Antihypertensive Drugs and the Sympathetic Nervous System

Heart rate deceleration and acceleration capacities associated with circadian rhythm of blood pressure in essential hypertension

BACKGROUND

This study aimed to investigate the potential association between the circadian rhythm of blood pressure and deceleration capacity (DC)/acceleration capacity (AC) in patients with essential hypertension.

METHODS

This study included 318 patients with essential hypertension, whether or not they were being treated with anti-hypertensive drugs, who underwent 24-hour ambulatory blood pressure monitoring (ABPM). Patients were categorized into three groups based on the percentage of nocturnal systolic blood pressure (SBP) dipping: the dipper, non-dipper and reverse dipper groups. Baseline demographic characteristics, ambulatory blood pressure monitoring parameters, Holter recordings (including DC and AC), and echocardiographic parameters were collected.

RESULTS

In this study, the lowest DC values were observed in the reverse dipper group, followed by the non-dipper and dipper groups (6.46 ± 2.06 vs. 6.65 ± 1.95 vs. 8.07 ± 1.79 ms, P < .001). Additionally, the AC gradually decreased (-6.32 ± 2.02 vs. -6.55 ± 1.95 vs. -7.80 ± 1.73 ms, P < .001). There was a significant association between DC (r = .307, P < .001), AC (r=-.303, P < .001) and nocturnal SBP decline. Furthermore, DC (β = 0.785, P = .001) was positively associated with nocturnal SBP decline, whereas AC was negatively associated with nocturnal SBP (β = -0.753, P = .002). By multivariate logistic regression analysis, deceleration capacity [OR (95% CI): 0.705 (0.594-0.836), p < .001], and acceleration capacity [OR (95% CI): 1.357 (1.141-1.614), p = .001] were identified as independent risk factors for blood pressure nondipper status. The analysis of ROC curves revealed that the area under the curve for DC/AC in predicting the circadian rhythm of blood pressure was 0.711/0.697, with a sensitivity of 73.4%/65.1% and specificity of 66.7%/71.2%.

CONCLUSIONS

Abnormal DC and AC density were correlated with a blunted decline in nighttime SBP, suggesting a potential association between the circadian rhythm of blood pressure in essential hypertension patients and autonomic nervous dysfunction.

Cerebral Blood Flow Assessed with Phase-contrast Magnetic Resonance Imaging during Blood Pressure Changes with Noradrenaline and Labetalol: A Trial in Healthy Volunteers

BACKGROUND

Adequate cerebral perfusion is central during general anesthesia. However, perfusion is not readily measured bedside. Clinicians currently rely mainly on mean arterial pressure (MAP) as a surrogate, even though the relationship between blood pressure and cerebral blood flow is not well understood. The aim of this study was to apply phase-contrast magnetic resonance imaging to characterize blood flow responses in healthy volunteers to commonly used pharmacologic agents that increase or decrease arterial blood pressure.

METHODS

Eighteen healthy volunteers aged 30 to 50 yr were investigated with phase-contrast magnetic resonance imaging. Intra-arterial blood pressure monitoring was used. First, intravenous noradrenaline was administered to a target MAP of 20% above baseline. After a wash-out period, intravenous labetalol was given to a target MAP of 15% below baseline. Cerebral blood flow was measured using phase-contrast magnetic resonance imaging and defined as the sum of flow in the internal carotid arteries and vertebral arteries. Cardiac output (CO) was defined as the flow in the ascending aorta.

RESULTS

Baseline median cerebral blood flow was 772 ml/min (interquartile range, 674 to 871), and CO was 5,874 ml/min (5,199 to 6,355). The median dose of noradrenaline was 0.17 µg · kg-1 · h-1 (0.14 to 0.22). During noradrenaline infusion, cerebral blood flow decreased to 705 ml/min (606 to 748; P = 0.001), and CO decreased to 4,995 ml/min (4,705 to 5,635; P = 0.01). A median dose of labetalol was 120 mg (118 to 150). After labetalol boluses, cerebral blood flow was unchanged at 769 ml/min (734 to 900; P = 0.68). CO increased to 6,413 ml/min (6,056 to 7,464; P = 0.03).

CONCLUSIONS

In healthy, awake subjects, increasing MAP using intravenous noradrenaline decreased cerebral blood flow and CO. These data do not support inducing hypertension with noradrenaline to increase cerebral blood flow. Cerebral blood flow was unchanged when decreasing MAP using labetalol.

EDITOR’S PERSPECTIVE

Improvement in Blood Pressure After Intermittent Fasting in Hipertension: Could Renin-Angiotensin System and Autonomic Nervous System Have a Role?

BACKGROUND

Although it has been reported that the intermittent fasting (IF) diet has positive effects on heart health and improvement in blood pressure, it has not been sufficiently clarified how it could have these positive effects yet.

OBJECTIVE

We aimed to evaluate the effects of IF on the autonomic nervous system (ANS) and renin-angiotensin system (RAS), which are closely related to blood pressure.

METHODS

Seventy-two hypertensive patients were included in the study, and the data of 58 patients were used. All the participants fasted for about 15-16 hours for 30 days. Participants were evaluated with 24-hour ambulatory blood pressure monitoring and Holter electrocardiography before and after IF; also, 5 ml venous blood samples were taken for assessment of Serum angiotensin I (Ang-I) and angiotensin II (Ang-II) levels and angiotensin-converting enzyme (ACE) activity. For data analysis, the p-value <0.05 was accepted as significant.

RESULTS

Compared to pre-IF, a significant decrease was observed in the patients' blood pressures in post-IF. An increase in high-frequency (HF) power and the mean root square of the sum of squares of differences between adjacent NN intervals (RMSSD) were observed after the IF protocol (p=0.039, p=0.043). Ang-II and ACE activity were lower in patients after IF (p=0.034, p=0.004), and decreasing Ang-II levels were determined as predictive factors for improvement of the blood pressure, like the increase in HF power and RMSSD.

