Increase In Renal Sympathetic Nerve Activity Research Articles

The inflammatory cytokine, interleukin‐1‐beta, drives central immune cell infiltration, changes in sympathetic nerve activity and blood pressure

IntroductionThe area postrema (AP) is a brain region that lacks a blood brain barrier allowing blood‐borne factors to access the brain. Since the AP is connected to numerous brain regions that play a key role blood pressure regulation, we hypothesised that blood‐borne inflammatory factors such as interleukin‐1 beta (IL‐1β) might play a role in the development of hypertension. In support of this hypothesis, plasma Interleukin‐1 beta is increased in hypertensive patients (Dalekos et al., 1997, J Lab Clin Med,129: 300–8). Furthermore, the receptors for IL‐1β are abundantly expressed in the AP. Here we test whether IL‐1β can act on the AP to cause an increase in blood pressure and renal sympathetic nerve activity (RSNA) in rats.MethodsBlood pressure and renal sympathetic nerve activity (RSNA) were recorded and analyzed after microinjection of different doses of IL‐1β into the AP (10ng and 25ng) of anaesthetised rats. In order to show that IL‐1β, specifically causes an increase in blood pressure, specific IL‐1 receptor blocking antibodies (IL‐1Ra) were injected into the AP prior to a 25ng IL‐1β injection. The AP was extracted for fluorescent activated cell sorting (FACS).ResultsExperiments showed that microinjection of 25ng IL‐1β caused a significant (p<0.01; Mann‐Whitney test) increase in both systolic blood pressure (19.6 ± 3.6 mmHg) and heart rate (55 ±10 bpm) compared with control injections of saline (SBP: 5.47 ± 1.58; HR 12 ± 6). Pre‐treatment with IL‐1Ra attenuated the response to IL‐1β, and was comparable with saline controls. IL‐1β also caused an increase in RSNA (137% ± 43%) and FACS revealed an increase in immune cell infiltration. Immunohistochemistry also revealed that IL‐1β injection results in Fos activation in the AP.ConclusionsIL‐1β injection appears to activate neurons in the area postrema which leads to an increase in blood pressure. By providing new insight into the actions of IL‐1β in the brain, we show that IL‐1β might be a potential target for future treatments for hypertension.Support or Funding InformationAustralian Research Council (FT170100363)National Health and Medical Research Council (GNT 1079680)Rebecca L Cooper Medical Research Foundation

Knockdown of Interleukin 17 Receptor A (IL‐17RA) in Paraventricular Nucleus of Hypothalamus Attenuates IL‐17‐induced Pressor Responses and Sympathetic Excitation

Inflammation contributes significantly to cardiovascular and autonomic dysfunction in hypertension and heart failure. Over the years, the pro‐inflammatory cytokine interleukin (IL)‐17 (also known as IL‐17A) has been recognized as a critical inflammatory regulator bridging immune responses and tissue inflammation. Our previous studies have demonstrated that peripherally or centrally administrated IL‐17A dramatically elevates blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in rats, and that its receptors IL‐17RA are richly expressed in the brain. The present work sought to determine whether IL‐17RA in the hypothalamic paraventricular nucleus (PVN), a key cardiovascular/autonomic brain center, mediate hemodynamic and sympathetic responses to systemically administered IL‐17A. In urethane anesthetized male SD rats, Mean BP (MBP, mmHg), HR (beats/min) and RSNA (% change) were recorded before and for 6–8 hours after an intravenous (IV) injection of IL‐17A (500 ng). In age‐matched control rats, IV IL‐17A induced a large and long‐lasting increase (*p<0.001 vs. baseline) in MBP (16.2 ± 2.3*), HR (49.8 ± 5.1*) and RSNA (165.6 ± 13.2 %*), beginning within 120 mins and peaking 6–8 hours after the injection. However, in rats pretreated with bilateral PVN microinjections of an IL‐17RA siRNA AAV virus and studied one week later, the IV IL‐17A‐elicited pressor responses in MBP (10.1 ± 2.1*), HR (22.1 ± 4.0*) and RSNA (68.5 ± 7.8 %*) were significantly (p<0.05) attenuated. mRNA for tumor necrosis factor‐α (TNF‐α), IL‐1β, monocyte chemoattractant protein‐1 (MCP‐1) and IL‐17RA in the PVN was measured by real‐time qPCR. Knockdown efficiency of IL‐17RA siRNA was confirmed by a reduction (−55%) of IL‐17RA mRNA level in the PVN. Additionally, the mRNA levels of TNF‐α (1.12 ± 0.24 vs. 0.51 ± 0.11*), IL‐1β (1.05 ± 0.16 vs. 0.64 ± 0.09*), and MCP‐1 (1.01 ± 0.10 vs. 0.60 ± 0.10*) induced by IV IL‐17A were significantly reduced in the PVN in rats pretreated with IL‐17RA siRNA. These data indicate that systemically administered IL‐17A acts upon IL‐17RA in the PVN to increase the expression of inflammatory mediators that drive sympathetic excitation, suggesting that PVN plays an important role in mediating the effects of circulating IL‐17A on sympathetic drive and cardiovascular function in inflammatory conditions such as hypertension and heart failure. IL‐17RA in the PVN is a potential target for therapeutic intervention in these diseases.Support or Funding InformationThis research was supported by NIH/NHLBI RO1 HL139521.

