Dahl Salt-sensitive Hypertensive Research Articles

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.

Abstract 475: The Transcription Factor ETS-1: A Critical Mediator of Renal Injury in Salt Sensitive Hypertension

The transcription factor ETS-1 regulates the expression of several growth factors, chemokines and cytokines. We have recently shown that ETS-1 is a mediator of the pro-inflammatory and pro-fibrotic effects of Angiotensin II in the kidney (HTN ’12). Herein, we tested the hypothesis that the renal expression of ETS-1 is increased in the Dahl salt-sensitive (DS) rat, a paradigm of salt-sensitive hypertension in humans, and that ETS-1 mediates renal injury in this model of hypertension. DS rats (n=6 per group) were fed a normal salt diet (0.5% NaCl, NS) or a high salt diet (4% NaCl, HS) for 4 weeks. Four additional groups (n=6 per group) on HS diet received: ETS-1 dominant negative peptide (HS/DN, 10mg/kg/day) to block ETS-1, a control ETS-1 mutant peptide (HS/MU, 10mg /kg/day), the AT1 receptor blocker Candesartan (HS/ARB 10 mg/kg/day) or a combination of DN and ARB (HS/DN/ARB). HS rats had a ~ 3 fold increase in the cortical expression of ETS-1 as assessed by western blot (WB). Treatment with DN, MU, ARB or DN/ARB resulted in small and non-significant reductions in BP as compared to HS. (Table). Compared with LS, HS rats had increased proteinuria (Bio-Rad), higher glomerular injury score (GIS), increased fibronectin expression (WB) and urinary TGF-β (ELISA) that were improved by DN but not by MU (table). ARB reduced proteinuria and GIS (table). Treatment with DN/ARB resulted in further improvements in renal injury as compared to DN and ARB (table). In conclusion we have demonstrated that hypertensive DS rats have increased cortical expression of ETS-1 and that blockade of ETS-1 improves renal injury in this model of hypertension.

A genetically based GPCR‐mediated central molecular mechanism underlying the pathophysiology of salt‐sensitive hypertension

AimWe have demonstrated endogenous up‐regulation of hypothalamic paraventricular nucleus (PVN) Gαi2‐proteins is required to suppress norepinephrine (NE) mediated sodium retention during high salt intake in the Sprague‐Dawley rat. In these studies we examined the role(s) of central Gαi2 proteins in sodium homeostasis and blood pressure regulation following elevated dietary salt‐intake in Brown Norway (BN), Dahl salt‐resistant (DSR), Dahl salt‐sensitive (DSS) and DSSBN8 congenic rat strains.MethodsBN, DSR, DSS or DSSBN8 rats were maintained on a normal (0.4% NaCl) or high (8% NaCl) diet for 21‐days Additional groups of DSR and DSS rats received a 21‐day i.c.v. infusion of a Gαi2 targeted oligodeoxynucleotide during high salt‐intake. On day‐21 MAP, 24h metabolic balance, plasma NE and PVN Gαi2 protein levels were determined (N=5/group).ResultsHS‐intake did not alter MAP, suppressed plasma NE (P<0.05), and evoked a site‐specific increase in PVN Gαi2 protein levels in salt‐resistant BN and DSR (4.8 and 4.2‐fold respectively, P<0.05), but not hypertensive DSS, rats. Brain Gαi2 protein downregulation evoked hypertension, sodium retention and elevated plasma NE content in DSR rats (P<0.05) and profoundly exacerbated DSS hypertension (P<0.05). In DSSBN8 rats BN chromosome 8 substitution attenuated hypertension, sodium retention and global sympathoexcitation vs. DSS rats (P<0.05) and restored PVN specific Gαi2 protein up‐regulation.ConclusionPVN Gαi2 protein‐gated pathways represent a genetically conserved central molecular mechanism that suppresses NE mediated renal sodium reabsorption to maintain a salt‐resistant phenotype. Owing to SNP's in the GNAI2 gene correlating with hypertension in human subjects our findings have translational implications for human hypertension ‐ HL107330.

