Dahl Salt-sensitive Hypertensive Research Articles

Sex Differences in Dietary Sodium evoked NCC Regulation and Blood Pressure in Male and Female Sprague Dawley, Dahl Salt-Resistant and Dahl Salt-Sensitive Rats.

Hypertension affects approximately 1 in 2 US adults and sex plays an important role in the pathogenesis of hypertension.​ The sodium chloride cotransporter (NCC), regulated by a kinase network including with-no-lysine kinases (WNK) 1 and WNK4, STE20/SPS1-related proline alanine rich kinase (SPAK), and oxidative stress response 1 (OxSR1) is critical to sodium reabsorption and blood pressure regulation. Dietary salt differentially modulates the NCC in salt-sensitive and salt-resistant rats, in part by modulation of WNK/SPAK/OxSR1 signaling. In these studies, we tested the hypothesis that sex-dependent differences in NCC regulation contribute to the development of the salt sensitivity of blood pressure using male and female Sprague Dawley, Dahl salt-resistant (DSR), and Dahl salt-sensitive (DSS) rats. In normotensive salt resistant SD and DSR rats a high salt diet evoked significant decreases in NCC activity, expression, and phosphorylation. In males these changes were associated with no change in WNK1 expression and a decrease in WNK4 levels and suppression of SPAK/OxSR1 expression and phosphorylation. In contrast in females decreased NCC activity associated with suppression of SPAK/OxSR1 expression and phosphorylation. In hypertensive DSS rats the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension. Collectively our findings support the existence of sex differences in male versus female rats with NCC regulation during dietary salt intake involving suppression of WNK4 expression in male rats only and the involvement of SPAK/OxSR1 signaling in both males and females.

Electroacupuncture Rebalances Autonomic Nervous Activities Decreasing Blood Pressure in Salt-Sensitive Hypertensive Rats

High blood pressure (BP) associated with sympathetic overactivity is observed in hypertensive animals and patients. We have recently reported that electroacupuncture (EA) at two sets of acupoints ST36-37 and SP6-7 attenuates BP in Dahl salt-sensitive hypertensive (DSSH) rats through a positive interaction between sympathetic nerve activity inhibition (sympathoinhibition, SI-EA) and anti-inflammation (AI-EA). Chronic inflammation is not only influenced by sympathetic (SNA) but also by parasympathetic nerve activity (PNA). However, it remains unclear if combined SI-EA + AI-EA (cEA) rebalances autonomic nerve activity by both inhibiting SNA and exciting PNA that alleviate hypertension (HTN). We hypothesized that cEA decreased SNA and increased PNA in DSSH rats. Dahl salt-sensitive (DSS) rats were fed 4% salt diet and randomly allocated into two groups: cEA or Sham-EA (no electrical stimulation). Another group of DSS rats studied as normotensive (NTNive) controls were fed a standard rat chow throughout the experiment. Systolic/diastolic BP (SBP/DBP) were measured with Tail-cuff via CODA system once a week. Once DSSH rats developed moderate HTN (SBP 160±5 mmHg), cEA or Sham-EA was applied twice weekly for five weeks, while the NTNive control groups received five weeks of similar study procedures (restraining) without the intervention. After five weeks of treatments, rats were anesthetized for the neuronal recording of SNA and PNA. Cervical vagal nerve (CVN) or splanchnic sympathetic nerve (SSN) was isolated from surrounding connective tissue under a dissecting microscope. Multiple-unit nerve activities were recorded and analyzed with Spike2 software. We observed that SBP (189.2±3.5 mmHg) and DBP (138.6±2.2 mmHg) in Sham-EA treated DSSH rats were higher than SBP (140.8±1.8 mmHg) by 25.6% and DBP (105.5±1.4 mmHg) by 23.9% in rats treated with repetitive cEA. Throughout the study, SBP (132.7±1.8 to 135.2±2.1 mmHg) and DBP (74.1±1.7 to 82.9±2.6 mmHg) in NTNive rats remained within normal range. Furthermore, activity of SSN was significantly greater in Sham-EA treated DSSH rats (23.1±1.6 imp/s) compared to cEA treated rats (15.2±2.0 imp/s, P=0.043) and NTNive rats (11.5 ±0.8 imp/s, P=0.004). Activity of CVN was higher in DSSH rats treated with cEA (27.8±2.9 imp/s) than Sham-EA (12.5±2.3 imp/s, P=0.016). Relative to Sham-EA, activity of CVN was higher (42.5±2.9 imp/s, P=0.001) in normal rats. In conclusion, cEA treatment effectively alleviates hypertension by restoring the balance of autonomic nervous functions through sympathoinhibition and parasympathoexcitation. Funding: NIH 1RO1AT011306-01A1. 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.

