Depressor Response Research Articles

Sex, Oxidative Stress, and Hypertension: Insights From Animal Models.

One of the mechanisms responsible for blood pressure (BP) regulation is thought to be oxidative stress. In this review, we highlight preclinical studies that strongly support a role for oxidative stress in development and maintenance of hypertension in male animals, based on depressor responses to antioxidants, particularly tempol and apocynin. In females, oxidative stress seems to be important in the initial development of hypertension. However, whether maintenance of hypertension in females is mediated by oxidative stress is not clear. In clinical studies, pharmacological intervention to reduce BP with antioxidants has conflicting results, mostly negative. This review will discuss the uncertainties regarding blood pressure control and oxidative stress and potential reasons for these outcomes.

Muscarinic Acetylcholine Receptor-2 in the Cerebellar Fastigial Nucleus is Involved in Acetylcholine-Mediated Blood Pressure Regulation in Rats

Our previous investigations have revealed that microinjection of acetylcholine (ACh) into the cerebellar fastigial nucleus (FN) induces a systemic blood pressure (BP) depressor response and that the muscarinic ACh (mACh) receptor contributes substantially to this process. This study was determined to explore the role of muscarinic ACh receptor-2 (M2 receptor) in ACh-mediated BP regulation and its underlying electrophysiological mechanism. ACh mixed with methoctramine hydrate (MCT, a selective M2 receptor antagonist) and normal saline (0.9% NaCl) were separately microinjected into the FN of anaesthetized rats, and the mean arterial pressure during the reactive time (the duration for BP to return to its basal level) was calculated; the responses of cholinergic reagents to the inward currents in FN neurons were also examined via patch-clamp recording in vitro; in addition, the receptor expression in the FN was confirmed by immunohistochemistry. The results demonstrated that MCT effectively blocked the ACh-mediated BP depressor response and the ACh-induced inward currents in FN neurons; moreover, M2 receptors were unequivocally distributed in the FN. Taken together, the results indicate that M2 receptors in the FN may be involved in ACh-mediated BP down-regulation by tuning neuronal excitation.

Nrf2 Dysfunction in the RVLM is Associated with Obesity‐Induced Sympathoexcitation

Sympathetic overactivity contributes to the pathogenesis of obesity‐induced hypertension. The rostral ventrolateral medulla (RVLM) is an important brainstem region that regulates sympathetic nerve activity (SNA) to peripheral tissues. Oxidative stress and neuroinflammation in the RVLM are believed to be important contributors for augmented SNA in obesity, however, the molecular mechanisms that initiate and sustain the pro‐inflammatory milieu in the RVLM during obesity are not clear. Nuclear factor erythroid 2‐related factor (Nrf2) is a master transcriptional factor that regulates the expression of anti‐oxidant and anti‐inflammatory genes. We hypothesized that obesity impairs Nrf2 signaling to increase oxidative stress in the RVLM leading to increases in SNA and hypertension. To test this, 2 months‐old male C57BL/6J mice were fed a high‐fat diet (HFD; 60% fat) or normal chow diet (10% fat for 16 weeks and were instrumented with radiotelemeters in the last 2 weeks for measuring blood pressure and SNA. Heart rate variability and depressor response to ganglionic blockade were used to assess SNA. At the end of 16 weeks, animals were sacrificed, brainstem was isolated and sectioned. Superoxide levels were assessed in the frozen sections by dihydroethidium staining (DHE). RVLM was microdissected for gene expression analysis. Data were analyzed by students t‐test and p<0.05 was considered statistically significant. HFD feeding resulted in a mild but significant increase in mean arterial pressure (103.7 ± 0.9 vs 108.6 ± 0.73 mmHg, normal chow diet vs HFD; P<0.05; n=4) and systolic blood pressure (121.2 ± 1.2 vs 129 ± 0.67 mmHg, p<0.05; n=4) compared to normal chow‐fed animals. Ganglionic blockade using hexamethonium showed greater depressor response (−0.21 ± 2.9 vs 13.13 ± 1.3 mmHg, normal chow diet vs HFD; p<0.05; n=4) to HFD feeding. Furthermore, low‐frequency blood pressure variability and the ratio of low‐frequency to high‐frequency heart rate variability in HFD mice were significantly higher than in the control mice suggesting HFD upregulated SNA. In addition, obesity‐induced sympathoexcitation was associated with increased superoxide levels (DHE staining) and decreased mRNA levels of Nrf2 (1.05 ± 0.16 vs 0.48 ± 0.06 fold, normal diet vs HFD; p<0.05) and its target genes (e.g. NQO1 1.08 ± 0.22 vs 0.51 ± 0.08 fold, p<0.05 and SOD2 1.03 ± 0.13 vs 0.48 ± 0.05 fold; p<0.05) in the RVLM of HFD mice. Collectively, our results show for the first time, evidence for obesity‐associated Nrf2 dysfunction in the RVLM. Future studies will investigate the mechanistic role of Nrf2 signaling in the RVLM in obesity‐induced sympathoexcitation.Support or Funding InformationRAC fund, CVHS, Oklahoma State UniversityThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Both Dietary Salt Restriction and Excess Dietary Salt Intake Exaggerate Cardiovascular Reflex Responses to Activation of the Sciatic Afferents, Aortic Depressor Nerve, and Vagal Afferents

