Dahl Salt-sensitive Rats Rats Research Articles

Abstract 13461: Early Vascular Aging is Associated With Early Cardiac Aging, Upregulation of Left Ventricle Pro-Fibrotic and Inflammatory Genes and Memory Decline in Aged Dahl Salt-Sensitive Rats

Introduction: Blood pressure (BP) begins to increase early in life in Dahl salt-sensitive rats (DSS) that consume a normal salt (NS) diet. Epidemiologic studies have shown that early vascular aging (EVA) is associated with central arterial stiffening (CAS) and hypertension, which develop earlier in life than expected in general population and contribute to cognitive impairment later in life. Hypotheses: (i) DSS rats will develop EVA earlier in life on NS diet, and with advancing age will exhibit early CV aging; (ii) In DSS, CV remodeling and CAS are implicated in memory decline. We tested these hypotheses using a longitudinal repeated measure design in DSS and their parental breed Sprague-Dawley rats (SD) at 3- & 12-mo of age. Methods: Male SD and DSS were kept on NS diet (0.5% NaCl; n=8/group) for entire experiment. Repeated measures of systolic BP (SBP), pulse wave velocity (PWV; an index of CAS), echocardiography, and non-repeated measures of Morris water maze (MWM) to test spatial memory, aortic collagen, elastin (histochemistry), and left ventricle (LV) mRNA expression (qPCR) were assessed at 3- & 12-mo. Data analyses: linear mixed-effect 2-way ANOVA, t-test & linear regression (LR) modeling. A 2-sided p<0.05 was considered significant. Results: SBP, PWV, aortic weight, wall thickness and collagen/elastin ratio were higher in DSS-3 vs. SD-3, and in DSS-12 vs. DSS-3. RWT and LV expression of pro-fibrotic, inflammatory and senescence genes were higher in DSS-12 vs. DSS-3 and vs. SD-12 (Table). DSS-12 spent more time to find a hidden platform in MWM vs. SD-12; their impaired spatial hippocampal memory was positively associated with PWV and LV mass by LR analysis. Conclusions: EVA, indexed as higher BP, PWV and aortic remodeling was associated with early CV aging, manifested by activation of LV senescence, inflammatory and pro-fibrotic genes and by higher rates of age-associated changes in BP, RWT and LV mass in DSS vs. SD. In DSS, early CV aging was associated with memory decline.

Curcumin, an Inhibitor of p300-HAT Activity, Suppresses the Development of Hypertension-Induced Left Ventricular Hypertrophy with Preserved Ejection Fraction in Dahl Rats.

We found that curcumin, a p300 histone acetyltransferase (HAT) inhibitor, prevents cardiac hypertrophy and systolic dysfunction at the stage of chronic heart failure in Dahl salt-sensitive rats (DS). It is unclear whether curcumin suppresses the development of hypertension-induced left ventricular hypertrophy (LVH) with a preserved ejection fraction. Therefore, in this study, we randomized DS (n = 16) and Dahl salt-resistant (DR) rats (n = 10) at 6 weeks of age to either curcumin or vehicle groups. These rats were fed a high-salt diet and orally administrated with 50 mg/kg/d curcumin or its vehicle for 6 weeks. Both curcumin and vehicle treatment groups exhibited similar degrees of high-salt diet-induced hypertension in DS rats. Curcumin significantly decreased hypertension-induced increase in posterior wall thickness and LV mass index, without affecting the systolic function. It also significantly reduced hypertension-induced increases in myocardial cell diameter, perivascular fibrosis and transcriptions of the hypertrophy-response gene. Moreover, it significantly attenuated the acetylation levels of GATA4 in the hearts of DS rats. A p300 HAT inhibitor, curcumin, suppresses the development of hypertension-induced LVH, without affecting blood pressure and systolic function. Therefore, curcumin may be used for the prevention of development of LVH in patients with hypertension.

Abstract 13940: Using an Angiotensin Converting Enzyme Inhibitor to Treat Cardiovascular and Cognitive Decline in a Rat Model of Vascular Dementia

