Angiotensin-(1–7) and angiotension II in the rostral ventrolateral medulla modulate the cardiac sympathetic afferent reflex and sympathetic activity in rats

Renin-angiotensin system blockade in the COVID-19 pandemic

In the early months of the coronavirus disease 2019 (COVID-19) pandemic, a hypothesis emerged suggesting that pharmacologic inhibitors of the renin–angiotensin system (RAS) may increase COVID-19 severity. This hypothesis was based on the role of angiotensin-converting enzyme 2 (ACE2), a counterregulatory component of the RAS, as the binding site for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), allowing viral entry into host cells. Extrapolations from prior evidence led to speculation that upregulation of ACE2 by RAS blockade may increase the risk of adverse outcomes from COVID-19. However, counterarguments pointed to evidence of potential protective effects of ACE2 and RAS blockade with regard to acute lung injury, as well as substantial risks from discontinuing these commonly used and important medications. Here we provide an overview of classic RAS physiology and the crucial role of ACE2 in systemic pathways affected by COVID-19. Additionally, we critically review the physiologic and epidemiologic evidence surrounding the interactions between RAS blockade and COVID-19. We review recently published trial evidence and propose important future directions to improve upon our understanding of these relationships.

Bisoprolol transdermal patch improves orthostatic hypotension in patients with chronic heart failure and hypertension

β blockers (BBs) play an important role in heart failure (HF) treatment. However, orthostatic hypotension (OH) is sometimes caused by BBs. The bisoprolol transdermal patch works more slowly and is long acting compared with the bisoprolol fumarate tablet. The risk of OH may be reduced by using the bisoprolol transdermal patch. We evaluated 57 consecutive patients who were taking the bisoprolol fumarate tablet for chronic HF with hypertension from November 2016 to September 2017. We switched the patients to the bisoprolol transdermal patch. Because 12 of 57 subjects could not continue using the bisoprolol transdermal patch, we analyzed the remaining 45 patients. We investigated BP, blood tests, and changes in BP from supine to standing positions before and after 6 months of switching from tablet to patch. OH was diagnosed by observing a systolic/diastolic BP drop of at least 20/10 mmHg or an absolute systolic BP (sBP) of <90 mmHg from the standing position. No significant changes were observed in the BP and BPs from supine to standing positions, whereas log brain natriuretic peptide was significantly reduced after switching from patch to tablet (2.102 to 2.070pg/dl, P = .039). OH, which occurred in originally 17 patients, showed improvement and eventually appeared in 4 patients. In these patients, changes in BP from supine to standing positions were also significantly improved (changes in sBP, -11 to -6mmHg, P = .016). This study demonstrated that switching from the bisoprolol fumarate tablet to transdermal patch reduced the morbidity of OH in HF patients.

The Elabela in hypertension, cardiovascular disease, renal disease, and preeclampsia: an update

: Although considerable success has been shown for antihypertensive medications, the resistant hypertension and hypertension-related organ damages are still the important clinical issues and pose as high health and economic pressure. Therefore, novel therapeutic techniques and antihypertensive drugs are needed to advance more effective therapy of hypertension and hypertension-related disease to ameliorate mortality and healthcare costs worldwide. In this review, we highlight the latest progress in supporting the therapeutic potential of Elabela (ELA), a recently discovered early endogenous ligand for G-protein-coupled receptor apelin peptide jejunum, apelin receptor. Systemic administration of ELA exerts vasodilatory, antihypertensive, cardioprotective, and renoprotective effects, whereas central application of ELA increases blood pressure and causes cardiovascular remodeling primarily secondary to the hypertension. In addition, ELA drives extravillous trophoblast differentiation and prevents the pathogenesis of preeclampsia (a gestational hypertensive syndrome) by promoting placental angiogenesis. These findings strongly suggest peripheral ELA's therapeutic potential in preventing and treating hypertension and hypertension-related diseases including cardiovascular disease, kidney disease, and preeclampsia. Since therapeutic use of ELA is mainly limited by its short half-life and parenteral administration, it may be a clinical application candidate for the therapy of hypertension and its complications when fused with a large inert chemicals (e.g. polyethylene glycol, termed polyethylene glycol-ELA-21) or other proteins (e.g. the Fc fragment of IgG and albumin, termed Fc-ELA-21 or albumin-ELA-21), and new delivery methods are encouraged to develop to improve the efficacy of ELA fragments on apelin peptide jejunum or alternative unknown receptors.