Pericyte detachment and renal congestion involve interstitial injury and fibrosis in Dahl salt-sensitive rats and humans with heart failure

Congestive heart failure produces fluid volume overload, central and renal venous pressure elevation, and consequently renal congestion, which results in worsening renal function. Pericyte detachment and pericyte-myofibroblast transition (PMT) were linked to renal interstitial fibrosis. Dahl salt-sensitive hypertensive (DahlS) rats are a non-surgical renal congestion model. The relation, however, between renal interstitial damage, pericyte morphology, and PMT in the renal congestion of DahlS rats has not been reported. DahlS rats (8-week-old) were fed normal salt (NS, 0.4% NaCl) or high salt (HS, 4% NaCl), and the left kidney was decapsulated to reduce renal interstitial hydrostatic pressure (RIHP) at 9 weeks old. One week after capsulotomy, both kidneys were analyzed by molecular and histological techniques. Renal pericyte structure was assessed in the body donors with/without venous stasis. Markers of tubulointerstitial damage, interstitial fibrosis, and PMT were upregulated in the right non-decapsulated kidney of DahlS rats fed HS. Renal tubular injury and fibrosis were detected in the HS diet groups in histological analysis. Pericyte detachment was observed in the right non-decapsulated kidney of DahlS rats fed HS by low vacuum-scanning electron microscopy. Decapsulation in DahlS rats fed HS attenuated these findings. Also, renal pericytes detached from the vascular wall in patients with heart failure. These results suggest that pericyte detachment and PMT induced by increased RIHP are responsible for tubulointerstitial injury and fibrosis in DahlS rats and humans with renal congestion. Renal venous congestion and subsequent physiological changes could be therapeutic targets for renal damage in cardiorenal syndrome.

Sympathoinhibitory electroacupuncture (EA) interacts positively with anti-inflammatory EA alleviating blood pressure in hypertensive rats.

Elevated sympathetic activity and chronic inflammation are known contributory factors observed in hypertension. We have observed that sympathoinhibitory electroacupuncture (SI-EA) at acupoints ST36-37 alleviates sympathetic activity and hypertension. Additionally, EA at acupoints SP6-7 exerts anti-inflammatory (AI-EA) effects. However, it is not known whether simultaneous stimulation of this combination of acupoints attenuates or enhances individual effects. A 2 × 2 factorial design was used to test the hypothesis that combining SI-EA and AI-EA (cEA) leads to greater reduction of hypertension by decreasing sympathetic activity and inflammation in hypertensive rats than either set of acupoints alone. Dahl salt-sensitive hypertensive (DSSH) rats were treated with four EA regimens including cEA, SI-EA, AI-EA, and sham-EA twice weekly for five weeks. A group of normotensive (NTN) rats served as control. Systolic and diastolic BP (SBP and DBP) and heart rate (HR) were measured non-invasively by tail-cuff. Plasma norepinephrine (NE), high-sensitivity C-reactive protein (hs-CRP) and interleukin 6 (IL-6) concentrations were determined with ELISA at the completion of treatments. DSSH rats on high salt diet progressively developed moderate hypertension within five weeks. DSSH rats treated with sham-EA showed continuous increase in SBP and DBP and elevations in plasma NE, hs-CRP, and IL-6 levels relative to NTN control. Both SI-EA and cEA decreased SBP and DBP, and had corresponding changes in biomarkers (NE, hs-CRP, and IL-6) compared with sham-EA. AI-EA prevented SBP and DBP elevation and decreased IL-6 and hs-CRP relative to sham-EA. Importantly in DSSH rats that received repetitive cEA treatment, SI-EA interacted positively with AI-EA leading to greater reduction of SBP, DBP, NE, hs-CRP, and IL-6 than SI-EA or AI-EA alone. These data suggest that by targeting both elevated sympathetic activity and chronic inflammation, cEA regimen results in a greater reduction of BP effects in treating hypertension compared to using individual SI-EA or AI-EA alone.

Alpha-7 Nicotinic Acetylcholine Receptors Contribute to the Combined Electroacupuncture Modulation of Hypertension in Salt-Sensitive Rats

Elevated sympathetic activities and low-grade chronic inflammation are observed in hypertensive (HTNive) patients and animals including dahl salt-sensitive hypertensive (DSSH) rats. We have shown that stimulation of the deep peroneal nerve and the tibial nerve by combined electroacupuncture (cEA) at the combination of two sets of acupoints ST36-37 and SP6-7 decreased blood pressure (BP) and proinflammatory cytokines in HTNive subjects through sympathoinhibition and anti-inflammation. Acetylcholine (ACh), the primary neurotransmitter of parasympathetic nerves, is known to participate in modulation of inflammation. We hypothesized that α-7 nicotinic acetylcholine receptors (α7nAChR) play an important role in the BP lowering effects of cEA in DSSH rats. DSS rats were fed with 4% salt diet and randomly allocated into three groups (4 rats/group). Once they developed moderate hypertension (SBP 160±5 mmHg), one group was treated with Sham-EA (no electrical stimulations), and two groups were treated with cEA. Both cEA and Sham-EA groups were given twice weekly for eight weeks. Methyllycaconitine (MLA) is a α7nAChR antagonist. MLA (2.4 mg/kg) was injected intraperitoneally (ip) daily into one group of cEA treated rats (n=4) during the last three weeks with cEA treatments. In a similar manner, the other cEA group and the Sham-EA group received daily saline ip injection for three weeks. Another four DSS rats were fed with standard rat chow and treated as the normotensive (NTN) controls. Systolic/diastolic BP (SBP/DBP) of rats were measured with Tail-cuff via CODA system once a week. At the end of the experiment, compared to Sham-EA rats (207.8±2.5 mmHg, DBP 144.6±3.2 mmHg), cEA decreased SBP (138.8±0.8 mmHg) by 33.2% and DBP (98.6±1.7 mmHg) by 24.25%. Blockade of α7nAChR with MLA partially reversed the cEA BP lowering effects (SBP 193.4±2.6 mmHg and DBP 136.5±2.4 mmHg), and BPs in cEA+MLA treated rats were still significantly lower than Sham-EA-treated rats after the reveral. BPs of NTNive rats remained in the normal BP ranges throughout the 13 weeks of the experiment (from 135.9±2.8 to 134.2±1.1 mmHg). In conclusion, systemic antagonism of α7nAChR with MLA partially reversed the BP lowering effects of cEA in DSSH rats. National Institute of Health National Center for Complementary & Integrative Health Grant (1RO1AT011306). 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.