CONCLUSION

The present findings of our study demonstrated an improvement in blood pressure and the relationship of blood pressure with positive outcomes, including HRV, ACE activity, and Ang-II levels after the IF protocol.

The position of renal denervation in treatment of hypertension: an expert consensus statement

Hypertension is an important risk factor for cardiovascular disease. In the Netherlands, there are approximately 2.8 million people with hypertension. Despite treatment recommendations including lifestyle changes and antihypertensive drugs, most patients do not meet guideline-recommended blood pressure (BP) targets. In order to improve BP control and lower the risk of subsequent cardiovascular events, renal sympathetic denervation (RDN) has been introduced and studied as a non-pharmacological approach. While early data on the efficacy of RDN showed conflicting results, improvements in treatment protocols and study design resulted in robust new evidence supporting the potential of the technology to improve patient care in hypertensive subjects. Recently, 5 randomised sham-controlled trials demonstrated the safety and efficacy of the technology. Modelling studies have further shown that RDN is cost-effective in the Dutch healthcare setting. Given the undisputable disease burden along with the shortcomings of current therapeutic options, we postulate a new, clearly framed indication for RDN as an adjunct in the treatment of hypertension. The present consensus statement summarises current guideline-recommended BP targets, proposed workup and treatment for hypertension, and position of RDN for those patients with primary hypertension who do not meet guideline-recommended BP targets (see central illustration).

Hypertension attenuates the link of osteoprotegerin to reduced baroreflex sensitivity in type 2 diabetes mellitus patients on oral antidiabetic and antihypertensive therapy - a cross sectional study

PURPOSE

Decreased baroreflex sensitivity (BRS) has been shown to be a marker of cardiovascular (CV) risk. In the present study, the difference in CV risk biomarkers in type 2 diabetes (T2D) patients receiving oral antidiabetic drugs (OAD) with and without hypertension has been assessed.

MATERIALS AND METHODS

Ninety-two T2D patients on OAD without hypertension (control group) and eighty-eight diabetic patients with hypertension on OAD and antihypertensive drugs (test group) matched for age, gender, body mass index, serum glucose, glycated haemoglobin, and duration of the disease were recruited for the study. Their blood pressure (BP) variability including BRS, heart rate variability (HRV), insulin, lipid profile, osteoprotegerin (OPG), and tumor necrosis factor-α (TNF-α) were estimated. The association of various factors with BRS was assessed by Spearman correlation and multiple regression analysis.

RESULTS

BRS was decreased (13.90 ± 5.27 vs 6.76 ± 4.58), HRV sympathetic indices [LFnu, LF-HF ratio (1.30 ± 0.49 vs 1.93 ± 0.62)], HOMA-IR, atherogenic index of plasma (AIP), OPG (223.08 ± 103.86 vs 287.60 ± 121.36) and TNF-α were increased, and parasympathetic indices [TP (1012.90 ± 316.18 vs 625.88 ± 229.84), RMSSD, SDNN, NN50, pNN50] were decreased in the test group compared to control group. In control group, parasympathetic indices, AIP, OPG, and TNF-α had a significant correlation and OPG had an independent association (β - 0.344; p 0.004) with BRS. In test group, BP, LF-HF ratio, parasympathetic indices, AIP, OPG, and TNF-α had significant correlation, and TNF-α alone (β - 0.297; p 0.022) had an independent contribution to decreased BRS.

CONCLUSION

Despite antidiabetic and antihypertensive treatments, T2D patients with hypertension had more cardiometabolic risks in comparison to normotensive T2D patients. Inflammation could be the inciting factor for rise in BP and decrease in BRS (CV risk) in hypertensive T2D patients. Hypertension in diabetes could attenuate the link of OPG to the reduction in BRS. Reduction in BRS could be a physiological marker of CV risk in T2D patients treated with OAD.

Evaluation of the Cardiac Electrophysiological and Haemodynamic Effects of Elsholtzia ciliata Essential Oil on Swine

The demand for the development of novel medicines with few side effects and no proarrhythmic properties is increasing. Extensive research on herbal extracts has been conducted with the expectation that the compounds will exert precise effects without harmful side effects. Elsholtzia ciliata (Thunb.) Hyl. essential oil (EO) possesses antiarrhythmic properties similar to those of class 1B antiarrhythmics, such as prolonging myocardial activation of the QRS complex and shortening the QT interval. In this study, we determined the kinetic profile of EO phytocompounds and the effects of EO on heart electrical activity and arterial blood pressure. For this study, we chose to use local breed pigs that were anaesthetized. The effects of an intravenous bolus of EO on ECG parameters, arterial blood pressure, heart rate variability, and blood levels of haematological and biochemical parameters were registered and evaluated. Following an intravenous injection of a bolus, EO exerted a vasodilatory effect, resulting in significant reductions in arterial blood pressure. EO also increased the heart rate and altered ECG parameters. The bolus of EO prolonged the QRS complex, shortened the QT interval, and nonmonotonically altered the PQ interval. After the administration of a bolus of EO, the activity of the autonomic nervous system was altered. This study confirms that EO possesses similar properties to class 1B antiarrhythmics and exerts a hypotensive effect; it reduces arterial blood pressure possibly by modulating peripheral vascular resistance.

The effect of endovascular baroreflex amplification on central sympathetic nerve circuits and cerebral blood flow in patients with resistant hypertension: A functional MRI study

BACKGROUND

Endovascular baroreflex amplification (EVBA) by implantation of the MobiusHD is hypothesized to lower blood pressure by decreasing sympathetic activity through the mechanism of the baroreflex. In the present exploratory study we investigated the impact of MobiusHD implantation on central sympathetic nerve circuits and cerebral blood flow (CBF) in patients with resistant hypertension.

