Hypertrophy In Dahl Salt-sensitive Rats Research Articles

Hypoxia-inducible factor-prolyl hydroxylase inhibitor Roxadustat (FG-4592) reduces renal fibrosis in Dahl salt-sensitive rats.

Although hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitors have been developed for the treatment of renal anemia, their effects on cardiac and renal dysfunction remain unknown. We previously reported on Dahl salt-sensitive rats, in a rat model of salt-sensitive hypertension, that exhibited anemia and impaired expression of duodenal iron transporters after the development of hypertensive cardiac and renal dysfunction. Therefore, we investigated the effects of Roxadustat (FG-4592), an HIF-PH inhibitor, on anemia, iron regulation, and cardiac and renal dysfunction in Dahl salt-sensitive rats. Six-week-old male Dahl salt-sensitive rats were fed a normal or high-salt diet for 8 weeks. A further subset of Dahl salt-sensitive rats, that were fed a high-salt diet, was administered Roxadustat for 8 weeks. Dahl salt-sensitive rats fed a high-salt diet developed hypertension, cardiac and renal dysfunction, and anemia after 8 weeks of feeding. Roxadustat increased hemoglobin and serum erythropoietin levels in Dahl salt-sensitive rats fed a high-salt diet. With regard to the iron-regulating system, Roxadustat lowered hepatic hepcidin gene expression and increased the gene expression of duodenal iron transporters, such as cytochrome b and divalent metal transporter 1 , in Dahl salt-sensitive rats fed a high-salt diet. Roxadustat did not affect the development of hypertension and cardiac hypertrophy in Dahl salt-sensitive rats with a high-salt diet; however, Roxadustat treatment attenuated renal fibrosis in these rats. Roxadustat ameliorated anemia with affecting the gene expression of the iron-regulating system, and did not affect cardiac hypertrophy but attenuated renal fibrosis in Dahl salt-sensitive rats fed a high-salt diet.

Doxercalciferol, a Pro-hormone of Vitamin D, Prevents the Development of Cardiac Hypertrophy in Rats

Background Activated vitamin D analog, paricalcitol, has been shown to attenuate the development of cardiac hypertrophy in Dahl salt sensitive (DSS) rats. To determine whether an antihypertrophic effect is class specific, we tested if doxercalciferol (a pro-hormone vitamin D2 analog) could also attenuate the development of cardiac hypertrophy in DSS rats. Methods and Results Male DSS rats were fed a high salt (HS) diet for 6 weeks beginning at 6 weeks of age. Doxercalciferol was administered intraperitoneally at 150 ng, 3 times per week (Monday, Wednesday, Friday) for 6 weeks. Pathological and echocardiographic findings demonstrated that rats on HS diet with doxercalciferol administration had significant decrease in cardiac hypertrophy and improved cardiac function compared to the HS + vehicle. In addition, there was a significant decrease in plasma brain natriuretic peptide (BNP) level and tissue atrial natriuretic factor (ANF) mRNA level with doxercalciferol treatment. Doxercalciferol also significantly reduced the level of protein kinase C-α (PKCα) suggesting that PKC-mediated cardiac hypertrophy may be associated with vitamin D deficiency. Conclusions Administration of doxercalciferol attenuated the development of HS diet induced cardiac hypertrophy and cardiac dysfunction in DSS rats.

Distinct genomic replacements from Lewis correct diastolic dysfunction, attenuate hypertension, and reduce left ventricular hypertrophy in Dahl salt-sensitive rats