PS-BPB10-6: THE RELATION BETWEEN PERICYTE DETACHMENT AND INTERSTITIAL FIBROSIS IN DAHL SALT-SENSITIVE HYPERTENSIVE (DAHLS) RATS

Background: Congestive heart failure produces the state of fluid volume overload, central venous pressure (CVP) elevation, and consequently renal venous pressure (RVP) elevation. We have recently developed a novel rat unilateral renal venous congestion model, in which ligation of the inferior vena cava between both renal veins artificially induced renal congestion in the left kidney only. In this model, pericyte detachment and pericyte-myofibroblast transition (PMT) around the vasa recta were involved in interstitial injury and fibrosis. Dahl salt-sensitive hypertensive (DahlS) rats on high salt diets exhibit hypertension, congestive heart failure, fluid volume overload, CVP and RVP elevation, and renal damage, considering to be a non-artificial renal congestion model. The relation, however, between renal interstitial injury and fibrosis, elevated RVP, and pericyte detachment in DahlS rats has not been reported. In the present study, we assessed the relation of pericyte detachment around the vasa recta and PMT with interstitial fibrosis in DahlS rats. Methods: Eight-week-old DahlS rats (Dahl/Mcwi) were divided into three groups: normal diet, 4% NaCl diet, and 8% NaCl diet groups, and their kidneys were analyzed after 2 weeks. Total mRNA and protein expression levels were quantified by real-time PCR and western blot, respectively. Tubulointerstitial damage and fibrosis were identified by histological analysis. Furthermore, we evaluated pericyte detachment around the vasa recta by low-vacuum scanning electron microscopy (LV-SEM). Results: The expression of KIM1, a tubulointerstitial damage marker; CNN1 and αSMA, interstitial fibrosis markers; and TAGLN, a smooth muscle protein22 and PMT marker; was significantly increased in a salt-dependent manner in DahlS rats. In histological analysis, hyperplasia of the extracellular matrix and renal tubular injury were detected in 4% and 8% NaCl diet groups. The positive area of PMT markers in the interstitial space around the vasa recta was also increased in the NaCl diet groups. Pericyte detachment from the vasa recta was observed in the NaCl diet groups by LV-SEM. Conclusions: Pericyte detachment and PMT are involved in tubulointerstitial injury and fibrosis of DahlS rats. Renal venous congestion and subsequent physiological changes could have a role in renal damage and fibrosis. Arterial hypertension has been emphasized for a long time in renal injury, and venous hypertension must also be focused on with the concept of renal congestion. Further understanding of this concept may lead to new therapeutic strategies for renal injury.

PS-BPB03-1: ASSOCIATION OF ANTIHYPERTENSIVE EFFECTS OF ESAXERENONE WITH THE INTERNAL SODIUM BALANCE IN DAHL SALT-SENSITIVE HYPERTENSIVE RATS

Background: We have recently shown that the nonsteroidal mineralocorticoid receptor blocker, esaxerenone elicits effective blood pressure reduction in Dahl salt-sensitive hypertensive (DSS) rats. Here, we investigated the potential contribution of alterations in sodium homeostasis to esaxerenone-induced blood pressure reduction. Methods: In the different experimental setups, we evaluated blood pressure by the radio-telemetry system and sodium homeostasis by an approach of sodium in (food intake) and out (urinary excretion) in a low-salt diet (LSD, 0.3% NaCl), high-salt diet (HSD, 8% NaCl), HSD with 0.001 % esaxerenone (w/w), and HSD with 0.05% furosemide fed DSS rats. Results: HSD-fed DSS rats exhibited a non-dipper type hypertension, while esaxerenone treatment but not furosemide significantly reduced the BP with a dipper pattern. The cumulative urinary sodium excretion was significantly elevated from day 6 onward both in esaxerenone- and furosemide-treated rats compared to their HSD-fed counterparts in the active period where a significant increase in Na+/K+ ratio was evident for only the esaxerenone treatment group. Sodium content in the skin, skinned carcass as well as total body level tended to reduce in esaxerenone-treated rats compared to the HSD-fed matching parts, while these values were not changed in furosemide-treated rats. Consistently, sodium balance tended to be reduced in esaxerenone-treated rats during the active period. Histological evaluation revealed that esaxerenone but not furosemide treatment significantly attenuated glomerulosclerosis and tubulointerstitial fibrosis in HSD-fed DSS rats. Collectively, these findings suggest that esaxerenone-induced blood pressure reduction is associated with the body sodium homeostasis in salt-loaded DSS rats.