Excess dietary salt intake exaggerates sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses to several cardiovascular reflexes in salt‐resistant animals. Recently, observational cohort studies suggest that salt restriction increases cardiovascular morbidity/mortality in several cardiovascular diseases, and the relationship between cardiovascular morbidity and dietary salt intake resembles a J‐shaped curve. However, little evidence exists to document the impact of salt restriction on cardiovascular reflex responses and whether this relationship resembles a J‐shaped curve. Thus, the aim of the present study was to determine whether salt restriction affects SNA and ABP responses to activation of sciatic afferents, the aortic depressor nerve, and cervical vagal afferents. To address this hypothesis, male Sprague‐Dawley rats were fed low (0.01% NaCl, D17010, Research diets), normal (0.1% NaCl, D17020, Research Diets), and high (4.0% NaCl, D17013, Research Diets) salt diet for 14–21 days. Then, reflex responses were measured in Inactin‐anesthetized animals. Baseline mean ABP was not different across groups (low: 112±4, normal: 101±5, high: 109±3mmHg; P>0.1 overall ANOVA). Electrical stimulation of sciatic afferents (1ms pulse, 500uA, 5s duration, 2–20Hz) produced frequency‐dependent increases in ABP. Interestingly, the pressor response to sciatic nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: 22±4, normal: 12±2, high: 27±2 mmHg, n=5–10, P<0.05). Activation of the aortic depressor nerve (2ms pulse, 500uA, 15s duration, 2–20Hz) produced frequency‐dependent decreases in ABP. The depressor response to aortic nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: −29±6, normal: −11±3, high: −29±4 mmHg; n=3–7, P<0.05). Finally, electrical stimulation of the cervical vagal afferents (1ms pulse, 500uA, 5s duration, 2–20Hz) produced frequency‐dependent decreases in ABP. Again, the depressor response to vagal nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: −25±3, normal: −15±2, high: −29±2 mmHg; n=5–10, P<0.05). Simultaneous recordings of lumbar, renal, and splanchnic SNA followed the changes in ABP across low, normal, and high NaCl diets. The present findings showed that both dietary salt restriction and excess dietary salt intake exaggerates sympathetic and cardiovascular responses. These cardiovascular responses to activation of sciatic afferents, the aortic depressor nerve, and vagal afferents as a function of dietary salt resemble a J‐shaped curve.Support or Funding InformationNIH R01 HL128388 (WBF, SDS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Varying frequency and pulse width duration during electrical stimulation of cervical sympathetic chain in Zucker Fat rats dramatically alters hemodynamics

The influence of electrical stimulation of the cervical sympathetic chain (CSC) on hemodynamics has not been thoroughly investigated. Previous studies using healthy strains of rats focused on upper airway dynamics as well as ventilatory parameters. This current study examined the changes in mean blood pressure (MAP), diaphragmatic electromyogram (EMG), and upper airway pressure (UAP) elicited by electrical stimulation of the CSC in Zucker‐fat rats, a model of obesity‐hypertension,. Under urethane anesthesia, male Zucker‐Fat rats (16 weeks of age, n=4), were instrumented to continuously record MAP, diaphragmatic EMG), and UAP. Both CSC were dissected, isolated and stimulated at 0.5 mA, with varying frequency (2.5, 5, 7.5, 10 and 20 Hz) and pulse widths duration (0.1, 0.2, 0.5 and 2.0 ms). Both frequency and pulse‐width dependent depressor response was observed with bilateral CSC stimulation. Lower frequency stimulations produced a 5% decrease in MAP and 12% decrease in UAP whereas the highest frequency of 20 Hz (0.5 mA, 0.2 ms kept constant) produced a 20% decrease in MAP and 25% decrease in UAP relative to baseline (panel A). The smallest pulse width (0.1 ms) produced a 3% decrease in MAP and 5% decrease in UAP whereas 2 ms produced a 25% MAP drop and 10% drop in UAP relative to baseline measures (panel B). Diaphragmatic changes were negligible with CSC stimulation. We conclude that bilateral electrical stimulation of the CSC effectively lowers MAP and UAP in an obesity‐hypertension rat model. In addition, both frequency and pulse width parameters can vary the hemodynamic response dramatically. Future studies will investigate optimal stimulation parameters and whether stimulation can lower hypertension in conscious Zucker‐Fat rats.Support or Funding InformationSupported by NIH1OT2OD023860‐01, Galvani BioelectronicsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Renal Denervation Mitigates Hypertension and Improves Glomerular Filtration Rate in an Adult Rat Model of Polycystic Kidney Disease