Hypertension and diastolic heart failure are two common cardiovascular diseases that inflict heavy morbidity and mortality, yet relatively little is understood about their pathophysiology. The identification of quantitative trait loci for blood pressure is important in unveiling the causes of polygenic hypertension. Although Dahl salt-sensitive strain is also an excellent model for the study of diastolic heart failure, virtually nothing is known about the quantitative trait loci determining diastolic heart failure. Diastolic dysfunction often represents the onset of diastolic heart failure. We first characterized the cardiac phenotype of Dahl salt-sensitive strain and normotensive Lewis control rats by echocardiography to ascertain diastolic function. We then analyzed corresponding features of four newly developed and two existing congenic strains, each of which carries a specific chromosome substitution of Dahl salt-sensitive strain by its Lewis homologue and each lowering blood pressure. Dahl salt-sensitive strain displayed diastolic dysfunction that was rectified in two of six congenic strains, designated as positive congenic strains, which represent the first rodent models exhibiting functional normalization of diastolic dysfunction caused by naturally occurring genetic variants. The two positive congenic strains also showed a reduction in left ventricular mass. In contrast, four of six congenic strains did not change diastolic function despite their blood pressure-lowering effects. Genes present in the replaced chromosome segments of the two positive congenic strains are not commonly known to affect blood pressure, diastolic function or left ventricular mass. Consequently, novel prognostic, diagnostic and therapeutic strategies for hypertensive diastolic heart failure likely emerge from this work.

Pioglitazone, a Thiazolidinedione Derivative, Attenuates Left Ventricular Hypertrophy and Fibrosis in Salt-Sensitive Hypertension

Thiazolidinediones, which stimulate peroxisome proliferator-activated receptor gamma, have been shown to prevent cardiovascular injury. However, little is known about their effects on salt-sensitive hypertension. We thus investigated whether or not pioglitazone affects left ventricular (LV) hypertrophy in Dahl salt-sensitive rats, then compared its effects to those of an angiotensin II receptor blocker, candesartan. Rats were used at 16 weeks of age after they had been fed either a low-salt (0.3%; DSL) or high-salt (8%; DSH) diet for 10 weeks; some of the DSH rats were treated with pioglitazone (10 mg/kg/day) or candesartan (4 mg/kg/day). Both drugs decreased the elevated blood pressure in DSH rats, although it was still higher than in DSL rats. Both drugs decreased plasma insulin levels, but neither affected plasma glucose levels. The thiobarbituric acid reactive substance level in the LV was decreased by both drugs. LV hypertrophy evaluated by echocardiography in DSH rats was nearly normalized by both drugs, whereas only candesartan decreased LV diameter. In histological analysis, both drugs ameliorated LV fibrosis and myocardial cell hypertrophy. Both drugs decreased elevated gene expression levels of transforming growth factor-beta1 and collagen type I, although the pioglitazone action was slightly modest. The metalloproteinase activity was increased in DSH rats, but both drugs decreased this level. Taken together, these findings indicate that pioglitazone reduced LV hypertrophy and fibrosis in salt-sensitive hypertension. Improvement in blood pressure, insulin level, and oxidative stress may be associated with this beneficial action of pioglitazone.

Congenic expression of tissue inhibitor of metalloproteinase in Dahl-salt sensitive hypertensive rats is associated with reduced LV hypertrophy

Although congenic translocation of a segment from chromosome 10 from Lewis rat, containing an extracellular proteinase inhibitor gene, decreased blood pressure in Dahl-salt sensitive (DSS) rats, the relationship between the levels of matrix metalloproteinase (MMP), tissue inhibitor of metalloproteinase (TIMP), and cardiac function was unclear. In this study we investigated the cardiac effects of congenic translocation of a segment from chromosome 10 from Lewis rat, containing an extracellular proteinase inhibitor gene, in Dahl-salt sensitive rats. To test the hypothesis that left ventricular (LV) hypertrophy in DSS rats was due to high MMP and low TIMP levels and the decrease in blood pressure in congenic rats was associated with increase in proteinase inhibitor expression, cardiac function and levels of MMP and TIMP were determined in 16 weeks male DSS (D), Lewis (L) and congenic (CL-10) rats. Cardiac function was assessed by electrocardiography, echocardiography and a Millar catheter in LV cavity. LV MMP and TIMP levels were measured by Q-RT-PCR and Western blot analyses. In L, D and CL-10 rats, heart weight/body weight (g/g) were 3.73 ± 0.06, 4.45 ± 0.04 and 3.35 ± 0.05 × 10−3, respectively, suggesting significant (p < 0.05) LV hypertrophy (LVH) in D group. The ST duration was longer in D group compared with L group, suggesting coronary vasospasm, but normalized in CL-10 rats. The fractional shortening and ejection fraction were decreased in D group as compared with L group, but normalized in CL-10 groups. LV diameter was increased in D group as compared to L group, but normalized in CL-10 groups. The levels of MMP-9 were higher and TIMP were lower in D as compared to L groups, but normalized in CL-10 rats. Compared with control non-congenic Dahl rats, congenic rats exhibited lower blood pressure, amelioration of LV remodelling and dysfunction, as well as coronary abnormalities. In addition, congenic animals exhibited reduced myocardial expression of MMP-9, but increased expression of MMP-2 and TIMP-4 compared to non congenic animals. We concluded that the congenic transfer of TIMP ameliorated LV hypertrophy and cardiac dysfunction.