Background: Aged Dahl salt sensitive rats (DSS) rats represent a model of vascular dementia, i.e., they develop central arterial stiffness (CAS), hypertension, and cognitive decline. DSS rats have compromised renin-angiotensin system (RAS) which is activated with age and contributes to hypertension. This study examined whether angiotensin converting enzyme (ACE) inhibitor, lisinopril, affects CAS and cognitive functions in aged male DSS (n=26). Methods & Results: Following initial measurements at 16-mo of age (baseline; BL), DSS were administered lisinopril through their water (LISI; 15mg/kg/day, n=11) or control treatment (n=15) for 2-mo. Pulse wave velocity (PWV), a marker of CAS, and systolic blood pressure (SBP) were measured at BL and at 18-mo of age. Open field test (OFT) to assess anxiety-like behavior and Morris water maze (MWM) to assess spatial memory were performed at 18-mo, then aortae and hearts were collected and weighed. Aortic wall collagen abundance was estimated by histochemistry. Statistical analyses were performed by 2-way ANOVA mixed effects model and t-test. The data are presented as mean ± SEM. At 18-mo of age, control animals had high SBP similar to BL (187±4 vs. 184±7 mmHg), while LISI-treated DSS had lower SBP by 39±4 mmHg vs. BL (p<0.01). PWV in control rats increased from 16 to 18-mo (7.0±0.6 vs. 10.8±1.0 m/s; p<0.05), while PWV in LISI-treated DSS decreased after 2-mo of treatment (7.1±0.3 vs. 5.4±0.3 m/s; p<0.01). Lower heart weights (2.9±0.1 vs. 3.7±0.3 g/kg BW; p<0.01), aortic weights (4.4±0.1 vs. 5.0±0.2 mg/mm/kg BW; p<0.01), and aortic medial collagen abundance (14.0±0.3 vs. 19.6±1.0 % of total; p<0.01) were observed in the LISI-treated rats vs. control rats. No differences between LISI-treated and control groups at 18-mo (38±10 vs. 25±6 cm traveled in center) were found in OFT. MWM results indicated that neither group at 18-mo of age was able to learn the task and therefore could not be accurately assessed for differences in spatial memory. Conclusion: Initiation of anti-hypertensive treatment in old age was effective in reducing aortic fibrosis and lowering SBP and PWV in DSS rats. Longer treatment may be needed to improve cognitive function in this model of vascular dementia. Supported by the NIH/NIA Intramural Research Program

Effect of Anti‐hypertensive Treatment Lisinopril on Central Arterial Stiffness and Cognitive Functions in Adult Hypertensive Dahl Salt‐Sensitive Rats

Effect of Anti‐hypertensive Treatment Lisinopril on Central Arterial Stiffness and Cognitive Functions in Adult Hypertensive Dahl Salt‐Sensitive Rats

The Natriuretic and Diuretic Response to Uroguanylin is Blunted in Dahl‐Salt Sensitive Rats

Uroguanylin (UGN) is a 17 aminoacids long peptide with diuretic and natriuretic activity. UGN, an intestinal natriuretic peptide, is delivered to the kidney as an unprocessed propeptide, prouroguanylin (pro‐UGN). Circulating pro‐UGN is processed to its active natriuretic form exclusively within the renal tubules. The circulating levels of pro‐UGN and the urinary levels of UGN are increased during sodium overload and this natriuretic peptide and the kidney response to UGN is increased in rats maintained in a high salt intake. We hypothesized that the diuretic and natriuretic response to UGN are altered in Dahl‐salt sensitive rats (DS) as compared to Wistar (WR) rats. Dahl‐salt sensitive (DS) rats (n=5/group) received water with 1% NaCl during 15 days and the tail systolic blood pressure (mmHg) increased from 108.0±2.0 to 145.9±2.6 while no remarkable changes were observed in Wistar rats. After the end of this period, rats were anesthetized and prepared for classical renal clearance and hemodynamics studies. After a 1‐hour control period, UGN was intravenously infused at 100nmoles/kg/min rate during 1‐hour period and heart rate (HR), mean arterial pressure (MAP), renal vascular resistance (RVR), glomerular filtration rate (GFR), renal blood flow (RBF), urine output (V′), UNaV and fractional sodium excretion (FENa+) were evaluated during infusion and for an additional 1‐hour post‐infusion period. No significant changes were observed for HR, MAP, RVR or RBF in any group or period during the whole experimental period. UGN did not change GFR (ml/g/min) in WR rats but increased it from 1.7±0.8 to 4.4±1.1 in DS rats. In addition, UGN infusion induced a significant diuresis that was stable during the infusion and post‐infusion period. The urinary output (μL/g of kidney/min) increased from 6.7±1.1 to 21.6±5.4 (p<0.001) during the infusion with UGN in WR and from 5.7±2.6 to 11.5±3.6 in DS. Strikingly, the basal levels of UnaV (μEq/g of kidney/min) in DS are significantly lower than the levels observed for WR (0.04±0.01‐DS vs. 0.23±0.07‐p<0.001). The infusion of UGN increases UNaV from 0.23±0.07 to 0.48±0.01 (p<0.01) in WR and from 0.04±0.01 to 0.27±0.08 (P<0.001). Similarly, the basal FENa+ is remarkably lower in DS when compared to WR. DS rats excrete 10 times less sodium than WR. The infusion of UGN does not increase FENa+ (%) in DS but induced a 60% increase in in WR from 1.5±0.12 to 2.5±0.16 at the end of the infusion period. The diuretic and natriuretic effects of UGN are blunted in DS rats. The defect of this counter regulatory mechanism may have a role in the genesis and maintenance of hypertension in this strain of rats.Support or Funding InformationCNPq, FUNCAP and CAPES