Neuroinflammation in hypertension: the renin-angiotensin system versus pro-resolution pathways

Overstimulation of the pro-inflammatory pathways within brain areas responsible for sympathetic outflow is well evidenced as a primary contributing factor to the establishment and maintenance of neurogenic hypertension. However, the precise mechanisms and stimuli responsible for promoting a pro-inflammatory state are not fully elucidated. Recent work has unveiled novel compounds derived from omega-3 polyunsaturated fatty acids (ω-3 PUFAs), termed specialized pro-resolving mediators (SPMs), which actively regulate the resolution of inflammation. Failure or dysregulation of the resolution process has been linked to a variety of chronic inflammatory and neurodegenerative diseases. Given the pathologic role of neuroinflammation in the hypertensive state, SPMs and their associated pathways may provide a link between hypertension and the long-standing association of dietary ω-3 PUFAs with cardioprotection. Herein, we review recent progress in understanding the RAS-driven pathophysiology of neurogenic hypertension, particularly in regards to the chronic low-grade neuroinflammatory response. In addition, we examine the potential for an impaired resolution of inflammation process in the context of hypertension.

Blockade of Endogenous Angiotensin-(1-7) in Hypothalamic Paraventricular Nucleus Attenuates High Salt-Induced Sympathoexcitation and Hypertension

Angiotensin (Ang)-(1-7) is an important biologically-active peptide of the renin-angiotensin system. This study was designed to determine whether inhibition of Ang-(1-7) in the hypothalamic paraventricular nucleus (PVN) attenuates sympathetic activity and elevates blood pressure by modulating pro-inflammatory cytokines (PICs) and oxidative stress in the PVN in salt-induced hypertension. Rats were fed either a high-salt (8% NaCl) or a normal salt diet (0.3% NaCl) for 10 weeks, followed by bilateral microinjections of the Ang-(1-7) antagonist A-779 or vehicle into the PVN. We found that the mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA), and plasma norepinephrine (NE) were significantly increased in salt-induced hypertensive rats. The high-salt diet also resulted in higher levels of the PICs interleukin-6, interleukin-1beta, tumor necrosis factor alpha, and monocyte chemotactic protein-1, as well as higher gp91^phox expression and superoxide production in the PVN. Microinjection of A-779 (3 nmol/50 nL) into the bilateral PVN of hypertensive rats not only attenuated MAP, RSNA, and NE, but also decreased the PICs and oxidative stress in the PVN. These results suggest that the increased MAP and sympathetic activity in salt-induced hypertension can be suppressed by blockade of endogenous Ang-(1-7) in the PVN, through modulation of PICs and oxidative stress.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Short hairpin RNA interference targeting interleukin 1 receptor type I in the paraventricular nucleus attenuates hypertension in rats

Blood pressure is controlled by tonic sympathetic activities, excessive activation of which contributes to the pathogenesis and progression of hypertension. Interleukin (IL)-1β in the paraventricular nucleus (PVN) is involved in sympathetic overdrive and hypertension. Here, we investigated the therapeutic effects of IL-1 receptor type I (IL-1R1) gene silencing in the PVN on hypertension. Recombinant lentivirus vectors expressing a short hairpin RNA (shRNA) targeting IL-1R1 (Lv-shR-IL-1R1) or a control shRNA were microinjected into PVN of spontaneously hypertensive rats (SHRs) and normotensive WKY rats. The fluorescence of green fluorescent protein-labelled vectors appeared at 2 weeks after injection and persisted for at least 8 weeks. IL-1R1 protein expression in the PVN was reduced 4 weeks after Lv-shR-IL-1R1 injection in SHRs. IL-1R1 interference also reduced basal sympathetic activity, cardiac sympathetic afferent reflex in SHRs. Depressor effects were observed from week 2 to 10 after Lv-shR-IL-1R1 treatment in SHRs, with the most prominent effects seen at the end of week 4. Furthermore, Lv-shR-IL-1R1 treatment decreased the ratio of left ventricular weight to body weight and cross-sectional areas of myocardial cells in SHRs. Additionally, Lv-shR-IL-1R1 treatment prevented an increase in superoxide anion and pro-inflammatory cytokines (PICs, TNF-α and IL-1β) in the PVN of SHR, and upregulated anti-inflammatory cytokine (AIC, IL-10) expression. These results indicate that shRNA interference targeting IL-1R1 in the PVN decreases arterial blood pressure, attenuates excessive sympathetic activity and cardiac sympathetic afferent reflex, and improves myocardial remodelling in SHRs by restoring the balance between PICs and AICs to attenuate oxidative stress.