Polycystic kidney disease (PKD) remains the most common form of inherited chronic kidney disease failure, and the only cure is renal transplantation. PKD is also strongly associated with increased arterial pressure (AP) and peripheral sympathetic nerve activity (SNA). Recent studies have shown ablation of renal nerves, or renal denervation (RDN), may be effective treatment for varying forms of HTN and renal disease; however, the role and mechanism for renal nerves in preexisting, PKD‐associated renal dysfunction and HTN remain unclear. Therefore, the aim of study was investigate the role of renal nerves in adult PKD, where we hypothesized RDN would reduce AP, lower peripheral sympathetic tone, and improve glomerular filtration rate (GFR) in the adult PKD rat.To test this hypothesis, 6‐month‐old male and female PKD rats underwent bilateral surgical RDN or sham surgery (Total n=18; 9/group; 3M/6F). RDN was achieved by surgical dissection followed by perivascular application of 10%(v/v) phenol. Cardiovascular parameters were recorded by radiotelemetry which was implanted two weeks prior to experimental treatment. Peripheral sympathetic tone was estimated by depressor response to acute ganglionic blockade (GB). GFR was assessed in unrestrained, conscious rats by acute FITC‐sinistrin clearance. Two weeks following RDN/Sham, rats were euthanized and tissues were collected for further analysis. Data was analyzed by a two‐way ANOVA, across sex and treatment groups (α=0.05). Data presented as mean+SEM.At baseline, no differences in 24‐hour mean AP (132 ± 2 vs. 129 ± 3mmHg), acute GB response (39 ± 3 vs. 42 ± 4ΔmmHg), nor GFR (0.93 ± 0.06 vs. 0.91 ± 0.04 mL/min/100g) were detected between treatment groups. No sex differences at baseline were detected at baseline. Two weeks following treatment, 24‐hour mean AP was lowered in RDN (121 ± 1.5mmHg) vs. sham (130 ± 2.8ΔmmHg), and no effect of sex was observed. Similarly, depressor response to GB was halved in RDN (−16 ± 2 ΔmmHg) compared to sham (−32 ± 3 ΔmmHg), and no effect of sex was detected. GFR was significantly increased in RDN vs. sham (1.18 ± 0.06 vs. 0.84 ± 0.08 mL/min/100g), and no effect of sex was detected. Lastly, no difference in renal cystic index was detected between RDN and sham (8.27 ± 1.39 vs. 8.74 ± 0.90%), and differences between male and female groups were observed.Together, these data support our initial hypothesis, where RDN effectively lowered AP and peripheral sympathetic tone in the PKD rat. This was paired with a significant increase in GFR in these animals, indicating an improvement in renal function despite no observable effect on renal cystic index Of note, the efficacy of RDN was similar across male and female groups. Further studies are underway to determine if the cardiovascular and renal effects observed in this study are primarily mediated by the ablation of the efferent or afferent nerves.Support or Funding InformationThis project was supported in part by NIH 1K99HL141650 (CTB) and R01HL116476 (JWO).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Adenosine A2a Receptor Mediated‐inhibitory Effects of Electroacupuncture on Sympathoexcitatory Reflexes Are Associated with Opioids in the Rostral Ventrolateral Medulla of Rats

It has been largely demonstrated that electroacupuncture (EA) lowers high blood pressure (BP). However, mechanisms underlying EA's effects on elevated BP remain unclear. Our previous studies have shown that EA attenuates reflex elevation in BP induced by gastric distension (GD) through its influence on rostral ventrolateral medulla (rVLM). Although adenosine is released during neuronal activation in the rVLM, its role in acupuncture‐cardiovascular regulation is unknown. Adenosine A2a rVLM receptors are known to contribute to depressor responses. The action of A2a receptor stimulation in the central nervous system may be regulated through an opioid mechanism. However, it is uncertain whether in the rVLM this putative action occurs. We hypothesized that adenosine in the rVLM contributes to EA modulation of sympathoexcitatory reflexes through an A2a‐opioid receptor mechanism. Repeated GD every 10 min was performed in Sprague‐Dawley male rats under ketamine and α‐chloralose anesthesia. EA (2 Hz, 0.5 ms, 1–4 mA) or sham‐EA (identical procedures as EA without electrical stimulation) was applied at the P5‐6 acupoints, overlying the median nerve, for 30 min after establishing two consistent reflex responses to GDs. We observed that EA (n=5) but not sham‐EA (n=5) at P5‐6 markedly (P<0.05) reduced GD‐induced elevations in BPs. EA modulation of sympathoexcitatory cardiovascular responses was reversed significantly after rVLM microinjection of an A2a receptor antagonist, SCH 58261 (1 mM in 50 nl; n=8; P<0.05), but not by the vehicle (5% dimethylsulfoxide; n=6). Furthermore, microinjection of an A2a receptor agonist, CGS‐21680 (0.4 mM in 50 nl) into the rVLM enhanced EA's inhibitory action (n=8; P<0.05). Blockade of opioid receptors with naloxone (0.1 μM in 50 nl) in the rVLM reversed EA's inhibitory effects on GD‐induced pressor responses and blunted the CGS‐21680‐associated enhancement of EA inhibition (n=6; P<0.05). Neurons labeled with adenosine A2a receptors were co‐localized with neurons stained with enkephalin as well as delta‐opioid receptors in the rVLM. These data suggest that the involvement of rVLM adenosine A2a receptors in EA modulation of GD‐induced pressor reflexes is, at least in part, dependent on the presence of opioids.Support or Funding InformationNCCIH grant, R01 AT009347This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Orexin Receptor-1 in the Rostral Ventrolateral Medulla Mediates the Antihypertensive Effects of Electroacupuncture.

