Intermedin in Paraventricular Nucleus Attenuates Sympathoexcitation and Decreases TLR4-Mediated Sympathetic Activation via Adrenomedullin Receptors in Rats with Obesity-Related Hypertension

Intermedin/adrenomedullin-2(IMD/AM2), a member of the calcitonin gene-related peptide/AM family,plays an important role in protecting the cardiovascular system. However, its role in the enhanced sympathoexcitation in obesity-related hypertension is unknown. In this study, we investigated the effects of IMD in the paraventricular nucleus(PVN) of the hypothalamus on sympathetic nerve activity(SNA), and lipopolysaccharide(LPS)-induced sympathetic activation in obesity-related hypertensive(OH)rats induced by a high-fat diet for 12 weeks. Acute experiments were performed under anesthesia. The dynamic alterations of sympathetic outflow were evaluated as changes in renal SNA and mean arterial pressure(MAP) in response to specific drugs. Male rats were fed a control diet(12% kcal as fat) or a high-fat diet(42% kcal as fat) for 12 weeks to induce OH. The results showed that IMD protein in the PVN was downregulated, but Toll-like receptor 4(TLR4) and plasma norepinephrine(NE, indicating sympathetic hyperactivity) levels, and systolic blood pressure were increased in OH rats. LPS(0.5 lg/50 nL)-induced enhancement of renal SNA and MAP was greater in OH rats than in obese or control rats. Bilateral PVN microinjection of IMD(50 pmol)caused greater decreases in renal SNA and MAP in OH rats than in control rats, and inhibited LPS-induced sympatheticactivation, and these were effectively prevented in OH rats by pretreatment with the AM receptor antagonist AM22-52.The mitogen-activated protein kinase/extracellular signalregulated kinase(ERK) inhibitor U0126 in the PVN partially reversed the LPS-induced enhancement of SNA. However,IMD in the PVN decreased the LPS-induced ERK activation,which was also effectively prevented by AM22-52. Chronic IMD administration resulted in significant reductions in the plasma NE level and blood pressure in OH rats. Moreover,IMD lowered the TLR4 protein expression and ERK activation in the PVN, and decreased the LPS-induced sympathetic overactivity. These results indicate that IMD in the PVN attenuates SNA and hypertension, and decreases the ERK activation implicated in the LPS-induced enhancement of SNA in OH rats, and this is mediated by AM receptors.

Chronic Intracerebroventricular Infusion of Metformin Inhibits Salt-Sensitive Hypertension via Attenuation of Oxidative Stress and Neurohormonal Excitation in Rat Paraventricular Nucleus

Metformin(MET), an antidiabetic agent, also has antioxidative effects in metabolic-related hypertension.This study was designed to determine whether MET has anti-hypertensive effects in salt-sensitive hypertensive rats by inhibiting oxidative stress in the hypothalamic paraventricular nucleus(PVN). Salt-sensitive rats received a highsalt(HS) diet to induce hypertension, or a normal-salt(NS)diet as control. At the same time, they received intracerebroventricular(ICV) infusion of MET or vehicle for 6 weeks. We found that HS rats had higher oxidative stress levels and mean arterial pressure(MAP) than NS rats. ICV infusion of MET attenuated MAP and reduced plasma norepinephrine levels in HS rats. It also decreased reactive oxygen species and the expression of subunits of NAD(P)H oxidase, improved the superoxide dismutase activity,reduced components of the renin-angiotensin system, and altered neurotransmitters in the PVN. Our findings suggest that central MET administration lowers MAP in saltsensitive hypertension via attenuating oxidative stress,inhibiting the renin-angiotensin system, and restoring the balance between excitatory and inhibitory neurotransmitters in the PVN.

Blockade of c-Src Within the Paraventricular Nucleus Attenuates Inflammatory Cytokines and Oxidative Stress in the Mechanism of the TLR4 Signal Pathway in Salt-Induced Hypertension

Toll-like receptor 4 (TLR4) and cellular Src (cSrc) are closely associated with inflammatory cytokines and oxidative stress in hypertension, so we designed this study to explore the exact role of c-Src in the mechanism of action of the TLR4 signaling pathway in salt-induced hypertension. Salt-sensitive rats were given a high salt diet for 10 weeks to induce hypertension. This resulted in higher levels of TLR4, activated c-Src, pro-inflammatory cytokines, oxidative stress, and arterial pressure. Infusion of a TLR4 blocker into the hypothalamic paraventricular nucleus (PVN) decreased the activated c-Src, while microinjection of a c-Src inhibitor attenuated the PVN levels of nuclear factor-kappa B, pro-inflammatory cytokines, and oxidative stress. Our findings suggest that a longterm high-salt diet increases TLR4 expression in the PVN and this promotes the activation of c-Src, which upregulates the expression of pro-inflammatory cytokines and results in the overproduction of reactive oxygen species.Therefore, inhibiting central c-Src activity may be a new target for treating 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-1 beta, tumor necrosis factor alpha, and monocyte chemotactic protein-1, as well as higher gp91 phoxexpression 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.