MATERIALS AND METHODS

In thirteen patients, we performed blood oxygenation level-dependent functional magnetic resonance imaging (BOLD fMRI) at rest and during Valsalva maneuvers, before and 3 months after EVBA. Data were analyzed using a whole-brain approach and a brainstem-specific analysis. CBF was assessed using arterial spin labeling MRI.

RESULTS

Resting-state fMRI analysis did not reveal significant differences in functional connectivity at 3 months after EVBA. For the Valsalva maneuver data, the whole-brain fMRI analysis revealed significantly increased activation in the posterior and anterior cingulate, the insular cortex, the precuneus, the left thalamus and the anterior cerebellum. The brainstem-specific fMRI analysis showed a significant increase in BOLD activity in the right midbrain 3 months after EVBA. Mean gray matter CBF (partial volume corrected) decreased significantly from 48.9 (9.9) ml/100 gr/min at baseline to 43.4 (13.0) ml/100 gr/min (p = 0.02) at 3 months.

CONCLUSIONS

This first fMRI pilot study in patients with resistant hypertension treated with EVBA showed a significant increase in BOLD activity during the Valsalva maneuver in brain regions related to sympathetic activity. No notable signal intensity changes were observed in brain areas involved in the baroreflex circuit. Future randomized controlled studies are needed to investigate whether the observed changes are directly caused by EVBA.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, identifier: NCT02827032.

Angiotensin II and the Cardiac Parasympathetic Nervous System in Hypertension

The renin-angiotensin-aldosterone system (RAAS) impacts cardiovascular homeostasis via direct actions on peripheral blood vessels and via modulation of the autonomic nervous system. To date, research has primarily focused on the actions of the RAAS on the sympathetic nervous system. Here, we review the critical role of the RAAS on parasympathetic nerve function during normal physiology and its role in cardiovascular disease, focusing on hypertension. Angiotensin (Ang) II receptors are present throughout the parasympathetic nerves and can modulate vagal activity via actions at the level of the nerve endings as well as via the circumventricular organs and as a neuromodulator acting within brain regions. There is tonic inhibition of cardiac vagal tone by endogenous Ang II. We review the actions of Ang II via peripheral nerve endings as well as via central actions on brain regions. We review the evidence that Ang II modulates arterial baroreflex function and examine the pathways via which Ang II can modulate baroreflex control of cardiac vagal drive. Although there is evidence that Ang II can modulate parasympathetic activity and has the potential to contribute to impaired baseline levels and impaired baroreflex control during hypertension, the exact central regions where Ang II acts need further investigation. The beneficial actions of angiotensin receptor blockers in hypertension may be mediated in part via actions on the parasympathetic nervous system. We highlight important unknown questions about the interaction between the RAAS and the parasympathetic nervous system and conclude that this remains an important area where future research is needed.

Autonomic nervous system activity changes in patients with hypertension and overweight: role and therapeutic implications

The incidence and prevalence of hypertension is increasing worldwide, with approximately 1.13 billion of people currently affected by the disease, often in association with other diseases such as diabetes mellitus, chronic kidney disease, dyslipidemia/hypercholesterolemia, and obesity. The autonomic nervous system has been implicated in the pathophysiology of hypertension, and treatments targeting the sympathetic nervous system (SNS), a key component of the autonomic nervous system, have been developed; however, current recommendations provide little guidance on their use. This review discusses the etiology of hypertension, and more specifically the role of the SNS in the pathophysiology of hypertension and its associated disorders. In addition, the effects of current antihypertensive management strategies, including pharmacotherapies, on the SNS are examined, with a focus on imidazoline receptor agonists.

Predictors of blood pressure response to ultrasound renal denervation in the RADIANCE-HTN SOLO study

The blood pressure (BP) lowering response to renal denervation (RDN) remains variable with about one-third of patients not responding to ultrasound or radiofrequency RDN. Identification of predictors of the BP response to RDN is needed to optimize patient selection for this therapy. This is a post-hoc analysis of the RADIANCE-HTN SOLO study. BP response to RDN was measured by the change in daytime ambulatory systolic blood pressure (dASBP) at 2 months post procedure. Univariate regression was used initially to assess potential predictors of outcome followed by multivariate regression analysis. In the univariate analysis, predictors of response to RDN were higher baseline daytime ambulatory diastolic blood pressure (dADBP), the use of antihypertensive medications at screening, and presence of orthostatic hypertension (OHTN) whilst the presence of untreated accessory arteries was a negative predictor of response. Multivariate analysis determined that dADBP and use of antihypertensive medications were predictors of response to RDN with a trend for OHTN to predict response. Obese females also appeared to be better responders to RDN in an interaction model. RDN is more effective in patients with elevated baseline dADBP and those with OHTN, suggesting increased peripheral vascular resistance secondary to heightened sympathetic tone. These assessments are easy to perform in clinical setting and may help in phenotyping patients who will respond better to RDN.

Efficacy and safety of nebivolol in Korean patients with hypertension by age and sex: a subanalysis from the BENEFIT-KOREA study

BACKGROUND

BENEFIT-KOREA (BEnefits after 24 weeks of NEbivolol administration For essential hypertensIon patients wiTh various comorbidities and treatment environments in Korea) study, an observational study in South Korea, demonstrated the efficacy and safety of nebivolol in Asian patients with essential hypertension with and without comorbidities in real-world settings. We present a subanalysis of the efficacy and safety of nebivolol across age and sex in the BENEFIT-KOREA cohort.

METHODS

Adult South Korean patients with essential hypertension participated in the prospective, single-arm, open, observational BENEFIT-KOREA study; 3011 patients received nebivolol as monotherapy or add-on therapy. Changes in systolic blood pressure (SBP) and diastolic blood pressure (DBP), and pulse rate at 12 and 24 weeks were evaluated. Participants were divided into three age groups-young males and females: < 50 years; middle-aged males and females: ≥50 years to < 70 years; and older males and females: ≥70 years.

