Development Of Hypertension In Spontaneously Hypertensive Rats Research Articles

Abstract P170: Angiotensin II Receptor Associated Protein Expression Within the PVN of Spontaneously Hypertensive Rats

Increased levels of circulating Angiotensin II (Ang II) have been linked to the development of neurogenic hypertension and elevated sympathetic activity, primarily through the Angiotensin II Receptor 1 (AT1R). Angiotensin II Receptor Associated Protein (ATRAP) is a transmembrane protein that regulates Ang II signaling by promoting the internalization of AT1R. Studies have demonstrated that in a model of Ang II-induced hypertension, enhancing ATRAP expression in the paraventricular nucleus of the hypothalamus (PVN) via Lentivirus infection reduced high blood pressure. However, whether ATRAP is differentially expressed in Spontaneously Hypertensive Rats (SHR) is unknown. We hypothesized that ATRAP gene and protein expression decreases during the development of hypertension in SHRs, leading to increased Ang II signaling. To test this, we used male SHRs at 4 (pre-hypertensive) and 12-weeks-old (wo, hypertensive; mean arterial pressure (MAP) 128.0±2.7 vs. 149.2±5.30 mmHg, respectively, measured by tail-cuff recording [Kent Scientific]) and age-matched normotensive Wistar rats (WIS, 92.6±3.3 vs. 123.6±4.6 mmHg, respectively). We measured ATRAP and AT1R mRNA expression in PVN samples using real-time PCR. Protein expression density of ATRAP was assessed using immunofluorescence (IF) and confocal imaging. We found no differences in ATRAP mRNA expression in the PVN between groups ( p >0.05). On the other hand, we found a significant increase in AT1R mRNA expression after hypertension is developed (WIS 12wo: 1.12 ± 0.35; vs. SHR 12wo: 4.17 ± 1.07, p =0.02). While no differences were found in ATRAP, using ATRAP/AT1R ratio as an indicator of AT1R overactivity and decrease in ratio after the development of hypertension (SHR 12wo: 0.23 ± 0.06 vs. WIS 12wo:1.05 ± 0.25) further indicate increased AngII signaling. As observed with ATRAP mRNA expression, no statistical differences were observed in ATRAP protein density within the SHR at 12wo as measured in a separate cohort of animals (MAP SHR 12wo:149.0 ± 3.7 vs. WIS 12wo:115.8 ± 4.0; p >0.05). These results suggest that the increased AngII signaling within the PVN of SHR are most likely due to increased AT1r expression rather than a differential expression of ATRAP. This work was partially funded by AHA 953524 to VCB.

Differential gene expression in the kidneys of SHR and WKY rats after intravenous administration of Akkermansia muciniphila-derived extracellular vesicles

Although Akkermansia muciniphila (Am) plays a beneficial role as a probiotic in the treatment of metabolic syndrome, the mechanisms remain elusive. We tested the hypothesis that Am extracellular vesicles (AmEVs) protect against hypertension through modulation of gene expression in the kidneys of spontaneously hypertensive rats (SHRs). Extracellular vesicles purified from anaerobically cultured Am (1.0 × 108 or 1.0 × 109 particles/kg) or vehicles were injected into the tail veins of Wistar-Kyoto rats (WKYs) and SHRs weekly for 4 weeks. Renal cortical tissues isolated from both rat strains were analyzed by trichrome stain and RT-qPCR. AmEVs protect against the development of hypertension in SHRs without a serious adverse reaction. AmEVs increased the expression of vasocontracting Agt and At1ar as well as vasodilating At2r, Mas1 and Nos2 in the kidneys of both strains. These results indicate that AmEVs have a protective effect against hypertension without a serious adverse reaction. Therefore, it is foreseen that AmEVs may be utilized as a novel therapeutic for the treatment of hypertension.

