Hypertension In Spontaneously Hypertensive Rats Research Articles

Pentoxifylline treatment enhances antihypertensive activity of captopril through hemorheological improvement in spontaneously hypertensive rats during development of arterial hypertension

The rheological properties of blood play a significant role in the onset and progression of arterial hypertension. The aim of our work was to evaluate the effect of the angiotensin-converting enzyme inhibitor captopril (20 mg/kg/d), pentoxifylline (PTX; 100 mg/kg/d), and the combination of captopril + PTX (20 + 100 mg/kg/d) on the hemodynamic and hemorheological parameters in spontaneously hypertensive rats (SHRs) during the development of arterial hypertension. In the group of animals that received captopril, the mean arterial pressure (MAP) was significantly lower by 30% due to a decrease in cardiac output of 23% and in total peripheral resistance (TPR) of 26% compared with the control group, whereas blood viscosity did not change significantly. PTX-treated SHRs had significantly lower MAP and TPR (by 19% and 31%, respectively) and blood viscosity (by 4%–6%) and a higher erythrocyte deformability index (by 1.5%–2%) than the control group. In the group of animals that received captopril + PTX, MAP and TPR were significantly lower, by 41% and 46%, than those in the control group, and by 16% and 27% than those in the captopril group. The combination of the angiotensin-converting enzyme inhibitor captopril and the hemorheological agent PTX, affecting various systems that are involved in blood pressure regulation, exhibits synergism and prevents an increase in arterial blood pressure during the development of arterial hypertension in SHRs (ie, from 5 to 11 weeks of life).

Genetics of hypertension: an assessment of progress in the spontaneously hypertensive rat.

The application of gene mapping methods to uncover the genetic basis of hypertension in the inbred spontaneously hypertensive rat (SHR) began over 25 yr ago. This animal provides a useful model of genetic high blood pressure, and some of its features are described. In particular, it appears to be a polygenic model of disease, and polygenes participate in human hypertension genetic risk. The SHR hypertension alleles were fixed rapidly by selective breeding in just a few generations and so are presumably common genetic variants present in the outbred Wistar strain from which SHR was created. This review provides a background to the origins and genesis of this rat line. It considers its usefulness as a model organism for a common cardiovascular disease. The progress and obstacles facing mapping are considered in depth, as are the emergence and application of other genome-wide genetic discovery approaches that have been applied to investigate this model. Candidate genes, their identification, and the evidence to support their potential role in blood pressure elevation are considered. The review assesses the progress that has arisen from this work has been limited. Consideration is given to some of the factors that have impeded progress, and prospects for advancing understanding of the genetic basis of hypertension in this model are discussed.

Abstract P409: Defective Renal Ang III and AT2 Receptor Signaling in Pre-hypertensive Spontaneously Hypertensive Rats (SHR)

The intrarenal renin-angiotensin (RAS) system controls blood pressure and electrolyte balance. Angiotensin II (Ang II), the principal RAS effector peptide, is metabolized by aminopeptidase A to des-apartyl 1 -Ang II (Ang III). Our previous studies showed that Ang III, not Ang II, is the preferred endogenous agonist for Ang type-2 receptor (AT 2 R)-induced natriuresis in normal rats, and that hypertensive 12-week old SHR lack natriuretic responses to Ang III. The present study tested whether Ang III induced natriuresis in 4 week old pre-hypertensive SHR by activating/translocating intrarenal AT 2 Rs and internalizing the major renal proximal tubule (RPT) sodium transporter NHE-3. Female 4 week old SHR (N=6) and WKY (N=6) rats were studied after 24 h systemic AT 1 R blockade with candesartan. The left kidney received a 30 min renal interstitial (RI) infusion of vehicle followed by cumulative RI infusions of Ang III (3.5, 7.0, 14, and 28 nmol/kg/min; each dose for 30 min). The right kidney received vehicle RI infusions. In 4 week old WKY, RI Ang III increased urine sodium excretion (U Na V) dose dependently from control of 0.04 ± 0.01 to 0.08 ± 0.02 (P<0.05), 0.09 ± 0.02 (P<0.01), 0.07 ± 0.01 (P<0.05), and 0.07 ± 0.01 (P<0.05) μmol/min. In 4 week old pre-hypertensive SHR, RI Ang III failed to induce natriuresis at all doses except 28 nmol/kg/min (0.03 ± 0.01 vs. 0.05 ± 0.01 μmol/min; P<0.05). There was no change in U Na V in right control kidneys of WKY or SHR. Also, Ang III had no effect on mean arterial pressure (MAP) in WKY or SHR. However, MAP was slightly higher, but normotensive, in SHR than WKY. Control and Ang III infused kidneys were processed for confocal microscopy from a separate group of rats. In WKY, RI Ang III induced translocation of AT 2 Rs from subapical to apical membranes of RPT cells [RPTC] (1767 ± 41 vs. 1313 ± 47 RFU; P<0.001). Simultaneously, Ang III induced retraction of NHE-3 from in SHR, intrarenal Ang III failed to induce AT 2 R translocation, NHE-3 retraction, and pSer 552 -NHE-3 upregulation. These results apical to subapical membranes of RPTCs (1703 ± 90 vs. 1388 ± 91 RFU; P<0.05). Consistent with NHE-3 retraction, Ang III increased pSer 552 -NHE-3 (1102 ± 57 vs. 830 ± 66 RFU; P<0.01). In contrast,demonstrate defective Ang III and AT 2 R signaling in pre-hypertensive SHR.