Hyperoxia blunts renal sympathetic nerve activity response to acute intermittent hypercapnia in rats.

Activation of the sympathetic nervous system plays an important role in the pathophysiology of sleep-related breathing disorders. The aim of the present study was to examine the effects of different levels of hypercapnia in the presence of various background oxygen levels on the magnitude of sympathoexcitation, measured by the renal sympathetic nerve activity (RSNA) in the acute intermittent hypercapnia (AIHc) rat model. The study was conducted on 56 urethane-anesthetized, vagotomized and mechanically ventilated Sprague-Dawley rats (n = 7/group). Each experimental group was subjected to a distinct AIHc protocol that varied in the applied levels of hypercapnia and background oxygen. Mean arterial pressure and RSNA were analyzed in 7 experimental time points: baseline, five hypercapnic episodes (each lasting 3 min) and 15 minutes following the last hypercapnic episode. Exposure to severe hypercapnia (FiCO2 = 0.15) evoked an increase in RSNA, which was preserved throughout the protocol, whereas in moderate hypercapnia (FiCO2 = 0.05) groups there was a trend of progressive diminution of RSNA magnitude following the first hypercapnic episode. Exposure to severe hypercapnia elicited significantly greater RSNA response during first hypercapnic episode and it was enhanced during subsequent episodes compared to exposure to moderate hypercapnia. Additionally, hyperoxic2 background (50% O2) blunted the RSNA response to AIHc compared to room air background, both in severe and moderate hypercapnia groups. Mean arterial blood pressure was preserved throughout the experimental protocol in all studied groups. These findings indicate that acute intermittent hypercapnia evokes increased renal sympathetic nerve activity that is dependent on the severity of hypercapnic exposures and the background oxygen level.

Abstract 136: The Ventromedial Hypothalamic BBSome is Required for Energy Homeostasis and Sympathetic Nerve Traffic Control

The BBSome, a protein complex of 8 Bardet-Biedl Syndrome (BBS) protein including BBS1, has emerged as an important regulator of metabolic and cardiovascular function. We previously demonstrated that conditional disruption of the BBSome, by deleting the Bbs1 gene, throughout the nervous system leads to obesity in mice. The ventromedial hypothalamus (VMH) play a key role in energy balance, but the contribution of the BBSome in the VMH to the control of energy homeostasis is not known. To address this, we specifically ablated the Bbs1 gene in the VMH by crossing the Bbs1 fl/fl mice with mice expressing Cre recombinase selectively in the VMH, driven by the steroidogenic factor 1 promoter (SF1 Cre ). VMH-selective Cre-recombination was verified using td-Tomato reporter mice. Importantly, SF1 Cre /Bbs1 fl/fl mice develop obesity as indicated by the increased (P<0.05) body weight (males: 43±2 vs 34±1 g in controls, and females: 33±2 vs 27±1 at age of 25 weeks) and fat mass (12.4±1 vs. 5.2±1 g). Of note, heterozygous SF1 Cre /Bbs1 fl/wt mice displayed an intermediate obesity phenotype (body weight: males: 39±2g and females: 30±1g). Daily food intake was not different in SF1 Cre /Bbs1 fl/fl mice relative to controls. However, energy expenditure (EE) was lower in SF1 Cre /Bbs1 fl/fl mice (ANCOVA corrected night EE: 0.27±0.06 vs 0.30±0.06 kcal/h in controls, P<0.05). Moreover, SF1 Cre /Bbs1 fl/fl mice exhibited a blunted cooling-induced increase in sympathetic nerve activity (SNA) subserving thermogenic brown adipose tissue (BAT), although basal BAT SNA activity was not different. Next, we assessed the consequence of SF1 neuron-specific Bbs1 gene deletion on SNA subserving cardiovascular beds. SF1 Cre /Bbs1 fl/fl mice displayed a modest, but significant increase in renal SNA (49±24%, P=0.03) and splanchnic SNA (85±18%, P<0.05), but not lumbar SNA (11±9%, P=0.14). Blood pressure, recoded under anesthesia, was not different in SF1 Cre /Bbs1 fl/fl mice relative to controls (P=0.2). Radiotelemetry measurement of blood pressure in SF1 Cre /Bbs1 fl/fl and control mice is under way. These findings highlight the importance of the VMH BBSome for the regulation of energy homeostasis and sympathetic nerve outflow.