Role of Cardiovascular Aldosterone in Hypertension

Aldosterone plays an important role in the pathogenesis of cardiovascular disease. We have reported that aldosterone is synthesized in cardiovascular tissues and local aldosterone synthesis plays important roles for hypertension and cardiac hypertrophy. High sodium intake develops and accelerates vascular injury and cardiac hypertrophy in SHRSP. Plasma aldosterone concentrations and PRA were decreased by high salt intake in SHRSP. Aldosterone production, the expression of CYP11B2 mRNA and angiotensin II receptor AT1R mRNA in blood vessels were significantly increased by high salt intake. These results suggest that high salt intake increases aldosterone production and expression of the AT1R mRNA in the vascular tissue in SHRSP, which may contribute to the development of malignant hypertension in salt-loaded SHRSP. However, there are several reports of conflicting data. Mineralocorticoid receptor (MR) binding is tightly regulated by the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) which selectively metabolizes glucocorticoids to inactive metabolites, thus allowing for MR activation by aldosterone. We have reported that decreased 11beta-HSD2 in blood vessels in Dahl salt-sensitive (DS) rats, a model for salt-sensitive hypertension. Local aldosterone excess may play a significant role in the salt sensitivity and development of hypertension. High sodium intake decreased circulating rennin-angiotensin-aldosterone system and increased blood pressure and cardiac hypertrophy in DS rats, which were prevented by the treatment with a selective MR antagonist, eplerenone. Eplerenone also improved endothelial nitric oxide synthase (eNOS) activity and eNOS mRNA expression in blood vessels in DS rats. These results further suggest that not only circulating aldosterone but also local aldosterone is of critical importance in the pathophysiology of cardiovascular disorders.

Saturated glucose uptake capacity and impaired fatty acid oxidation in hypertensive hearts before development of heart failure.

Abnormalities in energy metabolism may play an important role in the development of hypertensive heart failure. However, the transition from compensated hypertrophy to heart failure is not fully understood in terms of energy metabolism. In Dahl salt-sensitive (DS) and salt-resistant (DR) rats, myocardial fatty acid and glucose uptake values were determined using (131)I- or (125)I-labeled 9-methylpentadecanoic acid ((131)I- or (125)I-9MPA), and [(14)C]deoxyglucose ([(14)C]DG), fatty acid beta-oxidation was identified using thin-layer chromatography, and insulin-stimulated glucose-uptake was observed using a euglycemic hyperinsulinemic glucose clamp. Six-week-old rats were fed a diet that contained 8% NaCl, which resulted in development of compensated hypertrophy in DS rats at 12 wk of age and ultimately led to heart failure by 18 wk of age. Uptake of [(14)C]DG increased markedly with age in the DS rats, whereas (131)I-9MPA uptake was marginally but significantly increased only in animals aged 12 wk. The ratio of (125)I-9MPA beta-oxidation metabolites to total uptake in the DS rats was significantly lower (P < 0.05) at 12 (37%) and 18 (34%) wk compared with at 6 (45%) wk. Insulin increased [(14)C]DG uptake more than twofold in the DS rats at 6 wk, although this increase was markedly attenuated at 12 and 18 wk (11 and 8%, respectively). Our data suggest that in a hypertrophied heart before heart failure, fatty acid oxidation is impaired and the capacity to increase glucose uptake during insulin stimulation is markedly reduced. These changes in both glucose and fatty acid metabolism that occur in association with myocardial hypertrophy may have a pathogenic role in the subsequent development of heart failure.