297. The Influence of ELABELA AAV Gene Therapy on Cardiorenal Function in Rat Models of Salt-Induced Hypertension and Myocardial Infarction

Elabela (ELA) is a recently identified apelin receptor agonist essential for cardiac development, but its biology and therapeutic potential are unclear. The apelin receptor when bound to its original ligand, apelin, exerts peripheral vasodilatory and positive inotropic effects. We initially assessed endogenous ELA expression in normal and diseased rats. ELA was predominantly expressed in kidneys, especially in renal collecting duct cells and was not affected by disease. We then characterized the effects of long-term, adeno-associated virus (AAV)-ELA gene delivery on cardiorenal function in Dahl salt-sensitive rats (DS) on a high-salt diet. We overexpressed codon optimized rat ELA in the heart via AAV9 vector by a single intravenous injection. This led to a delayed onset of blood pressure (BP) elevation, and ELA-treated rats had lower BP than controls starting at 5 weeks post-injection (p.i.). As well, ELA significantly reduced fractional sodium and chloride excretion in treated (4 days p.i.), normotensive DS rats on low-salt diet, suggesting ELA's role in sodium and chloride readsorption. Glomerular architecture was better preserved in rats treated with the AAV9-ELA vector. A decrease in renal fibrosis and the significantly suppressed expression of fibrosis associated genes, including transforming growth factor beta (TGF-β), collagen, type 1, alpha 1 (COL1A1) and fibronectin 1 (FN1), was also seen in the treated group. Since ELA is essential for cardiac development, we additionally assessed the impact of the AAV9-ELA vector on cardiac repair in a rat myocardial infarction (MI) model. When compared with control MI rats, ELA treatment did not significantly improve cardiac function or structure. Thus, long-term ELA gene delivery may offer a potential therapy for hypertension and renal remodeling, but its application for MI may be limited.

MP4-04 URINE STORAGE DYSFUNCTION IN RATS WITH SALT-LOADING HYPERTENSION DEPENDS ON INCREASE IN ATP AND PGE2 RELEASE FROM THE UROTHELIUM

You have accessJournal of UrologyUrodynamics/Incontinence/Female Urology: Basic Research II1 Apr 2014MP4-04 URINE STORAGE DYSFUNCTION IN RATS WITH SALT-LOADING HYPERTENSION DEPENDS ON INCREASE IN ATP AND PGE2 RELEASE FROM THE UROTHELIUM Tetsuyuki Kurokawa, Keiko Nagase, Xinmin Zha, and Osamu Yokoyama Tetsuyuki KurokawaTetsuyuki Kurokawa More articles by this author , Keiko NagaseKeiko Nagase More articles by this author , Xinmin ZhaXinmin Zha More articles by this author , and Osamu YokoyamaOsamu Yokoyama More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.204AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Lifestyle factors, especially hypertension (HT) can influence lower urinary tract functions. HT is one of the risk factors for worsening lower urinary tract symptoms and decreasing the improvement of storage symptoms by α1-blocker. The spontaneous hypertensive rat is considered as a valuable tool for exploring the pathogenesis of detrusor overactivity, but pathological changes in the bladder are thought to be irreversible. It has not yet been determined whether salt sensitive HT contributes to lower urinary tract dysfunction. We investigated the underlying mechanisms of urine storage dysfunction in rats with HT caused by salt loading. METHODS The sympathetic nerve activity is augmented with salt loading in Dahl salt sensitive rats (DSr), but not in Dahl salt resistant rats (DRr). Six-week-old male DSr and DRr were fed with a normal (0.252%) or high-salt (8%) diet and 35 ml water/day for 12 weeks. Blood pressure was measured through the tail artery in a non-anesthetized state. Urine volume and frequency were recorded all day long in a metabolic cage. We calculated the inactive period (sleeping) urine volume ratio, which was defined as urine volume during inactive period divided by 24 h urine output. Whole bladders were excised from 18 week rats and distended in organ bath with Krebs solution. Adenosine triphosphate (ATP) and prostaglandin E2 (PGE2) release from the distended bladder epithelium were measured. Furthermore, changes in surface bladder blood flow were determined with a laser speckle blood flow imaging system (Omegazone OZ-1; Omegawave, Tokyo) . RESULTS In the inactive period, the mean voided volume gradually increased in DRr fed with a normal or high salt diet, while it did not change in DSr fed with a high-salt diet. There were significant differences in mean voided volume after 10 week salt loading between DRr and DSr fed with a high-salt diet. Bladder distension significantly increased ATP and PGE2 release from the urothelium in DSr rats fed a high-salt diet when compared to other 3 group. Bladder blood flow in DSr fed with a high-salt diet was found to decrease, when compared to DSr fed with a normal diet. CONCLUSIONS These results indicate that salt loading induces HT and decreases the voided volume possibly via excitatory effects of ATP and PGE2 from the epithelium on bladder afferent nerves. Increases in mediator release from the epithelial are believed to depend on the bladder ischemia caused by HT. This model is useful in defining the mechanisms governing the induction of storage dysfunction in patients with HT. © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e43 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Tetsuyuki Kurokawa More articles by this author Keiko Nagase More articles by this author Xinmin Zha More articles by this author Osamu Yokoyama More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Hyperphosphorylation of Na-K-2Cl Cotransporter in Thick Ascending Limbs of Dahl Salt-Sensitive Rats