Abstract 022: Role of Interleukin-17 in the Regulation of Hemodynamics and Renal Sympathetic Nerve Activity in Rats

Introduction: Central inflammation has been implicated in the pathophysiology of hypertension (HTN) and heart failure (HF). We previously reported that the pro-inflammatory cytokines (PIC) tumor necrosis factor-α and interleukin (IL)-1β act within the brain to increase blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) and contribute significantly to the neurohumoral activation in these diseases. Over the years, IL-17A, a PIC secreted mainly by Th17 cells and γδ T cells, has been identified as a critical inflammatory mediator promoting chronic inflammation in cardiovascular diseases. Growing evidence indicates that IL-17A penetrates the blood-brain barrier and that its receptors, IL-17RA and IL-17RC, are abundantly expressed in CNS. However, whether IL-17A contributes to sympathetic excitation remains unknown. Hypothesis: IL-17A acts centrally to influence sympathetic drive and cardiovascular dynamics. Methods: BP (mmHg), HR (bpm) and RSNA (% change) were recorded in urethane anesthetized male Sprague Dawley rats. IL-17A was administered by intravenous (IV, 500 ng) or intracerebroventricular (ICV, 100 ng) injection or by bilateral microinjection (25 ng/side) into hypothalamic paraventricular nucleus (PVN). IL-17RA expression in the PVN was visualized by confocal microscopy. Results: IV IL-17A (n=6) induced a substantial and long-lasting increase (*p<0.001 vs. baseline) in BP (16.7 ± 2.1*), HR (57 ± 8*) and RSNA (104.5 ± 4.8 %*), that began within 45-60 mins and peaked 5-6 hours after IV injection. Similarly, ICV (n=6) or PVN microinjection of IL-17A (n=6) elicited dramatic and long-lasting increases in BP (23.1 ± 2.5 and 19.6 ± 2.1, respectively), HR (78.6 ± 7.4 and 65.1 ± 6.8, respectively) and RSNA (223.6 ± 5.1 and 152.2 ± 3.3, respectively), with the peak responses at 5 to 6 hours or even later. Confocal images showed that IL-17RA was richly expressed in the PVN. Conclusion: These data demonstrate that IL-17A regulates cardiovascular function and sympathetic drive, suggesting that IL-17A may contribute to sympathetic excitation in chronic inflammatory conditions like HTN and HF via its actions within the brain. IL-17A is a potential target for therapeutic intervention in these diseases.

Does glucagon-like peptide-1 induce diuresis and natriuresis by modulating afferent renal nerve activity?

Glucagon-like peptide-1 (GLP-1), an incretin hormone, has diuretic and natriuretic effects. The present study was designed to explore the possible underlying mechanisms for the diuretic and natriuretic effects of GLP-1 via renal nerves in rats. Immunohistochemistry revealed that GLP-1 receptors were avidly expressed in the pelvic wall, the wall being adjacent to afferent renal nerves immunoreactive to calcitonin gene-related peptide, which is the dominant neurotransmitter for renal afferents. GLP-1 (3 μM) infused into the left renal pelvis increased ipsilateral afferent renal nerve activity (110.0 ± 15.6% of basal value). Intravenous infusion of GLP-1 (1 µg·kg-1·min-1) for 30 min increased renal sympathetic nerve activity (RSNA). After the distal end of the renal nerve was cut to eliminate the afferent signal, the increase in efferent renal nerve activity during intravenous infusion of GLP-1 was diminished compared with the increase in total RSNA (17.0 ± 9.0% vs. 68.1 ± 20.0% of the basal value). Diuretic and natriuretic responses to intravenous infusion of GLP-1 were enhanced by total renal denervation (T-RDN) with acute surgical cutting of the renal nerves. Selective afferent renal nerve denervation (A-RDN) was performed by bilateral perivascular application of capsaicin on the renal nerves. Similar to T-RDN, A-RDN enhanced diuretic and natriuretic responses to GLP-1. Urine flow and Na+ excretion responses to GLP-1 were not significantly different between T-RDN and A-RDN groups. These results indicate that the diuretic and natriuretic effects of GLP-1 are partly governed via activation of afferent renal nerves by GLP-1 acting on sensory nerve fibers within the pelvis of the kidney.

Neurohumoral interactions contributing to renal vasoconstriction and decreased renal blood flow in heart failure

In heart failure (HF), increases in renal sympathetic nerve activity (RSNA), renal norepinephrine spillover, and renin release cause renal vasoconstriction, which may contribute to the cardiorenal syndrome. To increase our understanding of the mechanisms causing renal vasoconstriction in HF, we investigated the interactions between the increased activity of the renal nerves and the renal release of norepinephrine and renin in an ovine pacing-induced model of HF compared with healthy sheep. In addition, we determined the level of renal angiotensin type-1 receptors and the renal vascular responsiveness to stimulation of the renal nerves and α1-adrenoceptors. In conscious sheep with mild HF (ejection fraction 35%-40%), renal blood flow (276 ± 13 to 185 ± 18 mL/min) and renal vascular conductance (3.8 ± 0.2 to 3.1 ± 0.2 mL·min-1·mmHg-1) were decreased compared with healthy sheep. There were increases in the burst frequency of RSNA (27%), renal norepinephrine spillover (377%), and plasma renin activity (141%), whereas the density of renal medullary angiotensin type-1 receptors decreased. In anesthetized sheep with HF, the renal vasoconstrictor responses to electrical stimulation of the renal nerves or to phenylephrine were attenuated. Irbesartan improved the responses to nerve stimulation, but not to phenylephrine, in HF and reduced the responses in normal sheep. In summary, in HF, the increases in renal norepinephrine spillover and plasma renin activity are augmented compared with the increase in RSNA. The vasoconstrictor effect of the increased renal norepinephrine and angiotensin II is offset by reduced levels of renal angiotensin type-1 receptors and reduced renal vasoconstrictor responsiveness to α1-adrenoceptor stimulation.