RESULTS

The mean age of study participants was 63.5 ± 12.9 years; majority were between 50 and 69 years of age and 40.4% were females. A significant decrease was observed in mean SBP, DBP, and pulse rate from baseline at 12 and 24 weeks in males and females across all age groups analyzed (all P < 0.001 vs. baseline), with no significant difference in mean reduction in SBP and DBP from baseline between sex within the age groups. Majority of reported adverse events were mild. The incidence of adverse events was lower in young participants versus middle-aged and older participants.

CONCLUSIONS

Our subanalysis from the real-world BENEFIT-KOREA study in Asian patients with essential hypertension demonstrated the efficacy and safety of once-daily nebivolol across age groups with no between-sex differences.

TRIAL REGISTRATION

Name of the registry: clinicaltrials.gov.

TRIAL REGISTRATION NUMBER

NCT03847350 . Date of registration: February 20, 2019 retrospectively registered.

Excessive Orthostatic Changes in Blood Pressure Are Associated With Incident Heart Failure in Older Men: A Prospective Analysis From the BRHS

[Figure: see text].

Neuroinflammation-Associated Alterations of the Brain as Potential Neural Biomarkers in Anxiety Disorders

Stress-induced changes in the immune system, which lead to neuroinflammation and consequent brain alterations, have been suggested as possible neurobiological substrates of anxiety disorders, with previous literature predominantly focusing on panic disorder, agoraphobia, and generalized anxiety disorder, among the anxiety disorders. Anxiety disorders have frequently been associated with chronic stress, with chronically stressful situations being reported to precipitate the onset of anxiety disorders. Also, chronic stress has been reported to lead to hypothalamic–pituitary–adrenal axis and autonomic nervous system disruption, which may in turn induce systemic proinflammatory conditions. Preliminary evidence suggests anxiety disorders are also associated with increased inflammation. Systemic inflammation can access the brain, and enhance pro-inflammatory cytokine levels that have been shown to precipitate direct and indirect neurotoxic effects. Prefrontal and limbic structures are widely reported to be influenced by neuroinflammatory conditions. In concordance with these findings, various imaging studies on panic disorder, agoraphobia, and generalized anxiety disorder have reported alterations in structure, function, and connectivity of prefrontal and limbic structures. Further research is needed on the use of inflammatory markers and brain imaging in the early diagnosis of anxiety disorders, along with the possible efficacy of anti-inflammatory interventions on the prevention and treatment of anxiety disorders.

Superoxide anions modulate the effects of alarin in the paraventricular nucleus on sympathetic activity and blood pressure in spontaneously hypertensive rats

Neuropeptides are involved in the regulation of the sympathetic activity and blood pressure in the paraventricular nucleus of the hypothalamus (PVN). The present study was designed to determine how alarin modulates the renal sympathetic nerve activity (RSNA), arterial blood pressure and mean arterial pressure (MAP) in the PVN, and whether superoxide anions regulate the effects of alarin in the PVN of spontaneously hypertensive rats (SHRs). Acute experiment was carried out with male Wistar-Kyoto rats (WKY) and SHRs under anesthesia. RSNA, systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP were measured. Alarin microinjection into the PVN increased RSNA (7.8 ± 1.8 vs. 14.8 ± 2.3%), SBP (5.9 ± 1.4 vs. 12.1 ± 1.6 mmHg), DBP (5.1 ± 0.8 vs. 10.0 ± 1.1 mmHg), and MAP (5.4 ± 1.2 vs. 10.7 ± 1.3 mmHg) in WKY rats and SHRs,. Alarin antagonist ala6-25 Cys decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin. The alarin level was increased in the PVN of SHR compared to WKY rats. (29.7 ± 4.9 vs. 14.6 ± 2.4 pg/mg protein). PVN microinjection of superoxide anion scavengers tempol and tiron, or NAD(P)H oxidase inhibitor apocynin, decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin, but the superoxide dismutase inhibitor diethyldithiocarbamic acid potentiated the effects of alarin. Superoxide anions and NAD(P)H oxidase activity levels in the PVN were increased by alarin, but decreased by alarin antagonist ala6-25 Cys. The alarin-induced increases in superoxide anions and NAD(P)H oxidase activity levels were abolished by pre-treatment with ala6-25 Cys. The results suggest that alarin in the PVN increases sympathetic outflow and blood pressure. The enhanced activity of endogenous alarin in the PVN contributes to sympathetic activation in hypertension, and the superoxide anion is involved in these alarin-mediated processes in the PVN.

TRPV1 (Transient Receptor Potential Vanilloid 1) Cardiac Spinal Afferents Contribute to Hypertension in Spontaneous Hypertensive Rat

Hypertension is associated with increased sympathetic activity. A component of this sympathoexcitation may be driven by increased signaling from sensory endings from the heart to the autonomic control areas in the brain. This pathway mediates the so-called cardiac sympathetic afferent reflex, which is also activated by coronary ischemia or other nociceptive stimuli in the heart. The cardiac sympathetic afferent reflex has been shown to be enhanced in the heart failure state and in renal hypertension. However, little is known about its role in the development or progression of hypertension or the phenotype of the sensory endings involved. To investigate this, we used the selective afferent neurotoxin, resiniferatoxin (RTX) to chronically abolish the cardiac sympathetic afferent reflex in 2 models of hypertension; the spontaneous hypertensive rats (SHRs) and AngII (angiotensin II) infusion (240 ng/kg per min). Blood pressure (BP) was measured in conscious animals for 2 to 8 weeks post-RTX. Epidural application of RTX to the T1-T4 spinal segments prevented the further BP increase in 8-week-old SHR and lowered BP in 16-week-old SHR. RTX did not affect BP in Wistar-Kyoto normotensive rats nor in AngII-infused rats. Epicardial application of RTX (50 µg/mL) in 4-week-old SHR prevented the BP increase whereas this treatment does not lower BP in 16-week-old SHR. When RTX was administered into the L2-L5 spinal segments of 16-week-old SHR, no change in BP was observed. These findings indicate that signaling via thoracic afferent nerve fibers may contribute to the hypertension phenotype in the SHR but not in the Ang II infusion model of hypertension.

