Aldosterone Contributes to Sympathoexcitation in Renovascular Hypertension

Genetic Deletion of AT1a Receptor or Na+/H+ Exchanger 3 Selectively in the Proximal Tubules of the Kidney Attenuates Two-Kidney, One-Clip Goldblatt Hypertension in Mice

The roles of angiotensin II (Ang II) AT1 (AT1a) receptors and its downstream target Na+/H+ exchanger 3 (NHE3) in the proximal tubules in the development of two-kidney, 1-clip (2K1C) Goldblatt hypertension have not been investigated previously. The present study tested the hypothesis that deletion of the AT1a receptor or NHE3 selectively in the proximal tubules of the kidney attenuates the development of 2K1C hypertension using novel mouse models with proximal tubule-specific deletion of AT1a receptors or NHE3. 2K1C Goldblatt hypertension was induced by placing a silver clip (0.12 mm) on the left renal artery for 4 weeks in adult male wild-type (WT), global Agtr1a−/−, proximal tubule (PT)-specific PT-Agtr1a−/− or PT-Nhe3−/− mice, respectively. As expected, telemetry blood pressure increased in a time-dependent manner in WT mice, reaching a maximal response by Week 3 (p < 0.01). 2K1C hypertension in WT mice was associated with increases in renin expression in the clipped kidney and decreases in the nonclipped kidney (p < 0.05). Plasma and kidney Ang II were significantly increased in WT mice with 2K1C hypertension (p < 0.05). Tubulointerstitial fibrotic responses were significantly increased in the clipped kidney (p < 0.01). Whole-body deletion of AT1a receptors completely blocked the development of 2K1C hypertension in Agtr1a−/− mice (p < 0.01 vs. WT). Likewise, proximal tubule-specific deletion of Agtr1a in PT-Agtr1a−/− mice or NHE3 in PT-Nhe3−/− mice also blocked the development of 2K1C hypertension (p < 0.01 vs. WT). Taken together, the present study provides new evidence for a critical role of proximal tubule Ang II/AT1 (AT1a)/NHE3 axis in the development of 2K1C Goldblatt hypertension.

Differential effects of estrogen receptors in the rostral ventrolateral medulla in Goldblatt hypertension

Previous studies have shown that 17β-estradiol plays a cardioprotective role in the central nervous system (CNS) of male rats. The aim of the present study was to determine the influence of 17β-estradiol on sympathetic vasomotor activity and blood pressure in a renovascular hypertensive Goldblatt two-kidney one-clip (2K-1C) male rat model. We also determined the influence of angiotensin II AT1 receptor on the expression of estrogen receptors (ERα, ERβ, and G protein-coupled ER (GPER)) in the rostral ventrolateral medulla (RVLM) of Goldblatt rats. Experiments were performed in Goldblatt and age-matched control rats six weeks after clipping of renal artery to induce hypertension. Microinjection of 17β-estradiol into the RVLM led to a greater reduction in mean arterial pressure and renal sympathetic nerve activity in controls than in 2K-1C rats. Microinjection of the GPER agonist G-1 into the RVLM led to a significantly greater increase in mean arterial pressure and renal sympathetic nerve activity in 2K-1C rats. Expression levels of estrogen receptors GPER and ERα, but not ERβ, were significantly higher in the RVLM of 2K-1C rats than in that of the control rats. Chronic treatment with losartan significantly reduced the expression levels of estrogen receptors in the RVLM of 2K-1C rats. Taken altogether, the data suggest that the imbalance of actions between ERα and GPER, particularly with the predominance of GPER in the RVLM, contributes to sympathetic overactivation in male rats with Goldblatt hypertension. AT1-Angiotensin II receptor in the RVLM upregulated estrogen receptor expression in male Goldblatt rats.

Mechanisms of nonalcoholic steatohepatitis-associated cardiomyopathy: key roles for liver-heart crosstalk

PURPOSE OF REVIEW

Nonalcoholic steatohepatitis (NASH) is a multisystem disease that affects not only the liver but also heart, pancreas, and kidney. We currently lack a comprehensive understanding of mechanisms responsible for the development of NASH-associated cardiomyopathy or the influence of sex on pathophysiology. There is a critical need to address these gaps in knowledge in order to accelerate translation of knowledge into clinical practice.