Salt-sensitive hypertension involves a renal defect preventing the kidney from eliminating excess NaCl. The thick ascending limb of Henle loop reabsorbs ≈ 30% of filtered NaCl via the apical Na-K-2Cl cotransporter (NKCC2). Higher NKCC2 activity and Cl reabsorption have been reported in the thick ascending limbs from Dahl salt-sensitive rats (DSS) fed normal salt. NKCC2 activity is primarily regulated by protein trafficking and phosphorylation at Thr(96)/Thr(101) via STE20- and SPS1-related proline and alanine-rich kinases and oxidative stress-responsive kinase 1. However, the mechanism for enhanced NKCC2 activity in DSS is unclear. We hypothesized that DSS exhibit enhanced NKCC2 trafficking and higher NKCC2 phosphorylation compared with Dahl salt-resistant rats on normal salt diet. We measured steady state surface NKCC2 expression and phosphorylation at Thr(96) and Thr(101) by surface biotinylation and Western blot. In DSS, the surface:total NKCC2 ratio was enhanced by 25% compared with Dahl salt-resistant rats (P<0.05) despite lower NKCC2 expression. Total NKCC2 phosphorylation at Thr(96) and Thr(101) was enhanced ≈5-fold in DSS thick ascending limbs. Moreover, total STE20- and SPS1-related proline and alanine-rich kinases expression, kidney-specific STE20- and SPS1-related proline and alanine-rich kinases, and oxidative stress-responsive kinase 1 were not different between strains, although STE20- and SPS1-related proline and alanine-rich kinases/oxidative stress-responsive kinase 1 phosphorylation was enhanced by 60% (P<0.05) in DSS rats, suggesting increased activity. We concluded that phosphorylation of NKCC2 Thr(96) and Thr(101) and surface:total NKCC2 ratio are enhanced in DSS rats. These differences in NKCC2 may be, in part, responsible for higher NKCC2 activity and abnormally enhanced thick ascending limb NaCl reabsorption in DSS rats.

A high fat diet reduces blood pressure, but not cardiac hypertrophy in spontaneously hypertensive rats

High fat diets can attenuate cardiac hypertrophy in Dahl Salt Sensitive rats (DSS), a model of severe hypertension, cardiac hypertrophy &amp; dysfunction, independent of changes in blood pressure. We hypothesized that a high fat diet can prevent hypertrophy in spontaneously hypertensive rats (SHR), a model of gradually increasing hypertension. Five‐week old SHR and Wistar Kyoto (WKY; normotensive control) rats were fed either a low fat (LF) or high fat (HF) diet with 10% and 60% of Calories from lard, respectively, for 10 weeks. In contrast to our hypothesis, cardiac hypertrophy was unchanged in SHR HF vs. SHR LF but, surprisingly, blood pressure was lower in SHR HF. Pooled statistical analysis also indicated lower plasma glucose (2 h fast) in HF vs. LF rats. These data indicate a markedly different response to high fat diets in the SHR vs. those previously reported in the DSS rats.(Different letters denote significant differences at p&lt;0.05)

Endogenous Cardiotonic Steroids and Differential Patterns of Sodium Pump Inhibition in NaCl-Loaded Salt-Sensitive and Normotensive Rats

Endogenous sodium pump inhibitors promote sodium excretion in normotensives and contribute to vasoconstriction in NaCl-sensitive hypertension. Marinobufagenin (MBG), an endogenous bufadienolide inhibitor of alpha-1 sodium pump, contributes to hypertension in Dahl salt-sensitive rats (DS). We hypothesized that in NaCl-loaded DS and normotensive Sprague-Dawley rats (S-D), MBG would elicit different patterns of sodium pump inhibition. We compared systolic blood pressure (SBP), renal sodium excretion, activity of the sodium pump in aorta and renal medulla, and levels of MBG, atrial natriuretic peptide (ANP), and cyclic guanosine monophosphate (cGMP) in salt-loaded DS and S-D (20% NaCl, 2.5 ml/kg, intraperitoneally). NaCl loading produced sustained elevations in renal MBG excretion in both DS (2.41 +/- 0.24 vs. 0.79 +/- 0.08 pmol/h/kg, P < 0.01) and S-D (1.97 +/- 0.37 vs. 0.60 +/- 0.07 pmol/h/kg, P < 0.01) vs. that at baseline (n = 10 for each group). In NaCl-loaded DS, SBP rose by 18 mm Hg (P < 0.01) and aortic sodium pump was inhibited by 22% (P < 0.05 vs. control), while in S-D, SBP and activity of aortic sodium pump did not change. NaCl-loaded S-D excreted twice as much sodium as DS; in S-D, renal sodium pump was inhibited by 24% vs. 14% inhibition in DS (P < 0.05). NaCl loading elicited increases in plasma ANP and in renal cGMP excretion in S-D but not in DS. Our present observations demonstrate that in NaCl-loaded S-D and DS, a comparable MBG response is associated with preferential inhibition of the sodium pump in the kidney and in vascular smooth muscle, respectively, resulting in an adaptive natriuresis in S-D but sodium retention and pressor response in DS.