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

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

Water deprivation does not augment sympathetic or pressor responses to sciatic afferent nerve stimulation in rats or to static exercise in humans.

Excess dietary salt intake excites central sympathetic networks, which may be related to plasma hypernatremia. Plasma hypernatremia also occurs following water deprivation (WD). The purpose of this study was to test the hypothesis that WD induces hypernatremia and consequently augments sympathetic and pressor responses to sympathoexcitatory stimuli in rats and humans. Sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses to sciatic afferent nerve stimulation (2-20 Hz) and chemical stimulation of the rostral ventrolateral medulla (RVLM) were assessed in rats after 48 h of WD and compared with normally hydrated control rats (CON). In a parallel randomized-crossover human experiment (n = 13 healthy young adults), sympathetic (microneurography) and pressor (photoplethysmography) responses to static exercise were compared between 16-h WD and CON conditions. In rats, plasma [Na+] was significantly higher in WD versus CON [136 ± 2 vs. 144 ± 2 (SD) mM, P < 0.01], but sciatic afferent nerve stimulation produced similar increases in renal SNA [5 Hz, 174 ± 34 vs. 169 ± 49% (SD), n = 6-8] and mean ABP [5 Hz, 21 ± 6 vs. 18 ± 7 (SD mmHg, n = 6-8]. RVLM injection of l-glutamate also produced similar increases in SNA and ABP in WD versus CON rats. In humans, WD increased serum [Na+] [140.6 ± 2.1 vs. 142.1 ± 1.9 mM (SD), P = 0.02] but did not augment sympathetic [muscle SNA: change from baseline (Δ) 6 ± 7 vs. 5 ± 7 (SD) bursts/min, P = 0.83] or mean ABP [Δ 12 ± 5 vs. 11 ± 8 (SD) mmHg, P = 0.73; WD vs. CON for all results] responses during the final minute of exercise. These findings suggest that despite eliciting relative hypernatremia, WD does not augment sympathetic or pressor responses to sciatic afferent stimulation in rats or to static exercise in humans. NEW & NOTEWORTHY Excess dietary salt intake excites central sympathetic networks, which may be related to plasma hypernatremia. Plasma hypernatremia also occurs following water deprivation (WD). We sought to determine whether plasma hypernatremia/hyperosmolality induced by WD augments sympathetic and pressor responses to sympathoexcitatory stimuli. Our findings suggest that WD does not augment sympathetic or pressor responses to sciatic afferent nerve stimulation in rats or to static exercise in humans.

An Exaggerated Muscle Mechanoreflex in Type 2 Diabetic Rats Is Mediated by Potentiated Skeletal Muscle Afferent Discharge to Mechanical Stimulation

The blood pressure response to exercise is heightened in patients with type 2 diabetes (T2D). Since such elevations in blood pressure increase the risk for developing an adverse cardiovascular event, elucidating the underlying mechanisms is clinically relevant. The exercise pressor reflex (EPR) plays an important role in regulating the cardiovascular system during exercise. Our group has previously demonstrated that the EPR is exaggerated in T2D rats contributing importantly to the augmented pressor response to physical activity. However, the mechanisms responsible for this abnormal EPR function in T2D remain to be elucidated. Sensory information from working muscle is generated, in part, by stimulation of mechanically sensitive afferent neurons (i.e. the skeletal muscle mechanoreflex, a component of the EPR). In this study, it was hypothesized that the EPR dysfunction characteristic of T2D is mediated by an exaggerated muscle mechanoreflex resulting from an increase in muscle afferent responsiveness to mechanical stimulation.PURPOSEIn T2D rats, to 1) investigatethe pressor and sympathetic responses to stimulation of the muscle mechanoreflex in vivo and 2) examine neuronal discharge to mechanical stimulation in skeletal muscle thin fiber afferents in vitro.METHODSFor 14–16 weeks, rats were given either a normal diet (control group) or a high fat diet in combination with a low dose (35 mg/kg) of streptozotocin (T2D group). In vivo, we measured changes in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) during passive stretch of hindlimb muscle in decerebrate rats. In vitro, muscle afferent neurons were mechanically activated via ramp‐shaped mechanical stimulation (0–196 mN) with the resulting action potentials assessed by obtaining single‐fiber recordings using an extensor digitorum longusmuscle‐nerve preparation.RESULTSCompared to control, induction of T2D evoked hyperglycemia (104±5 vs. 161±10 mg/dL, P&lt;0.05). Similarly, T2D elicited significant increases in plasma insulin (111±10 vs. 150±13 pmol/L, P&lt;0.05) and HOMA‐IR (3.9±0.3 vs. 9.3±1.2, P&lt;0.01). Mechanoreflex activationby passive stretch evoked significantly greater increases in RSNA and MAP in T2D (13±3 vs. 81±16 %, P&lt;0.01 and 7±3 vs. 29±7 mmHg, P&lt;0.05, respectively). Further, the response magnitude to mechanical stimulation tended to be greater in muscle afferents from T2D compared to control (20±7 vs. 40±8 spikes, P=0.10).CONCLUSIONSThese findings suggest that the muscle mechanoreflex is exaggerated in T2D resulting, at least in part, from augmentations in the responsiveness of thin muscle afferent fibers to mechanical stimuli. Importantly, these changes likely contribute significantly to the EPR overactivity manifest in T2D.Support or Funding InformationSupported by Lawson &amp; Rogers Lacy Research Fund in Cardiovascular Disease and the Southwestern School of Health Professions Interdisciplinary Research Grant Program.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Central Administration of Insulin Combined With Resistin Reduces Renal Sympathetic Nerve Activity in Rats Fed a High Fat Diet.

