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

Failure of Antihypertensive Treatment to Restore Normal Sympathetic Activity

BACKGROUND

Sympathetic deactivation represents a major goal of antihypertensive drug treatment. However, whether treatment normalizes the hypertension-related sympathetic cardiovascular overdrive remains uncertain.

METHODS

In 219 middle-aged essential hypertensives, we analyzed, along with office systolic and diastolic blood pressure (BP) and heart rate, muscle sympathetic nerve traffic (MSNA, microneurography) before and after 3-month treatment, either as monotherapy or as combination. Controls were represented by 100 age-matched normotensives.

RESULTS

Treatment caused, along with a small heart rate decrease, a clear BP reduction (from 160.5/95.5 to 142.3/85.0 mm Hg, P<0.01) and a significant MSNA inhibition (from 70.7±11.5 to 65.0±10.2 bursts/100 heartbeats, mean±SD, P<0.01). A similar pattern was detected in patients under monotherapy (n=81) or combination drug treatment (n=138). MSNA was significantly related to systolic BP before and during treatment but unrelated to heart rate. In treated patients achieving the lower BP (135.1/84.5 mm Hg, n=90), the MSNA reduction was greater than that detected in patients with the higher on-treatment BP (146.7/87.4 mm Hg, n=129). However, even in patients achieving a BP target <140/90 mm Hg, MSNA remained markedly higher (on average +66.4%) compared with controls. This was the case even when treated BP was <130/80 mm Hg. Data were similar for different antihypertensive drug classes.

CONCLUSIONS

Thus, antihypertensive treatment, even when effective in achieving BP control, fails to restore the level of normotension-related MSNA, with a persistence of the pattern of heightened sympathetic influences typical of untreated patients with hypertension. Failure of normalization may contribute to the development of the residual cardiovascular risk reported in treated hypertensives.

Impaired Neurocirculatory Control in Chronic Kidney Disease: New Evidence for Blunted Sympathetic Baroreflex and Reduced Sympathetic Transduction

Chronic kidney disease (CKD) is characterized by over-activation of the sympathetic nervous system (SNS) that increases cardiovascular risk. Whether sympathetic baroreflex sensitivity (sBRS) is impaired or intact in CKD remains under-studied and controversial. Furthermore, the downstream effect of SNS activation on blood pressure transduction has not been previously examined in CKD. We tested the hypothesis that sBRS is attenuated, while sympathetic transduction is augmented in CKD. In 18 sedentary patients with CKD stages III-IV (eGFR: 40±14 mL/min) and 13 age-matched controls (eGFR: 95±10 mL/min), beat-to-beat blood pressure (BP; finger photoplethysmography), heart rate (electrocardiography) and muscle sympathetic nerve activity (MSNA; microneurography) were recorded at rest for 10-min. Weighted linear regression analysis between MSNA burst incidence and diastolic BP was used to determine the spontaneous sBRS. Sympathetic-BP transduction was quantified using signal averaging, whereby the BP response to each MSNA burst was tracked over 15 cardiac cycles and averaged to derive the peak change in BP. Compared with controls, CKD patients had an attenuated sBRS [CKD: -1.34 ± 0.59 versus CON: -2.91 ± 1.09 bursts (100 heartbeats)-1 mmHg-1; P = 0.001]. |sBRS| was significantly associated with eGFR (r = 0.69, P < 0.001). CKD patients had attenuated sympathetic-BP transduction compared to controls (0.75 ± 0.7 vs. 1.60 ± 0.8 mmHg; P = 0.010). Resting MSNA was negatively associated with sympathetic transduction (r = -0.57, P = 0.002). CKD patients exhibit impaired sBRS that may contribute to SNS overactivation and cardiovascular risk in this patient population. In addition, CKD patients had an attenuated sympathetic transduction that may counteract the vascular effects of SNS overactivation.

Evaluation of the Effect of an α-Adrenergic Blocker, a PPAR-γ Receptor Agonist, and a Glycemic Regulator on Chronic Kidney Disease in Diabetic Rats

Diabetic nephropathy (DN) is a globally widespread complication of diabetes mellitus (DM). Research indicates that pioglitazone and linagliptin mitigate the risk of DN by reducing inflammation, oxidative stress, and fibrosis. The role of tamsulosin in DN is less studied, but it may contribute to reducing oxidative stress and inflammatory responses. The protective effects of combining pioglitazone, linagliptin, and tamsulosin on the kidneys have scarcely been investigated. This study examines the individual and combined effects of these drugs on DN in Wistar rats. Diabetic rats were treated with tamsulosin, pioglitazone, and linagliptin for six weeks. We assessed food and water intake, estimated glomerular filtration rate (eGFR), histological markers, urea, creatinine, glucose, NF-κB, IL-1, IL-10, TGF-β, and Col-IV using immunofluorescence and qPCR. The DN group exhibited hyperglycaemia, reduced eGFR, and tissue damage. Tamsulosin and linagliptin improved eGFR, decreased urinary glucose, and repaired tissue damage. Pioglitazone and its combinations restored serum and urinary markers and reduced tissue damage. Linagliptin lowered serum creatinine and tissue injury. In conclusion, tamsulosin, linagliptin, and pioglitazone demonstrated renoprotective effects in DN.

Ventricular arrhythmias in the context of chronic kidney disease and electrolyte imbalance

Patients with chronic kidney disease face a high risk of sudden cardiac death, particularly in more advanced stages of renal dysfunction. Ventricular arrhythmias are prevalent and contribute to the heightened cardiovascular mortality. This review aims to explore the intricate interplay of disease-specific risk factors, arrhythmic triggers, and electrolyte disorders that amplify susceptibility to ventricular arrhythmias and sudden cardiac death in this population and influence the efficacy of available treatments.

Concurrent exercise training potentiates the effects of angiotensin-converting enzyme inhibitor on regulatory systems of blood pressure control in ovariectomized hypertensive rats

OBJECTIVE

Enalapril has shown satisfactory potential in controlling increased and sustained blood pressure (BP). However, multiple dysregulated mechanisms that interact with each other and are involved in the pathophysiology of arterial hypertension may not be affected, contributing to the remaining cardiovascular risk. Using an exercise training protocol, we investigated whether adding both approaches to arterial hypertension management could promote higher modulation of regulatory mechanisms of BP in postmenopausal rats.

METHODS

Spontaneously hypertensive rats were allocated into sedentary (S) and ovariectomized groups: sedentary (OS), sedentary treated with enalapril maleate (OSE) and trained treated with enalapril maleate (OTE). Both the pharmacological and exercise training protocols lasted for 8 weeks. The BP was directly recorded. Inflammation and oxidative stress were evaluated in the cardiac tissue.

RESULTS

Although BP reduction was similar between OSE and OTE, trained group showed lower vasopressor systems outflow after sympathetic ganglion blocking by hexamethonium (mean BP) (OTE: -53.7 ± 9.86 vs. OS: -75.7 ± 19.2 mmHg). Bradycardic and tachycardic response were increased in OTE group (-1.4 ± 0.4 and -2.6 ± 0.4 vs. OS: -0.6 ± 0.3 and -1.3 ± 0.4 bpm/mmHg, respectively), as well as BP variability. In addition, the combination of approaches induced an increase in interleukin 10, antioxidant defense (catalase and glutathione peroxidase) and nitrite levels compared with the OS group.

CONCLUSION

Despite similar BP, the inclusion of exercise training in antihypertensive drug treatment exacerbates the positive adaptations induced by enalapril alone on autonomic, inflammatory and oxidative stress profiles, probably affecting end-organ damage and remaining risk.