Indoxyl Sulfate Activates NLRP3 Inflammasome to Induce Cardiac Contractile Dysfunction Accompanied by Myocardial Fibrosis and Hypertrophy.

In patients with chronic kidney diseases (CKD), high serum indoxyl sulfate (IS) levels correlate with cardiac fibrosis and hypertrophy and thus a critical risk factor for heart failure. The aim of this study was to determine the effects of IS on cardiac function and inflammasome pathway in a rat model of CKD. We assessed the physiological and pathological changes and measured biomarkers of fibrosis and hypertrophy in the hearts of Dahl salt-sensitive (DS), DS hypertensive (DH), and DH IS-treated rats (DH + IS). Low left ventricular (LV) ejection fraction, LV dilatation, and advanced myocardial fibrosis and hypertrophy were observed in DH + IS, which resemble changes found in uremic cardiomyopathy. These changes were independent of renal function and blood pressure. RT-PCR and western blotting analysis showed upregulation of fibrosis and hypertrophy-related biomarkers and adhesion molecules in the hearts of DH + IS rats. IS activated aryl hydrocarbon receptor (AHR) pathway, nuclear factor kappa B p65 (NF-κB p65), and inflammasome in the myocardium of DH + IS rat. Moreover, IS upregulated the expression of critical NLRP3 inflammasome components (NLRP3, ASC, and procaspase-1) and increased production of IL-1β and IL-18. Finally, IS upregulated various inflammatory cytokines, such as MCP-1, TNF-α, IL-6, and TGFβ1, in the myocardium. Our results suggested that IS induced cardiac fibrosis and hypertrophy and impaired LV function through activation of cardiac NLRP3 inflammasome via the AHR/NF-κB pathway.

Indoxyl Sulfate-induced Vascular Calcification is mediated through Altered Notch Signaling Pathway in Vascular Smooth Muscle Cells.

Introduction: The aim of this study was to determine the role of Notch in indoxyl sulfate (IS)-induced vascular calcification (VC).Materials and methods: VC and expression of Notch-related and osteogenic molecules were examined in Dahl salt-sensitive (DS), DS hypertensive (DH), and DH IS-treated rats (DH+IS). The effects of IS on expression of Notch receptors, apoptotic activity, and calcification were examined in cultured aortic smooth muscle cells (SMCs).Results: Medial calcification was noted only in aortas and coronary arteries of DH+IS rats. Notch1, Notch3, and Hes-1 were expressed in aortic SMCs of all rats, but only weakly in the central areas of the media and around the calcified lesions in DH+IS rats. RT-PCR and western blotting of DH+IS rat aortas showed downregulation of Notch ligands, Notch1 and Notch3, downstream transcriptional factors, and SM22, and conversely, overexpression of osteogenic markers. Expression of Notch1 and Notch3 in aortic SMCs was highest in incubation under 500 μM IS for 24hrs, and then decreased time- and dose-dependently. Coupled with this decrease, IS increased caspase 3/7 activity and TUNEL-positive aortic SMCs. In addition, pharmacological Notch signal inhibition with DAPT induced apoptosis in aortic SMCs. ZVAD, a caspase inhibitor abrogated IS-induced and DAPT-induced in vitro vascular calcification. Knockdown of Notch1 and Notch3 cooperatively increased expression of osteogenic transcriptional factors and decreased expression of SM22.Conclusion: Our results suggested that IS-induced VC is mediated through suppression of Notch activity in aortic SMCs, induction of osteogenic differentiation and apoptosis.

Abstract P3007: Effect of Anti-Hypertensive Treatment Lisinopril on Central Arterial Stiffness and Anxiety-Like Behavior in Adult Hypertensive Dahl Salt-Sensitive Rats

