverse-dipping was more apparent in proportion to renal dysfunction and the extent of proteinuria. Ageing (58 years), male gender, obesity, diabetic nephropathy and proteinuria (>300 mg g(-1) Cr or dipstick proteinuria1+) were independently associated with sustained uncontrolled hypertension. Diabetic nephropathy, old age, a history of stable angina/heart failure, advanced renal dysfunction and higher proteinuria levels were also significantly associated with non-dipping and reverse-dipping. Half of Korean chronic kidney disease patients had uncontrolled blood pressure and a non-dipping nocturnal blood pressure pattern. Future studies are warranted to assess the predictive values of ambulatory blood pressure for cardiorenal events in Korean chronic kidney disease patients.

The role and management of sympathetic overactivity in cardiovascular and renal complications of diabetes

Feedback activation of neurohormonal pathways in the setting of kidney or heart failure contributes to the development and progression of dysfunction in the other. Diabetes and its management independently activate these same pathogenic pathways, feeding into this vicious cycle and contributing to a poor prognosis. One of the most important of these neurohormonal pathways is the sympathetic nervous system (SNS). The activity of the SNS in increased in patients with chronic kidney disease, even in the absence of renal impairment or heart failure. There is a strong relationship between SNS overactivity and prognosis, and evidence that blockade of SNS reduces morbidity and mortality in patients with diabetes. However, modulation of SNS is underutilised as a strategy to protect both the diabetic kidney and the heart. This is partly because of the historically poor tolerability, adverse haemodynamic and metabolic effects, lack of selectivity of β-blockers and the lack of specificity of other interventions that might modify SNS activation. The advent of "vasodilating β-blockers" with better tolerability as well as more favourable effects on renal function and metabolic profiles opens the door for their more widespread utility in patients with diabetes. Radiofrequency renal sympathectomy and baroreflex activation technologies also offer exciting new ways to tackle the challenge of sympathetic overactivity.

Review of the state of renal nerve ablation for patients with severe and resistant hypertension

Through modulation of renin secretion, glomerular filtration rate, and renal absorption of sodium, the sympathetic innervation of the kidneys plays an important role in the pathogenesis of hypertension. Renal nerve ablation technology is being developed for treatment of drug-treatment-resistant hypertension worldwide. Preliminary research with the use of radiofrequency-based renal denervation systems have demonstrated encouraging results with significant reduction of blood pressure in patients inadequately controlled despite nearly maximal drug therapy regimens. From work done thus far, the renal denervation procedure has not been associated with serious adverse effects. Long-term efficacy and safety still needs to be established for renal nerve ablation. This review focuses on the impact of the renal sympathetic system on blood pressure regulation, the clinical rationale for renal nerve ablation in severe and drug-treatment-resistant hypertension, and current evidence from the more advanced renal denervation devices.

Enhanced blood pressure-lowering effect of olmesartan in hypertensive patients with chronic kidney disease-associated sympathetic hyperactivity: HONEST study

To investigate the blood pressure (BP)-lowering effect of olmesartan in relation to chronic kidney disease (CKD)-associated sympathetic nerve activity, a subanalysis was performed using data from the first 16 weeks of the Home BP Measurement With Olmesartan-Naive Patients to Establish Standard Target Blood Pressure (HONEST) study, a prospective observational study of hypertensive patients. Essential hypertensive patients who took no antihypertensive agent at baseline were classified based on baseline morning home systolic BP (MHSBP) in quartiles. In each class, patients were further classified based on baseline morning home pulse rate (MHPR). A subgroup analysis in patients with/without chronic kidney disease (CKD) was performed. A total of 5458 patients (mean age, 63.0 years; 51.6% women) were included. In the 4th quartile of baseline MHSBP (≥165 mm Hg), patients with MHPR ≥70 beats per minute had a greater BP reduction (by 3.2 mm Hg) than those with MHPR <70 beats per minute after 16 weeks of olmesartan-based treatment (P=.0005). An even greater BP reduction (by 6.6 mm Hg) was observed in patients with CKD than in patients without CKD in this group (P=.0084). Olmesartan was more effective in hypertensive patients with high MHSBP and MHPR ≥70 beats per minute, especially in patients with CKD. Olmesartan may have enhanced BP-lowering effects by improving renal ischemia in hypertensive CKD patients with potential increased sympathetic nerve activity.