Augmented resting beat-to-beat blood pressure variability in patients with chronic kidney disease

PURPOSE

Our aim was to test the hypothesis that patients with chronic kidney disease (CKD) would exhibit augmented resting beat-to-beat blood pressure variability (BPV) that is associated with poor clinical outcomes independent of mean blood pressure (BP). In addition, since the arterial baroreflex plays a critical role in beat-to-beat BP regulation, we further hypothesized that an impaired baroreflex control would be associated with an augmented resting beat-to-beat BPV.

METHODS

In 25 sedentary patients with CKD stages III-IV (62 ± 9 years) and 20 controls (57 ± 10 years), resting beat-to-beat BP (finger photoplethysmography) and heart rate (electrocardiography) were continuously measured for 10 min. We calculated the standard deviation (SD), average real variability (ARV) and other indices of BPV. The sequence technique was used to estimate spontaneous cardiac baroreflex sensitivity.

RESULTS

Compared with controls (CON), the CKD group had significantly increased resting BPV. The ARV (2.2 ± 0.6 versus 1.6 ± 0.5 mmHg, P < 0.001; 1.6 ± 0.7 versus 1.3 ± 0.3 mmHg, P = 0.039; 1.4 ± 0.5 versus 1.0 ± 0.2 mmHg, P < 0.001) of systolic, diastolic and mean BP, respectively, was increased in CKD versus controls. Other traditional measures of variability showed similar results. The cardiac baroreflex sensitivity was lower in CKD compared with controls (CKD: 8.4 ± 4.5 ms/mmHg versus CON: 14.0 ± 8.2 ms/mmHg, P = 0.008). In addition, cardiac baroreflex sensitivity was negatively associated with BPV [systolic blood pressure (SBP) ARV; r = -0.44, P = 0.003].

CONCLUSION

In summary, our data demonstrate that patients with CKD have augmented beat-to-beat BPV and lower cardiac baroreflex sensitivity. BPV and cardiac baroreflex sensitivity were negatively correlated in this cohort. These findings may further our understanding about cardiovascular dysregulation observed in patients with CKD.

Evaluation of Renin-Angiotensin-Aldosterone System Components and Enzymes in Systemically Hypertensive Cats Receiving Amlodipine

BACKGROUND

Chronic renin-angiotensin-aldosterone system (RAAS) activation is harmful. Amlodipine activates RAAS in humans and dogs, but contradictory data exist for systemically hypertensive (SHT) cats.

HYPOTHESIS

Cats with SHT and chronic kidney disease treated with amlodipine (SHT/CKD-A) are RAAS activated.

ANIMALS

Client-owned cats: unmedicated normotensive (NT) cats (n = 9); SHT/CKD-A cats (n = 5) with median systolic blood pressure of 170 mmHg (vs. 195 mmHg, pre-treatment), chronic kidney disease, and receiving no RAAS-suppressive therapy.

METHODS

Serum was frozen (-80 °C) until RAAS analysis via equilibrium analysis. The RAAS variables (reported as median (minimum-maximum)) were compared between groups, using Mann-Whitney U test.

RESULTS

Angiotensin 1, angiotensin 1,7, angiotensin III, and angiotensin 1,5, and angiotensin-converting enzyme (ACE)-2 activity were higher in SHT/CKD-A cats compared to NT cats, while ACE activity was lower in SHT/CKD-A cats compared to NT cats (p < 0.05 all). A marker for alternative RAAS influence (ALT-S) was significantly higher (69; 58-73 pmol/pmol) in SHT/CKD-A cats compared to NT cats (35; 14-63 pmol/pmol; p = 0.001). Aldosterone concentrations were significantly higher (393; 137-564 pmol/L) in SHT/CKD-A cats compared to NT cats (129; 28-206 pmol/L; p = 0.007).

CONCLUSION AND CLINICAL IMPORTANCE

Circulating RAAS is activated in systemically hypertensive cats receiving amlodipine. Although this study did not parse out the individual contributions of SHT, chronic kidney disease, and amlodipine, the findings suggest that the use of concurrent RAAS-suppressant therapy, specifically aldosterone antagonism, in amlodipine-treated SHT cats with chronic kidney disease might be indicated.

Role of hypertension in progression of pediatric CKD

Hypertension is frequent in children with chronic kidney disease (CKD). Its prevalence varies according to CKD stage and cause. It is relatively uncommon in children with congenital kidney disease, while acquired kidney disease is associated with a higher prevalence of hypertension. Studies in children with CKD utilizing ambulatory blood pressure monitoring also showed a high prevalence of masked hypertension. Uncontrolled and longstanding hypertension in children is associated with progression of CKD. Aggressive treatment of high blood pressure should be an essential part of care to delay CKD progression in children.

Differential relationship between decreased muscle oxygenation and blood pressure recovery during supraventricular and ventricular tachycardia

Vasoconstriction during tachyarrhythmia contributes to maintenance of arterial pressure (AP) by decreasing peripheral blood flow. This cross-sectional observational study aimed to ascertain whether the relationship between peripheral blood flow and AP recovery occurs during both paroxysmal supraventricular (PSVT, n = 19) and ventricular tachycardias (VT, n = 17). Peripheral blood flow was evaluated using forearm tissue oxygen index (TOI), and mean AP (MAP) was measured using a catheter inserted in the brachial or femoral artery during an electrophysiological study. PSVT and VT rapidly decreased MAP with a comparable heart rate (P = 0.194). MAP recovered to the baseline level at 40 s from PSVT onset, but not VT. The forearm TOI decreased during both tachyarrhythmias (P ≤ 0.029). The TOI response was correlated with MAPrecovery (i.e., MAP recovery from the initial rapid decrease) at 20-60 s from PSVT onset (r = -- 0.652 to - 0.814, P ≤ 0.0298); however, this association was not observed during VT. These findings persisted even after excluding patients who had taken vasoactive drugs. Thus, restricting peripheral blood flow was associated with MAP recovery during PSVT, but not VT. This indicates that AP recovery depends on the type of tachyarrhythmia: different cardiac output and/or vasoconstriction ability during tachyarrhythmia.

Cardiovascular complications in chronic kidney disease: a review from the European Renal and Cardiovascular Medicine Working Group of the European Renal Association

Chronic kidney disease (CKD) is classified into five stages with kidney failure being the most severe stage (stage G5). CKD conveys a high risk for coronary artery disease, heart failure, arrhythmias, and sudden cardiac death. Cardiovascular complications are the most common causes of death in patients with kidney failure (stage G5) who are maintained on regular dialysis treatment. Because of the high death rate attributable to cardiovascular (CV) disease, most patients with progressive CKD die before reaching kidney failure. Classical risk factors implicated in CV disease are involved in the early stages of CKD. In intermediate and late stages, non-traditional risk factors, including iso-osmotic and non-osmotic sodium retention, volume expansion, anaemia, inflammation, malnutrition, sympathetic overactivity, mineral bone disorders, accumulation of a class of endogenous compounds called 'uremic toxins', and a variety of hormonal disorders are the main factors that accelerate the progression of CV disease in these patients. Arterial disease in CKD patients is characterized by an almost unique propensity to calcification and vascular stiffness. Left ventricular hypertrophy, a major risk factor for heart failure, occurs early in CKD and reaches a prevalence of 70-80% in patients with kidney failure. Recent clinical trials have shown the potential benefits of hypoxia-inducible factor prolyl hydroxylase inhibitors, especially as an oral agent in CKD patients. Likewise, the value of proactively administered intravenous iron for safely treating anaemia in dialysis patients has been shown. Sodium/glucose cotransporter-2 inhibitors are now fully emerged as a class of drugs that substantially reduces the risk for CV complications in patients who are already being treated with adequate doses of inhibitors of the renin-angiotensin system. Concerted efforts are being made by major scientific societies to advance basic and clinical research on CV disease in patients with CKD, a research area that remains insufficiently explored.