RECENT FINDINGS

NASH and cardiovascular disease share common risk factors such as chronic inflammation, hyperlipidemia, and insulin resistance. Early cardiac dysfunction in NASH that is independent of obesity or other cardiometabolic risk factors suggests roles for liver-heart crosstalk in disease pathogenesis. Inflammation is a driving force in the pathogenesis of NASH, and it is likely that 'spill over' of NASH inflammation contributes to the development of cardiomyopathy. However, molecular and cellular mechanisms that mediate NASH-associated cardiomyopathy remain unclear because of inherent limitations of experimental models. Even so, recent studies implicate inflammatory, metabolic, and physiologic mechanisms that enhance our understanding of NASH-associated cardiomyopathy and the role of liver-heart crosstalk.

SUMMARY

An innovative, detailed, and mechanistic understanding of NASH-associated cardiomyopathy is relevant to public health and will be fundamental for the comprehensive care of these patients.

Role of ranolazine in heart failure: From cellular to clinic perspective

Ranolazine was approved by the US Food and Drug Administration as an antianginal drug in 2006, and has been used since in certain groups of patients with stable angina. The therapeutic action of ranolazine was initially attributed to inhibitory effects on fatty acids metabolism. As investigations went on, however, it developed that the main beneficial effects of ranolazine arise from its action on the late sodium current in the heart. Since late sodium currents were discovered to be involved in various heart pathologies such as ischemia, arrhythmias, systolic and diastolic dysfunctions, and all these conditions are associated with heart failure, ranolazine has in some way been tested either directly or indirectly on heart failure in numerous experimental and clinical studies. As the heart continuously remodels following any sort of severe injury, the inhibition by ranolazine of the underlying mechanisms of cardiac remodeling including ion disturbances, oxidative stress, inflammation, apoptosis, fibrosis, metabolic dysregulation, and neurohormonal impairment are discussed, along with unresolved issues. A projection of pathologies targeted by ranolazine from cellular level to clinical is provided in this review.

ANG II and Aldosterone Acting Centrally Participate in the Enhanced Sodium Intake in Water-Deprived Renovascular Hypertensive Rats

Renovascular hypertension is a type of secondary hypertension caused by renal artery stenosis, leading to an increase in the renin–angiotensin–aldosterone system (RAAS). Two-kidney, 1-clip (2K1C) is a model of renovascular hypertension in which rats have an increased sodium intake induced by water deprivation (WD), a common situation found in the nature. In addition, a high-sodium diet in 2K1C rats induces glomerular lesion. Therefore, the purpose of this study was to investigate whether angiotensin II (ANG II) and/or aldosterone participates in the increased sodium intake in 2K1C rats under WD. In addition, we also verified if central AT1 and mineralocorticoid receptor blockade would change the high levels of arterial pressure in water-replete (WR) and WD 2K1C rats, because blood pressure changes can facilitate or inhibit water and sodium intake. Finally, possible central areas activated during WD or WD followed by partial rehydration (PR) in 2K1C rats were also investigated. Male Holtzman rats (150–180 g) received a silver clip around the left renal artery to induce renovascular hypertension. Six weeks after renal surgery, a stainless-steel cannula was implanted in the lateral ventricle, followed by 5–7 days of recovery before starting tests. Losartan (AT1 receptor antagonist) injected intracerebroventricularly attenuated water intake during the thirst test. Either icv losartan or RU28318 (mineralocorticoid receptor antagonist) reduced 0.3 M NaCl intake, whereas the combination of losartan and RU28318 icv totally blocked 0.3 M NaCl intake induced by WD in 2K1C rats. Losartan and RU28318 icv did not change hypertension levels of normohydrated 2K1C rats, but reduced the increase in mean arterial pressure (MAP) produced by WD. c-Fos expression increased in the lamina terminalis and in the NTS in WD condition, and increased even more after WD-PR. These results suggest the participation of ANG II and aldosterone acting centrally in the enhanced sodium intake in WD 2K1C rats, and not in the maintenance of hypertension in satiated and fluid-replete 2K1C rats.

Effects of renal denervation on cardiovascular, metabolic and renal functions in streptozotocin-induced diabetic rats

Diabetes promotes renal sympathetic hyperactivity, autonomic imbalance, and cardiovascular and renal dysfunction. Bilateral renal denervation (BRD) has emerged as a treatment for diabetes; however, the mechanisms that underlie the beneficial effects of BRD are unknown.

AIMS

The present study evaluated the effects of BRD on autonomic, cardiovascular, metabolic, and renal function in streptozotocin-diabetic rats.