Nitric oxide attenuates overexpression of Giα proteins in vascular smooth muscle cells from SHR: Role of ROS and ROS-mediated signaling.

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit decreased levels of nitric oxide (NO) that may be responsible for the overexpression of Giα proteins that has been shown as a contributing factor for the pathogenesis of hypertension in SHR. The present study was undertaken to investigate if increasing the intracellular levels of NO by NO donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP) could attenuate the enhanced expression of Giα proteins in VSMC from SHR and explore the underlying mechanisms responsible for this response. The expression of Giα proteins and phosphorylation of ERK1/2, growth factor receptors and c-Src was determined by Western blotting using specific antibodies. Treatment of VSMC from SHR with SNAP for 24 hrs decreased the enhanced expression of Giα-2 and Giα-3 proteins and hyperproliferation that was not reversed by 1H (1, 2, 4) oxadiazole (4, 3-a) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, however, PD98059, a MEK inhibitor restored the SNAP-induced decreased expression of Giα proteins towards control levels. In addition, the increased production of superoxide anion, NAD(P)H oxidase activity, overexpression of AT1 receptor, Nox4, p22phox and p47phox proteins, enhanced levels of TBARS and protein carbonyl, increased phosphorylation of PDGF-R, EGF-R, c-Src and ERK1/2 in VSMC from SHR were all decreased to control levels by SNAP treatment. These results suggest that NO decreased the enhanced expression of Giα-2/3 proteins and hyperproliferation of VSMC from SHR by cGMP-independent mechanism and involves ROS and ROS-mediated transactivation of EGF-R/PDGF-R and MAP kinase signaling pathways.

Renal Denervation Prevents Nicotine‐Induced Hypertension and Reduces Renal IL‐17a

Interaction between the nervous and immune systems has become a major focus in the pathophysiology of essential hypertension. Cholinergic activation of nicotinic acetylcholine receptors are known to exert an anti‐inflammatory effect. However, we recently demonstrated that in vivo cholinergic activation with nicotine induces renal inflammation and premature development of hypertension in young Spontaneously Hypertensive Rat (SHR). We hypothesized that renal nerves contribute to nicotine‐induced renal inflammation and premature hypertension in young SHR. Following bilateral renal nerve denervation (RND) (or Sham surgery) in young (3–5 week old SHR), we continuously infused nicotine bitartrate (15mg/kg/day) or saline subcutaneously for 2 weeks. Systolic blood pressure was measured by tail cuff. Norepinephrine (NE) and IL‐17a were measured in kidneys by ELISA and Luminex assay, respectively. RND prevented the development of hypertension in response to nicotine infusion in young SHR (n=6), compared to nicotine‐infused Sham operated young SHR (n=3) (140 ± 4 vs 180 ± 5 mmHg, respectively, p<0.001). RND also significantly decreased IL‐17a in kidneys nicotine‐infused SHR, compared with kidneys from sham operated SHR (12 ± 0.7 pg/mL vs 17 ± 0.9 pg/mL, p<0.01). NE analysis of renal tissues confirmed renal denervation with over an 85% reduction in renal NE levels, compared to sham operation (31±11 ng/mg vs 225±43 ng/mg, P<0.05). We conclude that renal nerves mediate nicotine‐induced renal inflammation and hypertension.Support or Funding InformationUniversity of Iowa, Carver College of MedicineNIH/NHLBI‐HL119588‐01A1 and HL014388‐48

Brain Perivascular Macrophages Contribute to Developing Hypertension via Sensing Chronic Peripheral Inflammation