Hypotensive effect induced by microinjection of Alamandine, a derivative of angiotensin-(1-7), into caudal ventrolateral medulla of 2K1C hypertensive rats

In the present study we evaluated the cardiovascular effects produced by microinjection of the new component of the renin-angiotensin system, alamandine, into caudal ventrolateral medulla of urethane-anesthetized normotensive and hypertensive 2K1C rats. The participation of different angiotensin receptors in the effects of alamandine was also evaluated. Microinjection of angiotensin-(1-7) was used for comparison. The microinjection of 4, 40 and 140pmol of alamandine or angiotensin-(1-7) into caudal ventrolateral medulla induced similar hypotensive effects in Sham-operated rats. However, contrasting with angiotensin-(1-7), in 2K1C rats the MAP response to the highest dose of alamandine was similar to that observed with saline. The microinjection of A-779, a selective Mas receptor antagonist, blunted the angiotensin-(1-7) effects but did not block the hypotensive effect of alamandine in Sham or in 2K1C rats. However, microinjection of D-Pro⁷-angiotensin-(1-7), a Mas/MrgD receptor antagonist, blocked the hypotensive effect induced by both peptides. Furthermore, microinjection of PD123319, a putative AT2 receptor antagonist blocked the hypotensive effect of alamandine, but not of angiotensin-(1-7), in Sham and 2K1C rats. Microinjection of the AT1 receptor antagonist, losartan, did not alter the hypotensive effect of angiotensin-(1-7) or alamandine in both groups. These results provide new insights about the differential mechanisms participating in the central cardiovascular effects of alamandine and angiotensin-(1-7) in normotensive and 2K1C hypertensive rats.

The renin angiotensin system and the brain: New developments

The traditional renin-angiotensin system (RAS) is indispensable system in adjusting sodium homeostasis, body fluid volume, and controlling arterial blood pressure. The key elements are renin splitting inactive angiotensinogen to yield angiotensin (Ang-I). Ang-1 is then changed by angiotensin-1 converting enzyme (ACE) into angiotensin II (Ang-II). Using PubMed, Google Scholar, and other means, we searched the peer-reviewed literature from 1990 to 2013 for articles on newly discovered findings related to the RAS, especially focusing on how the system influences the central nervous system (CNS). The classical RAS is now considered to be only part of the picture; the discovery of additional RAS pathways in the brain and elsewhere has yielded a vastly improved understanding of how the RAS influences the CNS. Newly discovered effects of the RAS on brain tissue include neuroprotection, cognition, and cerebral vasodilation. A number of brain biochemical pathways are influenced by the brain RAS. Within various pathways, there are potential opportunities for classical pharmacologic interventions as well as the possibility of controlling gene expression.

Angiotensin-(1-7) in Paraventricular Nucleus Contributes to the Enhanced Cardiac Sympathetic Afferent Reflex and Sympathetic Activity in Chronic Heart Failure Rats

Background/Aims

Cardiac sympathetic afferent reflex (CSAR) enhancement contributes to exaggerated sympathetic activation in chronic heart failure (CHF). The current study aimed to investigate the roles of angiotensin (Ang)-(1-7) in CSAR modulation and sympathetic activation and Ang-(1-7) signaling pathway in paraventricular nucleus of CHF rats.

Methods

CHF was induced by coronary artery ligation. Responses of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) to epicardial application of capsaicin were used to evaluate CSAR in rats with anesthesia.

Results

Ang-(1-7) increased RSNA, MAP, CSAR activity, cAMP level, NAD(P)H oxidase activity and superoxide anion level more significantly in CHF than in sham-operated rats, while Mas receptor antagonist A-779 had the opposite effects. Moreover, Ang-(1-7) augmented effects of Ang II in CHF rats. The effects of Ang-(1-7) were blocked by A-779, adenylyl cyclase inhibitor SQ22536, protein kinase A inhibitor Rp-cAMP, superoxide anion scavenger tempol and NAD(P)H oxidase inhibitor apocynin. Mas and AT₁ receptor protein expressions, Ang-(1-7) and Ang II levels in CHF increased.

Conclusions

These results indicate that Ang-(1-7) in paraventricular nucleus enhances CSAR and sympathetic output not only by exerting its own effects but also by augmenting the effects of Ang II through Mas receptor in CHF. Endogenous Ang-(1-7)/Mas receptor activity contributes to CSAR enhancement and sympathetic activation in CHF, and NAD(P)H oxidase-derived superoxide anions and the cAMP-PKA signaling pathway are involved in mediating the effects of Ang-(1-7) in CHF.