Discontinuation of Renin-Angiotensin System Inhibitors and Clinical Outcomes in Chronic Kidney Disease: A Systemic Review and Meta-Analysis

BACKGROUND

Discontinuation of renin-angiotensin system (RAS) inhibitors is common in patients with chronic kidney disease (CKD), and the potential danger has been reported in several studies. However, a comprehensive analysis has not been conducted.

OBJECTIVES

This study sought to evaluate the effects of discontinuation of RAS inhibitors in CKD.

METHOD

Relevant studies up to November 30, 2022, were identified in the PubMed, Embase, Web of Science, and Cochrane Library databases. Efficacy outcomes included the composite of all-cause mortality, cardiovascular events, and end-stage kidney disease (ESKD). Results were combined using a random-effects or fixed-effects model, and sensitivity analysis used the leave-one-out method.

RESULTS

Six observational studies and one randomized clinical trial including 244,979 patients met the inclusion criteria. Pooled data demonstrated that discontinuation of RAS inhibitors was associated with an increased risk of all-cause mortality (HR 1.42, 95% CI 1.23-1.63), cardiovascular event risk (HR 1.25, 95% CI 1.17-1.22), and ESKD (HR 1.23, 95% CI 1.02-1.49). In sensitivity analyses, the risk for ESKD was reduced. Subgroup analysis showed that the risk of mortality was more pronounced in patients with eGFR above 30 mL/min/m2 and in patients with hyperkalemia-related discontinuation. In contrast, patients with eGFR below 30 mL/min/m2 were at great risk of cardiovascular events.

CONCLUSIONS

The discontinuation of RAS inhibitors in patients with CKD was associated with a significantly increased risk of all-cause mortality and cardiovascular events. These data suggest that RAS inhibitors should be continued in CKD if the clinical situation allows.

Baroreceptor Sensitivity in Individuals with CKD and Heart Failure

Background

Heart failure is the most common cardiovascular complication of chronic kidney disease (CKD) and foreshadows a high morbidity and mortality rate. Baroreflex impairment likely contributes to cardiovascular mortality. We aimed to study the associations between CKD, heart failure, and baroreflex sensitivity (BRS) and their association with cardiovascular outcomes.

Methods

We retrospectively analyzed data from a cohort of 247 individuals with moderate to severe HF. All subjects underwent BRS measurements after intravenous phenylephrine along with electrocardiography, echocardiography, and laboratory measurements. We used logistic regression models to assess the association of CKD (estimated glomerular filtration rate <60 ml/min per 1.73 m²) with BRS using iterative models. Cox proportional hazards models were used to assess associations of binary BRS and subgroups according to categorizations of CKD and BRS with cardiovascular mortality.

Results

Median eGFR among individuals with CKD was 52 (IQR 44-56) ml/min per 1.73 m². eGFR was lower in those with depressed BRS (65 [IQR 54-76] ml/min per 1.73 m²) compared with those with preserved BRS (73 [IQR 64-87] ml/min per 1.73 m²; P≤0.001). The majority of individuals with CKD had depressed BRS compared with those without CKD (60% versus 29%; P=0.05). In regression models, CKD and BRS were independently associated. Cardiovascular mortality was significantly increased in individuals with or without CKD and depressed BRS compared with those with preserved BRS and CKD.

Conclusions

Cardiac BRS is depressed in patients with mild to moderate CKD and HF and associated with cardiovascular mortality. Additional study to confirm its contribution to cardiovascular mortality, particularly in advanced CKD, is warranted.

Hypertension in chronic kidney disease: What lies behind the scene

Hypertension is a frequent condition encountered during kidney disease development and a leading cause in its progression. Hallmark factors contributing to hypertension constitute a complexity of events that progress chronic kidney disease (CKD) into end-stage renal disease (ESRD). Multiple crosstalk mechanisms are involved in sustaining the inevitable high blood pressure (BP) state in CKD, and these play an important role in the pathogenesis of increased cardiovascular (CV) events associated with CKD. The present review discusses relevant contributory mechanisms underpinning the promotion of hypertension and their consequent eventuation to renal damage and CV disease. In particular, salt and volume expansion, sympathetic nervous system (SNS) hyperactivity, upregulated renin–angiotensin–aldosterone system (RAAS), oxidative stress, vascular remodeling, endothelial dysfunction, and a range of mediators and signaling molecules which are thought to play a role in this concert of events are emphasized. As the control of high BP via therapeutic interventions can represent the key strategy to not only reduce BP but also the CV burden in kidney disease, evidence for major strategic pathways that can alleviate the progression of hypertensive kidney disease are highlighted. This review provides a particular focus on the impact of RAAS antagonists, renal nerve denervation, baroreflex stimulation, and other modalities affecting BP in the context of CKD, to provide interesting perspectives on the management of hypertensive nephropathy and associated CV comorbidities.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

Endovascular baroreflex amplification and the effect on sympathetic nerve activity in patients with resistant hypertension: A proof-of-principle study

BACKGROUND

First in human studies suggest that endovascular baroreflex amplification (EVBA) lowers blood pressure (BP). To explore potential mechanisms for BP reduction, this study examines the effects of EVBA on muscle sympathetic nerve activity (MSNA) and baroreceptor sensitivity (BRS).

METHODS

In a single-center sub-study of the CALM-DIEM study (Controlling And Lowering blood pressure with the MobiusHD-Defining Efficacy Markers), 14 patients with resistant hypertension were treated with EVBA. Microneurography and non-invasive continuous BP measurements were performed at baseline and three months after MobiusHD implantation. The primary outcome was change in MSNA. Secondary outcomes were change in baroreflex sensitivity (BRS), cardiovascular responses to a sympathetic stimulus, BP, heart rate (HR) and heart rate variability (HRV).

RESULTS

The primary endpoint was obtained in 10 of 14 patients enrolled in the sub-study. MSNA burst frequency and burst incidence decreased in 6 of 10 patients: mean change -4.1 bursts/min (95% confidence interval -12.2 to 4.0) and -3.8 bursts/100 heartbeats (-15.2 to 7.7). MSNA spike frequency and spike count decreased in 8 of 10 patients: mean change -2.8 spikes/sec (-7.3 to 1.8) and -3.0 spikes/heartbeat (-6.1 to 0.1). Change in MSNA and BP were not correlated. Office BP decreased by -14/-6 mmHg (-27 to -2/-15 to 3). We observed a trend towards decreased HR (-5 bpm, -10 to 1) and increased total power HRV (623 msec2, 78 to 1168). In contrast, BRS and cardiovascular responses remained unchanged after EVBA.

CONCLUSIONS

In this proof-of-principle study, EVBA did not significantly decrease MSNA in patients with resistant hypertension. EVBA did not impair baroreflex function.

TRIAL REGISTRATION

Clinical trial registration at NCT02827032.