Insulin receptors are widely distributed in the central nervous system and their activation by insulin elicits renal sympatho-excitatory effects. Resistin, an adipokine, promotes resistance to the metabolic effects of insulin. Resistin also induces increases in renal sympathetic nerve activity (RSNA) by acting in the brain, but whether it can influence insulin’s actions on RSNA is unknown. In the present study we investigated, in male Sprague-Dawley rats (7–8 weeks of age), the effects of central administration of insulin combined with resistin on RSNA following a normal diet (ND) and a high fat diet (HFD) (22% fat), since HFD can reportedly attenuate insulin’s actions. RSNA, mean arterial pressure (MAP) and heart rate (HR) responses were monitored and recorded before and for 180 min after intracerebroventricular injection of saline (control) (n = 5 HFD and ND), resistin (7 μg; n = 4 ND, n = 5 HFD), insulin (500 mU; n = 6 ND, n = 5 HFD), and the combination of both resistin and insulin (n = 7 ND, n = 5 HFD). The key finding of the present study was that when resistin and insulin were combined there was no increase in RSNA induced in rats fed a normal diet or the high fat diet. This contrasted with the sympatho-excitatory RSNA effects of the hormones when each was administered alone in rats fed the ND and the HFD.

Renal perfusion, oxygenation, and sympathetic nerve activity during volatile or intravenous general anaesthesia in sheep

BackgroundGlobal and intra-renal perfusion and oxygenation may be affected by the choice of anaesthetic. We compared the effects of isoflurane with those of propofol and fentanyl on renal blood flow (RBF) and intra-renal perfusion and oxygenation, and assessed how these were associated with renal sympathetic nerve activity (RSNA). MethodsA renal artery flow probe and laser Doppler and oxygen-sensing probes were surgically implanted in the renal medulla and cortex in 20 Merino ewes. RSNA was measured in 12 additional ewes. We compared the effects of volatile or i.v. anaesthesia on global RBF, renal oxygen delivery (RDO2), intra-renal perfusion, and RSNA with the non-anaesthetised state on postoperative day 3 as control reference. ResultsCompared with a non-anaesthetised state, volatile anaesthesia reduced global RBF [–76 (82–68)%], RDO2 [−76 (83–71)%], and cortical [–68 (74–54)%] and medullary [–76 (84–72)%] perfusion. I.V. anaesthesia reduced RBF [–55 (67–38)%], RDO2 [–55 (65–44)%], and cortical [–27 (45–6)%] and medullary [–35 (48–30)%] perfusion, but to a lesser extent than volatile anaesthesia. Renal PO2 was not influenced by anaesthesia, whilst RSNA was elevated during volatile, but not during i.v. anaesthesia. ConclusionsVolatile and i.v. general anaesthesia markedly reduced global RBF, RDO2, and regional kidney perfusion. These effects were greater with volatile anaesthesia, and were paralleled by an increase in RSNA. Our findings suggest a neurogenic modulatory effect of anaesthetics on renal perfusion and oxygenation.

Endothelin-1-Mediated Mechanisms in the Carotid Body Modulates Cardiovascular Responses in Rats Exposed to Chronic Intermittent Hypoxia

Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnea (OSA), is associated with hypertension. The increased of carotid body (CB) sensitivity due to enhanced sympathetic efferent may be mainly responsible for the elevation of blood pressure. Accordingly, we studied this effect of Endothelin-1 (ET-1)-induced CB chemosensory response to CIH, as a vasoactive peptide expressed in CB. The purpose of this study was to investigate the mean arterial blood pressure (MAP) and renal sympathetic nerve activity (RSNA) responses in CIH group by injecting ET-1 to directly stimulate CB chemoreceptor. Furthermore, whether ET receptor-mediated PKC and p38MAPK signaling pathway was involved in CIH-induced CB activation was also studied. Male Sprague–Dawley rats were exposed to CIH (8 h/day for 3 weeks) and the MAP and RSNA were recorded in CIH rats and Sham rats. Our results demonstrated that ET-1-induced MAP and RSNA increase were mainly mediated by ETA receptor activation in CB chemosensory after CIH exposure. Moreover, P38MAPK and PKC signaling pathway might be involved in ET-1-induced increase of MAP and RSNA in CIH group, which provided a potential therapeutic target of OSA.