Testosterone-dependent hypertension and upregulation of intrarenal angiotensinogen in Dahl salt-sensitive rats

Blood pressure (BP) is more salt sensitive in men than in premenopausal women. In Dahl salt-sensitive rats (DS), high-salt (HS) diet increases BP more in males than females. In contrast to the systemic renin-angiotensin system, which is suppressed in response to HS in male DS, intrarenal angiotensinogen expression is increased, and intrarenal levels of ANG II are not suppressed. In this study, the hypothesis was tested that there is a sexual dimorphism in HS-induced upregulation of intrarenal angiotensinogen mediated by testosterone that also causes increases in BP and renal injury. On a low-salt (LS) diet, male DS had higher levels of intrarenal angiotensinogen mRNA than females. HS diet for 4 wk increased renal cortical angiotensinogen mRNA and protein only in male DS, which was prevented by castration. Ovariectomy of female DS had no effect on intrarenal angiotensinogen expression on either diet. Radiotelemetric BP was similar between males and castrated rats on LS diet. HS diet for 4 wk caused a progressive increase in BP, protein and albumin excretion, and glomerular sclerosis in male DS rats, which were attenuated by castration. Testosterone replacement in castrated DS rats increased BP, renal injury, and upregulation of renal angiotensinogen associated with HS diet. Testosterone contributes to the development of hypertension and renal injury in male DS rats on HS diet possibly through upregulation of the intrarenal renin-angiotensin system.

Coordinated shifts in Na/K-ATPase isoforms and their endogenous ligands during cardiac hypertrophy and failure in NaCl-sensitive hypertension.

NaCl loading of Dahl salt-sensitive rats (DS) stimulates marinobufagenin (MBG), an alpha1 Na/K-ATPase (NKA) isoform ligand. Cardiac function depends on NKA, which is regulated in part by endogenous digitalis-like ligands. Our goal was to study whether changes occur in MBG and endogenous ouabain (EO) production during cardiac remodelling in hypertensive DS, and whether these are associated with changes in myocardial NKA isoforms and sensitivity to MBG and ouabain. Changes in MBG and EO levels, changes in myocardial NKA isoform composition, and sensitivity to endogenous ligands during development of cardiac hypertrophy and the transition to heart failure were studied in DS rats with an 8% NaCl intake. The animals developed compensated left ventricular hypertrophy after 4 weeks, which progressed to heart failure at 9-12 weeks. The hypertrophic stage was associated with increased plasma MBG levels (mean +/- SEM of 1.22 +/- 0.22 versus 0.31 +/- 0.03 nmol/l; P < 0.01), increased sensitivity of NKA to MBG, and an increased abundance of alpha1 NKA. Plasma levels of EO did not change, and the sensitivity of NKA to ouabain decreased. The transition to heart failure was accompanied by a decrease in alpha1 NKA, a reduction in plasma MBG, and decreased sensitivity of NKA to MBG. In addition, an increased abundance of ouabain-sensitive alpha3 NKA, a three-fold rise in plasma EO (1.01 +/- 0.13 versus 0.27 +/- 0.06 nmol/l), and a seven-fold increase in the ouabain sensitivity of NKA compared with controls were observed. During cardiac hypertrophy and the transition to heart failure, a shift in endogenous NKA ligands production is linked to a shift in myocardial NKA isoforms.

Placental 11β-hydroxysteroid dehydrogenase in Dahl and spontaneously hypertensive rats