Long-term intake of corn gluten meal protein hydrolysate attenuated hypertension development and modulated associated plasma metabolite levels in spontaneously hypertensive rats

This study evaluated the long-term antihypertensive effect of corn gluten meal protein hydrolysate (CGM-H) on spontaneously hypertensive rats (SHRs). Plausible pathways governing blood pressure were also evaluated based on untargeted metabolomic analysis. The casein diet containing 1 % of CGM-H and peptides obtained from ultrafiltration membranes attenuated the development of hypertension in SHRs after a 6-week oral administration with similar efficacy, while the control group showed progressive hypertension. Plasma renin and angiotensin converting enzyme (ACE) activity and total peroxides level of the corn peptides-treated groups decreased when compared with the control (p < 0.05). In addition, the corn peptides up-regulated antihypertensive metabolites such as prostaglandin K2 and 11-ketotestosterone, while corticosterone, biotin, and plasma fatty acids were down-regulated. This study demonstrates that corn peptides did not only inhibit ACE and renin activities, but also modulated the biosynthesis and metabolisms of fatty acids, sex hormones, and aldosterone, which would have contributed to attenuation of hypertension.

Kidney Stem Cell Reprogramming Drives Spontaneous Hypertension via Exosomes

The spontaneously hypertensive rat (SHR) is a commonly used animal model for studying primary hypertension. However, the precise mechanism of these rats developing hypertension remains to be defined. Here, we have first demonstrated that kidney stem cell reprogramming is a driver for the development of hypertension in SHR rats. In this study, we treated 5-week-old SHR rats with WKY-kidney stem cell-derived exosomes (WKY-Exo) and 5-week-old WKY rats with SHR-Exo, respectively, via i.p. injections. Notably, WKY-Exo effectively blocked the development of hypertension and arterial stiffening in SHRs. It is fascinating that WKY rats developed hypertension and arterial stiffening due to treatment of SHR-Exo. We confirmed that both WKY- and SHR-Exo were up taken into aortic endothelial and smooth muscle cells after i.p. delivery of CD63/GFP-labelled exosomes. We demonstrated that WKY-Exo can improve vascular functions and arterial compliance of SHR rats as evidenced by preventing the development of arterial stiffness and restoring renal artery endothelial function. We also demonstrated that the vascular functions were impaired in WKY rats after SHR-Exo treatment. Furthermore, our data show that expression of Elastin, Emilin1, and Myh11 was significantly downregulated in the aorta of SHR rats, which can be repaired by WKY-Exo treatment. SHR-Exo decreased expression of Elastin and Emilin1 without affecting Myh11 in the aorta of WKY rats, suggesting that Elastin and Emilin1 deficiency could contribute to arterial stiffening leading to the development of spontaneous hypertension. Proteomic analysis reveals the enrichment of protein-protein interaction network for elastic fiber assembling, blood vessel development, and regulation of angiogenesis in WKY-Exo vs SHR-Exo. In conclusion, our data first demonstrates that kidney stem cell reprograming is a driver for the development of spontaneous hypertension in SHR rats. WKY-KSCs-derived exosome contains a proteome profile promoting arterial repair, which may provide a therapeutic means to prevent and treat primary hypertension. NIH. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Akkermansia muciniphila extracellular vesicles have a protective effect against hypertension.

Akkermansia muciniphila (Am) shows a beneficial role as a probiotic in the treatment of metabolic syndrome. However, the mechanism remains to be elucidated. We tested the hypothesis that Am extracellular vesicles (AmEVs) have a protective effect against hypertension. Extracellular vesicles purified from anaerobically cultured Am were characterized by nanoparticle tracking analysis, transmission electron microscopy, and silver stain after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). AmEVs (1.0 × 1010 log particles/L) or vehicles were added into organ baths to induce vasorelaxation. In addition, AmEVs (1.0 × 108 or 1.0 × 109 particles/kg) or vehicles were injected into the tail veins of Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) weekly for 4 weeks. Peripheral blood mononuclear cells (PBMCs) and splenocytes isolated from both rat strains were analyzed by flow cytometry, RT-qPCR, and western blot. AmEVs affected neither vascular contraction nor endothelial relaxation in thoracic aortas. Moreover, AmEVs protected against the development of hypertension in SHRs without a serious adverse reaction. Additionally, AmEVs increased the population of T regulatory (Treg) cells and tended to reduce proinflammatory cytokines. These results indicate that AmEVs have a protective effect against hypertension without a serious adverse reaction. Therefore, it is foreseen that AmEVs may be utilized as a novel therapeutic for the treatment of hypertension.