Background: Independent of a high salt intake, Dahl Salt-Sensitive (DSS) rats demonstrate an age-associated increase in blood pressure (BP), and central arterial stiffness estimated by pulse wave velocity (PWV) accompanied by cognitive decline. We hypothesized, that anti-hypertensive treatment Lisinopril, in addition to BP decrease, will lower PWV and improve cognition of adult DSS. Methods: Twenty 6-mo old male DSS were kept on normal salt diet for the duration of the study; ten of them were continuously treated with Lisinopril (15 mg/kg/day) for 3 months. Systolic BP (SBP) and PWV (by doppler echocardiography) were measured, and open field test (OFT) was performed to assess locomotor and anxiety-like behavior at baseline prior to treatment and repeated in 3 months in 9-mo old rats. In a sub-cohort of DSS rats SBP was measured in 3-mo-old DSS. The data are presented as mean ± standard deviation and analyzed by 2-way ANOVA and T-test. Results: Prior to treatment, all DSS rats displayed hypertension and BP elevation with age (SBP: 170±11 vs. 142±5 mmHg, 6-mo vs. 3-mo; P<0.01). After 3 months, control untreated animals showed no difference in SBP and were hypertensive. Rats treated with Lisinopril for 3 months showed a decreased SBP (119±9 vs. 171±11 mmHg, P<0.0001) and a decreased PWV compared to their baseline prior to treatment (3.03±1.23 vs. 5.52±1.07 m/s p<0.05). In OFT, treatment with Lisinopril increased exploration of the center of the field compared to the control group (120±35 vs. 87±30% of distance traveled in center to baseline , p=0.05) without affecting total distance traveled, indicating a reduction in anxiety-like behavior. Conclusion: Lowering of BP and PWV is associated with reduced anxiety-like behavior in DSS, which indicate the connection of cardiovascular disorder and cognitive function in adult hypertensive DSS. Whether Lisinopril has an additional direct effect on brain structure and function in DSS rats will be further studied. This research was supported entirely by the Intramural research Program of the NIH, National institute on Aging

Effect of Anti‐hypertensive Treatment Lisinopril on Anxiety‐like Behavior in Adult Hypertensive Dahl Salt‐Sensitive Rats

BackgroundIndependent of a high salt intake, Dahl Salt‐Sensitive (DSS) rats demonstrate an age‐associated increase in blood pressure (BP) accompanied by cognitive decline. We sought to explore the effect of anti‐hypertensive treatment, Lisinopril, which lowers tissue angiotensin II levels, on BP and behavior in adult DSS rats. We hypothesized, that Lisinopril, in addition to BP decrease, will affect the cognitive status of adult DSS.MethodsSixteen 6‐month‐old male DSS rats were kept on normal salt diet for the duration of the study; eight of them were continuously treated with 250 mg/L Lisinopril administered through their water for 2 months (15 mg/kg/day), and eight DSS rats remained on regular water as a control. Systolic BP (SBP) was measured in conscious male DSS rats via tail‐cuff plethysmography, and open field test (OFT) was performed to assess locomotor and anxiety‐like behavior at baseline prior to treatment and repeated 2 months after treatment began. Statistical regression analyses were performed using Prizm 7: 1‐way and 2‐way ANOVA, T‐test when applicable. The data are presented as mean ± standard deviation.ResultsPrior to treatment, all DSS rats displayed hypertension and BP elevation with age (SBP: 170 ± 11 vs. 142 ± 5 mmHg, 6‐mo vs. 3‐mo, n=16; P<0.01). After 2 months, control untreated animals showed no difference in SBP and were hypertensive (170 ± 15 vs. 168 ± 13 mmHg, 8‐mo vs. 6‐mo, n=8; n/s). Rats treated with Lisinopril for 2 months showed a dramatically decreased SBP compared to their baseline prior to treatment (119 ± 9 vs. 171 ± 11 mmHg, P<0.0001, n=8; Fig. 1), verifying the efficacy of the drug. In OFT, treatment with Lisinopril increased exploration of the center of the field compared to the control group (160 ± 45 vs. 91 ± 55 % of distance traveled in center to baseline, p=0.0166, n=8/group; Fig. 2) without affecting total distance traveled, indicating a reduction in anxiety‐like behavior. Furthermore, there was a significant negative correlation between SBP and increased activity in the center of the field (Pearson R=−0.58, R2=0.34, P=0.018; Fig. 3), suggesting anxiolytic effects of BP lowering medication.ConclusionLowering of BP is associated with reduced anxiety‐like behavior in DSS, which indicate the connection of cardiovascular disorder and cognitive function in adult hypertensive DSS. Whether Lisinopril has an additional direct effect on brain functions in DSS rats will be further studied.Support or Funding InformationSupported by NIH/NIA Intramural Research ProgramThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hydrogen gas improves left ventricular hypertrophy in Dahl rat of salt-sensitive hypertension

ABSTRACTPurpose: Hypertension is an important risk factor for death resulting from stroke, myocardial infarction, and end-stage renal failure. Hydrogen (H2) gas protects against many diseases, including ischemia-reperfusion injury and stroke. The effects of H2 on hypertension and its related left ventricular (LV) function have not been fully elucidated. The purpose of this study was to investigate the effects of H2 gas on hypertension and LV hypertrophy using echocardiography.Methods: Dahl salt-sensitive (DS) rats were randomly divided into three groups: those fed an 8% NaCl diet until 12 weeks of age (8% NaCl group), those additionally treated with 2% H2 gas (8% NaCl + 2% H2 group), and control rats maintained on a diet containing 0.3% NaCl until 12 weeks of age (0.3% NaCl group). H2 gas was supplied through a gas flowmeter and delivered by room air (2% hydrogenated room air, flow rate of 10 L/min) into a cage surrounded by an acrylic chamber. We evaluated interventricular septal wall thickness (IVST), LV posterior wall thickness (LVPWT), and LV mass using echocardiography.Results: IVST, LVPWT, and LV mass were significantly higher in the 8% NaCl group than the 0.3% NaCl group at 12 weeks of age, whereas they were significantly lower in the 8% NaCl + 2% H2 group than the 8% NaCl group. There was no significant difference in systolic blood pressure between the two groups.Conclusion: Our findings suggest that chronic H2 gas inhalation may help prevent LV hypertrophy in hypertensive DS rats.