BackgroundRecent studies suggest an association between inflammation and hypertension. The essential pathophysiological mechanism by which peripheral inflammation induces sympathetic hyperactivity and blood pressure elevation is not fully clarified. Sympathetic nerve activity is regulated by the brain, which is separated from various peripheral substances by the blood brain barrier (BBB). Brain perivascular macrophages in the BBB can transfer peripheral inflammatory information to the brain. Therefore, we investigated whether peripheral proinflammatory cytokines accompany the development of hypertension, and if so, whether or not brain perivascular macrophage depletion attenuates the increase in blood pressure in hypertensive animal models.Methods and ResultsPeripheral proinflammatory interleukin‐6 levels measured by enzyme‐linked immunosorbent assay did not differ between young pre‐hypertensive spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY, 8‐week‐old SHR 64.8±9.5 pg/ml vs. 8‐week‐old WKY 42.8±9.5 pg/ml, p=0.15, respectively, n=4 for each). In adult hypertensive SHR, however, the interleukin‐6 level was significantly greater than that in WKY (12‐week‐old SHR 112.5±15.2 pg/ml vs. 12‐week‐old WKY 62.4±15.2 pg/ml, p<0.05, n=5 for each). Clodronate, a unique agent that induces apoptosis of perivascular macrophages, was administered intracerebroventricularly to 6‐week‐old SHR to investigate the role of brain perivascular macrophages in blood pressure elevation in SHR. Although established natural history of blood pressure in SHR clearly showed that mean arterial pressure would be elevated to approximately 120–125 mmHg at 8 weeks of age, intracerebrovantricular injection of clodronate successfully attenuated telemetered mean blood pressure elevation from 6 to 8 weeks of age (from 113.3±4.2 mmHg to 114.7±4.2 mmHg, n=2) in SHR.ConclusionBrain perivascular macrophages potentially contribute to developing hypertension via sensing chronic peripheral inflammation.

Alleviative effect of grape seed proanthocyanidin extract on small artery vascular remodeling in spontaneous hypertensive rats via inhibition of collagen hyperplasia.

Vascular remodeling is a primary contributor to the initiation and development of hypertension, which has a pathological association with subsequent multi-organ damage. Grape seed proanthocyanidin extracts (GSPE) exhibit protective cardiovascular effects, resulting from their anti‑oxidant and anti‑inflammatory properties. However, the function and mechanism underlying the effect of GSPE on small artery remodeling remain to be elucidated. The present study investigated the effect of GSPE on vascular remodeling in the mesenteric small arteries of spontaneous hypertensive rats (SHR). Parameters associated with hypertension, including systolic blood pressure, oxidative stress, morphological and ultrastructural alteration of vessels, deposition of collagen and transforming growth factor (TGF)-β1, were analyzed. The results revealed that GSPE alleviated hypertension-induced hypertrophic vascular remodeling in the small arteries of SHR, which was independent of blood pressure. GSPE decreased oxidative stress associated with hypertension in SHR and suppressed the increased expression of TGF‑β1, which blocked the translocation and differentiation of adventitia fibroblasts and eventually inhibited collagen hyperplasia in the blood vessel. The inhibitory effect of GSPE on small artery remodeling was achieved via its suppressive effect on oxidant production and the subsequent intercellular and intracellular cascades. The findings of the present study supported the potential therapeutic value of GSPE for the treatment of hypertension.

Evidence that remodeling of insular cortex neurovascular unit contributes to hypertension-related sympathoexcitation.

The intermediate region of the posterior insular cortex (intermediate IC) mediates sympathoexcitatory responses to the heart and kidneys. Previous studies support hypertension‐evoked changes to the structure and function of neurons, blood vessels, astrocytes and microglia, disrupting the organization of the neurovascular unit (NVU). In this study, we evaluated the functional and anatomical integrity of the NVU at the intermediate IC in the spontaneously hypertensive rat (SHR) and its control the Wistar‐Kyoto (WKY). Under urethane anesthesia, NMDA microinjection (0.2 mmol/L/100 nL) was performed at the intermediate IC with simultaneous recording of renal sympathetic nerve activity (RSNA), heart rate (HR) and mean arterial pressure (MAP). Alterations in NVU structure were investigated by immunofluorescence for NMDA receptors (NR1), blood vessels (70 kDa FITC‐dextran), astrocytes (GFAP), and microglia (Iba1). Injections of NMDA into intermediate IC of SHR evoked higher amplitude responses of RSNA, MAP, and HR. On the other hand, NMDA receptor blockade decreased baseline RSNA, MAP and HR in SHR, with no changes in WKY. Immunofluorescence data from SHR intermediate IC showed increased NMDA receptor density, contributing to the SHR enhanced sympathetic responses, and increased in vascular density (increased number of branches and endpoints, reduced average branch length), suggesting angiogenesis. Additionally, IC from SHR presented increased GFAP immunoreactivity and contact between astrocyte processes and blood vessels. In SHR, IC microglia skeleton analysis supports their activation (reduced number of branches, junctions, endpoints and process length), suggesting an inflammatory process in this region. These findings indicate that neurogenic hypertension in SHR is accompanied by marked alterations to the NVU within the IC and enhanced NMDA‐mediated sympathoexcitatory responses likely contributors of the maintenance of hypertension.