High blood pressure enhances brain stem neuronal nitric oxide synthase activity in Dahl salt-sensitive rats

The aims of the present study were to determine the mechanism underlying enhanced neuronal nitric oxide synthase (nNOS) activity in the brain of hypertensive Dahl salt-sensitive (DSS) rats and the consequences of enhanced nNOS activity. Male DSS rats were fed either a regular (0.4% NaCl) or high-salt (8% NaCl) diet, with or without 0.25% nifedipine, for 4 weeks. The effects of nifedipine, which lowers blood pressure peripherally, on central nNOS were determined by measuring nNOS activity, as well as the number of nNOS-positive neurons in the brain stem and diencephalon. The effects of chronic (12 days) infusion of 7 μg (0.5 μL/h, i.c.v.) S-methyl-L-thiocitrulline (SMTC; a stereoselective competitive nNOS inhibitor) on mean arterial pressure were assessed in conscious DSS rats using a radiotelemetry system. In addition, the number of central nNOS-positive neurons was compared between DSS and salt-insensitive Sprague-Dawley rats. Normalization of blood pressure by nifedipine attenuated the increase in nNOS activity in the brain stem of DSS rats. Chronic i.c.v. infusion of SMTC further enhanced hypertension in DSS rats. Feeding of a high-salt diet increased nNOS-positive neurons in the lateral parabrachial nucleus, rostral ventrolateral medulla and nucleus tractus solitarius of DSS compared with Sprague-Dawley rats, whereas nNOS-positive neurons in the paraventricular nucleus remained downregulated in DSS rats. The results of the present study suggest that hypertension, rather than a high-salt diet, increases central nNOS activity in hypertensive DSS rats to buffer high blood pressure. However, this compensatory response may be insufficient to relieve salt-induced hypertension.

Renoprotective Effect of Vasopressin V2 Receptor Antagonist Tolvaptan in Dahl Rats With End-Stage Heart Failure

Tolvaptan is a highly selective and orally effective arginine vasopressin V2 receptor antagonist, and is potentially useful for the treatment of heart failure (HF) patients. However, the renoprotective effect of long-term tolvaptan therapy and its underlying mechanisms remain unknown. We evaluated the effects of chronic treatment with tolvaptan on renal dysfunction, podocyte injury, inflammation, oxidative stress, Rho-kinase, epithelial-mesenchymal transition (EMT), and the extracellular signal-regulated protein kinase (ERK1/2) pathway in the renal cortex of Dahl salt-sensitive hypertensive (DS) rats with end-stage severe HF. DS and Dahl salt-resistant rats were fed a high-salt diet at 6 weeks of age. DS rats were treated with vehicle and tolvaptan (0.05% concentration in diet) from the age of 11 to 18 weeks. Vehicle-treated DS rats developed proteinuria, renal dysfunction, glomerulosclerosis, and interstitial fibrosis, which were ameliorated by tolvaptan without changing blood pressure. Decreased expression of nephrin and podocin and increased desmin-positive area in failing rats were restored by tolvaptan. Upregulation of NAD(P)H oxidase p22(phox), p47(phox), and gp91(phox), EMT markers such as transforming growth factor-β1, vimentin, and fibronectin expression, and Rho-kinase and ERK1/2 phosphorylation in DS rats were significantly suppressed by tolvaptan. Tolvaptan administration resulted in significant inhibition of tumor necrosis factor-α and monocyte chemoattractant protein-1 expression, and nuclear factor-κB phosphorylation. We concluded that long-term tolvaptan therapy may improve renal dysfunction, glomerulosclerosis, podocyte injury, and inflammation associated with oxidative stress, as well as EMT, ERK, and the Rho-kinase pathway in the failing heart of DS rats. Thus, tolvaptan may be a therapeutic strategy for end-stage severe HF.