Periodontitis accelerates the development of arterial hypertension in spontaneously hypertensive rats (SHR)

Objectives: Arterial hypertension and the inflammatory process are pathophysiologically associated. Of note, it is well understood that periodontitis is an inflammatory morbidity, epidemiologically related to cardiovascular mortality, particularly with the risk of developing arterial hypertension. Considering that in Spontaneously Hypertensive Rats (SHR) the elevation of arterial pressure starts from the 7th week of age, this study aimed to evaluate whether periodontitis accelerates the onset of arterial hypertension, for instance, in 5-week-old SHR. Methods: Induction of periodontitis was started in 3-week-old SHR and maintained for 2 weeks through the ligation of the left first molar with a silk suture, followed by the Porphyromonas gingivalis (strain W83) administration, p.o., 3 times a week. The femoral artery of 5-week-old SHR was cannulated, and 24 hours later, with the animals awakened, the systolic (SAP), diastolic (DAP), and mean (MAP) arterial pressures were recorded. Results: 5-week-old control SHR (SHAM) did not have installed arterial hypertension, while SHR with periodontitis (PER) exhibited a higher arterial pressure when compared to the SHAM group (SAP PER: 150±4 vs. SAP SHAM: 124±3 mmHg, n=8, p≤0.001; DAP PER: 103±5 vs. DAP SHAM: 85±5 mmHg, n=8, p≤0.05; MAP PER: 119±4 vs. MAP SHAM 98±4 mmHg n=8, p ≤0.01). Conclusion: The differences observed in the pressure values between the groups studied demonstrate that periodontitis accelerates the development of hypertension in SHR. Funding Sources: Fundação de Amparo à Pesquisa do Estados de São Paulo - FAPESP, Process 2021/08622-7 and 2020/06043-7. Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, Process 306994/2021-6 and 423999/2021-4. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Chronic stimulation of group II metabotropic glutamate receptors in the medulla oblongata attenuates hypertension development in spontaneously hypertensive rats.

Baroreflex dysfunction is partly implicated in hypertension and one responsible region is the dorsal medulla oblongata including the nucleus tractus solitarius (NTS). NTS neurons receive and project glutamatergic inputs to subsequently regulate blood pressure, while G-protein-coupled metabotropic glutamate receptors (mGluRs) play a modulatory role for glutamatergic transmission in baroreflex pathways. Stimulating group II mGluR subtype 2 and 3 (mGluR2/3) in the brainstem can decrease blood pressure and sympathetic nervous activity. Here, we hypothesized that the chronic stimulation of mGluR2/3 in the dorsal medulla oblongata can alleviate hypertensive development via the modulation of autonomic nervous activity in young, spontaneously hypertensive rats (SHRs). Compared with that in the sham control group, chronic LY379268 application (mGluR2/3 agonist; 0.40 μg/day) to the dorsal medulla oblongata for 6 weeks reduced the progression of hypertension in 6-week-old SHRs as indicated by the 40 mmHg reduction in systolic blood pressure and promoted their parasympathetic nervous activity as evidenced by the heart rate variability. No differences in blood catecholamine levels or any echocardiographic indices were found between the two groups. The improvement of reflex bradycardia, a baroreflex function, appeared after chronic LY379268 application. The mRNA expression level of mGluR2, but not mGluR3, in the dorsal medulla oblongata was substantially reduced in SHRs compared to that of the control strain. In conclusion, mGluR2/3 signaling might be responsible for hypertension development in SHRs, and modulating mGluR2/3 expression/stimulation in the dorsal brainstem could be a novel therapeutic strategy for hypertension via increasing the parasympathetic activity.

Larger endothelium-dependent contractions in iliac arteries of adult SHRs are attributed to differential downregulation of TP and EP3 receptors in the vessels of WKYs and SHRs during the transition from adolescence to adulthood

This study was to determine how endothelium-dependent contractions (EDCs) change in iliac arteries of Wistar-Kyoto (WKYs) and spontaneously hypertensive rats (SHRs) during the transition from adolescence to adulthood and the underlying mechanism(s). We also aimed to elucidate effects of L-798106, an EP3 receptor antagonist, on EDCs and the blood pressure increase in adolescent SHRs. Blood vessels were isolated for functional and biochemical analyses. EDCs were comparable in adolescent iliac arteries of both strains, and contractions to ACh, prostacyclin (PGI2), the EP3 receptor agonist sulprostone and the TP receptor agonist U46619 in adult vessels were less prominent compared with those in the adolescents, while the attenuation of vasoconstrictions to ACh, PGI2 or U46619 with age was to a lesser extent in SHRs. PGI2 production was decreased to a similar level in adult arteries. TP and EP3 expressions were downregulated in adult vessels, whereas the extent of TP downregulation was less in SHRs. L-798106 partially suppressed the vasoconstrictions to U46619 and attenuated EDCs to a greater extent than SQ29548, and administration of L-798106 blunted the blood pressure increase with age in prehypertensive SHRs. These results demonstrate the comparable EDCs in iliac arteries of the adolescents are decreased in the adults, but relatively larger EDCs in adult SHRs can be a reflection of differential downregulation of TP and EP3 receptors during the transition from adolescence to adulthood. Also, our data suggest that blockade of both TP and EP3 receptors starting from the prehypertensive stage suppresses EDCs and the development of hypertension in SHRs.