Neuropeptide Y as a risk factor for cardiorenal disease and cognitive dysfunction in CKD: translational opportunities and challenges

Neuropeptide Y (NPY) is a 36-amino-acid peptide member of a family also including peptide YY and pancreatic polypeptide, which are all ligands to Gi/Go coupled receptors. NPY regulates several fundamental biologic functions including appetite/satiety, sex and reproduction, learning and memory, cardiovascular and renal function and immune functions. The mesenteric circulation is a major source of NPY in the blood in man and this peptide is considered a key regulator of gut–brain cross talk. A progressive increase in circulating NPY accompanies the progression of chronic kidney disease (CKD) toward kidney failure and NPY robustly predicts cardiovascular events in this population. Furthermore, NPY is suspected as a possible player in accelerated cognitive function decline and dementia in patients with CKD and in dialysis patients. In theory, interfering with the NPY system has relevant potential for the treatment of diverse diseases from cardiovascular and renal diseases to diseases of the central nervous system. Pharmaceutical formulations for effective drug delivery and cost, as well as the complexity of diseases potentially addressable by NPY/NPY antagonists, have been a problem until now. This in part explains the slow progress of knowledge about the NPY system in the clinical arena. There is now renewed research interest in the NPY system in psychopharmacology and in pharmacology in general and new studies and a new breed of clinical trials may eventually bring the expected benefits in human health with drugs interfering with this system.

Autonomic cardiovascular alterations as therapeutic targets in chronic kidney disease

PURPOSE

The present paper will review the impact of different therapeutic interventions on the autonomic dysfunction characterizing chronic renal failure.

METHODS

We reviewed the results of the studies carried out in the last few years examining the effects of standard pharmacologic treatment, hemodialysis, kidney transplantation, renal nerve ablation and carotid baroreceptor stimulation on parasympathetic and sympathetic control of the cardiovascular system in patients with renal failure.

RESULTS

Drugs acting on the renin-angiotensin system as well as central sympatholytic agents have been documented to improve autonomic cardiovascular control. This has also been shown for hemodialysis, although with more heterogeneous results related to the type of dialytic procedure adopted. Kidney transplantation, in contrast, particularly when performed together with the surgical removal of the native diseased kidneys, has been shown to cause profound sympathoinhibitory effects. Finally, a small amount of promising data are available on the potential favorable autonomic effects (particularly the sympathetic ones) of renal nerve ablation and carotid baroreceptor stimulation in chronic kidney disease.

CONCLUSIONS

Further studies are needed to clarify several aspects of the autonomic responses to therapeutic interventions in chronic renal disease. These include (1) the potential to normalize sympathetic activity in uremic patients by the various therapeutic approaches and (2) the definition of the degree of sympathetic deactivation to be achieved during treatment.

Blunted natriuretic response to saline loading in sheep with hypertensive kidney disease following radiofrequency catheter-based renal denervation

Renal sympathetic nerves contribute to renal excretory function during volume expansion. We hypothesized that intact renal innervation is required for excretion of a fluid/electrolyte load in hypertensive chronic kidney disease (CKD) and normotensive healthy settings. Blood pressure, kidney hemodynamic and excretory response to 180 min of isotonic saline loading (0.13 ml/kg/min) were examined in female normotensive (control) and hypertensive CKD sheep at 2 and 11 months after sham (control-intact, CKD-intact) or radiofrequency catheter-based RDN (control-RDN, CKD-RDN) procedure. Basal blood pressure was ~ 7 to 9 mmHg lower at 2, and 11 months in CKD-RDN compared with CKD-intact sheep. Saline loading did not alter glomerular filtration rate in any group. At 2 months, in response to saline loading, total urine and sodium excretion were ~ 40 to 50% less, in control-RDN and CKD-RDN than intact groups. At 11 months, the natriuretic and diuretic response to saline loading were similar between control-intact, control-RDN and CKD-intact groups but sodium excretion was ~ 42% less in CKD-RDN compared with CKD-intact at this time-point. These findings indicate that chronic withdrawal of basal renal sympathetic activity impairs fluid/electrolyte excretion during volume expansion. Clinically, a reduced ability to excrete a saline load following RDN may contribute to disturbances in body fluid balance in hypertensive CKD.

Cardiovascular autonomic nervous system dysfunction in chronic kidney disease and end-stage kidney disease: disruption of the complementary forces

PURPOSE OF REVIEW

Several nontraditional risk factors have been the focus of research in an attempt to understand the disproportionately high cardiovascular morbidity and mortality in chronic kidney disease (CKD) and end-stage kidney disease (ESKD) populations. One such category of risk factors is cardiovascular autonomic dysfunction. Its true prevalence in the CKD/ESKD population is unknown but existing evidence suggests it is common. Due to lack of standardized diagnostic and treatment options, this condition remains undiagnosed and untreated in many patients. In this review, we discuss current evidence pointing toward the role of autonomic nervous system (ANS) dysfunction in CKD, building off of crucial historical evidence and thereby highlighting the areas in need for future research interest.

RECENT FINDINGS

There are several key mediators and pathways leading to cardiovascular autonomic dysfunction in CKD and ESKD. We review studies exploring the mechanisms involved and discuss the current measurement tools and indices to evaluate the ANS and their pitfalls. There is a strong line of evidence establishing the temporal sequence of worsening autonomic function and kidney function and vice versa. Evidence linking ANS dysfunction and arrhythmia, sudden cardiac death, intradialytic hypotension, heart failure and hypertension are discussed.

SUMMARY

There is a need for early recognition and referral of CKD and ESKD patients suspected of cardiovascular ANS dysfunction to prevent the downstream effects described in this review.There are many unknowns in this area and a clear need for further research.

Effect of differential music tempo on post-exercise cardiovascular recovery parameters in hypertensive individuals: a randomised control trial

Hypertensive individuals tend to have autonomic dysfunction indicated by sympathetic dominance or delayed parasympathetic reactivation. A complimentary therapy such as music following exercise is considered to be beneficial in improving autonomic recovery. The purpose of this study was to assess the effect of differential music tempo on post-exercise cardiovascular recovery parameters in hypertensive individuals. Thirty hypertensive individuals were recruited for the present study which were randomly allocated to no music (n=10), slow music (n=10) and fast music (n=10) group. Participants in all three groups were subjected to submaximal exercise bout by Harvard step test. The cardiovascular recovery parameters i.e. heart rate recovery (HRR), blood pressure recovery (BPR) and rating of perceived exertion recovery (RPER) were assessed in all three groups after 1 min, 2 min and 3 min following termination of exercise. A significant decline was observed in HRR (P=0.002) and RPER (P=0.008) following exercise in slow music group as compared to fast and no music while no significant differences were observed in BPR between the three groups. The study concluded that music accelerates post-exercise recovery and slow music has greater effect as compared to fast or no music. These findings may have potential implications in the cardiovascular recovery dynamics in hypertensive individuals participating in submaximal exercise.