Abstract 003: Mrap2 Dissociate Mc4r-Mediated Sympathetic Control of Metabolism and Blood Pressure

The brain melanocortin-4 receptor (MC4R) plays an important in the control of food intake and energy expenditure by increasing thermogenic sympathetic nerve activity (SNA). In addition, brain MC4R-mediated activation of SNA subserving cardiovascular organs such as the kidneys increase blood pressure. The melanocortin receptor accessory protein 2 (MRAP2) regulates the activity of the MC4R and other G-protein coupled receptors, but its specific role in MC4R-containing neurons is not clear . We hypothesized that MRAP2 in MC4R neurons is essential for the regulation of SNA, energy homeostasis and blood pressure. We generated mice (MRAP2 MC4R ) that lack MRAP2 in MC4R neurons by crossing MRAP2 fl/fl mice with MC4R Cre mice and confirmed Cre recombinase activity in MC4R neurons using td-Tomato reporter mice. Interestingly, the MRAP2 MC4R mice displayed obesity as indicated by the increased (p&lt;0.05) body weight (males: 40.1±2.2 vs 32.9±0.9g in littermate controls, females: 28.6±2.8 vs 24.2±1.3g in controls at 16 weeks of age) and fat mass, but not lean mass. Weights of fat pads and liver were also significantly elevated in the MRAP2 MC4R relative to littermate controls. Food intake was increased in the MRAP2 MC4R mice relative to littermate controls (males: 4.7±0.3 vs 3.9±0.3g and females: 3.5±0.2 vs 2.8±0.2g). Glucose and insulin tolerance tests revealed impaired glucose tolerance and insulin-induced glucose clearance in MRAP2 MC4R mice compared to littermate controls. Baseline brown adipose tissue (BAT) SNA tended to be lower in MRAP2 MC4R mice relative to controls. Moreover, intracerebroventricular (icv) injection of MTII (MC4R agonist, 1 μg) increased BAT SNA in control mice (107±31%) but not in MRAP2 MC4R mice (18±24%, p=0.02). On the other hand, icv the MTII (1 and 2 μg)-induced increase in renal SNA (p=0.2) and blood pressure (p=0.4) was not different in MRAP2 MC4R (100±32% and 15±8mmHg, respectively) relative to controls (74±24% and 12±6mmHg). These findings support a critical role for MRAP2 in uncoupling neuronal MC4R-mediated control of regional sympathetic traffic impacting energy metabolism versus blood pressure.

Sympatho-excitatory response to pulmonary chemosensitive spinal afferent activation in anesthetized, vagotomized rats.

The sensory innervation of the lung is well known to be innervated by nerve fibers of both vagal and sympathetic origin. Although the vagal afferent innervation of the lung has been well characterized, less is known about physiological effects mediated by spinal sympathetic afferent fibers. We hypothesized that activation of sympathetic spinal afferent nerve fibers of the lung would result in an excitatory pressor reflex, similar to that previously characterized in the heart. In this study, we evaluated changes in renal sympathetic nerve activity (RSNA) and hemodynamics in response to activation of TRPV1‐sensitive pulmonary spinal sensory fibers by agonist application to the visceral pleura of the lung and by administration into the primary bronchus in anesthetized, bilaterally vagotomized, adult Sprague‐Dawley rats. Application of bradykinin (BK) to the visceral pleura of the lung produced an increase in mean arterial pressure (MAP), heart rate (HR), and RSNA. This response was significantly greater when BK was applied to the ventral surface of the left lung compared to the dorsal surface. Conversely, topical application of capsaicin (Cap) onto the visceral pleura of the lung, produced a biphasic reflex change in MAP, coupled with increases in HR and RSNA which was very similar to the hemodynamic response to epicardial application of Cap. This reflex was also evoked in animals with intact pulmonary vagal innervation and when BK was applied to the distal airways of the lung via the left primary bronchus. In order to further confirm the origin of this reflex, epidural application of a selective afferent neurotoxin (resiniferatoxin, RTX) was used to chronically ablate thoracic TRPV1‐expressing afferent soma at the level of T1–T4 dorsal root ganglia pleura. This treatment abolished all sympatho‐excitatory responses to both cardiac and pulmonary application of BK and Cap in vagotomized rats 9–10 weeks post‐RTX. These data suggest the presence of an excitatory pulmonary chemosensitive sympathetic afferent reflex. This finding may have important clinical implications in pulmonary conditions inducing sensory nerve activation such as pulmonary inflammation and inhalation of chemical stimuli.