MAIN METHODS

Wistar rats were separated into three experimental groups: control (CTR), diabetic (DM), and diabetic that underwent BRD (DM BRD). BRD was performed two weeks after STZ-diabetes induction, the experiments were performed four weeks after DM induction. This study evaluated sympathetic vasomotor nerve activity in different territories (renal, lumbar and splanchnic), arterial baroreceptor reflex, metabolic and renal function.

KEY FINDINGS

BRD significantly reduced glycemia, glycosuria, albuminuria, and SGLT2 gene expression in the kidney in DM rats. Renal sympathetic nerve activity (rSNA) was significantly increased and splanchnic sympathetic nerve activity (sSNA) was significantly decreased in DM rats, without changes in lumbar sympathetic nerve activity (lSNA). BRD was able to normalize sSNA and significantly increase lSNA in DM rats compared to control rats. Additionally, cardiac baroreceptor sensitivity was impaired in DM rats, and BRD significantly improved baroreflex sensitivity.

SIGNIFICANCE

Our data suggest that renal nerves play an important role in autonomic, cardiovascular, and renal dysfunction in STZ-DM rats. Thus, sympathetic renal hyperactivity should be considered a possible therapeutic target in diabetic patients.

Effects of spironolactone on extrasystoles and heart rate variability in haemodialysis patients: a randomised crossover trial

BACKGROUND

Spironolactone treatment reduces mortality in haemodialysis (HD) patients. The objective of this study was to evaluate if spironolactone affects cardiac electric activity in this population.

METHODS

Participants were randomised to start with spironolactone 50 mg daily or observation (12 weeks) with subsequent washout (6 weeks) and crossover to the other intervention (12 weeks). Long-term electrocardiograms were recorded and assessed with blinding to treatment. The primary outcome was premature ventricular complexes (PVC), and secondary outcomes were atrial premature contractions (APC) and heart rate variability (HRV).

RESULTS

Thirty participants were recruited, and data for 16 participants were included in the analysis. Treatment was associated with an increase in PVCs by 9.7 [95% confidence interval (CI): 1.5 to 18] h^-1. HRV time-domain variables increased during treatment, the standard deviation of all beat-to-beat intervals by 18 (95% CI: 3.3 to 32) milliseconds (ms) and the standard deviation of the averages of beat-to-beat intervals in all 5-min segments of the entire recording by 16 (95% CI: 1.5 to 30) ms. There were no significant differences in other variables.

CONCLUSION

Spironolactone treatment increases PVCs in HD, indicating a possible proarrhythmic effect. However, improved cardiac autonomic function, as indicated by an increased HRV, may contribute to the survival benefit from spironolactone treatment in HD patients.

Aliskiren Reduces the Adrenal Zona Glomerulosa Apoptosis and Autophagy in Wistar Rats with 2K1C Hypertension

Hypertension is a disease classified as primary or secondary, manifested not only by elevation of blood pressure but also involved in structural and functional changes of target organs. Renal artery stenosis is a leading factor of secondary hypertension, and its progress is associated with overactivation of the renin-angiotensin-aldosterone system (RAAS). Aliskiren is a renin inhibiting drug that suppresses RAAS and culminates in decreased renin release, plasma angiotensin II concentration, and inhibition of aldosterone secretion. In this sense, the aim of the present study was to analyze the structural and ultrastructural morphophysiology of the adrenal glomerular zone, after treatment with aliskiren in Wistar rats with 2K1C hypertension. Parameters as structure and ultrastructure of the adrenal glomerular zone, cellular apoptosis, nuclear cell proliferation, and AT1 receptor expression were analyzed by immunostaining and electron microscopy. Our results showed that the hypertensive animals treated with aliskiren presented a reestablishment of AT1 receptor expression and decrease in apoptosis and autophagy. In addition, treatment with aliskiren improves the cell aspects in the adrenal glomerular zone, evidenced by ultrastructural analysis through preserved nuclei and well-developed mitochondria. Therefore, our evidence suggests that aliskiren has a beneficial effect on the adrenal glomerular zone remodeling in animals with renovascular hypertension.