Age-dependent increase in activity of eukaryotic elongation factor 2 kinase in mesenteric arteries from spontaneously hypertensive rats.

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) negatively regulates protein translation through the phosphorylation of its specific substrate, eEF2. We previously found that expression of eEF2K was increased in arteries from 13–15-week-old spontaneously hypertensive rats (SHR) as well as in left ventricles of cardiac hypertrophy models. Furthermore, we demonstrated that eEF2K mediates the development of essential hypertension and pulmonary arterial hypertension in animal models. Protein expression changes with age during development of hypertension in SHR. In the present study, we examined whether activity and expression of eEF2K change in isolated mesenteric arteries dependent on the age. After superior mesenteric arteries were isolated from 4–10-week-old Wistar Kyoto rats (WKY) and SHR, Western blotting was performed. The phosphorylation of eEF2K at Ser500, an activating phosphorylation site, was increased in the arteries from 10-week-old SHR, whereas the phosphorylation of eEF2K at Ser366, an inactivating phosphorylation site, was increased in the arteries from 4–5-week-old SHR compared with WKY. The expression of eEF2K was increased in the arteries from 10-week-old SHR compared with WKY. The phosphorylation of eEF2 at Thr56 was decreased in the arteries from 4–5-week-old SHR, whereas it was increased in the arteries from 10-week-old SHR compared with WKY. We for the first time revealed that eEF2K activity is lower in prehypertensive stage but higher in hypertensive stage in SHR, suggesting that an inhibition of eEF2K activity may be a potential therapeutic strategy for the treatment of essential hypertension.

Ketogenic diet aggravates hypertension via NF-κB-mediated endothelial dysfunction in spontaneously hypertensive rats

AimsKetogenic diet (KD) has been proposed to be an effective lifestyle intervention for metabolic syndrome. However, the effects of KD on hypertension have not been well investigated. The present study aimed to investigate the effects and underling mechanisms of KD on hypertension in spontaneously hypertensive rats (SHRs). Materials and methodsSHRs were subjected to normal diet or KD for 4 weeks, starting at the age of 10 weeks. Then, the blood pressure and vascular function were assessed. Next, the eNOS expression, inflammatory factors and relative signaling pathway were examined. Human umbilical vein endothelial cells were used to investigate the underlying mechanism account for the effect of ketone on inflammation and eNOS expression. Key findingsCompared with the normal diet, KD was indicated to aggravate hypertension and impaire endothelium-dependent relaxation in mesenteric arteries of SHRs. eNOS and CD31 expression in mesenteric arteries were also significantly suppressed by KD. In addition, KD markedly increased the activation of NF-κB pathway and the expression of IL1-β and TNF-α. In vitro, results showed that inhibition of NF-κB could rescue the adverse effects of ketone body and TGF-β on eNOS expression and inflammation response. SignificanceOur study indicated that KD impaired endothelium-dependent relaxation in mesenteric arteries and aggravated the development of hypertension in SHRs, suggesting that it should be more cautious to apply KD into clinical application in hypertensive individuals.