Animal models of cardiorenal syndrome: a review

The incidence of heart failure and renal failure is increasing and is associated with poor prognosis. Moreover, these conditions do often coexist and this coexistence results in worsened outcome. Various mechanisms have been proposed as an explanation of this interrelation, including changes in hemodynamics, endothelial dysfunction, inflammation, activation of renin-angiotensin-aldosterone system, and/or sympathetic nervous system. However, the exact mechanisms initializing and maintaining this interaction are still unknown. In many experimental studies on cardiac or renal dysfunction, the function of the other organ was either not addressed or the authors failed to show any decline in its function despite histological changes. There are few studies in which the dysfunction of both heart and kidney function has been described. In this review, we discuss animal models of combined cardiorenal dysfunction. We show that translation of the results from animal studies is limited, and there is a need for new and better models of the cardiorenal interaction to improve our understanding of this syndrome. Finally, we propose several requirements that a new animal model should meet to serve as a tool for studies on the cardiorenal syndrome.

Systemic arterial and venous determinants of renal hemodynamics in congestive heart failure

Heart and kidney interactions are fascinating, in the sense that failure of the one organ strongly affects the function of the other. In this review paper, we analyze how principal driving forces for glomerular filtration and renal blood flow are changed in heart failure. Moreover, renal autoregulation and modulation of neurohumoral factors, which can both have repercussions on renal function, are analyzed. Two paradigms seem to apply. One is that the renin-angiotensin system (RAS), the sympathetic nervous system (SNS), and extracellular volume control are the three main determinants of renal function in heart failure. The other is that the classical paradigm to analyze renal dysfunction that is widely applied in nephrology also applies to the pathophysiology of heart failure: pre-renal, intra-renal, and post-renal alterations together determine glomerular filtration. At variance with the classical paradigm is that the most important post-renal factor in heart failure seems renal venous hypertension that, by increasing renal tubular pressure, decreases GFR. When different pharmacological strategies to inhibit the RAS and SNS and to assist renal volume control are considered, there is a painful lack in knowledge about how widely applied drugs affect primary driving forces for ultrafiltration, renal autoregulation, and neurohumoral control. We call for more clinical physiological studies.

Aliskiren reduces morning blood pressure in hypertensive patients with diabetic nephropathy on hemodialysis

Our previous study indicated that the exchange from an angiotensin receptor blocker (ARB) to aliskiren reduced morning blood pressure and albuminuria in hypertensive patients with diabetic nephropathy. We extended the above study and assessed the effects of exchanging from an ARB to aliskiren on home blood pressure in hypertensive patients with diabetic nephropathy on chronic hemodialysis. The patients who were persistently hypertensive despite antihypertensive therapy, including ARB, were considered as candidates for the exchange from the ARB to aliskiren. Patients' age and durations of diabetes and hemodialysis were averaged as 62 ± 9 years old, 15 ± 8 and 7 ± 3 years, respectively. Aliskiren decreased morning systolic blood pressure (149 ± 14 to 144 ± 13 mm Hg, n = 30, P < .01) and plasma renin activity (3.5 ± 1.1 to 1.2 ± 0.6 ng/mL/h, P < .01) without changes in serum potassium. Aliskiren also reduced interdialytic weight gain (2.7 ± 0.6 to 2.5 ± 0.5 kg/interval, P < .05) and attenuated the magnitude of intradialytic declines in systolic (-20 ± 11 to -17 ± 10 mm Hg, P < .05) and diastolic blood pressure (-9 ± 6 to -5 ± 5 mm Hg, P < .01). The exchange from an ARB to aliskiren is safe and useful to control home blood pressure in hypertensive hemodialysis patients with diabetic nephropathy. Aliskiren reduced both intradialytic blood pressure drops and interdialytic weight gain in patients with DN.

Central Rho kinase inhibition restores baroreflex sensitivity and angiotensin II type 1 receptor protein imbalance in conscious rabbits with chronic heart failure