Silencing salusin-\u03b2 attenuates cardiovascular remodeling and hypertension in spontaneously hypertensive rats

Salusin-β is a bioactive peptide involved in vascular smooth muscle cell proliferation, vascular fibrosis and hypertension. The present study was designed to determine the effects of silencing salusin-β on hypertension and cardiovascular remodeling in spontaneously hypertensive rats (SHR). Thirteen-week-old male SHR and normotensive Wistar-Kyoto rats (WKY) were subjected to intravenous injection of PBS, adenoviral vectors encoding salusin-β shRNA (Ad-Sal-shRNA) or a scramble shRNA. Salusin-β levels in plasma, myocardium and mesenteric artery were increased in SHR. Silencing salusin-β had no significant effect on blood pressure in WKY, but reduced blood pressure in SHR. It reduced the ratio of left ventricle weight to body weight, cross-sectional areas of cardiocytes and perivascular fibrosis, and decreased the media thickness and the media/lumen ratio of arteries in SHR. Silencing salusin-β almost normalized plasma norepinephrine and angiotensin II levels in SHR. It prevented the upregulation of angiotensin II and AT1 receptors, and reduced the NAD(P)H oxidase activity and superoxide anion levels in myocardium and mesenteric artery of SHR. Knockdown of salusin-β attenuated cell proliferation and fibrosis in vascular smooth muscle cells from SHR. These results indicate that silencing salusin-β attenuates hypertension and cardiovascular remodeling in SHR.

Hypotensive effects of renal denervation in spontaneously hypertensive rat based on ultrasonic contrast imaging

BackgroundSympathetic nerves-fire rate is generally enhanced in some types of hypertension models. Renal sympathetic denervation(RSD) by the radiofrequency ablation was used to treat the hypertension has achieved curative effect.HTN-1 and HTN-2 trial reported catheter-based renal denervation may cause substantial and sustained blood-pressure reduction in patients with resistant hypertension. However, recent controlled HTN-3 trial questioned the BP lowering effect of Renal denervation treatment. The controversial results maybe arised from the incompleted RSD which implemented inside the renal artery. Now renal denervation therapy for resistant hypertension is in attractive and controversial status. Our aim is to define the hyotensive value of complete renal denervation in adult spontaneous hypertensive rats. MethodsMale spontaneous hypertensive rats(SHR) aged 12 weeks were randomly selected for either unilateral renal artery sympathetic nerves ablation (URSNA), or conventional technique of renal denervation (CRD), or bilateral renal artery sympathetic nerves ablation (BRSNA) and sham operation. Blood pressure, sodium and water balance,serum reninangiotensin II and Norepinephrine concentration were measured during 20 weeks after renal denervation operation. Internal diameters of renal arteries and renal blood flow rate was tested by ultrasonic contrast imaging. ResultsThe continued increased blood pressure in SHR was delayed and significantly reduced by conventional renal denervation over a period of 8 weeks. Both the bilateral and unilateral renal sympathetic nerve ablation procedure did not prevent the development of hypertension in SHR. The attenuation of hypertension was accompanied with the increase of urinary sodium excretion and depression of rennin angiotensin system (RAS). ConclusionsWe concluded that renal denervation may not be an effective therapeutic method in the long-term control of hypertension in adult SHR.

Abnormal CD161+ immune cells and retinoic acid receptor–related orphan receptor γt–mediate enhanced IL-17F expression in the setting of genetic hypertension

Hypertension is considered an immunologic disorder. However, the role of the IL-17 family in genetic hypertension in the spontaneously hypertensive rat (SHR) has not been investigated. We tested the hypothesis that enhanced TH17 programming and IL-17 expression in abundant CD161+ immune cells in SHRs represent an abnormal proinflammatory adaptive immune response. Furthermore, we propose that this response is driven by the master regulator retinoic acid receptor-related orphan receptor γt (RORγt) and a nicotinic proinflammatory innate immune response. We measured expression of the CD161 surface marker on splenocytes in SHRs and normotensive control Wistar-Kyoto (WKY) rats from birth to adulthood. We compared expression of IL-17A and IL-17F in splenic cells under different conditions. We then determined the functional effect of these cytokines on vascular reactivity. Finally, we tested whether pharmacologic inhibition of RORγt can attenuate hypertension in SHRs. SHRs exhibited an abnormally large population of CD161+ cells at birth that increased with age, reaching more than 30% of the splenocyte population at 38weeks. The SHR splenocytes constitutively expressed more RORγt than those of WKY rats and produced more IL-17F on induction. Exposure of WKY rat aortas to IL-17F impaired endothelium-dependent vascular relaxation, whereas IL-17A did not. Moreover, invivo inhibition of RORγt by digoxin decreased systolic blood pressure in SHRs. SHRs have a markedly enhanced potential for RORγt-driven expression of proinflammatory and prohypertensive IL-17F in response to innate immune activation. Increased RORγt and IL-17F levels contribute to SHR hypertension and might be therapeutic targets.