Superoxide anions mediate the effects of angiotensin (1-7) analog, alamandine, on blood pressure and sympathetic activity in the paraventricular nucleus

Microinjection of alamandine into the hypothalamic paraventricular nucleus (PVN) increased blood pressure and enhanced sympathetic activity. The aim of this study was to determine if superoxide anions modulate alamandine's effects in the PVN. Mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were recorded in anaesthetized normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Microinjection of alamandine into the PVN increased MAP and RSNA in both WKY rats and SHRs, although to a greater extent in SHRs. These effects were blocked by pretreatment with an alamandine receptor (MrgD) antagonist D-Pro⁷-Ang-(1-7). Pretreatment with superoxide anion scavengers, tempol and tiron, and NADPH oxidase inhibitor apocynin (APO), also blocked the effects of alamandine on MAP and RSNA. In addition, pretreatment in the PVN with a superoxide dismutase (SOD) inhibitor diethyldithiocarbamic acid (DETC) potentiated the increases of MAP and RSNA induced by alamandine administration, with a greater response observed in SHRs. Superoxide anions and NADPH oxidase levels in the PVN were higher in SHRs than that in WKY rats. Alamandine treatment increased the levels of superoxide anions and NADPH oxidase in WKY and SHRs, however, with greater effect in SHRs. These alamandine-induced increases were inhibited by D-Pro⁷-Ang-(1-7) pretreatment in the PVN of both rats. These results demonstrate that superoxide anions in the PVN modulate alamandine-induced increases in blood pressure and sympathetic activity in both normotensive and hypertensive rats. Alamandine increases NADPH oxidase activity to induce superoxide anion production, which is mediated by the alamandine receptor.

The Role of the Autonomic Nervous System in the Regulation of Aortic Stiffness

The autonomic nervous system is important in regulating blood pressure, but whether it regulates aortic stiffness is more contentious. We conducted 3 studies in young, healthy individuals to address this important question. Study 1 was a cross-sectional study of 347 subjects with detailed measurements of hemodynamics and heart rate variability. In study 2, 9 subjects were given a bolus of intravenous nicotinic ganglion blocker, pentolinium, or saline in a random order and hemodynamics and heart rate variability were assessed before and after. In study 3, changes in hemodynamics and heart rate variability were assessed during stimulation of the sympathetic nervous system with the use of isometric handgrip exercise in 12 subjects. Study 1: aortic pulse wave velocity (P=0.003) was lowest in the subjects with the highest parasympathetic activity, but after adjusting for mean arterial pressure, the effect was abolished (P=0.3). Study 2: after pentolinium, sympathetic and parasympathetic activity fell (P=0.001 for both), mean arterial pressure, and heart rate increased (P=0.004 and P=0.04, respectively), but there was no change in pulse wave velocity in comparison to placebo (P=0.1). Study 3: during handgrip exercise, sympathetic activity (P=0.003), mean arterial pressure (P<0.0001), and aortic pulse wave velocity increased (P=0.013). However, pulse wave velocity adjusted for mean arterial pressure did not change (P=0.1). The main finding of these studies is that in young healthy subjects, the autonomic nervous system does not have a pressure-independent role in the regulation of aortic stiffness. However, these findings may not apply to patients with increased sympathetic tone or hypertension.

Renal denervation for the management of resistant hypertension

Renal sympathetic denervation (RSD) as a therapy for patients with resistant hypertension has attracted great interest. The majority of studies in this field have demonstrated impressive reductions in blood pressure (BP). However, these trials were not randomized or sham-controlled and hence, the findings may have been overinflated due to trial biases. SYMPLICITY HTN-3 was the first randomized controlled trial to use a blinded sham-control and ambulatory BP monitoring. A surprise to many was that this study was neutral. Possible reasons for this neutrality include the fact that RSD may not be effective at lowering BP in man, RSD was not performed adequately due to limited operator experience, patients’ adherence with their anti-hypertensive drugs may have changed during the trial period, and perhaps the intervention only works in certain subgroups that are yet to be identified. Future studies seeking to demonstrate efficacy of RSD should be designed as randomized blinded sham-controlled trials. The efficacy of RSD is in doubt, but many feel that its safety has been established through the thousands of patients in whom the procedure has been performed. Over 90% of these data, however, are for the Symplicity™ system and rarely extend beyond 12 months of follow-up. Long-term safety cannot be assumed with RSD and nor should it be assumed that if one catheter system is safe then all are. We hope that in the near future, with the benefit of well-designed clinical trials, the role of renal denervation in the management of hypertension will be established.