Renovascular hypertension elevates pulmonary ventilation in rats by carotid body-dependent mechanisms

The two kidney-one clip (2K1C) renovascular hypertension depends on the renin-angiotensin system and sympathetic overactivity. The maintenance of 2K1C hypertension also depends on inputs from the carotid bodies (CB), which when activated stimulate the respiratory activity. In the present study, we investigated the importance of CB afferent activity for the ventilatory responses in 2K1C hypertensive rats and for phrenic and hypoglossal activities in in situ preparations of normotensive rats treated with angiotensin II. Silver clips were implanted around the left renal artery of male Holtzman rats (150 g) to induce renovascular hypertension. Six weeks after clipping, hypertensive 2K1C rats showed, in conscious state, elevated resting tidal volume and minute ventilation compared with the normotensive group. 2K1C rats also presented arterial alkalosis, urinary acidification, and amplified hypoxic ventilatory response. Carotid body removal (CBR), 2 wk before the experiments (4th week after clipping), significantly reduced arterial pressure and pulmonary ventilation in 2K1C rats but not in normotensive rats. Intra-arterial administration of angiotensin II in the in situ preparation of normotensive rats increased phrenic and hypoglossal activities, responses that were also reduced after CBR. Results show that renovascular hypertensive rats exhibit increased resting ventilation that depends on CB inputs. Similarly, angiotensin II increases phrenic and hypoglossal activities in in situ preparations of normotensive rats, responses that also depend on CB inputs. Results suggest that mechanisms that depend on CB inputs in renovascular hypertensive rats or during angiotensin II administration in normotensive animals increase respiratory drive.

Mineralocorticoid Receptor-Dependent Impairment of Baroreflex Contributes to Hypertension in a Mouse Model of Primary Aldosteronism

Primary aldosteronism (PA) is the most common cause of secondary hypertension. The paucity of good animal models hinders our understanding of the pathophysiology of PA and the hypertensive mechanism of PA remains incompletely known. It was recently reported that genetic deletion of TWIK-related acid-sensitive potassium-1 and potassium-3 channels from mice (TASK^−/−) generates aldosterone excess and mild hypertension. We addressed the hypertensive mechanism by assessing autonomic regulation of cardiovascular activity in this TASK^−/− mouse line that exhibits the hallmarks of PA. Here, we demonstrate that TASK^−/− mice were hypertensive with 24-h ambulatory arterial pressure. Either systemic or central blockade of the mineralocorticoid receptor (MR) markedly reduced elevated arterial pressure to normal level in TASK^−/− mice. The response of heart rate to the muscarinic cholinergic receptor blocker atropine was similar between TASK^−/− and wild-type mice. However, the responses of heart rate to the β-adrenergic receptor blocker propranolol and of arterial pressure to the ganglion blocker hexamethonium were enhanced in TASK^−/− mice relative to the counterparts. Moreover, the bradycardiac rather than tachycardiac gain of the arterial baroreflex was significantly attenuated and blockade of MRs to a large degree rescued the dysautonomia and baroreflex gain in TASK^−/− mice. Overall, the present study suggests that the MR-dependent dysautonomia and reduced baroreflex gain contribute to the development of hyperaldosteronism-related hypertension.

Importance of the commissural nucleus of the solitary tract in renovascular hypertension

The rodent renovascular hypertension model has been used to investigate the mechanisms promoting hypertension. The importance of the carotid body for renovascular hypertension has been demonstrated. As the commissural NTS (cNTS) is the first synaptic site in the central nervous system that receives information from carotid body chemoreceptors, we evaluated the contribution of cNTS to renovascular hypertension in the present study. Normotensive male Holtzman rats were implanted with a silver clip around the left renal artery to induce two-kidney, one-clip (2K1C) hypertension. Six weeks later, isoguvacine (a GABA_A agonist) or losartan (an AT1 antagonist) was injected into the cNTS, and the effects were compared with carotid body removal. Immunohistochemistry for Iba-1 and GFAP to label microglia and astrocytes, respectively, and RT-PCR for components of the renin-angiotensin system and cytokines in the NTS were also performed 6 weeks after renal surgery. The inhibition of cNTS with isoguvacine or the blockade of AT1 receptors with losartan in the cNTS decreased the blood pressure and heart rate of 2K1C rats even more than carotid body removal did. The mRNA expression of NOX2, TNF-α and IL-6, microglia, and astrocytes also increased in the cNTS of 2K1C rats compared to that of normotensive rats. These results indicate that tonically active neurons within the cNTS are essential for the maintenance of hypertension in 2K1C rats. In addition to signals from the carotid body, the present results suggest that angiotensin II directly activates the cNTS and may also induce microgliosis and astrogliosis within the NTS, which, in turn, cause oxidative stress and neuroinflammation.