Brain renin-angiotensin system in the pathophysiology of cardiovascular diseases

Cardiovascular diseases (CVD) are among the main causes of death globally and in this context hypertension represents one of the key risk factors for developing a CVD. It is well established that the peripheral renin-angiotensin system (RAS) plays an important role in regulating blood pressure (BP). All components of the classic RAS can also be found in the brain but, in contrast to the peripheral RAS, how the endogenous RAS is involved in modulating cardiovascular effects in the brain is not fully understood yet. It is a complex system that may work differently in diverse areas of the brain and is linked to the peripheral system by the circumventricular organs (CVO), which do not have a blood brain barrier (BBB). In this review, we focus on the brain angiotensin peptides, their interactions with each other, and the consequences in the central nervous system (CNS) concerning cardiovascular control. Additionally, we present potential drug targets in the brain RAS for the treatment of hypertension.

Mechanisms of Mas1 Receptor-Mediated Signaling in the Vascular Endothelium

OBJECTIVE

Angiotensin II (AngII) has been shown to regulate angiogenesis and at high pathophysiological doses to cause vasoconstriction through the AngII receptor type 1. Angiotensin 1 to 7 (Ang-(1-7)) acting through the Mas1 receptor can act antagonistically to high pathophysiological levels of AngII by inducing vasodilation, whereas the effects of Ang-(1-7) signaling on angiogenesis are less defined. To complicate the matter, there is growing evidence that a subpressor dose of AngII produces phenotypes similar to Ang-(1-7).

APPROACH AND RESULTS

This study shows that low-dose Ang-(1-7), acting through the Mas1 receptor, promotes angiogenesis and vasodilation similar to a low, subpressor dose of AngII acting through AngII receptor type 1. In addition, we show through in vitro tube formation that Ang-(1-7) augments the angiogenic response in rat microvascular endothelial cells. Using proteomic and genomic analyses, downstream components of Mas1 receptor signaling were identified, including Rho family of GTPases, phosphatidylinositol 3-kinase, protein kinase D1, mitogen-activated protein kinase, and extracellular signal-related kinase signaling. Further experimental antagonism of extracellular signal-related kinases 1/2 and p38 mitogen-activated protein kinase signaling inhibited endothelial tube formation and vasodilation when stimulated with equimolar, low doses of either AngII or Ang-(1-7).

CONCLUSIONS

These results significantly expand the known Ang-(1-7)/Mas1 receptor signaling pathway and demonstrate an important distinction between the pathological effects of elevated and suppressed AngII compared with the beneficial effects of AngII normalization and Ang-(1-7) administration. The observed convergence of Ang-(1-7)/Mas1 and AngII/AngII receptor type 1 signaling at low ligand concentrations suggests a nuanced regulation in vasculature. These data also reinforce the importance of mitogen-activated protein kinase/extracellular signal-related kinase signaling in maintaining vascular function.

Exercise Training Improves the Altered Renin-Angiotensin System in the Rostral Ventrolateral Medulla of Hypertensive Rats

The imbalance between angiotensin II (Ang II) and angiotensin 1-7 (Ang 1-7) in the brain has been reported to contribute to cardiovascular dysfunction in hypertension. Exercise training (ExT) is beneficial to hypertension and the mechanism is unclear. This study was aimed to determine if ExT improves hypertension via adjusting renin angiotensin system in cardiovascular centers including the rostral ventrolateral medulla (RVLM). Spontaneously hypertensive rats (SHR, 8 weeks old) were subjected to low-intensity ExT or kept sedentary (Sed) for 12 weeks. Blood pressure elevation coupled with increase in age was significantly decreased in SHR received ExT compared with Sed. The results in vivo showed that ExT significantly reduced or increased the cardiovascular responses to central application of sarthran (antagonist of Ang II) or A779 (antagonist of Ang 1-7), respectively. The protein expression of the Ang II acting receptor AT1R and the Ang 1-7 acting receptor Mas in the RVLM was significantly reduced and elevated in SHR following ExT, respectively. Moreover, production of reactive oxygen species in the RVLM was significantly decreased in SHR following ExT. The current data suggest that ExT improves hypertension via improving the balance of Ang II and Ang 1-7 and antioxidative stress at the level of RVLM.