Cardiac sympathetic afferent reflex and its implications for sympathetic activation in chronic heart failure and hypertension

Persistent excessive sympathetic activation greatly contributes to the pathogenesis of chronic heart failure (CHF) and hypertension. Cardiac sympathetic afferent reflex (CSAR) is a sympathoexcitatory reflex with positive feedback characteristics. Humoral factors such as bradykinin, adenosine and reactive oxygen species produced in myocardium due to myocardial ischaemia stimulate cardiac sympathetic afferents and thereby reflexly increase sympathetic activity and blood pressure. The CSAR is enhanced in myocardial ischaemia, CHF and hypertension. The enhanced CSAR at least partially contributes to the sympathetic activation and pathogenesis of these diseases. Nucleus of the solitary tract (NTS), hypothalamic paraventricular nucleus (PVN) and rostral ventrolateral medulla are the most important central sites involved in the modulation and integration of the CSAR. Angiotensin II, AT1 receptors and NAD(P)H oxidase-derived superoxide anions pathway in the PVN are mainly responsible for the enhanced CSAR in CHF and hypertension. Central angiotensin-(1-7), nitric oxide, endothelin, intermedin, hydrogen peroxide and several other signal molecules are involved in regulating CSAR. Blockade of the CSAR shows beneficial effects in CHF and hypertension. This review focuses on the anatomical and physiological basis of the CSAR, the interaction of CSAR with baroreflex and chemoreflex, and the role of enhanced CSAR in the pathogenesis of CHF and hypertension.

Cardiac sympathetic afferent reflex response to intermedin microinjection into paraventricular nucleus is mediated by nitric oxide and γ-amino butyric acid in hypertensive rats

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) and involves in the regulation of cardiovascular function in both peripheral tissues and central nervous system (CNS). Paraventricular nucleus (PVN) of hypothalamus is an important site in the control of cardiac sympathetic afferent reflex (CSAR) which participates in sympathetic over-excitation of hypertension. The aim of this study is to investigate whether IMD in the PVN is involved in the inhibition of CSAR and its related mechanism in hypertension. Rats were subjected to two-kidney one-clip (2K1C) surgery to induce renovascular hypertension or sham-operation (Sham). Acute experiments were carried out four weeks later under anesthesia. The CSAR was evaluated with the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to the epicardial application of capsaicin. The RSNA and MAP were recorded in sinoaortic-denervated, cervical-vagotomized and anesthetized rats. Bilateral PVN microinjection of IMD (25 pmol) caused greater decrease in the CSAR in 2K1C rats than in Sham rats, which was prevented by pretreatment with adrenomedullin (AM) receptor antagonist AM22-52, non-selective nitric oxide (NO) synthase (NOS) inhibitor l-NAME or γ-amino butyric acid (GABA)B receptor blocker CGP-35348. PVN pretreatment with CGRP receptor antagonist CGRP8-37 or GABAA receptor blocker gabazine had no significant effect on the CSAR response to IMD. AM22-52, l-NAME and CGP-35348 in the PVN could increase CSAR in Sham and 2K1C rats. These data indicate that IMD in the PVN inhibits CSAR via AM receptor, and both NO and GABA in the PVN involve in the effect of IMD on CSAR in Sham and renovascular hypertensive rats.

Spinal anesthesia with hyperbaric bupivacaine: a comparison of hypertensive and normotensive patients

Background

Hypotension is the most common problem with spinal anesthesia. This prospective study aimed to compare normotensive and hypertensive patients with respect to the hemodynamic effects of spinal anesthesia performed with hyperbaric bupivacaine.

Material/Methods

Sixty patients who were scheduled to undergo various elective operations under spinal anesthesia were included into the study. The patients were separated into 2 groups: hypertensive patients constituted Group H (n=30) and normotensive patients constituted Group N (n=30). After fluid loading, spinal anesthesia was performed with 3.5 ml 0.5% hyperbaric bupivacaine. Demographic characteristics and incidence of hypotension and bradycardia were compared. Systolic (SBP), diastolic (DBP), and mean blood pressures (MBP) and heart rate (HR) were also compared before and after spinal anesthesia.

Results

There was no significant difference between the groups with respect to demographic characteristics, maximal height of sensory block, incidences of hypotension and bradycardia, and the amount of fluids infused (p>0.05). In the hypertensive patient group, the SBP, DBP, and MBP values were significantly higher than in the normotensive patient group at all measurement times (p<0.05). Comparison within the groups did not reveal any significant differences in either group compared to the basal values (p>0.05). There were no significant differences in HR between or within groups (p>0.05).

Conclusions

There was no significant difference between normotensive and hypertensive patients in the incidences of hypotension caused by spinal anesthesia with 0.5% hyperbaric bupivacaine.

Lisinopril Indifferently Improves Heart Rate Variability During Day and Night Periods in Spontaneously Hypertensive Rats

The aim of this work was to investigate the effect of 10 weeks of lisinopril treatment to spontaneously hypertensive rats (SHRs) on day/night variations of blood pressure, heart rate and autonomic cardio-regulation parameters. Male SHR with surgically implanted radio-telemetry implant that provided direct measurements of arterial pressure and electrocardiogram wave were used. Animals were allocated to two groups (n=5 each). The first group was treated with lisinopril (20 mg/kg by gavage) daily for 10 weeks (treated group); whereas the second was gavaged daily with tap water (untreated group). Arterial blood pressure, ECG and other telemetry parameters were recorded at the start and at the end of 10-week treatment. Collected data were analyzed using specialized software and were statistically tested. In addition to the expected lowering of blood pressure, spectral analysis of R-R intervals revealed that lisinopril treatment for 10 weeks significantly caused 2-3 fold increase in heart rate variability (HRV) during both active and inactive periods. However, R-R interval durations demonstrated variable distribution patterns during those periods. The cause of observed distribution pattern of R-R intervals during active and inactive periods may be of significance to better understand HRV changes and warrants further investigations.