Electroacupuncture (EA) has been used to treat numerous diseases, including hypertension. This study aimed to investigate the long-term effect and underlying mechanisms of EA stimulation at the LI11 point on the hypertension and sympathetic nerve activity in two-kidney, one-clip (2K1C) hypertensive rats. EA (0.1–0.4 mA, 2 and 15 Hz) was applied to the acupoints LI11 overlying the deep radial nerve once a day for 6 weeks. The mean arterial pressure (MAP) and heart rate (HR) were determined by radiotelemetry, and the sympathetic nerve activity was evaluated by telemetric analyses of the low-frequency component of blood pressure (BP) and by plasma epinephrine and norepinephrine levels. The results showed 6 weeks of EA significantly lowered the increased BP effectively, inhibited the enhanced sympathetic nerve activities and attenuated cardiac hypertrophy in 2K1C hypertensive rats. The level of orexin receptor-1 (OX1R) in the rostral ventrolateral medulla (RVLM) after EA treatment was markedly reduced in 2K1C rats, while there was no difference in the RVLM expression of orexin receptor-2 (OX2R) in 2K1C and 2K1C+EA rats. Moreover, the increased pressor and depressor responses to microinjection of orexin A or OX1R antagonist SB408124 into the RVLM of 2K1C rats were significantly blunted by the EA treatment. These findings suggest that BP-lowering effect of EA on renovascular hypertension may be through inhibition of central sympathetic activities and modulation of functional orexin receptors in the RVLM.

Central blockade of the AT1 receptor attenuates pressor effects via reduction of glutamate release and downregulation of NMDA/AMPA receptors in the rostral ventrolateral medulla of rats with stress-induced hypertension.

Glutamatergic activity in the rostral ventrolateral medulla (RVLM), which is an important brain area where angiotensin II (Ang II) elicits its pressor effects, contributes to the onset of hypertension. The present study aimed to explore the effect of central Ang II type 1 receptor (AT1R) blockade on glutamatergic actions in the RVLM of stress-induced hypertensive rats (SIHR). The stress-induced hypertension (SIH) model was established by electric foot shocks combined with noises. Normotensive Sprague-Dawley rats (control) and SIHR were intracerebroventricularly infused with the AT1R antagonist candesartan or artificial cerebrospinal fluid for 14 days. Mean arterial pressure (MAP), heart rate (HR), plasma norepinephrine (NE), glutamate, and the expression of N-methyl-D-aspartic acid (NMDA) receptor subunit NR1, and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors in the RVLM increased in the SIH group. These increases were blunted by candesartan. Bilateral microinjection of the ionotropic glutamate receptor antagonist kynurenic acid, the NMDA receptor antagonist D-2-amino-5-phosphonopentanoate, or the AMPA/kainate receptors antagonist 6-cyano-7-nitroquinoxaline-2,3-dione into the RVLM caused a depressor response in the SIH group, but not in other groups. NR1 and AMPA receptors expressed in the glutamatergic neurons of the RVLM, and glutamate levels, increased in the intermediolateral column of the spinal cord of SIHR. Central Ang II elicits release of glutamate, which binds to the enhanced ionotropic NMDA and AMPA receptors via AT1R, resulting in activation of glutamatergic neurons in the RVLM, increasing sympathetic excitation in SIHR.

Stimulation of pulmonary vagal C-fibers by trans-4-methyl-β-nitrostyrene induces bradycardiac and depressor reflex in rats: Role of vanilloid TRPV1 receptors

Previously, we showed that the synthetic nitroderivative trans-4-methyl-β-nitrostyrene (T4MeN) induced vasorelaxant effects in rat isolated aortic rings. Here, we investigated the mechanisms underlying the cardiovascular effects of T4MeN in normotensive rats. In pentobarbital-anesthetized rats, intravenous (i.v.) injection of T4MeN (0.03–0.5 mg/kg) induced a rapid (onset time of 1–2 s) and dose-dependent bradycardia and hypotension. These cardiovascular responses to T4MeN were abolished by bilateral cervical vagotomy or selective blockade of neural conduction of vagal C-fiber afferents by perineural treatment of both cervical vagus nerves with capsaicin. Hypotension and bradycardia were also recorded when T4MeN was directly injected in the right, but not into the left ventricle. Furthermore, they were significantly reduced by i.v. pretreatment with capsazepine but remained unaltered by ondansetron or suramin. In conscious rats, the dose-dependent hypotension and bradycardia evoked by T4MeN were abolished by i.v. methylatropine pretreatment. In conclusion, bradycardiac and depressor responses induced by T4MeN has a vago-vagal reflex origin resulting from the vagal pulmonary afferents stimulation. The transduction mechanism seems to involve the activation of vanilloid TRPV1, but not purinergic (P2X) or 5-HT3 receptors located on vagal pulmonary sensory nerves.