CCL2‐CCR2 Signalling in the Hypothalamic Paraventricular Nucleus Elicits Sympathetic‐Mediated Blood Pressure Elevations Through Monocyte and Lymphocyte Recruitment

Chemokine C‐C motif ligand 2 (CCL2) is a chemotactic cytokine, which is elevated in the plasma of hypertensive patients. In experimental models of hypertension, CCL2 levels are increased by 3‐fold in the paraventricular nucleus of the hypothalamus (PVN). However, the underlying neural and molecular mechanisms leading to the development of hypertension still remain unknown. Here, we show for the first time that in Sprague‐Dawley rats activation of receptors for CCL2 (i.e. CCR2) in the PVN elicited biphasic blood pressure (BP) responses and changes in renal sympathetic nerve activity (RSNA), consisting of early reductions followed by long‐lasting increases in RSNA and mean arterial pressure (MAP). These responses were abolished by prior CCR2 blockade with the antagonist RS‐102895. Purinergic transmission between astrocytes and neurons mediated the initial sympathoinhibition, whereas monocyte and lymphocyte infiltration into the PVN were involved in the subsequent sympathoexcitation. Our anatomical results support these findings by showing that CCR2 are predominantly expressed in the membrane of astrocytes, which make close appositions with PVN neurons projecting to the rostral ventrolateral medulla (RVLM) ‐ where cardiovascular sympathetic premotor neurons are found. Finally, in renovascular hypertensive rats (2 kidney ‐ 1 clip) plasma and cerebrospinal fluid levels of CCL2 were elevated with an onset occurring on the first week ‐ prior to the development of hypertension. Microglia activation and lymphocyte infiltration in the PVN were also evident by the second week, when animals were still pre‐hypertensive. The results here suggest that CCL2 upregulation, microglia activation, and lymphocyte infiltration in the PVN precede the sustained increases in sympathetic activity and blood pressure observed in hypertension.Support or Funding InformationDepartment of Health, Australian Government | National Health and Medical Research Council (NHMRC): Song T Yao, GNT1079680. Rebecca L Cooper Medical Foundation: Willian S Korim. Australian Government Research Training Program Scholarships: Khalid Elsaafien. Department of Industry, Innovation, Science, Research and Tertiary Education, Australian Government | Australian Research Council (ARC): Song T Yao, FT170100363.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

TRPA1‐Induced Pulmonary Spinal Sympathetic Afferent Activation is Attenuated in Rats with Chronic Heart Failure

In a recent preliminary study (Association of the University Anesthesiologists 64th annual meeting, Abstract #1109, 2017), we reported that activation of pulmonary spinal afferents by topical application of bradykinin (BK) and the TRPV1 agonist capsaisin on to lung surfaces (especially on the ventral surface) evokes a previously undocumented potent sympatho‐excitatory reflex that includes increased bood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in urethane‐α‐chloralose anesthetized, vagotomized rats. These data suggested a new pulmonary sympathetic afferent reflex (PSAR) in rats. However, it remains unclear whether pulmonary sympathetic afferents can also be activated by the transient receptor potential ankyrin 1 (TRPA1) agonist, allyl isothiocyanate (AITC). In the current study, we examined the TRPA1‐induced PSAR in both normal and chronic heart failure (CHF) states. After bilateral vagotomy, we applied filter paper (3 × 3 mm) saturated with 30 mM AITC to the ventral lung surfaces to stimulate the PSAR in urethane‐ α‐chloralose anesthetized sham‐operated and CHF (8 weeks post myocardial infarction) rats. We found that application of AITC to the lungs resulted in a biphasic BP response whereas HR and RSNA remained elevated during the AITC application in sham rats (Table 1). Compared to sham rats, AITC caused a predominantly depressor response in CHF rats. The increases in HR and RSNA in response to AITC were also attenuated in CHF rats. These data suggest that activation of the TRPA1 receptor in pulmonary spinal afferents can cause sympatho‐excitation in normal rats whereas this response was blunted in CHF rats. Ongoing studies are validating TRPA1 receptor protein expression in pulmonary sensory neurons in sham and CHF rats.Support or Funding InformationThis work was, in part, supported by grants from the National Heart, Lung, and Blood Institute (1R01HL121012‐01 and 1R01HL126796‐01).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract P317: Sex Differences in the Hemodynamic and Sympathetic Responses to Centrally Administered Tumor Necrosis Factor-α in Rats