The renin-angiotensin system in cardiovascular autonomic control: recent developments and clinical implications

Complex and bidirectional interactions between the renin-angiotensin system (RAS) and autonomic nervous system have been well established for cardiovascular regulation under both physiological and pathophysiological conditions. Most research to date has focused on deleterious effects of components of the vasoconstrictor arm of the RAS on cardiovascular autonomic control, such as renin, angiotensin II, and aldosterone. The recent discovery of prorenin and the prorenin receptor have further increased our understanding of RAS interactions in autonomic brain regions. Therapies targeting these RAS components, such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, are commonly used for treatment of hypertension and cardiovascular diseases, with blood pressure-lowering effects attributed in part to sympathetic inhibition and parasympathetic facilitation. In addition, a vasodilatory arm of the RAS has emerged that includes angiotensin-(1-7), ACE2, and alamandine, and promotes beneficial effects on blood pressure in part by reducing sympathetic activity and improving arterial baroreceptor reflex function in animal models. The role of the vasodilatory arm of the RAS in cardiovascular autonomic regulation in clinical populations, however, has yet to be determined. This review will summarize recent developments in autonomic mechanisms involved in the effects of the RAS on cardiovascular regulation, with a focus on newly discovered pathways and therapeutic targets for this hormone system.

Aldosterone infusion into the 4th ventricle produces sodium appetite with baroreflex attenuation independent of renal or blood pressure changes

Aldosterone infusion into the 4th ventricle (4th V), upstream the nucleus of the solitary tract (NTS), produces strong 0.3 M NaCl intake. In the present study, we investigated whether aldosterone infusion into the 4th V activates HSD2 neurons, changes renal excretion, or alters blood pressure and cardiovascular reflexes. Chronic infusion of aldosterone (100 ng/h) into the 4th V increased daily 0.3 M NaCl intake (up to 44 ± 10, vs. vehicle: 5.6 ± 3.4 ml/24 h) and also c-Fos expression in HSD2 neurons in the NTS and in non-HSD2 neurons in the NTS. Natriuresis, diuresis and positive sodium balance were present in rats that ingested 0.3 M NaCl, however, renal excretion was not modified by 4th V aldosterone in rats that had no access to NaCl. 4th V aldosterone also reduced baroreflex sensitivity (-2.8 ± 0.5, vs. vehicle: -5.1 ± 0.9 bpm/mmHg) in animals that had sodium available, without changing blood pressure. The results suggest that sodium intake induced by aldosterone infused into the 4th V is associated with activation of NTS neurons, among them the HSD2 neurons. Aldosterone infused into the 4th V in association with sodium intake also impairs baroreflex sensitivity, without changing arterial pressure.

Direct Recording of Cardiac and Renal Sympathetic Nerve Activity Shows Differential Control in Renovascular Hypertension

There is increasing evidence that hypertension is initiated and maintained by elevated sympathetic tone. Increased sympathetic drive to the heart is linked to cardiac hypertrophy in hypertension and worsens prognosis. However, cardiac sympathetic nerve activity (SNA) has not previously been directly recorded in hypertension. We hypothesized that directly recorded cardiac SNA levels would be elevated during hypertension and that baroreflex control of cardiac SNA would be impaired during hypertension. Adult ewes either underwent unilateral renal artery clipping (n=12) or sham surgery (n=15). Two weeks later, electrodes were placed in the contralateral renal and cardiac nerves to record SNA. Baseline levels of SNA and baroreflex control of heart rate and sympathetic drive were examined. Unilateral renal artery clipping induced hypertension (mean arterial pressure 109±2 versus 91±3 mm Hg in shams; P<0.001). The heart rate baroreflex curve was shifted rightward but remained intact. In the hypertensive group, cardiac sympathetic burst incidence (bursts/100 beats) was increased (39±14 versus 25±9 in normotensives; P<0.05), whereas renal sympathetic burst incidence was decreased (69±20 versus 93±8 in normotensives; P<0.01). The renal sympathetic baroreflex curve was shifted rightward and showed increased gain, but there was no change in the cardiac sympathetic baroreflex gain. Renovascular hypertension is associated with differential control of cardiac and renal SNA; baseline cardiac SNA is increased, whereas renal SNA is decreased.