Chronic Dantrolene Treatment Does Not Affect Hypertension, but Attenuates Sympathetic Stimulation Enhanced Atrial Fibrillation Inducibility in SHR

Ryanodine receptor (RyR) dysfunction in skeletal muscle (RyR1) leads to malignant hyperthermia, and in cardiac muscle (RyR2) triggers cardiac arrhythmias. We hypothesized that RyR dysfunction in vascular smooth muscle could increase vascular resistance and hypertension, and may contribute to increased atrial fibrillation (AF) in hypertension. Thus, stabilizing RyR function with chronic dantrolene treatment may attenuate hypertension and AF inducibility in spontaneously hypertensive rats (SHR). Male SHR (16 weeks old) were randomized into vehicle- (n = 10) and dantrolene-treated (10 mg/kg/day, n = 10) groups for 4 weeks. Wistar Kyoto (WKY, n = 11) rats served as controls. Blood pressures (BP) were monitored before and during the 4-week treatment. After 4-week treatment, direct BP, echocardiography, and hemodynamics were recorded. AF inducibility tests were performed in vivo at baseline and repeated under sympathetic stimulation (SS). Compared with WKY, SHR had significantly higher BP throughout the experimental period. Dantrolene treatment had no effect on BP levels in SHR (final systolic BP 212 ± 9 mm Hg in vehicle group vs. 208 ± 16 mm Hg in dantrolene group, P > 0.05). AF inducibility was very low and not significantly different between 5-month-old WKY and SHR at baseline. However, under SS, AF inducibility and duration were significantly increased in SHR (20% in WKY vs. 60% in SHR-vehicle, P<0.05). Dantrolene treatment significantly attenuated AF inducibility under SS in SHR (60% in vehicle vs. 20% in dantrolene, P < 0.05). Stabilizing RyR with chronic dantrolene treatment does not affect hypertension development in SHR. SHR has increased vulnerability to AF induction under SS, which can be attenuated with dantrolene treatment.

Central Glucagon-like Peptide-1 Receptor Signaling via Brainstem Catecholamine Neurons Counteracts Hypertension in Spontaneously Hypertensive Rats

Glucagon-like peptide-1 receptor (GLP-1R) agonists, widely used to treat type 2 diabetes, reduce blood pressure (BP) in hypertensive patients. Whether this action involves central mechanisms is unknown. We here report that repeated lateral ventricular (LV) injection of GLP-1R agonist, liraglutide, once daily for 15 days counteracted the development of hypertension in spontaneously hypertensive rats (SHR). In parallel, it suppressed urinary norepinephrine excretion, and induced c-Fos expressions in the area postrema (AP) and nucleus tractus solitarius (NTS) of brainstem including the NTS neurons immunoreactive to dopamine beta-hydroxylase (DBH). Acute administration of liraglutide into fourth ventricle, the area with easy access to the AP and NTS, transiently decreased BP in SHR and this effect was attenuated after lesion of NTS DBH neurons with anti-DBH conjugated to saporin (anti-DBH-SAP). In anti-DBH-SAP injected SHR, the antihypertensive effect of repeated LV injection of liraglutide for 14 days was also attenuated. These findings demonstrate that the central GLP-1R signaling via NTS DBH neurons counteracts the development of hypertension in SHR, accompanied by attenuated sympathetic nerve activity.

Renal denervation and CD161a immune ablation prevent cholinergic hypertension and renal sodium retention

Cholinergic receptor activation leads to premature development of hypertension and infiltration of proinflammatory CD161a+/CD68+ M1 macrophages into the renal medulla. Renal inflammation is implicated in renal sodium retention and the development of hypertension. Renal denervation is known to decrease renal inflammation. The objective of this study was to determine the role of CD161a+/CD68+ macrophages and renal sympathetic nerves in cholinergic-hypertension and renal sodium retention. Bilateral renal nerve denervation (RND) and immune ablation of CD161a+ immune cells were performed in young prehypertensive spontaneously hypertensive rat (SHR) followed by infusion of either saline or nicotine (15 mg·kg-1·day-1) for 2 wk. Immune ablation was conducted by injection of unconjugated azide-free antibody targeting rat CD161a+. Blood pressure was monitored by tail cuff plethysmography. Tissues were harvested at the end of infusion. Nicotine induced premature hypertension, renal expression of the sodium-potassium chloride cotransporter (NKCC2), increases in renal sodium retention, and infiltration of CD161a+/CD68+ macrophages into the renal medulla. All of these effects were abrogated by RND and ablation of CD161a+ immune cells. Cholinergic activation of CD161a+ immune cells with nicotine leads to the premature development of hypertension in SHR. The effects of renal sympathetic nerves on chemotaxis of CD161a+ macrophages to the renal medulla, increased renal expression of NKCC2, and renal sodium retention contribute to cholinergic hypertension. The CD161a+ immune cells are necessary and essential for this prohypertensive nicotine-mediated inflammatory response.NEW & NOTEWORTHY This is the first study that describes a novel integrative physiological interaction between the adrenergic, cholinergic, and renal systems in the development of hypertension, describing data for the role of each in a genetic model of essential hypertension. Noteworthy findings include the prevention of nicotine-mediated hypertension following successful immune ablation of CD161a+ immune cells and the necessary role these cells play in the overexpression of the sodium-potassium-chloride cotransporter (NKCC2) in the renal medulla and renal sodium retention. Renal infiltration of these cells is demonstrated to be dependent on the presence of renal adrenergic innervation. These data offer a fertile ground of therapeutic potential for the treatment of hypertension as well as open the door for further investigation into the mechanism involved in inflammation-mediated renal sodium transporter expression. Taken together, these findings suggest immune therapy, renal denervation, and, possibly, other new molecular targets as having a potential role in the development and maintenance of essential hypertension.