Chemical Stimulation of Renal Tissue Induces Sympathetic Activation and a Pressor Response via the Paraventricular Nucleus in Rats

Sympathetic activation and the kidney play critical roles in hypertension and chronic heart failure.The role of the kidney in sympathetic activation is still not well known.In this study,we revealed an excitatory renal reflex(ERR)in rats induced by chemical stimulation of the kidney that regulated sympathetic activity and blood pressure.The ERR was induced by renal infusion of capsaicin,and evaluated by the changes in renal sympathetic outflow,blood pressure,and heart rate.Renal infusion of capsaicin dose-dependently increased the contralateral renal sympathetic nerve activity,mean arterial pressure,and heart rate.Capsaicin in the corticomedullary border had greater effects than in the cortex or medulla.Intravenous infusion of capsaicin had no significant effects.The effects of renal infusion of capsaicin were abolished by ipsilateral renal denervation,but were not affected by bilateral sinoaortic denervation.Renal infusion of capsaicin increased the ipsilateral renal afferent activity.The ERR was also induced by renal infusion of bradykinin,adenosine,and angiotensin II,but not by ATP.Renal infusion of capsaicin increased c-Fos expression in the paraventricular nucleus(PVN)of hypothalamus.Lesion of neurons in the PVN with kainic acid abolished the capsaicin-induced ERR.These findings indicate that chemical stimulation of kidney causes an excitatory reflex,leading to sympathetic activation,pressor response,and accelerated heart rate.The PVN is an important central nucleus in the pathway of the ERR.

Prostate-derived IL-1βupregulates expression of NMDA receptor in the paraventricular nucleus and shortens ejaculation latency in rats with experimental autoimmune prostatitis

Experimental autoimmune prostatitis(EAP)-induced persistent inflammatory immune response can significantly upregulate the expression of N-methyl-D-aspartic acid(NMDA)receptors in the paraventricular nucleus(PVN).However,the mechanism has not yet been elucidated.Herein,we screened out the target prostate-derived inflammation cytokines(PDICs)by comparing the inflammatory cytokine levels in peripheral blood and cerebrospinal fluid(CSF)between EAP rats and their controls.After identifying the target PDIC,qualified males in initial copulatory behavior testing(CBT)were subjected to implanting tubes onto bilateral PVN.Next,they were randomly divided into four subgroups(EAP-1,EAP-2,Control-1,and Control-2).After 1-week recovery,EAP-1 rats were microinjected with the target PDIC inhibitor,Control-1 rats were microinjected with the target PDIC,while the EAP-2 and Control-2 subgroups were only treated with the same amount of artificial CSF(aCSF).Results showed that only interleukin-1β(IL-1β)had significantly increased mRNA-expression in the prostate of EAP rats compared to the controls(P<0.001)and significantly higher protein concentrations in both the serum(P=0.001)and CSF(P<0.001)of the EAP groups compared to the Control groups.Therefore,IL-1βwas identified as the target PDIC which crosses the blood-brain barrier,thereby influencing the central nervous system.Moreover,the EAP-1 subgroup displayed a gradually prolonged ejaculation latency(EL)in the last three CBTs(all P<0.01)and a significantly lower expression of NMDA NR1 subunit in the PVN(P=0.043)compared to the respective control groups after a 10-day central administration of IL-1βinhibitors.However,the Control-1 subgroup showed a gradually shortened EL(P<0.01)and a significantly higher NR1 expression(P=0.004)after homochronous IL-1βadministration.Therefore,we identified IL-1βas the primary PDIC which shortens EL in EAP rats.However,further studies should be conducted to elucidate the specific molecular mechanisms through which IL-1βupregulates NMDA expression.

Angiotensin Type 1 Receptors and Superoxide Anion Production in Hypothalamic Paraventricular Nucleus Contribute to Capsaicin-Induced Excitatory Renal Reflex and Sympathetic Activation

Chemical stimulation of the kidney increases sympathetic activity and blood pressure in rats.The hypothalamic paraventricular nucleus(PVN)is important in mediating the excitatory renal reflex(ERR).In this study,we examined the role of molecular signaling in the PVN in mediating the capsaicin-induced ERR and sympathetic activation.Bilateral PVN microinjections were performed in rats under anesthesia.The ERR was elicited by infusion of capsaicin into the cortico-medullary border of the right kidney.The reflex was evaluated as the capsaicin-induced changes in left renal sympathetic nerve activity and mean arterial pressure.Blockade of angiotensin type 1 receptors with losartan or inhibition of angiotensin-converting enzyme with captopril in the PVN abolished the capsaicin-induced ERR.Renal infusion of capsaicin significantly increased NAD(P)H oxidase activity and superoxide anion production in the PVN,which were prevented by ipsilateral renal denervation or microinjection of losartan into the PVN.Furthermore,either scavenging of superoxide anions or inhibition of NAD(P)H oxidase in the PVN abolished the capsaicin-induced ERR.We conclude that the ERR induced by renal infusion of capsaicin is mediated by angiotensin type 1 receptor-related NAD(P)H oxidase activation and superoxide anion production within the PVN.