Studies in normotensive rats showed that excessive fetal exposure to maternal glucocorticoids retards growth and programs hypertension in later life. This excessive exposure is proposed to occur due to a reduction of the placental barrier to maternal glucocorticoids that is provided by 11β-hydroxysteroid dehydrogenase (11βHSD). To assess the possible alterations of glucocorticoid placental barrier in two genetic models of hypertension — spontaneously hypertensive (SHR) and Dahl salt-sensitive rats (DS) and their normotensive counterparts Wistar-Kyoto (WKY) and Dahl salt-resistant rats (DR)—we performed real-time reverse transcriptase–polymerase chain reaction analysis and bioactivity measurements of placental 11βHSD in the last third of gestation. Whereas 11βHSD2 mRNA expression was not different among the investigated strains, 11βHSD1 mRNA abundance was 2.4 times higher in WKY than in SHR and 9.6 times higher in DS than in DR placentae. The 11βHSD2 activity studies performed in placental homogenates revealed activity that did not differ among the strains. Concomitant with 11βHSD1 mRNA expression 11-oxoreductase activity was clearly evident in all strains and was higher in WKY and DS rats than in SHR and DR, respectively. Nevertheless, the net 11βHSD activity of tissue fragments (11β-dehydrogenase minus 11-oxoreductase) was tended toward dehydrogenase action, ie, toward corticosterone inactivation and was significantly lower in DS than in DR rats. The 11β-dehydrogenase/11–oxoreductase ratio was less than 2:1 in SHR and WKY rats, whereas this ratio was 9:1 in DR and 4.5:1 in DS rats. These data suggest that the placental glucocorticoid barrier is not decreased in SHR rats in comparison with normotensive WKY but is lower in DS than in DR counterparts. It cannot be excluded, therefore, that the placental glucocorticoid barrier in Dahl rats influences the pathways that might lead to the sensitivity of blood pressure to high salt intake in later life.

Impaired Ca2+ handling in perfused hypertrophic hearts from Dahl salt-sensitive rats.

To clarify the correlation between intracellular Ca2+ dynamics and level of Ca2+-regulatory proteins, changes in Ca2+ handling and these proteins were investigated in a whole-heart experimental model of pressure-overload hypertrophy. We used 17-18-week-old male Dahl salt-sensitive rats (DS) and Dahl salt-resistant rats (DR) fed a high-salt diet. We monitored the fura-2 fluorescence ratio, an index of cytoplasmic Ca2+ concentration ([Ca2+]i), using a Ca2+ analyzer in a retrograde perfused heart. Left ventricular pressure (LVP) and an electrocardiogram were simultaneously recorded. Ca2+ handling was assessed by exposing the hearts to 2 min of low-Na+ (70 mmol/l) perfusion to produce an increase in [Ca2+]i (n = 6), which was sensitive to Ni2+, a blocker of the Na+/Ca2+ exchanger (NCX). In another series, the hearts were stimulated at 2.5 to 5 Hz to determine the Ca2+-force-frequency relationship (n = 6). DS rats showed marked cardiac hypertrophy without any signs of failure. The time-to-peak Ca2+ transient was prolonged in DS compared with that in DR during normal beating. During low-Na+ exposure, the time-to-peak diastolic [Ca2+]i (TTP) and the decay-time from peak [Ca2+]i (DT) were prolonged in DS compared with DR (TTP, 43.3 +/- 4.0 vs. 32.5 +/- 2.5 s, p < 0.05; DT, 70.0 +/- 8.8 vs. 29.2 +/- 2.7 s, p < 0.005). Following pretreatment with 10 mmol/l caffeine to inhibit sarcoplasmic reticulum (SR) function, TTP and DT were still prolonged in DS compared with DR (TTP, 64.2 +/- 9.7 vs. 37.0 +/- 5.8 s, p < 0.05; DT, 55.8 +/- 12.6 vs. 26.0 +/- 5.7 s, p < 0.05). The force (LVP)-frequency relationship was initially positive in DR but was negative at all times in DS (%LVP/2.5 Hz: DS, 90.3 +/- 2.0%; DR, 112.2 +/- 4.5%; p < 0.05). Elevation of diastolic [Ca2+]i (percent increase of baseline) was greater in DS than in DR with increased stimulation (5 Hz: DS, 80.7 +/- 6.7%; DR, 52.1 +/- 5.9%; p < 0.05). In Western blot analysis, the protein level of NCX was equivalent, whereas that of SR Ca2+ ATPase (SERCA2) was significantly decreased in DS compared with DR. These results suggest that slowing of cellular Ca2+ mobilization and removal is related to impaired Ca2+ handling in late-phase cardiac hypertrophy. Both the activity of the NCX and that of the SR may be affected. The SR dysfunction may be associated with change in protein level of SERCA2.

Inhibition of NO Biosynthesis, but not Elevated Blood Pressure, Reduces Angiogenesis in Rat Models of Secondary Hypertension

Arterial hypertension (AH) is characterized by reduced nitric oxide (NO) biosynthesis, vasoconstriction, and reduced microvascular density. In this study we asked whether AH also reduces the number of microvessels by impairing angiogenesis. AH was induced in Dahl salt-sensitive rats (DSS) with a salt diet and in Wistar-Kyoto rats by inhibiting NO formation with N y -nitro-L-arginine (NNA). Three weeks after induction of AH, two wound chambers containing collagen I (Vitrogen) were sutured into the mesenteric cavity of each animal. After additional 14 days, wound chamber neovascularization and the extent of vascularized connective tissue ingrowth were quantified. In NNA-induced AH, the number of newly formed vessels and the ingrowth of vascularized connective tissue into the wound chamber decreased as compared to controls. However, the number of newly formed vessels and the ingrowth of vascularized connective tissue did not change with increasing blood pressure in salt-fed DSS rats as compared to those fed a normal diet. Inhibition of NO biosynthesis, but not necessarily elevating blood pressure, reduces angiogenesis. Microvascular rarefaction in AH may be partially due to reduced angiogenesis because of impaired NO biosynthesis.