The features of beta-cells organization in the pancreas of spontaneously hypertensive rat (SHR)

The control of b-cells pool in patients with hypertension is an actual problem, as it is possible that the hereditary genetic defects of arterial hypertension formation may affect the mechanisms of endocrine cell mass maintenance in pancreas and cause disruption of glucose metabolism and diabetes. In addition, violation of cytoarchitectonics of pancreatic islets may affect the adequate insulin secretion by the pancreas. This could be provoked by regional blood flow violations in patients with hypertension. The aim of our study was to assess the parameters of the allocation of pancreatic islets and characterize the b-cells morphofunctional state in SHR. Materials and methods. We assessed the amount of b-cells in islets, the concentration of immunoreactive material in them, specific indexes of allocation of islets, b-cells and insulin per unit area using immunohistochemical assay. Results were processed by statistical application package. We used Student’s t-test and Wilcoxon’s w-test when appropriate. Results and discussion . In normoglycemic SHR about 80 % of pancreatic islets are small islets, whereas in normotensive Wistar rats the portion of small islets is less than 45 %. In SHR rats we found the 1/3 decrease of b-cells in islets with area less than 1500 µm 2 , and 2-fold decrease in islets with area 3500–7500 µm 2 ; decrease of specific amount of b-cells (12,4 % compared with Wistar) and insulin contain (3-fold compared with Wistar). Conclusions: Formation of hereditary hypertension in SHR is accompanied by remodeling of the insular apparatus of pancreas with prevailing of small and middle-sized islets, 2-fold decrease of amount of pancreatic islets and 8-fold decrease of b-cells cell amount. In normoglycemic SHR we found a middle b-cells hypertrophy and increased concentration of insulin. Herewith the specific insulin contain is 3-fold less in hypertensive compared with normotensive rats due to decrease of b-cells cell pool.

TRPV1 attenuates intracranial arteriole remodeling through inhibiting VSMC phenotypic modulation in hypertension.

The phenotypic modulation of contractile vascular smooth muscle cell (VSMC) is widely accepted as the pivotal process in the arterial remodeling induced by hypertension. This study aimed to investigate the potential role of transient receptor potential vanilloid type 1 (TRPV1) on regulating VSMC plasticity and intracranial arteriole remodeling in hypertension. Spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY) rats and TRPV1-/- mice on a C57BL/6J background were used. By microscopic observation of the histopathological sections of vessels from hypertensive SHR and age-matched normotensive WKY control rats, we found that hypertension induced arterial remodeling. Decreased α-smooth muscle actin (α-SMA) and SM22α while increased osteopontin (OPN) were observed in aorta and VSMCs derived from SHR compared with those in WKY, and VSMCs derived from SHR upregulated inflammatory factors. TRPV1 activation by capsaicin significantly increased expression of α-SMA and SM22α, reduced expression of OPN, retarded proliferative and migratory capacities and inhibited inflammatory status in VSMCs from SHR, which was counteracted by TRPV1 antagonist 5'-iodoresiniferatoxin (iRTX) combined with capsaicin. TRPV1 activation by capsaicin ameliorated intracranial arteriole remodeling in SHR and deoxycorticosterone acetate (DOCA)-salt hypertensive mice. However, the attenuation of arteriole remodeling by capsaicin was not observed in TRPV1-/- mice. Furthermore, TRPV1 activation significantly decreased the activity of PI3K and phosphorylation level of Akt in SHR-derived VSMCs. Taken together, we provide evidence that TRPV1 activation by capsaicin attenuates intracranial arteriole remodeling through inhibiting VSMC phenotypic modulation during hypertension, which may be at least partly attributed to the suppression PI3K/Akt signaling pathway. These findings highlight the prospect of TRPV1 in prevention and treatment of hypertension.

Sympathoinhibitory Effect of Radiofrequency Renal Denervation in Spontaneously Hypertensive Rats With Established Hypertension.