Differential control of vasomotion by angiotensins in the rostral ventrolateral medulla of hypertensive rats

The central and peripheral renin-angiotensin systems are known for playing a key role in cardiovascular control. In the present study, we evaluated the hemodynamic effects produced by nanoinjections of angiotensin II (Ang II) or angiotensin-(1-7) [Ang-(1-7)] into the rostral ventrolateral medulla (RVLM) of adult male normotensive (Wistar-WT) and spontaneously hypertensive rats (SHR). Animals were anesthetized (urethane 1.2g/kg) and instrumented for recording blood pressure (BP), heart rate (HR) and blood flow (BF) in the femoral, renal or mesenteric arteries. Afterwards, rats were positioned in a stereotaxic and prepared for nanoinjections (100 nl) of saline (NaCl 0.9%), Ang-(1-7) (40 ng) or Ang II (40 ng) into the RVLM. The vascular resistance (VR) was calculated by ΔMAP/ΔBF ratio. In WT, Ang-(1-7) or Ang II caused equipotent pressor effects that were not accompanied by changes in vascular resistance. However, MAP changes were greater in SHR. This strain also showed a concomitant increase in relative vascular resistance (ΔVR/VRbaseline) of renal (0.31 ± 0.07 and 0.3 ± 0.07 vs. 0.02 ± 0.01; Ang-(1-7), Ang II and Saline, respectively) and mesenteric beds (0.3 ± 0.06 and 0.33 ± 0.04 vs. 0.05 ± 0.02; Ang-(1-7), Ang II and saline, respectively). We conclude that Ang II and Ang-(1-7) at the RVLM control the vascular resistance of renal and mesenteric beds during hypertension.

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.

A century old renin-angiotensin system still grows with endless possibilities: AT1 receptor signaling cascades in cardiovascular physiopathology

Ang II, the primary effector pleiotropic hormone of the renin-angiotensin system (RAS) cascade, mediates physiological control of blood pressure and electrolyte balance through its action on vascular tone, aldosterone secretion, renal sodium absorption, water intake, sympathetic activity and vasopressin release. It affects the function of most of the organs far beyond blood pressure control including heart, blood vessels, kidney and brain, thus, causing both beneficial and deleterious effects. However, the protective axis of the RAS composed of ACE2, Ang (1-7), alamandine, and Mas and MargD receptors might oppose some harmful effects of Ang II and might promote beneficial cardiovascular effects. Newly identified RAS family peptides, Ang A and angioprotectin, further extend the complexities in understanding the cardiovascular physiopathology of RAS. Most of the diverse actions of Ang II are mediated by AT1 receptors, which couple to classical Gq/11 protein and activate multiple downstream signals, including PKC, ERK1/2, Raf, tyrosine kinases, receptor tyrosine kinases (EGFR, PDGF, insulin receptor), nuclear factor κB and reactive oxygen species (ROS). Receptor activation via G12/13 stimulates Rho-kinase, which causes vascular contraction and hypertrophy. The AT1 receptor activation also stimulates G protein-independent signaling pathways such as β-arrestin-mediated MAPK activation and Src-JAK/STAT. AT1 receptor-mediated activation of NADPH oxidase releases ROS, resulting in the activation of pro-inflammatory transcription factors and stimulation of small G proteins such as Ras, Rac and RhoA. The components of the RAS and the major Ang II-induced signaling cascades of AT1 receptors are reviewed.

Ionotropic glutamate receptors in paraventricular nucleus mediate adipose afferent reflex and regulate sympathetic outflow in rats

AIM

Chemical stimulation of white adipose tissue (WAT) induces adipose afferent reflex (AAR) and results in increases in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP). The enhanced AAR contributes to sympathetic activation and hypertension in obesity rats. This study was designed to investigate whether N-methyl-D-aspartate receptors (NMDAR) and non-NMDAR in paraventricular nucleus (PVN) modulate AAR and sympathetic outflow.

METHODS

Renal sympathetic nerve activity and MAP were recorded in anesthetized rats. AAR was evaluated by the RSNA and MAP responses to the injection of capsaicin into the four sites of right inguinal WAT (8.0 nmol for each site).

RESULTS

Bilateral PVN microinjection of NMDAR antagonist AP5 or MK-801, or non-NMDAR antagonist CNQX attenuated AAR, RSNA and MAP. AP5 + CNQX caused greater effects than AP5 or CNQX alone and almost abolished AAR. NMDAR agonist NMDA or non-NMDAR agonist AMPA enhanced the AAR, and increased RSNA and MAP, which were prevented by AP5 or CNQX pre-treatment respectively. Casein kinase 2 inhibitor DRB, NR2A antagonist NVP-AAM077 or NR2B antagonist CP-101,606 attenuated AAR, RSNA and MAP. NVP-AAM077 + CP-101,606 caused greater effects than NVP-AAM077 or CP-101,606 alone. Bilateral baroreceptor denervation and vagotomy enhanced AAR, which was abolished by PVN pre-treatment with AP5 + CNQX. Furthermore, AP5 + CNQX abolished the AAR induced by leptin in iWAT.