Central administration of aminooxyacetate, an inhibitor of H2S production, affects thermoregulatory but not cardiovascular and ventilatory responses to hypercapnia in spontaneously hypertensive rats

Hydrogen sulfide (H2S) is classically known for its toxic effects. More recently H2S has been documented as a neuromodulator. Here we investigated the central effects of aminooxyacetate (AOA; inhibitor of the H2S-synthesizing enzyme cystathionine β-synthase, CBS) on cardiovascular, respiratory and thermoregulatory responses to hypercapnia in spontaneously hypertensive rats (SHR). To attain this goal we measured mean arterial pressure (MAP), heart rate (HR), ventilation (VE), and deep body temperature (Tb) of SHR and (normotensive) Wistar Kyoto (WKY) rats before and after microinjection of AOA (9 nmol/μL) or saline into the fourth ventricle immediately followed by 30-min hypercapnia exposure (7% inspired CO2). In saline-treated WKY rats, hypercapnia caused an increase in MAP accompanied by bradycardia, an increase in VE, and a drop in Tb. In AOA-treated WKY rats exposed to hypercapnia, the drug did not affect the increased MAP, potentiated the bradycardic response, attenuated the increased VE, and potentiated the drop in Tb. In saline-treated SHR, in comparison to the saline-treated WKY rats, hypercapnia elicited a minor, shorter-lasting increase in MAP with no changes in HR, evoked a greater increase in VE, and did not induce a drop in Tb. In AOA-treated SHR exposed to hypercapnia, the drug did not change the hypercapnia-induced cardiovascular and ventilatory responses while permitted a drop in Tb. Our findings indicate that AOA, an inhibitor of H2S production, modulates cardiorespiratory and thermoregulatory responses to hypercapnia in normotensive rats, whereas hypertension development in SHR is accompanied by suppression of the AOA effect on the cardiovascular and respiratory responses.

Eukaryotic elongation factor 2 kinase inhibitor, A484954 inhibits noradrenaline-induced acute increase of blood pressure in rats.

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) inhibits protein translation through the phosphorylation of its specific substrate, eEF2. We previously demonstrated that eEF2K expression increases in superior mesenteric artery from spontaneously hypertensive rats (SHR) and that eEF2K mediates development of hypertension in SHR. In addition, we recently revealed that A484954, a selective eEF2K inhibitor induced relaxation via opening smooth muscle inward rectifier K+ (Kir) channel in rat isolated superior mesenteric artery. Here, we further examined the effects of A484954 on contractility and blood pressure (BP) in rats. Isometric contraction of rat isolated superior mesenteric artery was measured. BP was measured by a carotid cannulation method. A484954 (10 µM) inhibited noradrenaline (NA)-induced contraction in a biphasic manner (magnitude of inhibition higher at high dose NA). A484954 also inhibited an α1-receptor agonist, phenylephrine-induced contraction, while it was not biphasic. Specifically, a β-receptor antagonist, propranolol (1 µM) prevented the A484954-mediated inhibition of NA (high-dose)-induced contraction. A484954 (10 µM) potentiated a β-receptor agonist, isoproterenol-induced relaxation, which was completely prevented by BaCl2 (1 mM), a Kir channel blocker. In vivo, A484954 (122 µg/kg) inhibited NA-induced increase of BP in rats. Another eEF2K inhibitor, NH125 (22 µg/kg) also inhibited the NA-induced BP increase in rats. In summary, it was concluded that A484954 lowers NA-induced BP rise perhaps through activation of β2-receptor-Kir channel and subsequent vasorelaxation via inhibiting eEF2K activity.