Increased excitatory regulation of the hypothalamic paraventricular nucleus and circulating vasopressin results in the hypertension observed in polycystic kidney disease.

Hypertension and baroreflex dysfunction confer poorer outcomes in patients with polycystic kidney disease (PKD). We examined whether hypothalamic paraventricular nucleus (PVN) activation or circulating vasopressin contribute to hypertension and baroreflex dysfunction in the Lewis polycystic kidney (LPK) rat. Bilateral PVN inhibition with muscimol reduced SBP further in urethane-anaesthetized adult LPK rats than in control Lewis rats (-43 ± 4 vs. -18 ± 3 mmHg; P < 0.0001, n = 14), but was not associated with a greater reduction in sympathetic nerve activity (SNA) or improvement in HR or SNA baroreflex function. Blockade of ionotropic glutamatergic input to the PVN with kynurenic acid also reduced SBP (P < 0.001), but not SNA, further in both adult and juvenile LPK rats. No differences in AMPA or NMDA receptor mRNA expression were noted. Systemic V1A receptor antagonism using OPC-21268 reduced SBP in adult LPK rats only (P < 0.001) and had no effect on the depressor response to PVN inhibition (P = 0.39). Combined peripheral V1A receptor antagonism and PVN inhibition, however, normalized SBP in adult LPK rats (122 ± 11 vs. 115 ± 6 mmHg; LPK vs. Lewis, P > 0.05, n = 10). Our data show that in the LPK rat model of PKD, hypertension is contributed to by increased PVN neuronal activity and, through an independent mechanism, systemic V1A receptor activation. Treatments that reduce PVN neuronal activity and/or inhibit peripheral V1A receptors may provide novel treatment strategies to ameliorate hypertension in individuals with PKD and limit overall disease progression.

Renal nerves contribute to hypertension in Schlager BPH/2J mice.

Schlager mice (BPH/2J) are hypertensive due to a greater contribution of the sympathetic nervous system (SNS) and renin-angiotensin system (RAS). The kidneys of BPH/2J are hyper-innervated suggesting renal nerves may contribute to the hypertension. We therefore determined the effect of bilateral renal denervation (RD) on hypertension in BPH/2J. Mean arterial pressure (MAP) was measured by radiotelemetry before and for 3 weeks after RD in BPH/2J and BPN/3J. The effects of pentolinium and enalaprilat were examined to determine the contribution of the SNS and RAS, respectively.After 3 weeks, MAP was -10.9 ± 2.1 mmHg lower in RD BPH/2J compared to baseline and -2.1 ± 2.2 mmHg in sham BPH/2J (P < 0.001, n = 8-10). RD had no effect in BPN/3J (P > 0.1). The depressor response to pentolinium was greater in BPH/2J than BPN/3J, but in both cases the response in RD mice was similar to sham. Enalaprilat decreased MAP more in RD BPH/2J compared to sham (-12 vs -3 mmHg, P < 0.001) but had no effect in BPN/3J. RD reduced renal noradrenaline in both strains but more so in BPH/2J. RD reduced renin mRNA and protein, but not plasma renin in BPH/2J to levels comparable with BPN/3J mice.We conclude that renal nerves contribute to hypertension in BPH mice as RD induced a sustained fall in MAP, which was associated with a reduction of intrarenal renin expression. The lack of inhibition of the depressor effects of pentolinium and enalaprilat by RD suggests that vasoconstrictor effects of the SNS or RAS are not involved.

PO-139 Effects of Exercise During Pregnancy on CaV1.2 Channel in Mesenteric Artery from SHR Offspring