Enhanced angiotensin II induced sodium appetite in renovascular hypertensive rats

Renovascular hypertensive 2-kidney, 1-clip (2K1C) rats have an increased activity of the renin-angiotensin system and an initial transitory increase in daily water and NaCl intake. However, the dipsogenic and natriorexigenic responses to angiotensin II (ANG II) have not been tested yet in 2K1C rats. Therefore, in the present study, we evaluated water and 0.3 M NaCl intake induced by water deprivation (WD)-partial rehydration (PR) or intracerebroventricular (icv) ANG II in 2K1C rats. In addition, the cardiovascular changes to these treatments were also evaluated. Male Holtzman rats received a silver clip around the left renal artery to induce 2K1C renovascular hypertension. In the 5th week, a group of animals received a guide cannula in the lateral ventricle for icv injections. Daily water intake increased from the 3rd week after surgery and remained elevated until the 6th week (last recording week), whereas daily 0.3 M NaCl intake transiently increased from the 2nd to the 5th week after surgery. On the 6th week, in spite of comparable daily 0.3 M NaCl intake between 2K1C and sham rats, WD-PR and icv ANG II induced an increased 0.3 M NaCl intake in 2K1C rats. Water intake induced by WD-PR, not by icv ANG II, also increased in 2K1C rats. The increase in arterial pressure to WD-PR or icv ANG II was similar in sham and 2K1C rats. Therefore, these results suggest that 2K1C rats are more responsive to the natriorexigenic effects of ANG II, whereas other responses to ANG II are not modified.

Variable role of carotid bodies in cardiovascular responses to exercise, hypoxia and hypercapnia in spontaneously hypertensive rats

KEY POINTS

Carotid bodies play a critical role in maintaining arterial pressure during hypoxia and this has important implications when considering resection therapy of the carotid body in disease states such as hypertension. Curbing hypertension in patients whether resting or under stress remains a major global health challenge. We demonstrated previously the benefits of removing carotid body afferent input into the brain for both alleviating sympathetic overdrive and reducing blood pressure in neurogenic hypertension. We describe a new approach in rats for selective ablation of the carotid bodies that spares the functional integrity of the carotid sinus baroreceptors, and demonstrate the importance of the carotid bodies in the haemodynamic response to forced exercise, hypoxia and hypercapnia in conditions of hypertension. Selective ablation reduced blood pressure in hypertensive rats and re-set baroreceptor reflex function accordingly; the increases in blood pressure seen during exercise, hypoxia and hypercapnia were unaffected, abolished and augmented, respectively, after selective carotid body removal. The data suggest that carotid body ablation may trigger potential cardiovascular risks particularly during hypoxia and hypercapnia and that suppression rather than obliteration of their activity may be a more effective and safer route to pursue.

ABSTRACT

The carotid body has recently emerged as a promising therapeutic target for treating cardiovascular disease, but the potential impact of carotid body removal on the dynamic cardiovascular responses to acute stressors such as exercise, hypoxia and hypercapnia in hypertension is an important safety consideration that has not been studied. We first validated a novel surgical approach to selectively resect the carotid bodies bilaterally (CBR) sparing the carotid sinus baroreflex. Second, we evaluated the impact of CBR on the cardiovascular responses to exercise, hypoxia and hypercapnia in conscious, chronically instrumented spontaneously hypertensive (SH) rats. The results confirm that our CBR technique successfully and selectively abolished the chemoreflex, whilst preserving carotid baroreflex function. CBR produced a sustained fall in arterial pressure in the SH rat of ∼20 mmHg that persisted across both dark and light phases (P < 0.001), with baroreflex function curves resetting around lower arterial pressure levels. The cardiovascular and respiratory responses to moderate forced exercise were similar between CBR and Sham rats. In contrast, CBR abolished the pressor response to hypoxia seen in Sham animals, although the increases in heart rate and respiration were similar between Sham and CBR groups. Both the pressor and the respiratory responses to 7% hypercapnia were augmented after CBR (P < 0.05) compared to sham. Our finding that the carotid bodies play a critical role in maintaining arterial pressure during hypoxia has important implications when considering resection therapy of the carotid body in disease states such as hypertension as well as heart failure with sleep apnoea.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Effects of voluntary exercise on blood pressure, angiotensin II, aldosterone, and renal function in two-kidney, one-clip hypertensive rats