Ghrelin counteracts salt-induced hypertension via promoting diuresis and renal nitric oxide production in Dahl rats

Ghrelin is the endogenous ligand for the growth hormone-secretagogue receptor expressed in various tissues including the heart, blood vessels and kidney. This study sought to determine the effects of long-term treatment with ghrelin (10 nmol/kg, twice a day, intraperitoneally) on the hypertension induced by high salt (8.0% NaCl) diet in Dahl salt-sensitive hypertensive (DS) rats. Systolic blood pressure (SBP) was measured by a tail cuff method. During the treatment period for 3 weeks, high salt diet increased blood pressure compared to normal salt (0.3% NaCl) diet, and this hypertension was partly but significantly (P<0.01) attenuated by simultaneous treatment with ghrelin. Ghrelin significantly increased urine volume and tended to increase urine Na⁺ excretion. Furthermore, ghrelin increased urine nitric oxide (NO) excretion and tended to increase renal neuronal nitric oxide synthase (nNOS) mRNA expression. Ghrelin did not alter the plasma angiotensin II level and renin activity, nor urine catecholamine levels. Furthermore, ghrelin prevented the high salt-induced increases in heart thickness and plasma ANP mRNA expression. These results demonstrate that long-term ghrelin treatment counteracts salt-induced hypertension in DS rats primarily through diuretic action associated with increased renal NO production, thereby exerting cardio-protective effects.

Effects of Aged Garlic Extract on Left Ventricular Diastolic Function and Fibrosis in a Rat Hypertension Model

Daily consumption of garlic is known to lower the risk of hypertension and ischemic heart disease. In this study, we examined whether aged garlic extract (AGE) prevents hypertension and the progression of compensated left ventricular (LV) hypertrophy in Dahl salt-sensitive (DS) rats. DS rats were randomly divided into three groups: those fed an 8% NaCl diet until 18 weeks of age (8% NaCl group), those additionally treated with AGE (8% NaCl + AGE group), and control rats maintained on a diet containing 0.3% NaCl until 18 weeks of age (0.3% NaCl group). AGE was administered orally by gastric gavage once a day until 18 weeks of age. LV mass was significantly higher in the 8% NaCl + AGE group than in the 0.3% NaCl group at 18 weeks of age, but significantly lower in the 8% NaCl + AGE group than in the 8% NaCl group. No significant differences were observed in systolic blood pressure (SBP) between the 8% NaCl and 8% NaCl + AGE groups at 12 and 18 weeks of age. LV end-diastolic pressure and pressure half-time at 12 and 18 weeks of age were significantly lower in the 8% NaCl + AGE group compared with the 8% NaCl group. AGE significantly reduced LV interstitial fibrosis at 12 and 18 weeks of age. Chronic AGE intake attenuated LV diastolic dysfunction and fibrosis without significantly decreasing SBP in hypertensive DS rats.

448 CARDIOPROTECTIVE EFFECT OF A COMBINATION OF RHO-KINASE INHIBITOR AND P38 MAPK INHIBITOR ON CARDIOVASCULAR REMODELING IN DAHL RATS

Objectives: Rho-kinase plays a critical role in various cellular functions. p38 mitogen-activated protein kinase (p38 MAPK) plays a central role in the inflammatory cytokine response to immune challenge. We evaluated the effects of a combination of fasudil, a Rho-kinase inhibitor, and FR167653, a p38 MAPK inhibitor, on cardiovascular remodeling, inflammation, and oxidative stress in Dahl salt-sensitive hypertensive (DS) rats. Design and Methods: DS and Dahl salt-resistant (DR) rats were fed a high-salt diet at 6 weeks of age. Vehicle, fasudil (100 mg/kg per day), FR167653 (2 mg/kg per day), and combination of fasudil and FR167653 were administered to 6-week-old DS rats for 5 weeks. Results: At age of 11 weeks, DS rats in the left ventricle were characterized by increased myocardial fibrosis, phosphorylation of p38 MAPK, and myosin phosphatase targeting subunit (MYPT-1), and NAD(P)H oxidase p22phox, p47phox, gp91phox, tumor necrosis factor-α and interleukin-1β expression compared with DR rats. Fasudil improved cardiovascular remodeling, inflammation, NAD(P)H oxidase subunits, and phosphorylation of p38 MAPK and MYPT-1. FR167653 also similarly ameliorated these indices but not MYPT-1 phosphorylation. Compared with either agent alone, a combination of fasudil and FR167653 was more effective for the improvement of myocardial damage, inflammation and oxidative stress. Conclusions: These findings suggest that Rho-kinase and p38 MAPK pathway may play a pivotal role in the ventricular hypertrophy, and that a combination of Rho-kinase inhibitor and p38 MAPK inhibitor may provide a potential therapeutic target in hypertension with cardiovascular remodeling.