Sustained Activation of Guanylate Cyclase-A with TDT, a Natriuretic Peptide Derivative, Exhibits Cardiorenal Protection in Dahl Salt-Sensitive Hypertensive Rats.

Heart failure often presents with prognosis-relevant impaired renal function. To investigate whether the chronic activation of guanylate cyclase-A (GC-A) protects both heart and kidney, we examined the effects of TDT, a neprilysin (NEP)-resistant natriuretic peptide (NP) derivative, on cardiac and renal dysfunction in Dahl salt-sensitive hypertensive (DS) rats. Pretreatment with NEP or NEP inhibitor did not influence GC-A activation by TDT both in vitro and in vivo, resulting in a long-acting profile of TDT compared with native human atrial NP (hANP). The repeated administration of TDT to DS rats suppressed the progress of cardiac hypertrophy, systolic/diastolic dysfunction, and proteinuria in a dose-dependent manner. Compared with vehicle and hANP, salt diet-induced podocyte injury was reduced by TDT, as analyzed by urinary podocalyxin concentration, renal expression of nephrin mRNA, and glomerular expression of desmin protein. Since glomerular TRPC6 plays detrimental roles in podocyte homeostasis, we examined the renal expression of TRPC6 in DS rats and found that salt diet upregulated the expression of TRPC6. Importantly, TRPC6 induction was significantly decreased in TDT-treated rats, compared with vehicle and hANP. Consistently, in primary-culture podocytes from DS rats, TDT inhibited ATP-induced calcium influx, similar to TRPC inhibitor SKF96365. Finally, TDT-mediated protection of podocytes was abolished by protein kinase G inhibitor KT5823. In conclusion, TDT treatment attenuated heart and kidney dysfunction, accompanied by podocyte protection through inhibition of TRPC6. Thus, long-acting NPs could be a new avenue for treatment of heart failure.

Abstract P285: Hydralazine Attenuates the Development of Hypertension in the Female Dahl Salt-sensitive Rat in a T Cell-independent Manner

Introduction: Several studies in Dahl salt-sensitive ( DS ) rats suggest that T cells play a role in salt-sensitive hypertension. To further investigate the role of T cells, we compared T cell profiles in hypertensive DS and normotensive Dahl salt-resistant ( DR ) rats as well as in DS rats treated with hydralazine ( HYD ) to attenuate the development of hypertension. Methods: Mean arterial pressure ( MAP ) was measured by telemetry in DS rats (n=13) from 1 to 4.5 months ( mo ) of age. At 1.5 mo, all of the DR (n=8) and half of the DS rats were treated with vehicle (VEH, n=7). The other half of the DS rats (n=6) received HYD (25 mg/kg/day) in the drinking water. At 4.5 mo, renal T helper ( Th ) and cytotoxic ( Tc ) cells were assessed by multicolor flow cytometry. Results: In the DS kidney, the frequency of CD4 + Th cells [(%): DS-VEH, 76±1.2* vs. DR-VEH, 55±0.7; *p<0.0001; n=7-8/group] was higher while the frequency of CD8 + Tc cells [(%): DS-VEH, 14±1.2* vs. DR-VEH, 35±1; *p<0.0001; n=7-8/group] was lower compared to DR rats. 10 weeks of HYD treatment attenuated the age-associated increase in MAP observed in DS rats [p<0.0001, Two-Way ANOVA (time, treatment); MAP (mmHg): DS-VEH, 157±4 vs. DS-HYD, 133±3; *p<0.0004; n=6-7/group]. HYD had no effect on the frequency of CD4 + [(%):77±1.5] or CD8 + [(%):15.5±0.9] T cells in the kidney of DS rats [(CD4 + ): DS-VEH vs. DS-HYD, p=0.83; (CD8 + ): DS-VEH vs. DS-HYD, p=0.5; n=7-8/group]. In summary, the ratio of Th (CD4 + ) to Tc (CD8 + ) cells is higher in the kidney of DS compared to DR rats and HYD had no effect on the T cell profile in the DS rat kidney under conditions in which the MAP was attenuated by 20 mm Hg. Conclusions: These findings indicate the DS rat has more active Th cells in the kidney compared to the DR rat. Our study also suggests that vasodilators can attenuate the development of hypertension in the DS rat in a Th- and Tc-independent manner.

Upregulation of nuclear factor-κB activity mediates CYP24 expression and reactive oxygen species production in indoxyl sulfate-induced chronic kidney disease.