The small GTPase RhoA and its associated kinase ROCKII are involved in vascular smooth muscle cell contraction and endothelial NO synthase mRNA destabilization. Overactivation of the RhoA/ROCKII pathway is implicated in several pathologies, including chronic heart failure (CHF), and may contribute to the enhanced sympathetic outflow seen in CHF as a result of decreased NO availability. Thus, we hypothesized that central ROCKII blockade would improve the sympathovagal imbalance in a pacing rabbit model of CHF in an NO-dependent manner. CHF was induced by rapid ventricular pacing and characterized by an ejection fraction of ≤45%. Animals were implanted with an intracerbroventricular cannula and osmotic minipump (rate, 1 μL/h) containing sterile saline, 1.5 µg/kg per day fasudil (Fas, a ROCKII inhibitor) for 4 days or Fas+100 µg/kg per day Nω-Nitro-l-arginine methyl ester hydrochloride, a NO synthase inhibitor. Arterial baroreflex control was assessed by intravenous infusion of sodium nitroprusside and phenylephrine. Fas infusion significantly lowered resting heart rate by decreasing sympathetic and increasing vagal tone. Furthermore, Fas improved baroreflex gain in CHF in an NO-dependent manner. In CHF Fas animals, the decrease in heart rate in response to intravenous metoprolol was similar to Sham and was reversed by Nω-Nitro-l-arginine methyl ester hydrochloride. Fas decreased angiotensin II type 1 receptor and phospho-ERM protein expression and increased endothelial NO synthase expression in the brain stem of CHF animals. These data strongly suggest that central ROCKII activation contributes to cardiac sympathoexcitation in the setting of CHF and that central Fas restores vagal and sympathetic tone in an NO-dependent manner. ROCKII may be a new central therapeutic target in the setting of CHF.

The pathogenesis and management of hypertension in diabetic kidney disease

Hypertension commonly coexists with diabetes, and its prevalence is even higher in the presence of diabetic kidney disease. The pathogenesis of hypertension in this population stems from increased extracellular volume and increased vasoconstriction that results from mechanisms that may be attributed to both diabetes and the eventual impairment of renal function. Antihypertensive therapy aimed at reducing blood pressure remains a primary goal in preventing the incidence of diabetic kidney and slowing its progression. Initial therapy should consist of an ACE inhibitor or ARB titrated to the maximally tolerated dose. Using combination RAAS therapy further reduces proteinuria, but the benefits of this strategy compared with the potential risks of hyperkalemia and acute deterioration of renal function are still unknown. Endothelin receptor antagonists also lower proteinuria, but these can be associated with volume overload and edema with no clear long-term benefit on renal function yet identified. Further large clinical trials are needed to better understand how progression to ESRD can be slowed or halted in patients with diabetic kidney disease.

Exercise pressor response and arterial baroreflex unloading during exercise in chronic kidney disease

Patients with chronic kidney disease (CKD) have poor exercise capacity, which contributes to cardiovascular risk. We sought to determine whether patients with stage 2 or stage 3 CKD have an augmented blood pressure (BP) response during exercise, and if so, whether overactivation of the sympathetic nervous system (SNS) during exercise might play a role. In 13 patients with CKD and hypertension and 13 controls with hypertension, we measured hemodynamics and muscle sympathetic nerve activity (MSNA) during the following maneuvers: low-level rhythmic handgrip (RHG 20%), which primarily stimulates mechanoreceptors, and moderate static handgrip exercise (SHG 30%) followed by posthandgrip circulatory arrest (PHGCA), which isolates metaboreceptors. During baseline studies, patients with CKD had significantly greater increases in mean arterial pressure (MAP) during SHG 30% (P = 0.045), RHG 20% (P = 0.031), and PHGCA (P = 0.043); however, the MSNA response was not augmented in patients with CKD compared with controls. We hypothesized that an augmented SNS response during exercise might be revealed in CKD if arterial baroreflex constraint was equalized using nitroprusside (NTP). These exercise maneuvers were repeated in patients with CKD during NTP infusion to equalize the BP response between groups, thereby relieving baroreflex-mediated suppression of SNS activity. With NTP infusion, patients with CKD had significantly increased MSNA responses during SHG 30% (P = 0.0044), and RHG 20% (P = 0.0064), but not during PHGCA (P > 0.05), suggesting increased reflex activation of the SNS during exercise, which may be mediated by mechanoreceptors but not metaboreceptors. Patients with CKD have an exaggerated BP response during rhythmic and static exercise with underlying SNS overactivation that is revealed during arterial baroreflex unloading during exercise.

Renal denervation in human hypertension: mechanisms, current findings, and future prospects

Denervating the human kidney to improve blood pressure control is an old therapeutic concept first applied on a larger scale by surgeons in the 1920s. With the advent of modern pharmacology and the development of powerful drugs to lower blood pressure, approaches to directly target the sympathetic nerves were more or less abandoned. Over the past 2-3 years, however, we have witnessed enormous renewed interest in novel and minimally invasive device-based approaches to specifically target the renal nerves. The enthusiasm is fueled by promising results from proof-of-concept studies and clinical trials demonstrating convincing blood pressure-lowering effects in the majority of treated patients, and perhaps even more so by observations indicating potential additional benefits relating to common comorbidities of hypertension, such as impaired glucose metabolism, renal impairment, left ventricular hypertrophy, and others. Herein we review the current findings and assess whether these high hopes are justified.