Bone marrow transplantation improves endothelial function in hypertensive Dahl salt-sensitive rats

Bone marrow-derived endothelial progenitor cells (EPCs) constitute an important endogenous system in the maintenance of endothelial integrity and vascular homeostasis. Cardiovascular risk factors are associated with a reduced number and functional capacity of EPCs. Here we investigated the effect of transplantation of bone marrow–derived cells from Dahl salt-resistant rat into age-matched Dahl salt-sensitive (DS) rat on blood pressure, endothelial function, and circulating EPC number. The recipient DS rats were fed a normal (0.5% NaCl, NS) or high-salt (4% NaCl, HS) diet for 6 weeks after bone marrow transplantation (BMT). DS rats on a NS or a HS diet without BMT were used as controls. Hypertensive DS (HS-DS) rat (systolic blood pressure: 213 ± 4 mm Hg vs. 152 ± 4 mm Hg in NS, P < .05) manifested impaired endothelium-dependent relaxation to acetylcholine (EDR), increased gene expression of vascular oxidative stress and proinflamamtory cytokines, and decreased eNOS expression. BMT on HS-DS rat significantly improved EDR and eNOS expression, reduced oxidative stress without reduction in SBP (206 ± 6 mm Hg). Flow cytometry analysis showed that there was no difference in the number of circulating EPCs, demonstrated by expression of EPC markers CD34, cKit, and vascular endothelial growth factor, between hypertensive and normotensive rats. Surprisingly, BMT resulted in a 5- to 10-fold increase in the previously mentioned EPC markers in hypertensive, but not normotensive rat. These results suggest that DS rat has an impaired ability to increase bone marrow–derived EPCs in response to HS diet challenge, which may contribute to endothelial dysfunction.

889 CARDIOPROTECTIVE EFFECT OF APELIN-13 ON CARDIOVASCULAR REMODELING IN END-STAGE HEART FAILURE

Objectives: Apelin and its cognate G protein-coupled receptor APJ constitute a signaling pathway with a positive inotropic effect on cardiac function. Recently, we and other investigator demonstrated that reduction in myocardial apelin/APJ expression might play a critical role in experimental models with end-stage heart failure. Therefore, we evaluate whether exogenous apelin infusion restores apelin/APJ expression and improves cardiac function in failing heart of Dahl salt-sensitive hypertensive (DS) rats. Design and Methods: High salt-loaded DS rats were treated with vehicle and pyroglutamylated apelin-13 (Pyr-AP13; 200 μg/kg per day, ip) from the age of 11 to 18 weeks. Results: Decreased end-systolic elastance (Ees) and percent fractional shortening in failing rats was significantly ameliorated by Pyr-AP13. Pyr-AP13 effectively inhibited the vascular lesion formation and suppressed inflammation factors such as tumor necrosis factor-α and interleukin-1β protein expression. Downregulation of apelin and APJ expression, and phosphorylation of eNOS at Ser1177 and Akt at Ser473 in failing rats was significantly increased by Pyr-AP13. Upregulation of NAD(P)H oxidase p22phox, p47phox, and gp91phox in DS rats was significantly suppressed by Pyr-AP13. Conclusions: These findings suggest that exogenous apelin-13 infusion may ameliorate cardiac dysfunction and remodeling and restore apelin/APJ expression in DS rats with end-stage heart failure. Thus, apelin-13 may have significant therapeutic potential in the treatment of end-stage heart failure.