CONCLUSION

Both NMDAR and non-NMDAR in the PVN mediate AAR and contribute to the tonic control of sympathetic outflow and blood pressure. CK2, NR2A and NR2B subunits of NMDAR in the PVN are involved in the NMDAR-mediated tonic control of AAR, RSNA and MAP.

The effects of angiotensin II and angiotensin-(1-7) in the rostral ventrolateral medulla of rats on stress-induced hypertension

We have shown that angiotensin II (Ang II) and angiotensin-(1–7) [Ang-(1–7)] increased arterial blood pressure (BP) via glutamate release when microinjected into the rostral ventrolateral medulla (RVLM) in normotensive rats (control). In the present study, we tested the hypothesis that Ang II and Ang-(1–7) in the RVLM are differentially activated in stress-induced hypertension (SIH) by comparing the effects of microinjection of Ang II, Ang-(1–7), and their receptor antagonists on BP and amino acid release in SIH and control rats. We found that Ang II had greater pressor effect, and more excitatory (glutamate) and less inhibitory (taurine and γ-aminobutyric acid) amino acid release in SIH than in control animals. Losartan, a selective AT₁ receptor (AT₁R) antagonist, decreased mean BP in SIH but not in control rats. PD123319, a selective AT₂ receptor (AT₂R) antagonist, increased mean BP in control but not in SIH rats. However, Ang-(1–7) and its selective Mas receptor antagonist Ang779 evoked similar effects on BP and amino acid release in both SIH and control rats. Furthermore, we found that in the RVLM, AT₁R, ACE protein expression (western blot) and ACE mRNA (real-time PCR) were significantly higher, whereas AT₂R protein, ACE2 mRNA and protein expression were significantly lower in SIH than in control rats. Mas receptor expression was similar in the two groups. The results support our hypothesis and demonstrate that upregulation of Ang II by AT₁R, not Ang-(1–7), system in the RVLM causes hypertension in SIH rats by increasing excitatory and suppressing inhibitory amino acid release.

γ-Aminobutyric acid-mediated neurotransmission in cerebellar-hypothalamic circuit attenuates gastric mucosal injury induced by ischemia-reperfusion

BACKGROUND

Excessive greater splanchnic nerve (GSN) activation contributes to the progression of gastric ischemia-reperfusion (GI-R) injury. This study was designed to investigate the protective mechanism of cerebellar fastigial nucleus (FN) stimulation against GI-R injury.

METHODS

The GI-R injury model was induced in rats by clamping the celiac artery for 30 min, and then reperfusion for 30 min, 1, 3, 6, or 24 h, respectively.

KEY RESULTS

Microinjection of L-Glu (3, 6, 12 μg) into the FN dose-dependently attenuated GI-R injury and GSN activity. In addition, there was an enhancement of gastric mucosal blood flow in GI-R rats. Pretreatment with the glutamic acid decarboxylase antagonist into the FN, the GABAA receptor antagonist into the lateral hypothalamic area or lesion of superior cerebellar peduncle all reversed the protective effects of the FN stimulation. Furthermore, the FN stimulation reduced the TUNEL-positive gastric mucosal cell and Bax-positive gastric mucosal cell in GI-R rats.

CONCLUSIONS & INFERENCES

These results indicate that the protective effects of the FN stimulation against GI-R injury may be mediated by attenuation of the excessive GSN activation, gastric mucosal cell apoptosis, and Bax expression in GI-R rats.

Neuromodulatory role of angiotensin-(1–7) in the central nervous system

Ang-(1–7) [angiotensin-(1–7)] constitutes an important functional end-product of the RAS (renin–angiotensin system) endogenously formed from AngI (angiotensin I) or AngII (angiotensin II) through the catalytic activity of ACE2 (angiotensin-converting enzyme 2), prolyl carboxypeptidase, neutral endopeptidase or other endopeptidases. Ang-(1–7) lacks the pressor, dipsogenic or stimulatory effect on aldosterone release characteristic of AngII. In contrast, it produces vasodilation, natriuresis and diuresis, and inhibits angiogenesis and cell growth. At the central level, Ang-(1–7) acts at sites involved in the control of cardiovascular function, thus contributing to blood pressure regulation. This action may result from its inhibitory neuromodulatory action on NE [noradrenaline (norepinephrine)] levels at the synaptic cleft, i.e. Ang-(1–7) reduces NE release and synthesis, whereas it causes an increase in NE transporter expression, contributing in this way to central NE neuromodulation. Thus, by selective neurotransmitter release, Ang-(1–7) may contribute to the overall central cardiovascular effects. In the present review, we summarize the central effects of Ang-(1–7) and the mechanism by which the peptide modulates NE levels in the synaptic cleft. We also provide new evidences of its cerebroprotective role.