Evidence That Reduced Renal Medullary NOS Activity of Dahl S Rats Enables Small Elevations of Avp to Produce Sustained Hypertension

27 It remains unclear why sustained elevations of plasma arginine vasopressin (AVP), a potent vasoconstrictor and fluid retaining hormone, do not generally result in hypertension. Related to this, there have been 4 general observations: 1) AVP is elevated in many forms of human and experimental hypertension, including Dahl S rats; 2) AVP can stimulate nitric oxide synthases (NOS) and nitric oxide (NO) production in the renal medulla of normal rats; 3) AVP stimulated NO production can buffer AVP induced reductions of medullary blood flow; 4) partial reduction of medullary NOS activity (via medullary L-NAME infusion) unmasks chronic hypertensive effects of small elevations of plasma AVP (Hypertension. 2000; 35:740-745). In the present study, we hypothesize that Dahl salt-sensitive rats (DS) have reduced capacity to synthesize medullary NO which sensitizes them to the hypertensive effects of small elevations of circulating AVP. DS and Brown Norway (BN) rats with implanted arterial and venous catheters were fed a 0.4% salt diet and infused continuously for 14 days with a chronic “subpressor” dose of AVP (2 ng/kg/min). Conscious mean arterial pressure (MAP) was measured 2 hours daily with rats maintained in their home cages. MAP in DS rats increased during day1 of AVP infusion from a control level of 127 ± 0.9 mmHg to an average of 147 ± 1.6 mmHg after 14 days. MAP did not return to control values even within three days following the end of AVP infusion. BN rats showed no changes of MAP during 14 days of AVP infusion (90.4 ± 0.6 mmHg and 92.3 ± 0.4 mmHg). Northern blot analysis of renal tissue from vehicle (saline) infused rats demonstrated that NOS I and NOS III mRNA expression was significantly less in DS rats in the renal outer medulla compared to BN rats. We conclude that small, normally subpressor elevations of plasma AVP can produce chronic hypertension in DS rats, a phenomenon probably related to reduced renal medullary NO synthesis.

Evidence That Reduced Renal Medullary NOS Activity of Dahl S Rats Enables Small Elevations of Avp to Produce Sustained Hypertension

27 It remains unclear why sustained elevations of plasma arginine vasopressin (AVP), a potent vasoconstrictor and fluid retaining hormone, do not generally result in hypertension. Related to this, there have been 4 general observations: 1) AVP is elevated in many forms of human and experimental hypertension, including Dahl S rats; 2) AVP can stimulate nitric oxide synthases (NOS) and nitric oxide (NO) production in the renal medulla of normal rats; 3) AVP stimulated NO production can buffer AVP induced reductions of medullary blood flow; 4) partial reduction of medullary NOS activity (via medullary L-NAME infusion) unmasks chronic hypertensive effects of small elevations of plasma AVP (Hypertension. 2000; 35:740-745). In the present study, we hypothesize that Dahl salt-sensitive rats (DS) have reduced capacity to synthesize medullary NO which sensitizes them to the hypertensive effects of small elevations of circulating AVP. DS and Brown Norway (BN) rats with implanted arterial and venous catheters were fed a 0.4% salt diet and infused continuously for 14 days with a chronic “subpressor” dose of AVP (2 ng/kg/min). Conscious mean arterial pressure (MAP) was measured 2 hours daily with rats maintained in their home cages. MAP in DS rats increased during day1 of AVP infusion from a control level of 127 ± 0.9 mmHg to an average of 147 ± 1.6 mmHg after 14 days. MAP did not return to control values even within three days following the end of AVP infusion. BN rats showed no changes of MAP during 14 days of AVP infusion (90.4 ± 0.6 mmHg and 92.3 ± 0.4 mmHg). Northern blot analysis of renal tissue from vehicle (saline) infused rats demonstrated that NOS I and NOS III mRNA expression was significantly less in DS rats in the renal outer medulla compared to BN rats. We conclude that small, normally subpressor elevations of plasma AVP can produce chronic hypertension in DS rats, a phenomenon probably related to reduced renal medullary NO synthesis.

A nuclear complex containing PPARalpha/RXRalpha is markedly downregulated in the hypertrophied rat left ventricular myocardium with normal systolic function.