Radiofrequency ablation of the renal arteries (RF-ABL) has been shown to decrease blood pressure (BP) in drug-resistant hypertensive patients who receive antihypertensive drug therapy. However, there remain questions regarding how RF-ABL influences BP independent of drug therapy and whether complete renal denervation is necessary to maximally lower BP. To study these questions, we examined the cardiovascular, sympathetic, and renal effects produced by RF-ABL of the proximal renal arteries in spontaneously hypertensive rats (SHR) with established hypertension. SHR were instrumented (telemetry) for measurement of systolic/diastolic BP (SBP/DBP). Rats then underwent Sham-ABL or RF-ABL adjacent to the renal ostium and BP was recorded for 8 weeks. Changes in sympathetic activity, 24-hour water/sodium excretion, and levels of urinary angiotensinogen (AGT), plasma renin activity, and kidney renin content (KRC) were measured in SHR. Compared with Sham-ABL, RF-ABL produced a sustained decrease in BP. At 8 weeks, SBP/DBP was 171±6/115±3 and 183±4/129±3mm Hg for RF-ABL and Sham-ABL SHR, respectively. Correlating with the reduction in BP, RF-ABL significantly decreased the low frequency/total and low frequency/high frequency of BP variability and attenuated the hypotensive response to chlorisondamine. Kidney norepinephrine levels were markedly decreased at 8 weeks in RF-ABL vs. Sham-ABL SHR. There were no group differences in 24-hour sodium/water excretion or urinary AGT excretion rate (6 weeks) or plasma renin activity or KRC (8 weeks). In other studies, concurrent RF-ABL plus surgical denervation initially decreased BP to a greater level than RF-ABL alone, but thereafter the reduction in BP between groups was not different. In hypertensive SHR, bilateral RF-ABL of the proximal renal arteries produced a sustained decease in sympathetic activity and BP without changes in sodium/water excretion or activity of the systemic/renal renin-angiotensin system.

Blockade of Rostral Ventrolateral Medulla (RVLM) Bombesin Receptor Type 1 Decreases Blood Pressure and Sympathetic Activity in Anesthetized Spontaneously Hypertensive Rats.

Intrathecal injection of bombesin (BBS) promoted hypertensive and sympathoexcitatory effects in normotensive (NT) rats. However, the involvement of rostral ventrolateral medulla (RVLM) in these responses is still unclear. In the present study, we investigated: (1) the effects of BBS injected bilaterally into RVLM on cardiorespiratory and sympathetic activity in NT and spontaneously hypertensive rats (SHR); (2) the contribution of RVLM BBS type 1 receptors (BB1) to the maintenance of hypertension in SHR. Urethane-anesthetized rats (1.2 g · kg−1, i.v.) were instrumented to record mean arterial pressure (MAP), diaphragm (DIA) motor, and renal sympathetic nerve activity (RSNA). In NT rats and SHR, BBS (0.3 mM) nanoinjected into RVLM increased MAP (33.9 ± 6.6 and 37.1 ± 4.5 mmHg, respectively; p < 0.05) and RSNA (97.8 ± 12.9 and 84.5 ± 18.1%, respectively; p < 0.05). In SHR, BBS also increased DIA burst amplitude (115.3 ± 22.7%; p < 0.05). BB1 receptors antagonist (BIM-23127; 3 mM) reduced MAP (–19.9 ± 4.4 mmHg; p < 0.05) and RSNA (−17.7 ± 3.8%; p < 0.05) in SHR, but not in NT rats (−2.5 ± 2.8 mmHg; −2.7 ± 5.6%, respectively). These results show that BBS can evoke sympathoexcitatory and pressor responses by activating RVLM BB1 receptors. This pathway might be involved in the maintenance of high levels of arterial blood pressure in SHR.

An augmented CO2 chemoreflex and overactive orexin system are linked with hypertension in young and adult spontaneously hypertensive rats.

Activation of central chemoreceptors by CO2 increases sympathetic nerve activity (SNA), arterial blood pressure (ABP) and breathing. These effects are exaggerated in spontaneously hypertensive rats (SHRs), resulting in an augmented CO2 chemoreflex that affects both breathing and ABP. The augmented CO2 chemoreflex and the high ABP are measureable in young SHRs (postnatal day30-58) and become greater in adult SHRs. Blockade of orexin receptors can normalize the augmented CO2 chemoreflex and the high ABP in young SHRs and normalize the augmented CO2 chemoreflex and significantly lower the high ABP in adult SHRs. In the hypothalamus, SHRs have more orexin neurons, and a greater proportion of them increase their activity with CO2 . The orexin system is overactive in SHRs and contributes to the augmented CO2 chemoreflex and hypertension. Modulation of the orexin system may be beneficial in the treatment of neurogenic hypertension. Activation of central chemoreceptors by CO2 increases arterial blood pressure (ABP), sympathetic nerve activity and breathing. In spontaneously hypertensive rats (SHRs), high ABP is associated with enhanced sympathetic nerve activity and peripheral chemoreflexes. We hypothesized that an augmented CO2 chemoreflex and overactive orexin system are linked with high ABP in both young (postnatal day30-58) and adult SHRs (4-6 months). Our main findings are as follows. (i)An augmented CO2 chemoreflex and higher ABP in SHRs are measureable at a young age and increase in adulthood. In wakefulness, the ventilatory response to normoxic hypercapnia is higher in young SHRs (mean±SEM: 179±11% increase) than in age-matched normotensive Wistar-Kyoto rats (114±9% increase), but lower than in adult SHRs (226±10% increase; P<0.05). The resting ABP is higher in young SHRs (122±5mmHg) than in age-matched Wistar-Kyoto rats (99±5mmHg), but lower than in adult SHRs (152±4mmHg; P<0.05). (ii)Spontaneously hypertensive rats have more orexin neurons and more CO2 -activated orexin neurons in the hypothalamus. (iii)Antagonism of orexin receptors with a dual orexin receptor antagonist, almorexant, normalizes the augmented CO2 chemoreflex in young and adult SHRs and the high ABP in young SHRs and significantly lowers ABP in adult SHRs. (iv)Attenuation of peripheral chemoreflexes by hyperoxia does not abolish the augmented CO2 chemoreflex (breathing and ABP) in SHRs, which indicates an important role for the central chemoreflex. We suggest that an overactive orexin system may play an important role in the augmented central CO2 chemoreflex and in the development of hypertension in SHRs.