Objective To investigate the effect of exercise during pregnancy on L-type Ca2+ (CaV1.2) channel in mesenteric artery from spontaneously hypertensive rats (SHR) offspring.&#x0D; Methods Female (11 weeks old) and male (12 weeks old) SHR, female (11 weeks old) and male (12 weeks old) WKY rats were selected to use for breeding. The day when the vaginal bolt was found was considered day 1 of gestation. The pregnant rats were randomly divided into four groups: WKY sedentary group (WKY-SED), WKY exercise group (WKY-EX), SHR sedentary group (SHR-SED) and SHR exercise group (SHR-EX). The exercise groups were subjected to swimming at the first day of pregnancy, 1h/d，6 days/week for 3 weeks. The 6-month-old male offspring were operated with femoral arterial and venous cannulation, and the blood pressure after intravenous (i.v.) injection of CaV1.2 channel opener BayK8644 and blocker nifedipine were monitored in vivo. In vitro study, the mesenteric arteries were removed and used for isometric contraction studies. The non-selective NOS inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 100 μM) was added after 60mM KCl measurement. To investigate the contribution of CaV1.2 channels in vascular tone regulation, the vascular responses to nifedipine (10−9–10−5M) were examined. Western blot was applied to examine the protein expression levels of CaV1.2 channel.&#x0D; Results (1) The mean arterial pressure(MAP) were higher in the 6M offspring of SHR-SED group than that of WKY-SED group (P＜0.01), but there was no significant difference between the 6M offspring of SED and Ex groups. (2) The pressor responses induced by i.v. injection of BayK8644（0.1mg/Kg）were increased in the 6M offspring of SHR-SED group (P＜0.05) compared with the WKY-SED group. Exercise during pregnancy markedly decreased the pressor responses in 6M offspring of SHR-EX group (P＜0.05). (3) Compared with the 6M offspring of WKY-SED group, the depressor responses induced by i.v. injection of nifedipine（1mg/Kg）were increased in the 6M offspring of SHR-SED group (P＜0.01). Exercise during pregnancy markedly attenuated the depressor responses in 6M offspring of SHR-EX group (P＜0.05). (4) The isometric contraction study revealed that nifedipine induced concentration-dependent vasorelaxation in mesenteric artery precontracted with noradrenaline. The sensitivity of tissues to nifedipine in 6M offspring of SHR-SED group was significantly higher than that of WKY-SED group (P＜0.01). Exercise during pregnancy normalized the increased sensitivity of tissues to nifedipine in 6M offspring of SHR (P＜0.05). (5) Compared with the 6M offspring of WKY-SED group, the protein expression of CaV1.2α1C was significantly increased in SHR-SED group(P＜0.01). Exercise during pregnancy markedly inhibited the expression of CaV1.2α1C in 6M offspring of SHR-EX group (P＜0.05).&#x0D; Conclusions Pregnancy exercise has no significant effect on basic blood pressure in 6M offspring of SHR; but the increased function and protein expression of CaV1.2 channel in 6M offspring of SHR may be normalized by exercise during pregnancy.

A18700 Differential central modulation of right versus left baroreceptor afferent input in hypertension

Objectives: Baroreflex activation therapy (BAT) is a novel therapy that utilizes electrical field stimulation of the carotid sinus nerve to reduce blood pressure in patients with resistant hypertension. Electrical stimulation of the baroreceptor afferents via the aortic depressor nerve (ADN) in rats may bring new insights into the mechanisms underlying BAT. In this study, we examine cardiovascular responses to electrical stimulation of the left versus right ADN in spontaneously hypertensive rats (SHR). Methods: Male pentobarbital-anesthetized SHRs (25–27 weeks, n = 8–9) were instrumented for right and left ADN stimulation (1–40 Hz, 0.2 ms, 0.4 mA for 20 s) and recording of mean arterial pressure (MAP), heart rate (HR) and mesenteric (MVR) and femoral (FVR) vascular resistance. Results: Both right and left ADN stimulation evoked frequency-dependent (P < 0.001) drops in MAP, HR, MVR and FVR (Fig. 1). However, stimulation of the left ADN evoked greater (P < 0.001) reflex depressor and bradycardic responses and preferential reductions in FVR (hindquarter) over MVR relative to the stimulation of the right side (Fig. 1). Conclusion: Enhanced hypotensive responses to left ADN stimulation are likely due to more potent baroreflex-mediated reductions in HR and vascular resistance relative to the right ADN. These results show a differential central processing of afferent neurotransmission promoted by the left versus right ADN. Clinically, this may have implications in fine-tuning the magnitude of BAT-driven blood pressure drop in patients in relation to the severity and chronicity of hypertension. Further studies are required to understand the mechanisms responsible for differences in the central integration of left versus right afferent input.

Electroacupuncture Improves Baroreflex and γ-Aminobutyric Acid Type B Receptor-Mediated Responses in the Nucleus Tractus Solitarii of Hypertensive Rats.

Electroacupuncture (EA) has been reported to benefit hypertension, but the underlying mechanisms are still unclear. We hypothesized that EA attenuates hypertension, in part, through modulation of γ-aminobutyric acid (GABA) receptor function in the nucleus tractus solitarii (NTS). In the present study, the long-term effect of EA on GABA receptor function and expression was examined in the NTS of two-kidney, one-clip (2K1C) renovascular hypertensive rats. EA (0.1–0.4 mA, 2 and 15 Hz) was applied at Zusanli (ST36) acupoints overlying the deep fibular nerve for 30 min once a day for two weeks. The results showed that long-term EA treatment improved blood pressure (BP) and markedly restored the baroreflex response in 2K1C hypertensive rats. The increased pressor and depressor responses to microinjection of GABAB receptor agonist and antagonist into the NTS in the hypertensive rats were blunted by the EA treatment. Moreover, EA treatment attenuated the increased GABAB receptor expression in the NTS of hypertensive rats. In contrast, EA had no significant effect on the GABAA receptor function and expression in the NTS of 2K1C hypertensive rats. These findings suggest that the beneficial effects of EA on renovascular hypertension may be through modulation of functional GABAB receptors in the NTS.

Hemodynamic Response to Gabapentin in Conscious Spontaneously Hypertensive Rats.