The expression of genes encoding fatty acid utilization enzymes is coordinately downregulated during the development of cardiac hypertrophy and failure. However, molecular mechanisms that mediate this downregulation are unknown. Peroxisome proliferator-activated receptor (PPAR) response elements (PPREs) have been identified in promoters of many genes involved in fatty acid utilization, where they function as positive regulatory elements. PPARs bind to PPREs as heterodimers with retinoid X receptors (RXRs). Primary cardiac myocytes from neonatal rats were transfected with a reporter construct driven by the C promoter of rat acyl-coenzyme A synthetase (ACS) gene. Stimulation with phenylephrine, a potent inducer of hypertrophy, markedly downregulated the activity of this promoter. By use of electrophoretic mobility-shift assays (EMSAs) using PPRE in the rat ACS promoter as a probe, we found a sequence-specific protein-DNA complex in the nuclear extract from adult rat left ventricular (LV) myocardium. Supershift experiments revealed that this complex was immunoreactive for PPARalpha and RXRalpha. We compared the activity of this complex in LV nuclear extracts from Dahl salt-sensitive rats (DSs) with hypertension and control age-matched Dahl salt-resistant rats (DRs). Even at the stage of concentric LV hypertrophy with normal systolic function, the activity of the band was markedly diminished in DSs compared with DRs. However, immunoblot analyses showed no difference in LV expression levels of PPARalpha or RXRalpha between DSs and DRs. These findings indicate that a nuclear complex of PPARalpha/RXRalpha is present in adult rat LV and is markedly downregulated in the hypertrophied LV from DS rats, which may account for the loss of transcriptional activation. The downregulation of this complex precedes LV systolic dysfunction and is mediated at the posttranslational levels.

Sympathetic and platelet adrenergic activity and salt sensitivity: an experimental study.

The objective of the study was to evaluate the advanced hypothesis that genetically predisposed salt-sensitivity contributes to an increased adrenergic susceptibility and platelet activity and both these factors play a role in the pathogenesis of hypertension in a Dahl rat model. The results showed: i) Dahl salt-sensitive rats (DS) gradually develop a diastolic hypertension by the end of 3 months of age, in spite of the diet they are fed. Low-Na diet (0.5% NaCl) does not prevent hypertension but delays its development. High-Na diet (8%) exacerbates their hypertension. ii) After 2 months of Na-loading, DS rats expressed significantly increased sodium and water retention and increased plasma volume by 15%, compared with 2.8% in Dahl salt-resistant (DR) rats on high-Na diet. iii) The increased activity of the sympathetic nervous system (SNS) in DS rats paralleled the development of hypertension and was stimulated by Na-loading. It was assessed by their catecholamines status and heart rate changes. iv) Platelet activity of DS rats was increased as reflected in collagen-induced nonstimulated and adrenaline-stimulated aggregation, and an increased plasma T x B2/6-keto PGF1 alpha ratio. Na-loading further increased platelet activity. v) Both DR and DS rat platelets displayed alpha 2-adrenoceptors (A2) of low binding capacity (Bmax 25 and 35 fmol/mg protein, respectively) and low affinity (KD 5.6 nM for both groups), suggesting that platelet alpha 2 adrenoceptors in this strain of rats might not play a significant biological role in their increased platelet activity. The fact that platelet alpha 2-adrenoceptors do not define the stimulation of SNS in DS rat do not exclude their participation in development of salt-dependent hypertension, since a genetic defect(s) of these ubiquitous receptors (brain, kidney, blood vessels) could still contribute to the pathogenesis of the disease.

Glucose Metabolism and Insulin Receptor Binding and mRNA Levels in Tissues of Dahl Hypertensive Rats

Increased insulinemic response to an oral glucose load has been demonstrated in Dahl salt-sensitive hypertensive rats. To determine whether this abnormality is mediated at the level of the insulin receptor, we compared insulin receptor binding and mRNA levels in tissues of Dahl salt-sensitive rats (DS) and in their normotensive controls, Dahl salt-resistant rats (DR). To evaluate possible influences of dietary sodium intake, rats were fed either low (0.07% NaCl) or high salt (7.5% NaCl) chow until the DS became hypertensive, and then were killed by decapitation. Fasting plasma glucose and plasma insulin levels did not differ between DR and DS rats and were not affected by salt intake. In response to an oral glucose load, plasma glucose had a similar increase in DR and DS rats, but the increase in plasma insulin was significantly greater in DS rats. Scatchard analysis of binding was obtained from in situ autoradiographic studies performed in frozen skeletal muscle and kidney sections, and insulin receptor mRNA levels were measured by slot-blot hybridization. Number and affinity of insulin receptors were comparable in skeletal muscle and kidney of DR and DS rats and, in both groups, binding parameters were not affected by dietary sodium chloride. Hepatic and renal insulin receptor mRNA levels were also comparable in DR and DS rats fed either low or high salt chow. Thus, increased plasma insulin response to oral glucose load is associated with normal insulin receptor binding and gene expression in peripheral tissues in rats with Dahl hypertension. A postreceptor defect is likely responsible for the decreased sensitivity to insulin in this model of genetic hypertension.