Spontaneous dynamic exercise promotes sympathoinhibition and decreases arterial pressure in two-kidney, one-clip (2K-1C) hypertensive rats. Renal sympathetic nerves stimulate renin secretion and increase renal tubular sodium reabsorption. We hypothesized that daily voluntary wheel running exercise by 2K-1C rats will decrease mean arterial pressure (MAP), plasma angiotensin II (Ang II), and aldosterone as well as normalize urinary sodium and potassium excretion independent of changes in glomerular filtration rate (GFR). Five-week-old male Sprague Dawley rats underwent sham clipping (Sham) or right renal artery clipping (2K-1C). Rats were randomized to standard caging (SED) or cages with running wheels (EX). After 12 weeks, rats were assigned to either collection of aortic blood for measurement of Ang II and aldosterone or assessment of inulin clearances and excretory function. Running distances were comparable in both EX groups. MAP was lower in 2K-1C EX vs 2K-1C SED rats (P<0.05). Plasma Ang II and aldosterone were significantly higher in 2K-1C SED rats and decreased in 2K-1C EX rats to levels similar to Sham SED or Sham EX rats. Clipped kidney weights were significantly lower in both 2K-1C groups, but GFR and urine flow rates were no different from right and left kidneys among the four groups. Total and fractional sodium excretion rates from the unclipped kidney of 2K-1C SED rats were higher vs either Sham group (P<0.05). Values in 2K-1C EX rats were similar to the Sham groups. Potassium excretion paralleled sodium excretion. These studies show that voluntary dynamic exercise in 2K-1C rats decreases plasma Ang II and aldosterone, which contribute to the lower arterial pressure without deleterious effects on GFR. The effects on sodium excretion underscore the impact of pressure natriuresis despite elevated plasma Ang II and aldosterone in sedentary 2K-1C rats. In contrast, potassium excretion is primarily regulated by circulating aldosterone and distal sodium delivery.

Differential effects of renal denervation on arterial baroreceptor function in Goldblatt hypertension model

Sympathetic vasomotor activity is significantly increased in renovascular hypertension. Renal denervation (DnX) has emerged as a novel therapy for resistant hypertension to drug therapy. However, the underlying mechanisms regarding the reduction in blood pressure (BP) after DnX remain unclear. Thus, the aim of this study was to evaluate the effects of DnX of a clipped kidney on the baseline and baroreceptor reflex control of post-ganglionic sympathetic activity to the contralateral kidney (rSNA) and lumbar (lSNA) nerves in Goldblatt hypertensive rats (2K1C). Renal denervation of an ischaemic kidney (DxX - all visible bundles of nerves were dissected - 10% phenol) was performed 5weeks after clipping (gap width: 0.2mm). Ten days after DnX, BP was significantly reduced (16%) in the 2K1C compared with the undenervated 2K1C (p<0.05). DnX significantly reduced basal rSNA (control group (CT): 110±8, n=14; 2K1C: 150±8, n=12; 2K1C DnX: 89±7, spikes per second (spikes/s); p<0.05, n=8) and lSNA (CT: 137±8, n=8; 2K1C: 202±7, n=11; 2K1C DnX: 131±7, spikes/s; p<0.05, n=8) only in 2K1C rats. DnX significantly improved the arterial baroreceptor sensitivity of rSNA (CT: -2.3±0.2, n=11; 2K1C: -0.7±0.1, n=8; 2K1C DnX: -1.5±0.2, spikes/s/mmHg; p<0.05, n=5) and heart rate for tachycardic response (CT: -3.9±0.5, n=7; 2K1C: -1.9±0.1, n=8; 2K1C DnX: -3.3±0.4, bpm/mmHg; p<0.05, n=8), but not for lSNA in 2K1C rats. The results show that DnX normalized baseline sympathetic vasomotor activity to the lumbar and renal nerves, followed by a differential improvement in the arterial baroreceptor sensitivity. Whether the baroreceptor function sensitivity improvement induced by DnX is a cause or a consequence of BP reduction remains to be determined.

Aldosterone-Renin Ratio and Side-Selective Renal Perfusion in Essential Hypertension

BACKGROUND

The decrease in kidney perfusion as often observed in hypertensive individuals does not necessarily occur in a symmetrical fashion, thereby potentially introducing left-right differences in response to vasoactive agents. Increased aldosterone levels have been associated with reduced renal perfusion in normotensive and hypertensive individuals, but it is unknown whether both kidneys are equally affected in this respect and how angiotensin II is involved in this relationship. Therefore, our aim was to investigate the association of both aldosterone and the aldosterone-renin ratio with side-selective renal blood flow in essential hypertension.

METHODS

We studied 146 essential hypertensive patients with patent renal arteries who had undergone renal angiography for exclusion of renal artery stenosis. Prior to contrast administration, blood samples were drawn for the determination of renin and aldosterone levels, and side-selective renal blood flow was measured using the 133Xenon washout technique.