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.

SOD1 gene transfer into paraventricular nucleus attenuates hypertension and sympathetic activity in spontaneously hypertensive rats

Excessive sympathetic activity contributes to the initiation and progression of hypertension. Reactive oxygen species in the paraventricular nucleus (PVN) is involved in sympathetic overdrive and hypertension. The present study was designed to investigate whether superoxide dismutase 1 (SOD1) overexpression in the PVN attenuated sympathetic activation and hypertension. Adenoviral vectors containing human SOD1 or null adenoviral vectors were microinjected into the PVN of Wistar rats and spontaneously hypertensive rats (SHR). Significant depressor effects were observed from weeks 1 to 4 after SOD1 gene transfer in SHR. Acute experiments were carried out at the end of the 3rd week. In the PVN, superoxide anion and angiotensin II levels were increased while SOD1 activity and protein expression were decreased in SHR, which were attenuated by SOD1 overexpression in the PVN. However, SOD1 overexpression had no significant effect on the SOD2 activity in the PVN. The blood pressure response to ganglionic blockade, cardiac sympathetic nerve activity, and cardiac sympathetic afferent reflex (CSAR) were enhanced, and the plasma norepinephrine level was increased in SHR, which were prevented by SOD1 gene transfer in the PVN. Furthermore, SOD1 overexpression decreased the ratio of left ventricular weight to body weight, cross-sectional areas of myocardial cells, media thickness, and the media/lumen ratio of small arteries in the heart in SHR. These results indicate that SOD1 overexpression in the PVN reduces arterial blood pressure, attenuates excessive sympathetic activity and CSAR, and improves myocardial and vascular remodeling in SHR.

Role of angiotensin-(1-7) in rostral ventrolateral medulla in blood pressure regulation via sympathetic nerve activity in Wistar-Kyoto and spontaneous hypertensive rats

Angiotensin (Ang)-(1-7) Ang-(1-7) is formed from angiotensin II by angiotensin-converting enzyme 2 (ACE2) and modulates the renin-angiotensin system. We evaluated whether the Ang-(1-7)-Mas axis in the rostral ventrolateral medulla (RVLM) contributes to neural mechanisms of blood pressure (BP) regulation. We microinjected Ang-(1-7), Ang-(1-7)-Mas receptor antagonist A-779, and ACE2 inhibitor DX600 into the RVLM of anesthetized Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHRs). Unilateral Ang-(1-7) microinjection induced a significantly greater increase in AP (arterial blood pressure) in SHR than in WKY. Bilateral A-779 microinjection induced a significantly greater decrease in AP and renal sympathetic nerve activity in SHR than in WKY. Bilateral DX600 microinjection induced a significantly greater decrease in AP in SHR than in WKY. Our results suggest that endogenous Ang-(1-7) in the RVLM contributes to maintain AP and renal sympathetic nerve activity both in SHR and WKY and that its activity might be enhanced in SHR.

SOD1 overexpression in paraventricular nucleus improves post-infarct myocardial remodeling and ventricular function

Excessive sympathetic activation contributes to the progression of chronic heart failure. Reactive oxygen species in paraventricular nucleus (PVN) play an important role in the enhanced sympathetic outflow. This study was designed to determine whether superoxide dismutase 1 (SOD1) overexpression in the PVN attenuated the sympathetic activation and cardiac dysfunction in rats after an episode of myocardial infarction (MI). Adenoviral vectors containing human SOD1 (Ad-SOD) or null adenoviral vectors (Ad-null) were immediately microinjected into the PVN of rats with coronary artery ligation or sham operation. At the eighth week, the SOD1 protein level and activity in the PVN increased while the superoxide anions in the PVN decreased in Ad-SOD rats. The SOD1 overexpression in the PVN prevented the increases in left ventricular end-diastolic pressure and volume, and the decreases in ejection fraction and peak velocities of contraction in MI rats. In addition, there was an attenuation of renal sympathetic nerve activity, cardiac sympathetic afferent reflex and plasma norepinephrine level in MI rats. Furthermore, the SOD1 overexpression in the PVN reduced cardiomyocyte size, collagen deposition and the TUNEL-positive cardiomyocytes in MI rats. These results indicate that the SOD1 overexpression in the PVN attenuates the excessive sympathetic activation, myocardial remodeling, cardiomyocyte apoptosis and ventricular dysfunction in MI rats.