Angiotensin-(1-7) in the rostral ventrolateral medulla modulates enhanced cardiac sympathetic afferent reflex and sympathetic activation in renovascular hypertensive rats

Enhancement of the cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic excitation in hypertension. The aim of the present study was to determine whether angiotensin (Ang)-(1-7) in the rostral ventrolateral medulla (RVLM) modulated the enhanced CSAR and sympathetic activation, and the signaling pathways that mediated these effects in the 2-kidney, 1-clip renovascular hypertension model. Cardiac sympathetic afferent reflex was evaluated using renal sympathetic nerve activity and mean arterial pressure responses to epicardial capsaicin application in anesthetized sinoaortic-denervated and cervical-vagotomized rats. RVLM microinjection of Ang-(1-7) induced greater increases in renal sympathetic nerve activity and mean arterial pressure, and greater enhancement in CSAR in 2-kidney, 1-clip rats than in sham-operated rats, which was blocked by Mas receptor antagonist A-779, adenylyl cyclase inhibitors SQ22536 and MDL-12,330A, and protein kinase A inhibitors rp-adenosine-3',5'-cyclic monophosphorothionate and H-89. Mas receptor expression in RVLM was increased in 2-kidney, 1-clip rats. Treatment with A-779, SQ22536, MDL-12,330A, rp-adenosine-3',5'-cyclic monophosphorothionate, or H-89 in RVLM inhibited CSAR and decreased renal sympathetic nerve activity and mean arterial pressure in 2-kidney, 1-clip rats, whereas cAMP analogue dibutyryl-cAMP had the opposite effects. Ang-(1-7) in RVLM increased, whereas A-779 decreased the cAMP level and the epicardial capsaicin application-induced increases in the cAMP level in RVLM. These results indicate that Ang-(1-7) in the RVLM enhances the CSAR and increases the sympathetic outflow and blood pressure via Mas receptor activation. The increased endogenous Ang-(1-7) and Mas receptor activity in RVLM contributes to the enhanced CSAR and sympathetic activation in renovascular hypertension, and the cAMP-protein kinase A pathway is involved in these Ang-(1-7)-mediated effects in the RVLM.

Angiotensin II and angiotensin-(1-7) in paraventricular nucleus modulate cardiac sympathetic afferent reflex in renovascular hypertensive rats

BACKGROUND

The enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation that contributes to the pathogenesis and progression of hypertension. Activation of AT(1) receptors by angiotension (Ang) II in the paraventricular nucleus (PVN) augments the enhanced CSAR and sympathetic outflow in hypertension. The present study is designed to determine whether Ang-(1-7) in PVN plays the similar roles as Ang II and the interaction between Ang-(1-7) and Ang II on CSAR in renovascular hypertension.

METHODOLOGY/PRINCIPAL FINDINGS

The two-kidney, one-clip (2K1C) method was used to induce renovascular hypertension. The CSAR was evaluated by the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to epicardial application of capsaicin in sinoaortic-denervated and cervical-vagotomized rats with urethane and α-chloralose anesthesia. Either Ang II or Ang-(1-7) in PVN caused greater increases in RSNA and MAP, and enhancement in CSAR in 2K1C rats than in sham-operated (Sham) rats. Mas receptor antagonist A-779 and AT(1) receptor antagonist losartan induced opposite effects to Ang-(1-7) or Ang II respectively in 2K1C rats, but losartan had no effects in Sham rats. Losartan but not the A-779 abolished the effects of Ang II, while A-779 but not the losartan blocked the effects of Ang-(1-7). PVN pretreatment with Ang-(1-7) dose-dependently augmented the RSNA, MAP, and CSAR responses to the Ang II in 2K1C rats. Ang II level, AT(1) receptor and Mas receptor protein expression in PVN increased in 2K1C rats compared with Sham rats but Ang-(1-7) level did not.

CONCLUSIONS

Ang-(1-7) in PVN is as effective as Ang II in enhancing the CSAR and increasing sympathetic outflow and both endogenous Ang-(1-7) and Ang II in PVN contribute to the enhanced CSAR and sympathetic outflow in renovascular hypertension. Ang-(1-7) in PVN potentiates the effects of Ang II in renovascular hypertension.

Angiotensin-(1-7) in paraventricular nucleus modulates sympathetic activity and cardiac sympathetic afferent reflex in renovascular hypertensive rats

Background

Excessive sympathetic activity contributes to the pathogenesis and progression of hypertension. Enhanced cardiac sympathetic afferent reflex (CSAR) is involved in sympathetic activation. This study was designed to determine the roles of angiotensin (Ang)-(1–7) in paraventricular nucleus (PVN) in modulating sympathetic activity and CSAR and its signal pathway in renovascular hypertension.

Methodology/Principal Findings

Renovascular hypertension was induced with two-kidney, one-clip method. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in sinoaortic-denervated and cervical-vagotomized rats with anesthesia. CSAR was evaluated with the RSNA and MAP responses to epicardial application of capsaicin. PVN microinjection of Ang-(1–7) and cAMP analogue db-cAMP caused greater increases in RSNA and MAP, and enhancement in CSAR in hypertensive rats than in sham-operated rats, while Mas receptor antagonist A-779 produced opposite effects. There was no significant difference in the angiotensin-converting enzyme 2 (ACE2) activity and Ang-(1–7) level in the PVN between sham-operated rats and hypertensive rats, but the Mas receptor protein expression in the PVN was increased in hypertensive rats. The effects of Ang-(1–7) were abolished by A-779, adenylyl cyclase inhibitor SQ22536 or protein kinase A (PKA) inhibitor Rp-cAMP. SQ22536 or Rp-cAMP reduced RSNA and MAP in hypertensive rats, and attenuated the CSAR in both sham-operated and hypertensive rats.

Conclusions

Ang-(1–7) in the PVN increases RSNA and MAP and enhances the CSAR, which is mediated by Mas receptors. Endogenous Ang-(1–7) and Mas receptors contribute to the enhanced sympathetic outflow and CSAR in renovascular hypertension. A cAMP-PKA pathway is involved in the effects of Ang-(1–7) in the PVN.

Inflammatory cytokines in paraventricular nucleus modulate sympathetic activity and cardiac sympathetic afferent reflex in rats

AIM

This study was to determine the roles of inflammatory cytokines in paraventricular nucleus (PVN) in modulating sympathetic activity, blood pressure and cardiac sympathetic afferent reflex (CSAR).