RESULTS

Left mean renal blood flow (MRBF) was significantly lower than right MRBF (227±74 vs. 250±76mL * min-1 * 100g kidney-1, P = 0.01). We could not demonstrate a correlation of ln aldosterone or ln renin with left or right kidney perfusion. Ln aldosterone-renin ratio (ARR), however, was inversely and independently associated with left MRBF (β = -13.993, P = 0.02; fully adjusted model) but not with right MRBF.

CONCLUSIONS

A higher ARR corresponds to reduced perfusion of the left kidney, yet is not associated with right kidney perfusion. Especially under circumstances of diminished right renal blood flow, this may affect blood pressure and kidney function.

Carotid sinus denervation ameliorates renovascular hypertension in adult Wistar rats

KEY POINTS

Peripheral chemoreflex sensitization is a feature of renovascular hypertension. Carotid sinus nerve denervation (CSD) has recently been shown to relieve hypertension and reduce sympathetic activity in other rat models of hypertension. We show that CSD in renovascular hypertension halts further increases in blood pressure. Possible mechanisms include improvements in baroreceptor reflex sensitivity and renal function, restoration of cardiac calcium signalling towards control levels, and reduced neural inflammation. Our data suggest that the peripheral chemoreflex may be a viable therapeutic target for renovascular hypertension.

ABSTRACT

The peripheral chemoreflex is known to be hyper-responsive in both spontaneously hypertensive (SHR) and Goldblatt hypertensive (two kidney one clip; 2K1C) rats. We have previously shown that carotid sinus nerve denervation (CSD) reduces arterial blood pressure (ABP) in SHR. In the present study, we show that CSD ameliorates 2K1C hypertension and reveal the potential underlying mechanisms. Adult Wistar rats were instrumented to record ABP via telemetry, and then underwent CSD (n = 9) or sham CSD (n = 9) 5 weeks after renal artery clipping, in comparison with normal Wistar rats (n = 5). After 21 days, renal function was assessed, and tissue was collected to assess sympathetic postganglionic intracellular calcium transients ([Ca²⁺ ]_i ) and immune cell infiltrates. Hypertensive 2K1C rats showed a profound elevation in ABP (Wistar: 98 ± 4 mmHg vs. 2K1C: 147 ± 8 mmHg; P < 0.001), coupled with impairments in renal function and baroreflex sensitivity, increased neuroinflammatory markers and enhanced [Ca²⁺ ]_I in stellate neurons (P < 0.05). CSD reduced ABP in 2K1C+CSD rats and prevented the further progressive increase in ABP seen in 2K1C+sham CSD rats, with a between-group difference of 14 ± 2 mmHg by week 3 (P < 0.01), which was accompanied by improvements in both baroreflex control and spectral indicators of cardiac sympatho-vagal balance. Furthermore, CSD improved protein and albuminuria, decreased [Ca²⁺ ]_i evoked responses from stellate neurons, and also reduced indicators of brainstem inflammation. In summary, CSD in 2K1C rats reduces the hypertensive burden and improves renal function. This may be mediated by improvements in autonomic balance, functional remodelling of post-ganglionic neurons and reduced inflammation. Our results suggest that the peripheral chemoreflex may be considered as a potential therapeutic target for controlling renovascular hypertension.

Effect of combined drospirenone with estradiol for hypertensive postmenopausal women: a systemic review and meta-analysis

Postmenopausal hypertensive is associated with estrogen deficiency. This meta-analysis was performed to assess the efficacy and safety of drospirenone combined with 17-β-estradiol (DRSP/E2) in postmenopausal hypertensive women. A systemic literature search of PubMed, Embase, Cochrane Library, Web of Science (up to Oct. 2015) was performed. Studies were screened independently by two researchers according to the inclusion and exclusion criteria which included only the randomized controlled trials (RCT) about the drospirenone with 17-β-estradiol for postmenopausal women with hypertension. The methodological quality was evaluated by Cochrane handbook 5.1.0 and meta-analysis was conducted using RevMan 5.3.0 software. Five randomized controlled trials involved 1121 patients who met the eligibility criteria. Overall, DRSP/E2 group was superior in reducing clinical blood pressure (BP) and 24-h mean BP. There was no significant change in potassium levels on DRSP/E2 group versus control group, suggesting probability potassium sparing effect of this hormone therapy. The incidences of adverse events were low and similar. The current evidences indicate that DRSP 3 mg/E2 2 mg can significantly lower both systolic and diastolic blood pressure in postmenopausal hypertensive women.