Angiotensin II and the Renal Hemodynamic Response to an Isolated Increased Renal Venous Pressure in Rats

Elevated central venous pressure increases renal venous pressure (RVP) which can affect kidney function. We previously demonstrated that increased RVP reduces renal blood flow (RBF), glomerular filtration rate (GFR), and renal vascular conductance (RVC). We now investigate whether the RAS and RBF autoregulation are involved in the renal hemodynamic response to increased RVP. Angiotensin II (ANG II) levels were clamped by infusion of ANG II after administration of an angiotensin-converting enzyme (ACE) inhibitor in male Lewis rats. This did not prevent the decrease in ipsilateral RBF (-1.9±0.4ml/min, p<0.05) and GFR (-0.77±0.18ml/min, p<0.05) upon increased RVP; however, it prevented the reduction in RVC entirely. Systemically, the RVP-induced decline in mean arterial pressure (MAP) was more pronounced in ANG II clamped animals vs. controls (-22.4±4.1 vs. -9.9±2.3mmHg, p<0.05), whereas the decrease in heart rate (HR) was less (-5±6bpm vs. -23±4bpm, p<0.05). In animals given vasopressin to maintain a comparable MAP after ACE inhibition (ACEi), increased RVP did not impact MAP and HR. RVC also did not change (0.018±0.008ml/minˑmmHg), and the reduction of GFR was no longer significant (-0.54±0.15ml/min). Furthermore, RBF autoregulation remained intact and was reset to a lower level when RVP was increased. In conclusion, RVP-induced renal vasoconstriction is attenuated when ANG II is clamped or inhibited. The systemic effect of increased RVP, a decrease in HR related to a mild decrease in blood pressure, is attenuated also during ANG II clamp. Last, RBF autoregulation remains intact when RVP is elevated and is reduced to lower levels of RBF. This suggests that in venous congestion, the intact RBF autoregulation could be partially responsible for the vasoconstriction.

Sympathetic Hyperactivity—A Hidden Enemy in Chronic Kidney Disease Patients

Chronic kidney disease is often characterized by the presence of sympathetic hyperactivity. The aim of this brief review is to summarize available knowledge on the pathogenesis of sympathetic hyperactivity and to discuss its clinical relevance, the consequences of this knowledge for the choice of treatment, and the yet unresolved issues.

Sympathetic nerve traffic overactivity in chronic kidney disease: a systematic review and meta-analysis

BACKGROUND

Studies based on microneurographic sympathetic nerve activity (MSNA) recordings have shown that the sympathetic system is overactivated in chronic kidney disease (CKD) patients but the relationship between MSNA and renal function and other risk factors has not been systematically reviewed in this population.

DESIGN AND MEASUREMENTS

This meta-analysis compares MSNA in cardiovascular complications-free CKD patients (n = 638) and healthy individuals (n = 372) and assesses the relationship of MSNA with the eGFR, age, BMI and hemodynamic variables.

RESULTS

In a global analysis, MSNA was higher in CKD patients than in healthy control individuals (P < 0.001). The difference in MSNA between patients and healthy individuals was more marked in end-stage kidney diseases patients than in stage 3A 3B CKD patients (P < 0.001). In an analysis combining patients and healthy individuals, MSNA rose gradually across progressively lower eGFR categories (P < 0.01). In separate meta-regression analyses in CKD patients and in healthy individuals, MSNA associated directly with age (CKD: r = 0.57, P = 0.022; healthy individuals: r = 0.71, P = 0.031) and with the BMI (r = 0.75, P = 0.001 and r = 0.93, P = 0.003). In both groups, MSNA correlated with heart rate (r = 0.77, P = 0.02 and r = 0.66, P = 0.01) but was unrelated to plasma norepinephrine.

CONCLUSION

Independently of comorbidities, MSNA is markedly increased in CKD patients as compared with healthy individuals and it is related to renal function, age, the BMI and heart rate. Sympathetic activation intensifies as CKD progresses toward kidney failure and such an intensification is paralleled by a progressive rise in heart rate but it is not reflected by plasma norepinephrine.

Norepinephrine turnover in the left ventricle of subtotally nephrectomized rats

Increased activity of the sympathetic nervous system (SNS) has been proposed as a risk factor for increased cardiovascular mortality in patients with chronic kidney disease (CKD). Information on the activity of cardiac sympathetic innervation is non-homogeneous and incomplete. The aim of our study was to evaluate the tonic effect of SNS on heart rate, norepinephrine turnover and direct and indirect effects of norepinephrine in left ventricles of subtotally nephrectomized rats (SNX) in comparison with sham-operated animals (SHAM). Renal failure was verified by measuring serum creatinine and urea levels. SNX rats developed increased heart rates and blood pressure (BP). The increase in heart rate was not caused by sympathetic overactivity as the negative chronotropic effect of metipranolol did not differ between the SNX and SHAM animals. The positive inotropic effects of norepinephrine and tyramine on papillary muscle were not significantly different. Norepinephrine turnover was measured after the administration of tyrosine hydroxylase inhibitor, pargyline, tyramine, desipramine, and KCl induced depolarization. The absolute amount of released norepinephrine was comparable in both groups despite a significantly decreased norepinephrine concentration in the cardiac tissue of the SNX rats. We conclude that CKD associated with renal denervation in rats led to adaptive changes characterized by an increased reuptake and intracellular norepinephrine turnover which maintained normal reactivity of the heart to sympathetic stimulation.

Neural control of cardiovascular function in black adults: implications for racial differences in autonomic regulation

Black adults are at increased risk for developing hypertension and cardiovascular and chronic kidney disease and have greater associated morbidity/mortality than white adults who are otherwise demographically similar. Despite the key role of the autonomic nervous system in the regulation of cardiovascular function, the mechanistic contributions of sympathetic nerves to racial differences in cardiovascular dysfunction and disease remain poorly understood. In this review, we present an update and synthesis of current understanding regarding the roles of autonomic neural mechanisms in normal and pathophysiological cardiovascular control in black and white adults. At rest, many hemodynamic and autonomic variables, including blood pressure, cardiac output, and sympathetic nerve activity, are similar in healthy black and white adults. However, resting sympathetic vascular transduction and carotid baroreflex responses are altered in ways that tend to promote increased vasoconstriction and higher blood pressure, even in healthy, normotensive black adults. Acute sympathoexcitatory maneuvers, including exercise and cold pressor test, often result in augmented sympathetic and hemodynamic responses in healthy black adults. Clinically, although mechanistic evidence is scarce in this area, existing data support the idea that excessive sympathetic activation and/or transduction into peripheral vasoconstriction contribute importantly to the pathophysiology of hypertension and chronic kidney disease in black compared with white adults. Important areas for future work include more detailed study of sympathetic and hemodynamic reactivity to exercise and other stressors in male and female black adults and, particularly, sympathetic control of renal function, an important area of clinical concern in black patients.

Neuropeptide Y and chronic kidney disease progression: a cohort study

Background

Neuropeptide Y (NPY) is a sympathetic neurotransmitter that has been implicated in various disorders including obesity, gastrointestinal and cardiovascular diseases.

Methods

We investigated the relationship between circulating NPY and the progression of the glomerular filtration rate (GFR) and proteinuria and the risk for a combined renal endpoint (>30% GFR loss, dialysis/transplantation) in two European chronic kidney disease (CKD) cohorts including follow-up of 753 and 576 patients for 36 and 57 months, respectively.

Results

Average plasma NPY was 104 ± 32 pmol/L in the first CKD cohort and 119 ± 41 pmol/L in the second one. In separate analyses of the two cohorts, NPY associated with the progression of the estimated GFR (eGFR) and proteinuria over time in both unadjusted and adjusted {eGFR: -3.60 mL/min/1.73 m2 [95% confidence interval (CI): -4.46 to - 2.74] P < 0.001 and -0.83 mL/min/1.73 m2 (-1.41 to - 0.25, P = 0.005); proteinuria: 0.18 g/24 h (0.11-0.25) P < 0.001 and 0.07 g/24 h (0.005-0.14) P = 0.033} analyses by the mixed linear model. Accordingly, in a combined analysis of the two cohorts accounting for the competitive risk of death (Fine and Gray model), NPY predicted (P = 0.005) the renal endpoint [sub-distribution hazard ratio (SHR): 1.09; 95% CI: 1.03-1.16; P = 0.005] and the SHR in the first cohort (1.14, 95% CI: 1.04-1.25) did not differ (P = 0.25) from that in the second cohort (1.06, 95% CI: 0.98-1.15).