Chronic, low-dose TMAO treatment reduces diastolic dysfunction and heart fibrosis in hypertensive rats.

Several studies have suggested negative effects of trimethylamine oxide (TMAO) on the circulatory system. However, a number of studies have shown protective functions of TMAO, a piezolyte and osmolyte, in animals exposed to high hydrostatic and/or osmotic stress. We evaluated the effects of TMAO treatment on the development of hypertension and its complications in male spontaneously hypertensive rats (SHRs) maintained on water (SHR-Water) and SHRs drinking TMAO water solution from weaning (SHR-TMAO). Wistar-Kyoto (WKY) rats were used as normotensive controls to discriminate between age-dependent and hypertension-dependent changes. Telemetry measurements of blood pressure were performed in rats between the 7th and 16th weeks of life. Anesthetized rats underwent echocardiographic, electrocardiographic, and direct left ventricular end-diastolic pressure (LVEDP) measurements. Hematoxylin and eosin as well as van Gieson staining for histopathological evaluation were performed. Plasma TMAO measured by chromatography coupled with mass spectrometry was significantly higher in the SHR-Water group compared with the WKY group (~20%). TMAO treatment increased plasma TMAO by four- to fivefold and did not affect the development of hypertension in SHRs. Sixteen-week-old rats in the SHR-Water and SHR-TMAO groups (12-wk TMAO treatment) showed similar blood pressures, angiopathy, and cardiac hypertrophy. However, the SHR-TMAO group had lower plasma NH2-terminal pro-B-type natriuretic peptide, LVEDP, and cardiac fibrosis. In contrast to age-matched WKY rats, 60-wk-old SHRs showed hypertensive angiopathy and heart failure with preserved ejection fraction. Compared with the SHR-Water group, the SHR-TMAO group (56-wk TMAO treatment) showed significantly lower plasma NH2-terminal pro-B-type natriuretic peptide and vasopressin, significantly lower LVEDP, and cardiac fibrosis. In conclusion, a four- to fivefold increase in plasma TMAO does not exert negative effects on the circulatory system. In contrast, increased dietary TMAO seems to reduce diastolic dysfunction in pressure-overloaded hearts in rats. NEW & NOTEWORTHY Chronic, low-dose trimethylamine oxide (TMAO) treatment that increases plasma TMAO by four- to fivefold reduces plasma NH2-terminal pro-B-type natriuretic peptide and vasopressin, left ventricular end-diastolic pressure, and cardiac fibrosis in pressure-overloaded hearts in hypertensive rats. Our study provides evidence that a moderate increase in plasma TMAO does not have a negative effect on the circulatory system. In contrast, increased dietary TMAO seems to reduce diastolic dysfunction in the pressure-overloaded heart.

Early Exercise Training Postpones Hypertension Progression via Activation of Central ACE2‐Ang(1–7)‐Mas Axis in Prehypertensive Rats

ObjectivesTo investigate the effects of exercise training on the development of hypertension in spontaneously hypertensive rats (SHR) and explore the underlying mechanisms by focusing on the central ACE2‐Ang (1–7)‐MAS axis.MethodsThe male SHR (n=20, 5 weeks old) and 20 normotensive Wistar Kyoto rats (WKY) were randomly assigned to sedentary (Sed) group or exercise training (ExT) group. The trained rats run on a treadmill in 20 m/min, 30 min/day, 5 day/week for 20 weeks. Systolic blood pressure (SBP) were measured by a tail‐cuff method. The baroreflex sensitivity (BRS) was assessed by intravenous injection of phenylephrine under anesthesia. The expression of ACE2 and MAS receptors mRNA and protein in the cardiovascular centers was determined by real‐time PCR and Western blot. Alterations in the BRS were evaluated before and after intracerebroventricular injection of MAS receptor agonist Ang (1–7) and its antagonist A779, respectively.Results(1) Exercise training significantly postponed the development of hypertension in SHR and decreased SBP in both SHR and WKY as compared with Sed groups (P&lt;0.01 and P&lt;0.05). (2) Exercise training enhanced blood pressure regulation and improved the BRS in the SHR (P&lt;0.01). (3) The expression of ACE2 and MAS receptor mRNA and protein in rostral ventrolateral medulla (RVLM), nucleus tract solitarius (NTS), and paraventricular nucleus (PVN) was up‐regulated in SHR+ExT group (P&lt;0.05, P&lt;0.01). (4) Central administration of A779 abolished the benefits of exercise‐induced improvement of BRS in the SHR+ExT rats (P&lt;0.01). In contrast, Ang (1–7) improved the BRS in both SHR+Sed group and SHR +ExT group (P&lt;0.05).ConclusionExercise training postpones hypertension progression and improves blood pressure regulation, which is associated with the enhancement of central ACE2‐Ang(1–7)‐Mas axis.Support or Funding InformationNational Natural Science Foundation of China (No. 81372111) and Natural Science Foundation of Fujian Province of China (No. 2014J01339)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inhibition of Necrosis Via Necrox‐5 Attenuates The Development Of Hypertension In Male, But Not Female Spontaneously Hypertensive Rats (SHR)