NARROW CONGENICS REVEAL MULTIPLE GENDER‐SPECIFIC BLOOD PRESSURE LOCI AROUND THE RENIN GENE

Recent studies in humans and animal models suggest that hypertension is determined by different genes in male and females. The Dahl Salt‐Sensitive hypertensive (SS) rat develops salt‐sensitive hypertension and substitution of Chr 13 from the normotensive Brown Norway (BN) rat onto the SS genetic background (SS.13BN consomic), attenuates the development of salt‐sensitive hypertension in both males and females, and restores renin levels and vasodilatory function. Introgression of a 4Mbp BN segment harboring the renin gene attenuated the development of salt‐sensitive hypertension in female but not in male SS rats, suggesting a sex‐specific effect of this gene on blood pressure. In order to narrow the region responsible for renin regulation and blood pressure we developed sequentially narrow overlapping subcongenic strains for this region. We measured blood pressure in these subcongenic strains, and we found two blood pressure loci located within 1 Mbp in females, with a 30 mmHg effect on blood pressure, 50 kb below the renin gene. We also found a locus for blood pressure in males 1 Mbp below renin, with a 20 mmHg effect on blood pressure. The data suggests that there are a different set of genes that regulate blood pressure in males and females in the renin region. By sequence and expression analysis of the candidate regions, we identified all sequence variants and prioritized the candidate genes for hypertension. HL‐82798

Gene silencing of HIF prolyl‐hydroxylase 2 in the renal medulla attenuated sodium retention in Dahl S Rats

We previously showed that high salt intake (HS) inhibited HIF prolyl‐hydroxylase 2 (PHD2), an enzyme that promotes the degradation of hypoxia inducible factor (HIF)‐1α, and upregulated HIF‐1α and its target genes nitric oxide synthase (NOS)2 and heme oxygenase (HO)‐1 in the renal medulla, which stimulated the excretion of extra sodium load. This HS‐induced inhibition in PHD2 was not observed in Dahl Salt‐sensitive hypertensive (DS) rats. The present study determined whether silencing PHD2 gene would increase the levels of HIF‐1α and its target genes in the renal medulla, consequently enhancing the sodium excretion in DS rats. PHD2‐shRNA plasmid was transfected into the renal medulla in uninephrectomized DS rats. Ten days after the transfection PHD2 mRNA levels were decreased by 60% and the expression of HIF‐1α target genes NOS2 and HO‐1 were increased by &gt;2 folds in the renal medulla. Functionally, urinary sodium excretion in PHD2‐shRNA rats was doubled compared with control after acute IV sodium loading. Furthermore, chronic HS‐induced sodium retention was remarkably attenuated in PHD2‐shRNA rats. It is suggested that impaired PHD2 response to high salt in the renal medulla may represent a novel mechanism for hypertension in DS rats and that inhibition of PHD2 in the renal medulla could be a therapeutic approach for salt‐sensitive hypertension. (support: NIH grants HL89563, HL106042 and DK54927).

Cardioprotective Effect of Apelin-13 on Cardiac Performance and Remodeling in End-Stage Heart Failure

Apelin and its cognate G protein-coupled receptor, APJ, constitute a signaling pathway with a positive inotropic effect on cardiac function. Recently, we and other investigators demonstrated that a reduction in myocardial apelin/APJ expression might play a critical role in experimental models of end-stage heart failure (HF). Therefore, we evaluated whether exogenous apelin infusion restores apelin/APJ expression and improves cardiac function in the failing heart of Dahl salt-sensitive hypertensive (DS) rats. High salt-loaded DS rats were treated with vehicle and pyroglutamylated apelin-13 (Pyr-AP13; 200µg·kg(-1)·day(-1), IP) from the age of 11 to 18 weeks. Decreased end-systolic elastance and percent fractional shortening in failing rats was significantly ameliorated by Pyr-AP13. Pyr-AP13 effectively inhibited vascular lesion formation and suppressed expression of inflammation factors such as tumor necrosis factor-α and interleukin-1β protein. Downregulation of apelin and APJ expression, and phosphorylation of endothelial nitric oxide synthase at Ser(1177) and Akt at Ser(473) in failing rats was significantly increased by Pyr-AP13. Upregulation of NAD(P)H oxidase p22(phox), p47(phox), and gp91(phox) in DS rats was significantly suppressed by Pyr-AP13. Exogenous apelin-13 may ameliorate cardiac dysfunction and remodeling and restore apelin/APJ expression in DS rats with end-stage HF. Thus, apelin-13 may have significant therapeutic potential for end-stage HF.