Conclusions

NPY associates with proteinuria and faster CKD progression as well as with a higher risk of kidney failure. These findings suggest that the sympathetic system and/or properties intrinsic to the NPY molecule may play a role in CKD progression.

Cardiorenal Syndrome and Heart Failure-Challenges and Opportunities

Cardiorenal syndromes (CRS) describe concomitant bidirectional dysfunction of the heart and kidneys in which 1 organ initiates, perpetuates, and/or accelerates decline of the other. CRS are common in heart failure and universally portend worsened prognosis. Despite this heavy disease burden, the appropriate diagnosis and classification of CRS remains problematic. In addition to the hemodynamic drivers of decreased renal perfusion and increased renal vein pressure, induction of the renin-angiotensin-aldosterone system, stimulation of the sympathetic nervous system, disruption of balance between nitric oxide and reactive oxygen species, and inflammation are implicated in the pathogenesis of CRS. Medical therapy of heart failure including renin-angiotensin-aldosterone system inhibition and β-adrenergic blockade can blunt these deleterious processes. Renovascular disease can accelerate the progression of CRS. Volume overload and diuretic resistance are common and complicate the management of CRS. In heart failure and CRS being treated with diuretics, worsening creatinine is not associated with worsened outcome if clinical decongestion is achieved. Adjunctive therapy is often required in the management of volume overload in CRS, but evidence for these therapies is limited. Anemia and iron deficiency are importantly associated with CRS and might amplify decline of cardiac and renal function. End-stage cardiac and/or renal disease represents an especially poor prognosis with limited therapeutic options. Overall, worsening renal function is associated with significantly increased mortality. Despite progress in the area of CRS, there are still multiple pathophysiological and clinical aspects of CRS that need further research to eventually develop effective therapeutic options.

Altered Autonomic Reactivity During Lower Body Negative Pressure in End-Stage Renal Disease

BACKGROUND

End stage renal disease (ESRD) is characterized by autonomic dysfunction. During orthostatic stress, sympathetic (SNS) activity increases and parasympathetic (PNS) activity decreases to maintain arterial blood pressure (BP). We hypothesized that ESRD patients have impaired ability to adjust cardiac SNS and PNS activity during orthostasis, which could contribute to increased blood pressure variability, orthostatic intolerance and falls.

METHODS

We measured beat-to-beat BP and Electrocardiography at baseline and during increasing lower body negative pressure (LBNP) in 20 ESRD patients and 18 matched controls (CON). Heart rate variability was quantified as total power (TP) and standard deviation of the N-N interval, reflecting both SNS and PNS; high frequency (HF), root mean square of successive differences of neighboring N-N intervals (RMSSD), and percent of consecutive N-N intervals differing >50 milliseconds (pNN50), reflecting cardiac PNS activity; and low frequency (LF) and LF/HF, reflecting sympoathovagal balance. BP variability was quantified as the standard deviation in systolic (SDSAP) and diastolic (SDDAP) BP.

RESULTS

Baseline HF, RMSSD, and pNN50 were significantly lower in ESRD (P < 0.05). While CON had a significant decrease in HF (P = 0.015), RMSSD (P = 0.003), and pNN50 (P = 0.005) during LBNP, there was no change in heart rate variability in ESRD. There was no significant difference in BP response, but ESRD had a significantly blunted heart rate response during graded LBNP compared to controls (P < 0.001). There was no significant difference in SDSAP or SDDAP during LBNP between groups (P > 0.05).

CONCLUSIONS

These data suggest that ESRD patients have impaired autonomic adjustments to orthostatic stress.

Sympathetic overactivity in dialysis patients-Underappreciated and clinically consequential

Cardiovascular morbidity and mortality remain frustratingly common in dialysis patients. A dearth of established evidence-based treatment calls for alternative therapeutic avenues to be embraced. Sympathetic hyperactivity, predominantly due to afferent nerve signaling from the diseased native kidneys, has been established to be prognostic in the dialysis population for over 15 years. Despite this, tangible therapeutic interventions have, to date, been unsuccessful and the outlook for patients remains poor. This narrative review summarizes established experimental and clinical data, highlighting recent developments, and proposes why interventions to ameliorate sympathetic hyperactivity may well be beneficial for this high-risk population.

Hypertension in patients on dialysis: diagnosis, mechanisms, and management

Hypertension (blood pressure > 140/90 mm Hg) is very common in patients undergoing regular dialysis, with a prevalence of 70-80%, and only the minority has adequate blood pressure (BP) control. In contrast to the unclear association of predialytic BP recordings with cardiovascular mortality, prospective studies showed that interdialytic BP, recorded as home BP or by ambulatory blood pressure monitoring in hemodialysis patients, associates more closely with mortality and cardiovascular events. Although BP is measured frequently in the dialysis treatment environment, aspects related to the measurement technique traditionally employed may be unsatisfactory. Several other tools are now available and being used in clinical trials and in clinical practice to evaluate and treat elevated BP in chronic kidney disease (CKD) patients. While we wait for the ongoing review of the CKD Blood Pressure KIDGO guidelines, there is no guideline for the dialysis population addressing this important issue. Thus, the objective of this review is to provide a critical analysis of the information available on the epidemiology, pathogenic mechanisms, and the main pillars involved in the management of blood pressure in stage 5-D CKD, based on current knowledge.

Delayed systolic blood pressure recovery following exercise as a mechanism of masked uncontrolled hypertension in chronic kidney disease

Background

Among people treated for hypertension, the presence of elevated blood pressure (BP) out of the clinic but normal BP in the clinic is called masked uncontrolled hypertension (MUCH). What causes MUCH remains unknown. The purpose of this study was to answer the question of whether patients with MUCH have an increased hemodynamic reactivity to exercise and delayed hemodynamic recovery following exercise.

Methods

Four groups were compared: controlled hypertension (CH, n = 58), MUCH (n = 34) and uncontrolled hypertension (UCH, n = 12), all of which had chronic kidney disease (CKD), and a group of healthy normal volunteers who did not have hypertension or CKD (n = 16). All participants underwent assessment of 24-h ambulatory BP monitoring, BP measurement during a graded symptom-limited exercise using a cycle ergometer and BP recovery over 7 min following exercise.

Results

Exercise-induced increase in systolic BP was similar among the four groups. When compared with healthy controls, recovery of systolic BP following termination of exercise was blunted among the CKD groups in unadjusted (P < 0.0001) and adjusted (P < 0.001) models. During recovery, the healthy control group had 5.9% decline in systolic BP per minute. In contrast, MUCH had only 3.3% per minute reduction and the UCH group had 0.3% reduction per minute. A test of linear trend was significant (P = 0.002, adjusted model).

Conclusion

Because there was no impairment in the heart rate recovery among groups, we speculate that the parasympathetic pathway appears intact among treated hypertensives with CKD. However, the failure to withdraw sympathetic tone upon termination of exercise causes ongoing vasoconstriction and delayed systolic BP recovery providing a biological basis for MUCH. Delayed recovery from exercise-induced hypertension in those with poorly controlled BP provides potentially a new target to assure round-the-clock BP control.

Preferred Fourth-Line Pharmacotherapy for Resistant Hypertension: Are We There Yet?