It is well established that hypertension is accompanied by cell death, however, less is known regarding the role of cell death in blood pressure (BP) control. Necrosis is an uncontrolled pathologic form of cell death that is associated with inflammation. Therefore, the goal of the current study was to test the hypothesis that necrosis contributes to the development of hypertension in SHR. Initial studies measured renal necrosis in 13 wk old male and female SHR (n=9) using flow cytometry. Male SHR had greater renal necrosis compared to female SHR (3.7±0.4% vs. 0.4±0.2% of total renal cells, respectively; p&lt;0.0001). Additional male and female SHR were then randomized to receive vehicle or Necrox‐5 from 6–12 weeks of age (1 mg/kg via IP injection twice weekly; n=4); Necrox‐5 is a cell permeable inhibitor of necrosis that blocks oxidative stress induced necrotic cell death. BP was measured weekly via tail‐cuff analysis and via carotid catheter at sacrifice. Following 6 wks of treatment, kidneys were isolated and necrosis was measured by flow cytometry. Treatment with Necrox‐5 beginning at 6 wks of age attenuated maturation‐induced increases in BP in male SHR (Necrox‐5: 152±11 vs Control: 177±4 mmHg; p=0.07). BP in female SHR was not altered by chronic Necrox‐5 treatment (Necrox‐5: 152±14 vs. Control: 146±11 mmHg; p=0.72). In addition, the sex difference in BP apparent in control rats was abolished by Necrox‐5 treatment. Consistent with these results, Necrox‐5 treatment for 6 wks decreased renal necrosis only in males (Necrox‐5: 1.5±0.5% vs Control: 3±0% of total renal cells). Taken together, our data suggest that greater cell death in male SHR compared to female SHR contributes to sex differences in BP by exacerbating age‐related increases in BP in males.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Intranasal vaccination against angiotensin II type 1 receptor and pneumococcal surface protein A attenuates hypertension and pneumococcal infection in rodents.

To combat global increases in the prevalence of lifestyle-related diseases and concomitant infectious diseases, we aimed to develop an innovative intranasal vaccine that simultaneously targets both hypertension and pneumonia, is not given by invasive injection, and offers prolonged therapeutic effect and reduced frequency of administration. Angiotensin II type 1 receptor-pneumococcal surface protein A (AT1R-PspA) vaccine, consisting of a cationic nanometer-sized hydrogel incorporating AT1R partial peptide conjugated with PspA and cyclic diguanylate monophosphate adjuvant, was created and given intranasally to spontaneously hypertensive rats (SHRs). Antigen-specific antibodies and blood pressure were examined to evaluate immune responses and the antihypertensive effect of the vaccine. To examine the protective effect of antibodies induced by vaccination on pneumococcal infection, sera obtained from immunized SHRs were incubated with a lethal dose of Streptococcus pneumoniae and then administered to mice. Five doses of AT1R-PspA nasal-vaccine-induced AT1R-specific serum IgG antibody production and attenuated the development of hypertension in SHRs in the long term. Both in-vitro and in-vivo studies revealed that responses to angiotensin II were suppressed in vaccinated rats. Mice passively immunized with sera obtained from AT1R-PspA-vaccinated SHRs were protected from lethal pneumococcal infection. Intranasal immunization with AT1R-PspA vaccine has the potential to simultaneously attenuate the development of hypertension and protect from lethal pneumococcal infection.

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.