Cardioprotective Effect of a Combination of Rho-Kinase Inhibitor and P38 MAPK Inhibitor on Cardiovascular Remodeling and Oxidative Stress in Dahl Rats

Rho-kinase plays a critical role in various cellular functions. p38 mitogen-activated protein kinase (p38 MAPK) plays a central role in the inflammatory cytokine response to immune challenge. We evaluated the effects of a combination of fasudil, a Rho-kinase inhibitor, and FR167653, a p38 MAPK inhibitor, on cardiovascular remodeling, inflammation, and oxidative stress in Dahl salt-sensitive hypertensive (DS) rats. DS and Dahl salt-resistant (DR) rats were fed a high-salt diet at 6 weeks of age. Vehicle, fasudil (100 mg/kg per day), FR167653 (2 mg/kg per day), and a combination of fasudil and FR167653 were administered to 6-week-old DS rats for 5 weeks. At the age of 11 weeks, in the left ventricle, DS rats were characterized by increased myocardial fibrosis, phosphorylation of p38 MAPK, and myosin phosphatase targeting subunit (MYPT-1), and NAD(P)H oxidase p22(phox), p47(phox), gp91(phox), tumor necrosis factor-α and interleukin-1β expression compared with DR rats. Fasudil improved cardiovascular remodeling, inflammation, NAD(P)H oxidase subunits, and phosphorylation of p38 MAPK and MYPT-1. FR167653 also similarly ameliorated these indices but not MYPT-1 phosphorylation. Compared with either agent alone, a combination of fasudil and FR167653 was more effective for the improvement of myocardial damage, inflammation and oxidative stress. These findings suggest that the Rho-kinase and p38 MAPK pathways may play a pivotal role in ventricular hypertrophy; thus, we obtained the first evidence that a combination of Rho-kinase inhibitor and p38 MAPK inhibitor may provide a potential therapeutic target in hypertension with cardiovascular remodeling.

Narrowing of candidate region on rat chromosome 18 responsible for attenuating the development of hypertension in the Dahl S hypertensive rat

The Dahl Salt-Sensitive hypertensive (SS) rat develops salt-induced hypertension. Previous linkage studies suggest the presence of a locus for salt-sensitive hypertension in Chr 18. Substitution of Chr 18 from the Brown Norway rat onto the SS genetic background (SS.18BN consomic rat) attenuates the development of salt-sensitive hypertension. We have previously identified a 68.3 Mbp candidate region on Chr 18 (Line 4 congenic) that confers this protective phenotype. The present study aims to narrow the candidate region within congenic Line 4. A series of five overlapping subcongenic strains were developed through marker assisted breeding. Mean arterial pressure (MAP) was measured by telemetry in male rats on low salt diet (0.4% NaCl) and after 3 weeks of high salt diet (8% NaCl) and urine was collected for protein measurement. MAP was not significantly different between strains on low-salt diet. However, after three weeks of high-salt diet, our preliminary results localize a blood pressure locus in a 16.2 Mbp segment within Chr 18 that spans from 61.2 Mbp to 77.4 Mbp. This region is delimited by congenic line 11, which develops hypertension (162+/−13 mmHg), and congenic line 9, with a significantly lower blood pressure (139+/−6 mmHg). Protein excretion followed the blood pressure phenotypes in Line 11 and Line 9, respectively (280+/−80mg/day and 151+/−19mg/day).

Effects of Olmesartan on Apelin/APJ and Akt/Endothelial Nitric Oxide Synthase Pathway in Dahl Rats With End-stage Heart Failure

Apelin and its cognate G protein-coupled receptor APJ constitute a signaling pathway with a positive inotropic effect on cardiac function, and the apelin/APJ pathway seems to have opposing physiological role to the renin-angiotensin system. We investigated whether angiotensin II receptor blocker olmesartan could improve cardiac function associated with apelin/APJ and Akt/endothelial nitric oxide synthase (eNOS) pathway in Dahl salt-sensitive hypertensive (DS) rats with end-stage heart failure using NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME). High salt-loaded DS rats were treated with (1) vehicle, (2) olmesartan, and (3) olmesartan plus L-NAME for 7 weeks. Decreased end-systolic elastance and percent fractional shortening in failing rats were significantly ameliorated by olmesartan. Increased atherosclerosis and vascular remodeling and fibrosis factors such as procollagen type I and III and fibronectin expression in DS rats were inhibited by olmesartan. Downregulation of apelin and APJ expression and phosphorylation of Akt and eNOS in failing rats were significantly increased by olmesartan. In addition,administration of L-NAME completely abrogated the olmesartan-mediated improvement of cardiac function and remodeling, and apelin/APJ expression and Akt/eNOS phosphorylation. These findings suggest that olmesartan may improve cardiac dysfunction and remodeling associated with apelin/APJ and Akt/eNOS pathway in DS rats with end-stage heart failure.