Inhibition of cardiac sympathetic afferent reflex and sympathetic activity by baroreceptor and vagal afferent inputs in chronic heart failure

Background

Cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation and angiotensin II (Ang II) in paraventricular nucleus (PVN) augments the CSAR in vagotomized (VT) and baroreceptor denervated (BD) rats with chronic heart failure (CHF). This study was designed to determine whether it is true in intact (INT) rats with CHF and to determine the effects of cardiac and baroreceptor afferents on the CSAR and sympathetic activity in CHF.

Methodology/Principal Findings

Sham-operated (Sham) or coronary ligation-induced CHF rats were respectively subjected to BD+VT, VT, cardiac sympathetic denervation (CSD) or INT. Under anesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded, and the CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Either CSAR or the responses of RSNA, MAP and CSAR to Ang II in PVN were enhanced in CHF rats treated with BD+VT, VT or INT. Treatment with VT or BD+VT potentiated the CSAR and the CSAR responses to Ang II in both Sham and CHF rats. Treatment with CSD reversed the capsaicin-induced RSNA and MAP changes and the CSAR responses to Ang II in both Sham and CHF rats, and reduced the RSNA and MAP responses to Ang II only in CHF rats.

Conclusions

The CSAR and the CSAR responses to Ang II in PVN are enhanced in intact CHF rats. Baroreceptor and vagal afferent activities inhibit CSAR and the CSAR responses to Ang II in intact Sham and CHF rats.

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.

Angiotensin-converting enzyme 2 overexpression improves central nitric oxide-mediated sympathetic outflow in chronic heart failure

Angiotensin (ANG)-converting enzyme (ACE)2 in brain regions such as the paraventricular nucleus (PVN) controlling cardiovascular function may be involved in the regulation of sympathetic outflow in chronic heart failure (CHF). The purpose of this study was to determine if ACE2 plays a role in the central regulation of sympathetic outflow by regulating neuronal nitric oxide (NO) synthase (nNOS) in the PVN. We investigated ACE2 and nNOS expression within the PVN of rats with CHF. We then determined the effects of ACE2 gene transfer in the PVN on the contribution of NO-mediated sympathoinhibition in rats with CHF. The results showed that there were decreased expressions for ACE2, the ANG-(1-7) receptor, and nNOS within the PVN of rats with CHF. After the application of adenovirus vectors encoding ACE2 (AdACE2) into the PVN, the increased expression of ACE2 in the PVN was confirmed by Western blot analysis. AdACE2 transfection significantly increased nNOS protein levels (change of 50 ± 5%) in the PVN of CHF rats. In anesthetized rats, AdACE2 treatment attenuated the responses of renal sympathetic nerve activity (RSNA), mean arterial pressure, and heart rate to the NOS inhibitor N-monomethyl-L-arginine in rats with CHF (RSNA: 28 ± 3% vs. 16 ± 3%, P < 0.05) compared with CHF + AdEGFP group. Furthermore, neuronal NG-108 cells incubated with increasing doses of AdACE2 showed a dose-dependent increase in nNOS protein expression (60% at the highest dose). Taken together, our data highlight the importance of increased expression and subsequent interaction of ACE2 and nNOS within the PVN, leading to a reduction in sympathetic outflow in the CHF condition.

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.

Superoxide anions in the paraventricular nucleus mediate the enhanced cardiac sympathetic afferent reflex and sympathetic activity in renovascular hypertensive rats

An enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation in renovascular hypertension. The present study was designed to determine the role of superoxide anions in the paraventricular nucleus (PVN) in mediating the enhanced CSAR and sympathetic activity in renovascular hypertension in the two-kidney, one-clip (2K1C) model. Sinoaortic denervation and vagotomy were carried out, and renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded under anesthesia. The CSAR was evaluated by the response of RSNA to the epicardial application of capsaicin. Superoxide anion levels and NAD(P)H oxidase activity in the PVN increased in 2K1C rats and were much higher in 2K1C rats than in sham-operated (sham) rats after the epicardial application of capsaicin or PVN microinjection of ANG II. In both 2K1C and sham rats, PVN microinjection of the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin abolished the CSAR, whereas the SOD inhibitor diethyldithiocarbamic acid (DETC) potentiated the CSAR. Tempol and apocynin decreased but DETC increased baseline RSNA and MAP. ANG II in the PVN caused larger responses of the CSAR, baseline RSNA, and baseline MAP in 2K1C rats than in sham rats. The effects of ANG II were abolished by pretreatment with tempol or apocynin in both 2K1C and sham rats and augmented by DETC in the PVN in 2K1C rats. These results indicate that superoxide anions in the PVN mediate the CSAR and the effects of ANG II in the PVN. Increased superoxide anions in the PVN contribute to the enhanced CSAR and sympathetic activity in renovascular hypertension.

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.