Resistant hypertension (RH) is defined as blood pressure (BP) that remains above target levels despite adherence to at least three different antihypertensive medications, typically including a diuretic. Epidemiological studies estimate that RH is increasing in prevalence, and is associated with detrimental health outcomes. The pathophysiology underlying RH is complex, involving multiple, overlapping contributors including activation of the renin-angiotensin aldosterone system and the sympathetic nervous system, volume overload, endothelial dysfunction, behavioural and lifestyle factors. Hypertension guidelines currently recommend specific pharmacotherapy for 1st, 2nd and 3rd-line treatment, however no specific fourth-line pharmacotherapy is provided for those with RH. Rather, five different antihypertensive drug classes are generally suggested as possible alternatives, including: mineralocorticoid receptor antagonists, α1-adrenergic antagonists, α2-adrenergic agonists, β-blockers, and peripheral vasodilators. Each of these drug classes vary in their efficacy, tolerability and safety profile. This review summarises the available data on each of these drug classes as a potential fourth-line drug and reveals a lack of robust clinical evidence for preferred use of most of these classes in the setting of RH. Moreover, there is a lack of direct comparative trials that could assist in identifying a preferred fourth-line pharmacologic approach and in providing evidence for hypertensive guidelines for adequate treatment of RH.

Beta blockers in patients with end-stage renal disease-Evidence-based recommendations

For patients who require hemodialysis, beta blockers offer a simultaneous opportunity and challenge in the treatment of cardiovascular disease. Beta blockers are well supported by data from nondialysis populations and directly mitigate the sympathetic overactivity that links chronic kidney disease with cardiovascular sequelae. However, the evidence supporting their use in patients receiving hemodialysis is sparse and the heterogeneity of the beta blocker class makes it difficult to prescribe these medications with confidence. Despite these limitations, both trial and observational data exist that can help guide the use of these medications. In this review, we outline the reasons to consider beta blockers for patients receiving hemodialysis, discuss the barriers to their use, and provide specific evidence-based recommendations for beta blocker use in patients with heart failure, hypertension, ischemic heart disease and arrhythmia.

Physician perceptions of blood pressure control in patients with chronic kidney disease and target blood pressure achievement rate

Background

Blood pressure (BP) control is the most-established method for the prevention of chronic kidney disease (CKD) progression. However, the ideal BP target for CKD patients is still under debate.

Methods

We performed a survey of regular registered members of the Korean Society of Nephrology to determine physician perceptions of BP control in patients with CKD. In addition, we evaluated the target BP achievement rate using data from the APrODiTe-2 study.

Results

Two-thirds of physicians considered the target BP for CKD to be < 130/85 mmHg. The systolic BP (SBP) thresholds for diabetic CKD, proteinuria ≥ 300 mg/day, 30 ≤ glomerular filtration rate (GFR) < 60 mL/min/1.73 m², age < 60 years, and the presence of atherosclerotic (ASO) complications were significantly lower than the SBP thresholds of the opposite parameters. The three major hurdles to controlling BP were non-compliance with lifestyle modification and medications, and self-report of well-controlled home BP. Most physicians prescribed home and ambulatory BP monitoring to less than 50% of their patients. The target BP achievement rates using the SBP thresholds in this survey were as follows: non-diabetic (69.3%); diabetic (29.5%); proteinuria < 300 mg/day (72.3%); proteinuria > 300 mg/day (33.7%); GFR ≥ 60 (76.4%); GFR < 30 (47.8%); no evidence of ASO (67.8%); and the presence of ASO (42.9%).

Conclusion

The target BP was lower in patients with higher cerebro-cardiovascular risks. These patient groups also showed lower target BP achievement rates. We also found a relatively lower application and clinical reflection rate of home or ambulatory BP monitoring.

Understanding the Two Faces of Low-Salt Intake

Fierce debate has developed whether low-sodium intake, like high-sodium intake, could be associated with adverse outcome. The debate originates in earlier epidemiological studies associating high-sodium intake with high blood pressure and more recent studies demonstrating a higher cardiovascular event rate with both low- and high-sodium intake. This brings into question whether we entirely understand the consequences of high- and (very) low-sodium intake for the systemic hemodynamics, the kidney function, the vascular wall, the immune system, and the brain. Evolutionarily, sodium retention mechanisms in the context of low dietary sodium provided a survival advantage and are highly conserved, exemplified by the renin-angiotensin system. What is the potential for this sodium-retaining mechanism to cause harm? In this paper, we will consider current views on how a sodium load is handled, visiting aspects including the effect of sodium on the vessel wall, the sympathetic nervous system, the brain renin-angiotensin system, the skin as "third compartment" coupling to vascular endothelial growth factor C, and the kidneys. From these perspectives, several mechanisms can be envisioned whereby a low-sodium diet could potentially cause harm, including the renin-angiotensin system and the sympathetic nervous system. Altogether, the uncertainties preclude a unifying model or practical clinical guidance regarding the effects of a low-sodium diet for an individual. There is a very strong need for fundamental and translational studies to enhance the understanding of the potential adverse consequences of low-salt intake as an initial step to facilitate better clinical guidance.

Renal Sympathetic Denervation: A Viable Option for Treating Resistant Hypertension

Accumulating evidence from mainly uncontrolled clinical studies with various types of ablation catheters have shown that renal denervation (RDN) can be applied safely and is effective in lowering blood pressure (BP) in patients with treatment-resistant hypertension. Sustained BP lowering has been documented up to 3 years. Furthermore, RDN has been associated with regression of target organ damage, such as left ventricular hypertrophy, arterial stiffness, and others. Several studies indicate potential benefit in other common clinical conditions associated with increased sympathetic tone including chronic kidney disease and heart failure. However, the recently published Symplicity HTN-3 study, the largest and most rigorously designed sham-controlled clinical trial, while confirming the safety of the procedure, failed to demonstrate a BP lowering effect beyond that of a sham procedure in patients with resistant hypertension. Efforts to unravel the reasons for the discrepant results from Symplicity HTN-3 have focused on a range of potential confounders including anatomical and procedural aspects. Indeed, data from post-hoc analyses indicate that sufficient RDN may not have been achieved in the majority of patients in Symplicity HTN-3. Furthermore, recent evidence from human postmortem and functional animal studies revealed new insights into the anatomical distribution of renal nerves and their accessibility by intravascular approaches. Initial results from recent clinical trials integrating these important findings indeed seem to confirm that RDN remains a viable option for the treatment of hypertension. Thorough further investigations will be key to determine the true potential of RDN in clinical conditions characterized by increased sympathetic drive.

Sympathetic Overactivity in Chronic Kidney Disease: Consequences and Mechanisms

The incidence of chronic kidney disease (CKD) is increasing worldwide, with more than 26 million people suffering from CKD in the United States alone. More patients with CKD die of cardiovascular complications than progress to dialysis. Over 80% of CKD patients have hypertension, which is associated with increased risk of cardiovascular morbidity and mortality. Another common, perhaps underappreciated, feature of CKD is an overactive sympathetic nervous system. This elevation in sympathetic nerve activity (SNA) not only contributes to hypertension but also plays a detrimental role in the progression of CKD independent of any increase in blood pressure. Indeed, high SNA is associated with poor prognosis and increased cardiovascular morbidity and mortality independent of its effect on blood pressure. This brief review will discuss some of the consequences of sympathetic overactivity and highlight some of the potential pathways contributing to chronically elevated SNA in CKD. Mechanisms leading to chronic sympathoexcitation in CKD are complex, multifactorial and to date, not completely understood. Identification of the mechanisms and/or signals leading to sympathetic overactivity in CKD are crucial for development of effective therapeutic targets to reduce the increased cardiovascular risk in this patient group.