Chronic kidney disease (CKD) is associated with an inflammation-mediated process, and the vitamin D (3) catabolizing enzyme, CYP24, is frequently overexpressed in CKD, where it may play a crucial role in kidney disease. Herein, in this study, we investigated CYP24, reactive oxygen species (ROS), and inflammatory responses in an indoxyl sulfate (IS)-induced CKD model to elucidate the role of CYP24 in CKD. Our results showed that IS upregulates proinflammatory cytokine, CYP24 and nuclear factor-κB (NF-κB) expression in human renal proximal tubule epithelial cells. In addition, IS treatment increased ROS production and simultaneously upregulated CYP24 expression and NF-κB translocation. Moreover, the IS-induced upregulation of CYP24 expression was alleviated by an inhibitor of NF-κB, as well as a siRNA specific to NF-κB p65. Furthermore, the renal cortex of DN (Dahl salt-resistant normotensive) + IS, DH (Dahl salt-sensitive hypertensive), and DH + IS rats showed increased expression of NF-κB p65, CYP24, 8-hydroxydeoxyguanosine (8-OHdG), a marker of ROS and macrophage infiltration compared with DN rats. These results provide evidence that administration of IS in human renal tubular epithelial cells upregulates NF-κB, which leads to increase CYP24 expression and ROS production. They also suggest that suppressing NF-κB signalling is promising for the development into a strategy for CKD treatment.

ROS Production Is Increased in the Kidney but Not in the Brain of Dahl Rats With Salt Hypertension Elicited in Adulthood

Enhanced production of superoxide radicals by nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase in the brain and/or kidney of salt hypertensive Dahl rats has been proposed to participate in the pathogenesis of this form of experimental hypertension. Most information was obtained in young Dahl salt-sensitive (DS) rats subjected to high salt intake prior to sexual maturation. Therefore, the aim of our study was to investigate whether salt hypertension induced in adult DS rats is also accompanied with a more pronounced oxidative stress in the brain or kidney as compared to Dahl salt-resistant (DR) controls. NADPH oxidase activity as well as the content of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (oxidative index), which indicate a degree of lipid peroxidation, were evaluated in two brain regions (containing either hypothalamic paraventricular nucleus or rostral ventrolateral medulla) as well as in renal medulla and cortex. High salt intake induced hypertension in DS rats but did not modify blood pressure in DR rats. DS and DR rats did not differ in NADPH oxidase-dependent production of ROS, TBARS content or oxidative index in either part of the brain. In addition, high-salt diet did not change significantly any of these brain parameters. In contrast, the enhanced NADPH oxidase-mediated ROS production (without significant signs of increased lipid peroxidation) was detected in the renal medulla of salt hypertensive DS rats. Our findings suggest that there are no signs of enhanced oxidative stress in the brain of adult Dahl rats with salt hypertension induced in adulthood.

Critical role of renal dipeptidyl peptidase-4 in ameliorating kidney injury induced by saxagliptin in Dahl salt-sensitive hypertensive rats

Saxagliptin, a potent dipeptidyl peptidase-4 (DPP-4) inhibitor, is currently used to treat type 2 diabetes mellitus, and it has been reported to exhibit a slower rate of dissociation from DPP-4 compared with another DPP-4 inhibitor, sitagliptin. In this study, we compared the effects of saxagliptin and sitagliptin on hypertension-related renal injury and the plasma and renal DPP-4 activity levels in Dahl salt-sensitive hypertensive (Dahl-S) rats. The high-salt diet (8% NaCl) significantly increased the blood pressure and quantity of urinary albumin excretion and induced renal glomerular injury in the Dahl-S rats. Treatment with saxagliptin (14mg/kg/day via drinking water) for 4 weeks significantly suppressed the increase in urinary albumin excretion and tended to ameliorate glomerular injury without altering the blood glucose levels and systolic blood pressure. On the other hand, the administration of sitagliptin (140mg/kg/day via drinking water) did not affect urinary albumin excretion and glomerular injury in the Dahl-S rats. Meanwhile, the high-salt diet increased the renal DPP-4 activity but did not affect the plasma DPP-4 activity in the Dahl-S rats. Both saxagliptin and sitagliptin suppressed the plasma DPP-4 activity by 95% or more. Although the renal DPP-4 activity was also inhibited by both drugs, the inhibitory effect of saxagliptin was more potent than that of sitagliptin. These results indicate that saxagliptin has a potent renoprotective effect in the Dahl-S rats, independent of its glucose-lowering actions. The inhibition of the renal DPP-4 activity induced by saxagliptin may contribute to ameliorating renal injury in hypertension-related renal injury.

Skeletal muscle insulin resistance in salt-sensitive hypertension: role of angiotensin II activation of NFκB.