Ligands of auxiliary α2δ subunit of voltage-dependent calcium channels (VDCCs) decrease elevated L-type VDCCs surface expression in arterial myocytes and arterial constriction in spontaneously hypertensive rats (SHR). However, their effect on blood pressure (BP) is unclear. In this study, we investigated the hemodynamic response to acute and chronic administration of gabapentin, a ligand of auxiliary α2δ subunit of VDCCs, in adult SHR with established neurogenic hypertension. The acute gabapentin administration lowered BP and heart rate more in conscious SHR than Wistar-Kyoto rats. Both nifedipine (L-type VDCCs blocker) and ω-conotoxin GVIA (N-type VDCCs blocker) also decreased BP more in SHR, but only gabapentin and ω-conotoxin GVIA abolished the nitroprusside-induced reflex tachycardia of baroreceptor-heart rate control. Hypotensive effect of gabapentin was accompanied by a reduction of (1) plasma norepinephrine level, (2) depressor response to ganglionic blocker pentolinium, (3) power of low frequency component of systolic BP variability, and (4) pressor response of mesenteric vascular bed to periarterial nerve stimulation, suggesting the decrease of peripheral sympathetic nerve transmission. Moreover, gabapentin effects on BP and baroreflex were absent in sympathectomized rats. In conclusion, the acute (but not chronic) administration of gabapentin lowered BP more in SHR than in Wistar-Kyoto rats. Besides the known L-type VDCCs involvement in the vascular effect of gabapentin, our data revealed the important role of N-type VDCCs in acute gabapentin effect on sympathetic control of BP. Gabapentin-induced changes of sympathetic nerve transmission indicated major hemodynamic mechanism of the acute response to this drug.

Abstract P119: Hypertension and Renal Dysfunction Are Mitigated by Surgical Renal Denervation in an Adult Rat Model of Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common form of inherited chronic kidney disease failure. PKD is also associated with hypertension (HTN) and increased peripheral sympathetic activity (SNA). Recent studies have shown ablation of renal nerves may be effective treatment for varying forms of HTN and renal disease; however, the role and mechanism for renal nerves in PKD-associated renal dysfunction and HTN are unclear. Therefore, this study was conducted to test the hypothesis that renal denervation (RDN) would reduce AP, lower peripheral SNA, and improve renal function in the adult PKD rat. To test this hypothesis, 6-month-old male and female PKD rats underwent bilateral surgical RDN or sham surgery (Total n=18; 9/group; 3M/6F). Cardiovascular parameters were monitored by implanted radiotelemeter. Peripheral sympathetic tone was estimated by depressor response to acute ganglionic blockade (GB). Renal function was assessed by measuring glomerular filtration rate (GFR) by FITC-sinistrin clearance. Two weeks following treatment, rats were euthanized and tissues were collected for further analysis. Data was analyzed by a two-way ANOVA, across sex and treatment groups (α=0.05). Data presented as mean+SEM. At baseline, no differences in mean AP (132±2 vs. 129±3 mmHg), GB response (39±3vs. 42±4 ΔmmHg), nor GFR (0.93±0.06 vs. 0.91±0.04 mL/min/100g) were detected between RDN vs. sham. Two weeks following treatment, AP was lower in RDN (120±2mmHg) vs. sham (128±3mmHg). Similarly, GB was halved in RDN (-16±2 ΔmmHg) compared to sham (-32±3 ΔmmHg). GFR was increased in RDN rats vs. sham (1.18±0.06 vs. 0.84±0.08 mL/min/100g). Lastly, no difference in renal cystic area was detected between RDN and sham (8.27±1.39 vs. 8.74±0.90 %). No effect of sex was detected in any of the reported measurements. Altogether, these data support our initial hypothesis, where RDN effectively lowered AP and peripheral sympathetic tone in the PKD rat. Interestingly, we also observed a substantial increase in GFR in these animals, indicating an improvement in renal function despite no observable effect on cystic area. Of note, RDN was effective in both males and female rats. Further studies using repeated measurements are required to elucidate the order in which these effects occur.

Abstract P304: Sex Differences in Mechanisms of Adiposity-Associated Hypertension in Dahl S Rats

In humans, excessive accumulation of visceral adipose tissue is often associated with hypertension, but there is evidence that the mechanisms responsible may differ between men and women. Dahl S rats fed a high fat diet (HFD) from weaning gain visceral fat and develop a progressively higher arterial pressure compared to Dahl S rats fed a control diet (CD). We previously showed that the magnitude of this effect is similar in males and females. Here we used pharmacological interventions to compare in males and females the contributions of brain prostanoids, the renin-angiotensin system and the sympathetic nervous system to the development of hypertension in this rat model. Dahl S rats were placed on CD or HFD at weaning. All rats received telemetry implants at 15-16 weeks of age to measure arterial pressure, heart rate, and activity. Studies were conducted from 19-23 weeks of age, a time when hypertension is still developing. Drug interventions were separated by at least a week. Mean arterial pressure (MAP) was significantly higher in male HFD (156.0+/- 6.5 mmHg) versus male CD (133.3+/-1.6 mmHg) rats, and in female HFD (140+/-2.6 mmHg) versus female CD (131.4+/-1.2 mmHg) rats during the experimental period. Treatment for one week with the ACE inhibitor enalapril (250 mg/L in the drinking water) lowered MAP significantly more in male HFD (-38.3+/-5.9 mmHg) than in male CD (-23.9+/-1.6 mmHg) rats, but female HFD (-33.2+/-2.2 mmHg) and CD (-28.4+/-1.5 mmHg) rats responded similarly. Treatment for one week with the centrally acting sympatholytic clonidine (2 mg/L in the drinking water) reduced MAP more in females than males, but there were no differences between CD and HFD groups. One week treatment with the prostanglandin D synthase inhibitor AT56 (5.8 nmol/hr sc) caused only a slight fall in MAP (~3 mmHg) that was similar in all groups. Finally, a single injection of the ganglion blocker hexamethonium (30 mg/kg, ip) caused a short-term depressor response that was not significantly different in magnitude among the groups. We conclude that the renin-angiotensin system may have a greater role in adiposity-associated hypertension in Dahl S males versus females, but that sympathetic overactivity or prostaglandin D are not factors in either sex in the age range studied here.