Lysine deacetylase inhibition attenuates hypertension and is accompanied by acetylation of mineralocorticoid receptor instead of histone acetylation in spontaneously hypertensive rats.

Inhibition of lysine deacetylase (KDAC) attenuated development of hypertension in spontaneously hypertensive rats (SHRs). We hypothesized that KDAC inhibition attenuates hypertension and is accompanied by acetylation of mineralocorticoid receptors (MR) instead of histone acetylation in SHRs. Valproate (VPA, 0.71% wt/vol), an inhibitor of class I KDACs, was administered in drinking water to 7-week-old SHRs and Wistar Kyoto rats for 11weeks. MR acetylation was determined by immunoprecipitation with anti-MR antibody followed by western blot with anti-acetyl-lysine antibody. Expression levels of acetylated histone H3, KDACs, MR target genes, or MR corepressors in the kidney cortex were measured by using western blot analysis or real-time PCR. Recruitment of MR and RNA polymerase II (Pol II) and histone modifications on promoters of target genes were analyzed by performing a chromatin immunoprecipitation (ChIP) assay. Treatment of SHR with VPA increased MR acetylation without affecting MR expression, which attenuated development of hypertension in SHR VPA decreased expression of KDAC class I but globally increased acetylated histone H3. Although VPA treatment increased histone 3 acetylation (H3Ac) and trimethylation of the fourth lysine (H3K4me3) in the promoter regions of MR target genes, it decreased the expression of target genes as well as recruitment of MR and Pol II. These results suggest that KDAC inhibition attenuates the development of hypertension in SHRs and is accompanied by acetylation of MR that is independent of histone acetylation.

Cholinergic Stimulation of Immune Cells with Nicotine Induces Renal Inflammation and Pre‐mature Development of Hypertension in Young SHR

We have shown that nicotinic cholinergic stimulation of immune cells in vitro and in vivo exaggerates pro‐inflammatory innate immune responses and increases proliferation of a CD161a+/CD68+ macrophage population in isolated bone marrow cells and splenocytes in young pre‐hypertensive Spontaneously Hypertensive Rat (SHR). In vivo administration of nicotine also led to renal infiltration of macrophages within 24 hours, without any increase in arterial pressure and independent of renal sympathetic innervation. We also found that 2 week subcutaneous infusion of nicotine not only leads to continued CD161a+/CD68+ macrophage infiltration, but also the development of premature hypertension in young SHR. We hypothesized 1) that the nicotine induced CD161a+/CD68+ macrophage infiltration is caused by increased renal expression of Vascular Cell Adhesion Molecule‐1 (VCAM‐1) and 2) this renal macrophage infiltration results in renal damage/toxicity. Nicotine (15mg/kg/day) was infused subcutaneously for 2 weeks. Systolic blood pressures (SBP) were measured twice weekly by tail cuff and urine, serum, and kidney tissue were collected at the end of nicotine infusion. Tissues and fluid were analyzed by luminex assay. Renal lysates were also analyzed by Western blot for the presence of VCAM‐1. Nicotine infusion led to the pre‐mature development of hypertension in SHR (153.2 ± 3 mmHg vs 138.6 ± 3 mmHg in saline infused SHR, respectively, n=10, p &lt;0.001). There was no significant increase in SBP in control Wistar Kyoto (WKY) rats infused with nicotine, compared to saline. There was a greater infiltration of the kidney with CD161a+/CD68+ macrophages with nicotine infusion (16±2 cells per 400× field), compared to saline infusion (9±1 cells per 400× field) (n=6, p&lt;0.001). In contrast, there was no significant renal macrophage infiltration in nicotine infused WKY, compared to saline (1±1 cells vs 1±1 cells per 400× field) (n=6, p&gt;0.05). CD161a+/CD68+ renal macrophage infiltration in the young SHR was not associated with an increase in VCAM‐1 expression. However, nicotine induced renal CD161a+/CD68+ macrophage infiltration was associated with renal damage/toxicity, as measured by an increase in urinary Interleukin −18 (IL‐18) (283±42 pg/mL vs 101±10 pg/mL, n=4, p&lt;0.001) and Monocyte Chemoattracatant Protein‐1 (MCP‐1) (241±22 pg/mL vs 145±23 pg/mL, n=4, p&lt;0.05). We conclude that cholinergic stimulation with nicotine leads to renal infiltration with a CD161a+/CD68+ macrophage population that is not explained by renal expression of VCAM‐1, but is associated with renal damage, as well as the pre‐mature development of hypertension. Thus, renal damage from infiltration of this CD161a+/CD68+ macrophage population is one of the mechanisms involved in nicotine induced hypertension in the young pre‐hypertensive SHR.Support or Funding InformationNIH K08 HL11958NIH PPG HL014388