BackgroundWe have previously shown that in hypertensive Dahl salt-sensitive (DS) rats, impaired endothelium-dependent relaxation to acetylcholine and to insulin is mechanistically linked to up-regulation of angiotensin (Ang) II actions and the production of reactive oxygen species (ROS) and to activation of the proinflammatory transcription factor (NF)κB. Here we investigated whether Ang II activation of NFκB contributed to insulin resistance in the skeletal muscle of this animal model.MethodsDS rats were fed either a normal (NS, 0.5% NaCl) or high (HS, 4% NaCl) salt diet for 6 weeks. In addition, 3 separate groups of HS rats were given angiotensin receptor 1 blocker candesartan (ARB, 10 mg/kg/day in drinking water), antioxidant tempol (1 mmol/L in drinking water) or NFκB inhibitor PDTC (150 mg/kg in drinking water).ResultsDS rats manifested an increase in soleus muscle Ang II content, ROS production and phosopho-IκBα/IκBα ratio, ARB or tempol reduced ROS and phospho-IκBα/IκBα ratio. Hypertensive DS rats also manifested a reduction in glucose infusion rate, impaired insulin-induced Akt phosphorylation and Glut-4 translocation in the soleus muscle, which were prevented with treatment of either ARB, tempol, or PDTC. Data from the rat diabetes signaling pathway PCR array showed that 8 genes among 84 target genes were altered in the muscle of hypertensive rats with the increase in gene expression of ACE1 and 5 proinflammatory genes, and decrease of 2 glucose metabolic genes. Incubation of the muscle with NFκB SN50 (a specific peptide inhibitor of NFκB) ex vivo reversed changes in hypertension-induced gene expression.ConclusionThe current findings strongly suggest that the activation of NFκB inflammatory pathway by Ang II play a critical role in skeletal muscle insulin resistance in salt-sensitive hypertension.

Nicorandil suppresses urinary protein excretion and activates eNOS in Dahl salt-sensitive hypertensive rats

Hypertension is a risk factor common to both chronic kidney disease and cardiovascular disease. Nicorandil is widely used for the treatment of angina. We investigated the benefits of nicorandil with respect to renal dysfunction in Dahl salt-sensitive hypertensive (DS) rats. DS rats were fed a high-salt (HS) diet and nicorandil was administered via the drinking water. Blood pressure and renal function were measured for 4 weeks after starting the rats on the HS diet. In rats fed the HS diet, renal dysfunction was manifested by an increase in urinary protein and N-acetyl-β-D-glucosaminidase excretion. Nicorandil ameliorated renal function with a concomitant reduction in urinary 8-hydroxy-2'-deoxyguanosine and an increase in urinary NOx. Significant upregulation of endothelial nitric oxide synthase (eNOS) expression and an increase in the eNOS dimer/monomer ratio (reduction of eNOS uncoupling) was demonstrated in glomeruli following nicorandil treatment. The blood pressure of DS rats was increased by salt loading; however, no significant change in blood pressure was observed with nicorandil treatment. In DS rats fed a HS diet, nicorandil prevented the development of renal dysfunction, which was accompanied by an increase in eNOS expression in the kidneys.

Antifibrotic response of cardiac fibroblasts in hypertensive hearts through enhanced TIMP-1 expression by basic fibroblast growth factor

Cardiac fibroblasts (CFs) play a pivotal role in the development of myocardial fibrosis. We previously demonstrated that direct injection of basic fibroblast growth factor (bFGF) into the hypertensive Dahl salt-sensitive (DS) rat heart prevented systolic dysfunction and left ventricular dilation effectively. However, the precise role played by bFGF in fibrotic response of CFs remains unclear. We suggested potential effects of bFGF on the fibrotic response of CFs in vitro. Histopathologic assessment of cardiac fibrosis demonstrated a marked decline in the extent of perivascular and interstitial fibrosis in bFGF-injected hypertensive DS rat hearts. CFs harvested from the hearts of noninjected DS rats demonstrated a significantly increased messenger RNA (mRNA) expression of matrix metalloproteinase (MMP)-2, MMP-9, and both collagen I and III. In contrast, bFGF treatment in the CFs induced a marked increase in tissue inhibitor of MMP (TIMP)-1 expression and a marked decline in MMP-9 activation. bFGF also induced a decline in α-smooth muscle actin and collagen I and III mRNA expression in the CFs accompanied by inhibited differentiation of CFs into myofibroblasts. Small interfering RNA targeting FGF receptor 1 confirmed a specific interference of the mRNA expression changes elicited by bFGF. In vivo examination confirmed many TIMP-1-positive CFs in perivascular spaces of bFGF-injected hearts. Up-regulated TIMP-1 expression and down-regulated MMP-9 activation by bFGF in CFs could prevent excessive ECM degradation and collagen deposition in perivascular spaces effectively, leading to prevention of cardiac fibrosis during hypertensive heart failure. Cardiac fibroblasts (CFs) play a pivotal role in myocardial fibrosis. The precise role of CFs in fibrotic response played by growth factors remains unclear. Our results indicates that basic fibroblast growth factor could up-regulate TIMP-1 expression and down-regulate MMP-9 activation in CFs in perivascular spaces, leading to inhibited progression of cardiac fibrosis during hypertensive heart failure.