Abstract P212: Splanchnic and Hepatic Portal Hemodynamics in the Hypotensive Actions of 5-HT

Circulating 5-hydroxytryptamine (5-HT) regulates mean arterial pressure (MAP) under some conditions. Infusion of low doses of 5-HT into rats leads to a sustained decrease in MAP which is prevented by the selective 5-HT7 receptor (5-HT7R) antagonist SB269970 or by inhibition of nitric oxide (NO) production. Time-dependent changes in the splanchnic circulation play a critical role in the sustained depressor response to 5-HT. We hypothesized that activation of 5-HT7Rs reduces MAP in part by causing decreased splanchnic vascular resistance and/or increased hepatic portal vascular resistance. Anesthetized male Sprague Dawley rats were instrumented with arterial and venous lines for pressure measurements and 5-HT/SB269970 infusion, and a Transonic probe on the portal vein to measure portal flow. Within 20 minutes of starting an infusion of 5-HT (25 ug/kg/min), MAP was significantly reduced (63±2 vs baseline 82±4 mmHg), whereas splanchnic vascular resistance (4.1±0.6 vs 2.4±0.1 ml/min/mmHg) and portal vascular resistance (0.18±0.08 vs 0.11±0.3) were increased. In a separate group of rats subjected to 24 hours of 5-HT infusion, MAP was reduced compared to control values (70±3 vs 84±2 mmHg), but portal vascular resistance (0.23±0.07 vs 0.17±0.04) and splanchnic vascular resistance (2.6±0.3 vs 2.4±0.1) were near control values. These animals then received an infusion of SB269970 to determine the direct contribution of the 5HT7R to hemodynamics after 24 hours of 5-HT exposure. After 20 minutes of SB269970 infusion, MAP (83±3 mmHg) was completely restored to baseline values while splanchnic vascular resistance (2.1 ±0.1 vs 2.6±0.1) and portal vascular resistance (0.12±0.3 vs 0.23±0.7) were decreased. These data suggest that the ability of 5-HT7R activation to increase splanchnic vascular resistance is effectively opposed over time by an endogenous vasodilator, which we suspect is nitric oxide. The data also indicate that changes in splanchnic vascular resistance are unlikely to participate in the chronic hypotensive effect of 5-HT, whereas increased resistance to flow through the hepatic portal system could play a role.

Intracerebroventricular administration of bone marrow-derived cells attenuates angiotensin II-initiated neurogenic hypertension in rats.

Bone marrow-derived cells exert anti-inflammatory actions and can migrate into the brain. However, their role in the development of neurogenic hypertension remains unclear. A hyperactive renin-angiotensin system and inflammation in the brain are mechanisms that contribute to angiotensin II-initiated neurogenic hypertension. We hypothesized that bone marrow-derived cells in the brain attenuate the overactive brain renin-angiotensin system and inflammation, thereby reducing neurogenic hypertension. We cultured plastic-adherent bone marrow-derived cells for 3 weeks. Seven days after initiation of vehicle or angiotensin II infusions, the rats underwent intracerebroventricular administration of either serum-free medium or autologous bone marrow-derived cells (106 cells). After 23 days of infusion, the mean arterial pressure was recorded, and the sympathetic tone was evaluated. Rats infused with angiotensin II demonstrated significant increases in the resting mean arterial pressure and the peak depressor response to ganglionic blockade (vehicle vs. angiotensin II infusion, 119 ± 4 vs. 178 ± 6 mmHg and -34 ± 6 vs. -74 ± 5 mmHg, respectively). Intracerebroventricularly administered bone marrow-derived cells attenuated the angiotensin II-mediated increases in the resting mean arterial pressure and peak depressor response (142 ± 11 and -52 ± 4 mmHg, respectively). The cells also reduced the angiotensin II-induced increases in angiotensin II type 1 receptor and transforming growth factor-β expression in the brain. In conclusion, bone marrow-derived cells in the brain may have a protective role against the development of angiotensin II-induced neurogenic hypertension by modulating angiotensin II type 1 receptor expression and inflammatory processes.