Radiofrequency Renal Denervation Protects the Ischemic Myocardium

The sympathetic nervous system plays a critical role in the pathogenesis of acute myocardial infarction (AMI) and heart failure. This study tested whether pre‐conditioning with radiofrequency renal artery ablation (RF‐ABL) protects the heart against myocardial ischemia/reperfusion (MI/R) in the setting of hypertension. Spontaneously hypertensive rats (SHR) received either bilateral RF‐ABL (n=14) or Sham‐ABL (n=14) (Biosense Webster Stockert 70 RF generator). Four weeks following treatment, hypertensive SHR were subjected to 30 minutes of left coronary artery occlusion. After 24 hours reperfusion, the myocardial infarct size/area‐at‐risk (AAR) were determined. In addition, the left ventricle (LV) was collected for measurement of nitric oxide (NO) metabolites, nitrite (NO2−) and S‐nitrosothiol (RSNO), and oxidative stress. RF‐ABL produced a significant decrease in myocardial infarct size per AAR compared to Sham‐ABL (26.8 vs. 43.9%) and lower plasma cardiac troponin‐I (6.8 vs. 10.3 ng/ml). Cardiac NO2− levels increased from 2.6 to 3.2 nmol/mg and RSNO levels increased from 0.5 to 1.1 nmol/mg following RF‐ABL. Myocardial oxidative stress was markedly attenuated as measured by 8‐Isoprostane, carbonyl content, and MDA levels. Greater transcription (RT‐PCR) of antioxidants, SOD1 and GPX‐1 were also observed following RF‐ABL. These findings translated to a significant increase in 24‐hr survival of RF‐ABL (13 of 14) as compared to Sham‐ABL (8 of 14) SHR to MI/R. Together, these findings demonstrate that in hypertensive SHR, RF‐ABL produced a sustained increase in myocardial NO bioavailability and attenuation of oxidative stress, both of which can contribute to preconditioning the myocardium against subsequent MI/R injury. These findings provide new insights into the remote cardioprotective effects of RF‐ABL in the setting of AMI.Support or Funding InformationBiosense Webster IIS‐175 to DRK &amp; FS; P30 GM103514 to DRK. 1R01 HL092141, 1R01 HL093579, 1U24 HL 094373, &amp; 1P20 HL113452 to DJL.

Diminished Lipid Raft SNAP23 Increases Blood Pressure by Inhibiting the Membrane Fluidity of Vascular Smooth-Muscle Cells

Synaptosomal-associated protein 23 (SNAP23) is involved in microvesicle trafficking and exocytosis in various cell types, but its functional role in blood pressure (BP) regulation has not yet been defined. Here, we found that lipid raft SNAP23 expression was much lower in vascular smooth-muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) than in those from normotensive Wistar-Kyoto (WKY) rats. This led us to investigate the hypothesis that this lower expression may be linked to the spontaneous hypertension found in SHR. The expression level of lipid raft SNAP23 and the fluidity in the plasma membrane of VSMCs were lower in SHR than in WKY rats. Cholesterol content in the VSMC membrane was higher, but the secreted cholesterols found in VSMC-conditioned medium and in the blood serum were lower in SHR than in WKY rats. SNAP23 knockdown in WKY rat VSMCs reduced the membrane fluidity and increased the membrane cholesterol level. Systemic overexpression of SNAP23 in SHR resulted in an increase of cholesterol content in their serum, a decrease in cholesterol in their aorta and the reduction of their BP. Our findings suggest that the low expression of the lipid raft SNAP23 in VSMCs might be a potential cause for the characteristic hypertension of SHR.