Telmisartan improves endothelial dysfunction and renal autoregulation in Dahl salt-sensitive rats

Hypertensive vascular disorders are characterized by endothelial dysfunction. Loss of renal autoregulation causes glomerular hypertension. However, the relationship between the autoregulatory response and glomerular damage has not been well examined. We examined the contributions of uncoupled endothelial nitric oxide synthase (eNOS) in hypertensive renal disease, and the relationship between the degree of autoregulation impairment and glomerular injury. We also investigated the effects of telmisartan on eNOS coupling and renal autoregulation. Male Dahl salt-sensitive hypertensive (DS) rats (14-week old) fed an 8% salt diet were used to examine endothelial dysfunction and impaired renal autoregulation caused by glomerular hypertension. Some DS rats were treated with telmisartan (3.0 mg kg(-1) day(-1)), an angiotensin receptor blocker, for 2 weeks. Increased superoxide production and decreased nitric oxide production, as detected by fluorescent indicator perfusion methods, were observed in the glomeruli and arterioles of hypertensive DS rats. Telmisartan improved the imbalance of superoxide and nitric oxide in the glomeruli and arterioles. Decreased serum tetrahydrobiopterin levels and coupled eNOS seen in the DS rat kidney were improved with telmisartan treatment. The endothelial relaxation reaction was impaired in DS rat aortic arteries. Autoregulatory capacity in response to step changes in perfusion pressure was also impaired in DS rat kidney. Treatment with telmisartan improved these abnormalities. Endothelial dysfunction in the glomeruli and impaired renal autoregulation, which may cause glomerular sclerosis, were observed in DS rat kidney. Telmisartan treatment improves these dysfunctions in hypertensive renal disease.

Central but not peripheral G‐alpha i/o protein inhibition potentiates hypertension in hypertensive Dahl salt‐sensitive rats: a protective role for central G‐alpha i/o proteins

We have shown that intracerebroventricular (i.c.v.) pre‐treatment of rats with pertussis toxin (PTX) prevents the hypotensive and bradycardic responses to the Gαi/o‐protein coupled receptor ligands, nociceptin/orphanin FQ and clonidine. These studies examined whether central Gαi/o protein inhibition alters blood pressure in hypertensive Dahl salt sensitive (DSS) rats.Methods DSS rats were implanted with radio‐telemetry probes and MAP and HR were continuously monitored. After 1‐week, rats were maintained on 8% NaCl chow for 3 weeks then administered either i.c.v. iso‐saline vehicle (N=6), i.c.v. PTX (1 μg) (N=6), or intraperitoneal (i.p.) PTX (15 μg/kg) (N=6).Results DSS rats on 8% NaCl chow showed a significant increase in MAP (normal chow MAP, 130 ± 2 mmHg; 8% NaCl chow, 164 ± 8 mmHg, P&lt;0.05). In hypertensive DSS rats, central PTX significantly increased MAP (day 4 post i.c.v. PTX; MAP Δ +25 ± 2 mmHg, P&lt;0.05). In contrast, peripheral PTX administration produced a significant hypotension (day 4 post i.p. PTX; MAP Δ −58 ± 9 mmHg, P&lt;0.05).Conclusion In hypertensive DSS rats, endogenous central Gαi/o protein pathways participate in reducing the severity of high NaCl‐induced hypertension. This is in contrast to the role of peripheral Gαi/o proteins, which in these (DSS) and previous studies (spontaneously hypertensive rats) play a pathological role in the maintenance of hypertension. Thus, endogenous central vs. peripheral Gαi/o proteins have differential affects on blood pressure control and potentially in the etiology of hypertension. DK43337, HL 071212, P20 RR018766