Introduction: Accumulating evidence indicates that sex differences exist in the clinical and experimental outcomes of various cardiovascular diseases. In addition to its protective effect on renin-angiotensin system activity, estrogen has an anti-inflammatory influence. The central actions of pro-inflammatory cytokines (PICs) contribute significantly to cardiovascular and autonomic dysfunction in hypertension and heart failure. In male adult rat, central administration of PICs induces substantial increases in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA), and blocking PICs reduces sympathetic excitation in experimental models of hypertension and heart failure. Whether PICs have similar central sympatho-excitatory effects in the female rat remains unknown. Hypothesis: We hypothesized that female rats may be protected from the central cardiovascular and autonomic effects of PICs. Methods: Urethane anesthetized male and female Sprague Dawley rats (10-12 weeks) underwent an intracerebrovascular (ICV) injection of the prototypical PIC tumor necrosis factor-α (TNF-α, 100 ng). BP (mmHg), HR (beats/min) and RSNA (% change) responses were continuously recorded for 4-5 hours. Results: In male rats (n=6), ICV TNF-α induced a dramatic and long-lasting increase (*p&lt;0.001 vs. baseline) in BP (23.1 ± 2.5*), HR (82 ± 8*) and RSNA (109.5 ± 4.3 %*), that began within 20-30 mins and peaked at 90-120 mins after ICV injection. In the female rats (n=6), ICV TNF-α elicited significantly (p&lt;0.05) smaller increases (*p&lt;0.001 vs. baseline) in BP (14.8 ± 1.8*), HR (55 ± 6*) and RSNA (78.5 ± 6.3*), compared with the male rats. Conclusion: These data demonstrate a sex difference in the cardiovascular and sympathetic responses to centrally administered PICs. Whether the observed differences can be explained by an estrogen effect on TNF-α signaling per se or by an estrogen effect on TNF-α-induced renin-angiotensin activity remains to be determined. However, a reduced response of female rats to central inflammation may be an important contributor to sex differences in pathophysiology of hypertension and heart failure.

Effects of central administration of resistin on renal sympathetic nerve activity in rats fed a high‐fat diet: a comparison with leptin

Similar to leptin, resistin acts centrally to increase renal sympathetic nerve activity (RSNA). In high-fat fed animals, the sympatho-excitatory effects of leptin are retained, in contrast to the reduced actions of leptin on dietary intake. In the present study, we investigated whether the sympatho-excitatory actions of resistin were influenced by a high-fat diet. Further, because resistin and leptin combined can induce a greater sympatho-excitatory response than each alone in rats fed a normal chow diet, we investigated whether a high-fat diet (22%) could influence this centrally-mediated interaction. Mean arterial pressure (MAP), heart rate (HR) and RSNA were recorded before and for 3hours after i.c.v. saline (control; n=5), leptin (7μg; n=4), resistin (7μg; n=5) and leptin and resistin combined (n=6). Leptin alone and resistin alone significantly increased RSNA (71±16%, 62±4%, respectively). When leptin and resistin were combined, there was a significantly greater increase in RSNA (195±41%) compared to either hormone alone. MAP and HR responses were not significantly different between hormones. When the responses in high-fat fed rats were compared to normal chow fed rats, there were no significant differences in the maximum RSNA responses. The findings indicate that sympatho-excitatory effects of resistin on RSNA are not altered by high-fat feeding, including the greater increase in RSNA observed when resistin and leptin are combined. Our results suggest that diets rich in fat do not induce resistance to the increase in RSNA induced by resistin alone or in combination with leptin.

Exaggerated sympathetic and pressor responses to exercise pressor reflex activation are attenuated by intracerebroventricular insulin administration in type 2 diabetic rats

The cardiovascular response to exercise is abnormally exaggerated in patients with type 2 diabetes mellitus (T2D). We have previously demonstrated that stimulation of the exercise pressor reflex (EPR) during muscle contraction elicits exaggerated increases in renal sympathetic nerve activity (RSNA) contributing significantly to this heightened circulatory responsiveness. However, the mechanisms underlying this EPR dysfunction remain to be elucidated. Evidence suggests that the availability of brain insulin is reduced in T2D. Given that sympathetic activity is primarily regulated within the brain, we hypothesized that a decrease in brain insulin contributes to EPR‐induced sympathetic overactivity in this disease. To test this hypothesis, we measured changes in RSNA and mean arterial pressure (MAP) during stimulation of the EPR in decerebrated Sprague‐Dawley rats given either a normal diet (control) or a high fat diet (in combination with a one‐time low dose of streptozotocin to produce T2D) for 14–16 weeks. Compared to normal diet‐fed rats, animals receiving the high fat diet had significantly increased plasma insulin (1.6±0.2 vs. 4.1±0.4 ng/mL, P&lt;0.05) as well as fasting blood glucose (94±5 vs. 120±5 mg/dL, P&lt;0.05). Compared to control animals, stimulation of the EPR by electrically‐induced muscle contraction evoked significantly greater increases in RSNA (Δ = 36±10 vs. 122±20 %, P&lt;0.05) and MAP (Δ = 15±1 vs. 49±5 mmHg, P&lt;0.05) in T2D rats. Intracerebroventricular insulin administration significantly attenuated the exaggerated sympathetic (Δ = 111±20 vs. 50±17 %, P=0.05) and pressor responses (Δ = 49±5 vs. 12±4 mmHg, P&lt;0.05) to EPR activation in T2D rats but did not have a significant effect in control animals (RSNA: Δ = 43±2 vs. 33±13 %; MAP: Δ = 15±1 vs. 7±4 mmHg). These findings suggest that the heightened cardiovascular response to exercise in T2D may be mediated by EPR‐induced sympathetic dysfunction resulting as a consequence of decreased insulin availability within the brain.Support or Funding InformationSupported by the Lawson &amp; Rogers Lacy Research Fund in Cardiovascular Disease.