METHODS

Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in anaesthetized rats with bilateral sinoaortic denervation and vagotomy. The CSAR was evaluated by the RSNA response to epicardial application of bradykinin (BK). The levels of inflammatory cytokines were measured with ELISA.

RESULTS

The PVN microinjection of pro-inflammatory cytokines (PIC), tumour necrosis factor (TNF)-α or interleukin (IL)-1β, increased the baseline MAP and RSNA, and enhanced the CSAR. Anti-inflammatory cytokines (AIC), IL-4 or IL-13, in the PVN only increased the baseline MAP. In the rats pretreated with TNF-α or IL-1β but not in the rats pretreated with IL-4 or IL-13, sub-response dose of angiotensin II caused significant increases in the MAP and RSNA and enhancement in the CSAR. AT(1) receptor antagonist losartan in the PVN attenuated the effects of angiotensin II, TNF-α and IL-1β, but not the effects of IL-4 and IL-13. Stimulation of cardiac sympathetic afferents with epicardial application of BK increased the levels of TNF-α, IL-1β but not IL-4 in the PVN.

CONCLUSION

TNF-α or IL-1β in the PVN increases blood pressure and sympathetic outflow and enhances the CSAR, which is partially dependent on the AT(1) receptors, while IL-4 or IL-13 in the PVN only increases blood pressure. There is a synergetic effect of Ang II with TNF-α or IL-1β on blood pressure, sympathetic activity and CSAR.

Endogenous hydrogen peroxide in paraventricular nucleus mediates sympathetic activation and enhanced cardiac sympathetic afferent reflex in renovascular hypertensive rats

An enhancement of the cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation in renovascular hypertension. Angiotensin II in the paraventricular nucleus (PVN) augments the CSAR and increases sympathetic outflow and blood pressure. The present study aimed to determine whether endogenous hydrogen peroxide in the PVN mediated the enhanced CSAR, sympathetic activity and the effects of angiotensin II in the PVN in renovascular hypertension induced by the two-kidney, one-clip method (2K1C) in rats. At the end of the fourth week, the rats underwent sino-aortic and vagal denervation under general anaesthesia with urethane and α-chloralose. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. The CSAR was evaluated by the RSNA response to epicardial application of bradykinin. Microinjection of polyethylene glycol-catalase (PEG-CAT), an analogue of endogenous catalase, into the PVN decreased the RSNA and MAP and abolished the CSAR in both sham-operated and 2K1C rats. Microinjection into the PVN of the catalase inhibitor, aminotriazole, increased the RSNA and MAP and enhanced the CSAR. The effects of PEG-CAT or aminotriazole were greater in 2K1C rats than in sham-operated animals. The effects of angiotensin II in the PVN were abolished by pretreatment with PEG-CAT in both sham-operated and 2K1C rats; however, aminotriazole failed to potentiate the effects of angiotensin II. The catalase activity was decreased but the H(2)O(2) levels were increased in the PVN of 2K1C rats. These results indicate that endogenous H(2)O(2) in the PVN not only mediates the enhanced sympathetic activity and CSAR, but also the effects of angiotensin II in the PVN in renovascular hypertensive rats.

c-Src in paraventricular nucleus modulates sympathetic activity and cardiac sympathetic afferent reflex in renovascular hypertensive rats

Enhanced cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation in renovascular hypertension. The study was to determine whether c-Src in paraventricular nucleus (PVN) is involved in the enhanced CSAR and sympathetic activation in hypertensive rats induced by two-kidney one-clip (2K1C). At the end of the fourth week after 2K1C surgery, renal sympathetic nerve activity (RSNA) was recorded in anesthetized rats with baroreceptor denervation and vagotomy. The CSAR was evaluated by the RSNA response to epicardial application of capsaicin. In the PVN, c-Src activity was higher in 2K1C rats than sham-operated (Sham) rats while c-Src expression was not. Epicardial application of capsaicin or PVN microinjection of angiotensin II (Ang II) increased c-Src activity more in 2K1C than Sham rats. PVN microinjection of selective Src family kinase inhibitor 4-Amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazol [3,4-D] pyrimidine (PP2) or 2,3-Dihydro-N,N-dimethyl-2-oxo-3-[(4,5,6,7-tetrahydro-1 H-indol-2-yl)methylene]-1 H-indole-5-sulfonamide (SU6656) abolished the CSAR and decreased RSNA more in 2K1C than Sham rats. The Ang II-induced RSNA and CSAR enhancement was abolished by PP2 or SU6656 pretreatment in 2K1C and Sham rats. NAD(P)H oxidase activity and superoxide anion level in PVN were higher in 2K1C rats, which was attenuated by PP2 but increased by epicardial application of capsaicin or PVN microinjection of Ang II. The effects of capsaicin or Ang II were abolished by PP2. These results indicate that c-Src in the PVN is involved in the enhanced CSAR and sympathetic activation in renovascular hypertension, and mediates the excitatory effects of Ang II in the PVN on the CSAR and sympathetic activity via NAD(P)H oxidase-derived generation of superoxide anions.

In utero beta 2 adrenergic agonist exposure and adverse neurophysiologic and behavioral outcomes

Beta 2 adrenergic receptor overstimulation during critical periods of prenatal development can induce a permanent shift in the balance of sympathetic-to-parasympathetic tone. This is a biologically plausible mechanism whereby beta 2 adrenergic agonists can induce functional and behavioral teratogenesis, which explains their association with increases in autism spectrum disorders, psychiatric disorders, poor cognitive, motor function and school performance, and changes in blood pressure in the offspring. The use of beta 2 adrenergic agonists should be limited to proven indications when alternate drugs are ineffective or unavailable; the risks of untreated disease to the mother and fetus are greater than the risk of the beta 2 adrenergic agonist.