Estrogen effects on MMP-13 and MMP-14 regulation of left ventricular mass in Dahl salt-induced hypertension

Female Dahl salt-sensitive (DS) rats fed a low-salt diet develop hypertension at 6 months of age. Ovariectomy at 2 months of age accelerates the development of hypertension, and estrogen replacement delays it. Although acute pressure overload induces structural changes in the left ventricle (LV) further effects of gradual hypertension on LV remodeling have not been examined in the DS rat model. The purpose of this study was to test the hypothesis that aging and estrogen loss in hypertensive DS rats are accompanied by changes in LV remodeling. Four groups of DS rats were examined: young intact, middle-aged (MA) intact, MA ovariectomized (MA-OVX), and MA-OVX with 17beta-eestradiol (E(2)) supplementation (MA-OVX+E(2)). Myocardial matrix metalloproteinases (MMPs),tissue inhibitors of metalloproteinases (TIMPs),and extracellular matrix (ECM) proteins were assessed by immunoblotting. Each of the 4 groups comprised 6 animals. Mean (SEM) LV mass was significantly greater in the MA-intact and the MA-OVX groups (1257 [31] mg and 1199 [25] mg, respectively; both, P < 0.05) compared with the young-intact group (697 [6] mg). LV mass in the MA-OVX+E(2) group was significantly lower compared with the MA-intact and MA-OVX groups (both, P < 0.05), suggesting that estrogen may attenuate LV remodeling. Fibronectin and collagen III and IV concentrations increased significantly in the MA-intact and MA-OOVX groups (all, P < 0.05),indicating increased fibrosis. Multiple MMPs also increased in the MA-intact an nd MA-OVX rats, including MMP-3, -7, -99, -113, and -114, and all TIMPs. In contrast, estrogen attenuated fibrosis by increasing MMP-8 concentrations and increasing collagen III fragments. From good-fit regression modeling, MMP-13 and MMP-14 concentrations correlated positively with LV mass for the MA-intact and MA-OVX groups, respectively. Gradual hypertension stimulated ECM turnover by increasing both MMP/TIMP production and ECM degradation. Estrogen loss or gain resulted in a shift in MMP profiles, suggesting that MMP-13 and MMP-14 may be differentially regulated in postmenopausal hypertension.

Abstract 670: Immediate And Sustained Blood Pressure Lowering by CRF-receptor Stimulation: A Novel Approach To Antihypertensive Therapy?

Background: Recently, novel corticotropin-releasing factor (CRF)-related peptides, named urocortin I (UcnI), UcnII, and UcnIII were described. Available data suggest that the Ucns are part of a peripheral CRF system modulating cardiovascular function and mediating cardiovascular responses to stress. Blood pressure (BP) lowering effects have been described after administration of UcnI. However, no data are available on effects of UcnII on BP in an animal model of systemic arterial hypertension. Methods: Experiments were performed in Dahl salt-sensitive (DSS) and salt-resistant rats (DSR, control). Animals were fed a diet containing 4% NaCl (high salt) to induce arterial hypertension in DSS rats. At the end of week 2 of high salt diet, both DSS and DSR rats were randomly assigned to i.p. injections of either UcnII (2.5 μg/kg body weight) or vehicle b.i.d. for five weeks. Animals underwent repetitive tail cuff BP measurements at baseline (prior to first injection), at 5 and 15 minutes after the first injection and at week 1, 2, and 5 of b.i.d. treatment. At week 5 animals were sacrificed to determine heart weight /body weight ratio. Results: Systolic BP (SBP, mmHg) and heart rate (HR, min −1 ) are given in the following table as mean ± SD (n=10 per group). Conclusions: In hypertensive DSS rats, acute CRF-receptor stimulation by UcnII immediately lowered BP to the range observed in DSR rats. Compared to vehicle-treated DSS rats, sustained BP reduction was observed with further chronic administration of UcnII. No severe reflex tachycardia was observed after administration of UcnII. Thus, CRF-receptor stimulation might represent a novel approach to the treatment of arterial hypertension.