Acute effects of angiotensin-converting enzyme inhibition versus angiotensin II receptor blockade on cardiac sympathetic activity in patients with heart failure

The beneficial effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (ANG II) receptor antagonists in patients with heart failure secondary to reduced ejection fraction (HFrEF) are felt to result from prevention of the adverse effects of ANG II on systemic afterload and renal homeostasis. However, ANG II can activate the sympathetic nervous system, and part of the beneficial effects of ACE inhibitors and ANG II antagonists may result from their ability to inhibit such activation. We examined the acute effects of the ACE inhibitor captopril (25 mg, n = 9) and the ANG II receptor antagonist losartan (50 mg, n = 10) on hemodynamics as well as total body and cardiac norepinephrine spillover in patients with chronic HFrEF. Hemodynamic and neurochemical measurements were made at baseline and at 1, 2, and 4 h after oral dosing. Administration of both drugs caused significant reductions in systemic arterial, cardiac filling, and pulmonary artery pressures (P < 0.05 vs. baseline). There was no significant difference in the magnitude of those hemodynamic effects. Plasma concentrations of ANG II were significantly decreased by captopril and increased by losartan (P < 0.05 vs. baseline for both). Total body sympathetic activity increased in response to both captopril and losartan (P < 0.05 vs. baseline for both); however, there was no change in cardiac sympathetic activity in response to either drug. The results of the present study do not support the hypothesis that the acute inhibition of the renin-angiotensin system has sympathoinhibitory effects in patients with chronic HFrEF.

Effects of multielectrode renal denervation on elevated sympathetic nerve activity and insulin resistance in metabolic syndrome

OBJECTIVE

This study aimed to investigate the effects of renal denervation (RDN) on sympathetic nerve activity and insulin resistance in patients with metabolic syndrome.

METHODS

Seventeen patients fulfilled at least four of five criteria for metabolic syndrome and under stable use of at least two antihypertensive drugs were randomized in 3 : 1 ratio to RDN (n = 13, 12 men, age: 58 ± 7 years) and control groups (n = 4, three men, age: 60 ± 5 years) and followed up for 3 months. Muscle sympathetic nerve activity (MSNA) at rest and during standard 75 g oral glucose tolerance test (OGTT) was assessed.

RESULTS

In the RDN group, office and average 24-h blood pressures reduced by 16 ± 21/10 ± 11 mmHg (P = 0.01/0.007) and 14 ± 16/5 ± 8 mmHg (P = 0.008/0.03) respectively; waist circumference reduced by 3.1 ± 3.6 cm (P = 0.008); and resting MSNA reduced from 55 ± 9 bursts per minute to 46 ± 8 bursts per minute (P = 0.0008) at month 3 post-RDN. During OGTT, although blunted MSNA responses were noted at baseline throughout the 120-min test, improved MSNA responses with burst frequency increased to 52 ± 8 bursts per minute (P < 0.001 vs. the resting MSNA, n = 13) at 30 min and to 54 ± 8 bursts per minute (P = 0.004 vs. the resting MSNA, n = 10) at 120 min and were observed at month 3 post-RDN. No such improvements were observed in the controls. No significant change was observed in the HOMA-IR in both groups at month 3.

CONCLUSION

In this pilot study of patients with metabolic syndrome and associated hypertension, RDN reduced elevated sympathetic nerve activity and restored the normal neural response to oral glucose loading.

Uraemia: an unrecognized driver of central neurohumoral dysfunction in chronic kidney disease?

Chronic kidney disease (CKD) carries a large cardiovascular burden in part due to hypertension and neurohumoral dysfunction - manifesting as sympathetic overactivity, baroreflex dysfunction and chronically elevated circulating vasopressin. Alterations within the central nervous system (CNS) are necessary for the expression of neurohumoral dysfunction in CKD; however, the underlying mechanisms are poorly defined. Uraemic toxins are a diverse group of compounds that accumulate as a direct result of renal disease and drive dysfunction in multiple organs, including the brain. Intensive haemodialysis improves both sympathetic overactivity and cardiac baroreflex sensitivity in renal failure patients, indicating that uraemic toxins participate in the maintenance of autonomic dysfunction in CKD. In rodents exposed to uraemia, immediate early gene expression analysis suggests upregulated activity of not only pre-sympathetic but also vasopressin-secretory nuclei. We outline several potential mechanisms by which uraemia might drive neurohumoral dysfunction in CKD. These include superoxide-dependent effects on neural activity, depletion of nitric oxide and induction of low-grade systemic inflammation. Recent evidence has highlighted superoxide production as an intermediate for the depolarizing effect of some uraemic toxins on neuronal cells. We provide preliminary data indicating augmented superoxide production within the hypothalamic paraventricular nucleus in the Lewis polycystic kidney rat, which might be important for mediating the neurohumoral dysfunction exhibited in this CKD model. We speculate that the uraemic state might serve to sensitize the central actions of other sympathoexcitatory factors, including renal afferent nerve inputs to the CNS and angiotensin II, by way of recruiting convergent superoxide-dependent and pro-inflammatory pathways.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in the stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to loss of appetite or dietary restriction.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to the loss of appetite or dietary restriction.

Short-Term Angiotensin Subtype 1 Receptor Blockade Does Not Alter the Circulatory Responses to Sympathetic Nervous System Modulation in Healthy Volunteers Before and During Sevoflurane Anesthesia: Results of a Pilot Study

OBJECTIVE

The mechanism of perioperative hypotension in patients taking an angiotensin-receptor blocker up to the time of surgery remains unclear. This study tested the hypothesis that short-term angiotensin-receptor blocker treatment attenuated the sympathetic and vascular responses to autonomic stimuli in volunteers undergoing anesthesia.

DESIGN

Randomized, crossover, blinded, pilot design.

SETTING

Zablocki Veterans Affairs Medical Center, Milwaukee, WI.

PARTICIPANTS

The study comprised 8 male and 6 female healthy, young volunteers (age 23±1.2 years [mean±standard error of the mean]).

INTERVENTIONS

Volunteers were studied after receiving oral placebo or 50 mg of losartan (angiotensin-receptor blocker) for 3 days before each test day. The effectiveness of angiotensin-receptor blocker treatment was confirmed using the mean arterial blood pressure response to intravenous angiotensin II (1-µg bolus). Eight volunteers underwent direct mean arterial pressure and forearm bloodflow measurements during conscious baseline, a cold pressor test, induction of anesthesia, tracheal intubation, maintenance of anesthesia with 1 minimum alveolar concentration of sevoflurane, and airway irritation with 12% desflurane. Six volunteers experienced mean arterial pressure responses to 0.1 mg of phenylephrine at baseline and during 1 minimum alveolar concentration of sevoflurane.

MEASUREMENTS AND MAIN RESULTS

Comparisons were made over time and across groups. Angiotensin-receptor blocker treatment significantly reduced-mean arterial pressure and forearm vascular resistance (forearm blood flow/mean arterial pressure) over time and blocked the mean arterial pressure response to angiotensin-II challenge. The changes in mean arterial pressure and forearm vascular resistance in response to all stressors did not differ between treatments. Mean arterial pressure increases from phenylephrine were preserved.

CONCLUSIONS

In healthy, young volunteers, sympathetically-mediated responses from the short-term use of an angiotensin-receptor blocker were not altered and most likely did not contribute to perioperative hypotension during the intraoperative period.