Calcineurin inhibitor attenuates the development and induces the regression of cardiac hypertrophy in rats with salt-sensitive hypertension.

It remains unclear how hemodynamic overload induces cardiac hypertrophy. Recently, activation of calcium-dependent phosphatase, calcineurin, has been elucidated to induce cardiac hypertrophy. In the present study, we examined the role of calcineurin in load-induced cardiac hypertrophy by using Dahl salt-sensitive (DS) rats, which develop both pressure and volume overload when fed a high salt diet. In the DS rat heart, the activity of calcineurin was increased and cardiac hypertrophy was induced by high salt diet. Treatment of DS rats with the calcineurin inhibitor FK506 (0.1 or 0.01 mg/kg twice daily) from the age of 6 weeks to 12 weeks inhibited the activation of calcineurin in the heart in a dose-dependent manner and attenuated the development of load-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Additionally, treatment with 0.1 mg/kg twice daily but not with 0.01 mg/kg twice daily of FK506 from the age of 12 weeks to 16 weeks induced regression of cardiac hypertrophy in DS rats. Load-induced reprogramming of gene expression was also suppressed by the FK506 treatment. These results suggest that calcineurin is involved in the development of cardiac hypertrophy in rats with salt-sensitive hypertension and that inhibition of calcineurin could induce regression of cardiac hypertrophy.

Gene Therapy for Hypertension

Somatic gene delivery approaches have received wide attention as a new technique for studying gene expression and as a potential therapeutic tool in treating both inherited and acquired diseases. Recent studies using nonviral and viral vectors have shown great promise for gene therapy in hypertensive diseases. Potential targets for prospective gene therapy in hypertension include vasopressor renin-angiotensin system components and a number of vasodilator polypeptides such as tissue kallikrein-kinin, atrial natriuretic peptide, adrenomedullin and nitric oxide synthase. Antisense inhibition with oligonucleotides or cDNAs encoding renin, angiotensinogen, angiotensin-converting enzyme and angiotensin receptors has been shown to cause a prolonged blood pressure reduction in spontaneously hypertensive rats. To evaluate the therapeutic potential of vasodilator proteins or peptides in high blood pressure, we delivered the genes encoding human tissue kallikrein, atrial natriuretic peptide, nitric oxide synthase, and adrenomedullin into hypertensive rat models and showed that a single injection resulted in a significant and sustained reduction of blood pressure for several weeks. The potency and duration of blood pressure reduction depends on the dose and the promoter of the gene administered, age and sex of the hypertensive animals as well as the vehicle used for gene delivery. Somatic gene transfer of human tissue kallikrein or atrial natriuretic peptide not only attenuated hypertension but also exerted a protective effect against salt-induced renal damage and cardiac hypertrophy in Dahl salt-sensitive rats after high salt loading. These results suggest that the application of antisense inhibition of vasopressors, or gene delivery of vasodepressors for gene therapy, may have potential in treating human hypertension, and cardiovascular and renal disorders.

Effects of renin-angiotensin system blockade and dietary salt intake on left ventricular hypertrophy in Dahl salt-sensitive rats.

We studied the effects of chronic blockade of the renin-angiotensin system on hypertension and cardiac left ventricular hypertrophy (LVH) in Dahl salt-sensitive (DS) rats given a high-salt or low-salt diet. [Experiment 1] Twelve-week-old male DS rats were fed an 8% NaCl diet and received the angiotensin II receptor (AT1) antagonist, candesartan (3 mg/kg/d), the angiotensin converting enzyme inhibitor enalapril (30 mg/kg/d), or vehicle for 6 wk after 3 wk of 8% salt-loading. Neither candesartan nor enalapril with concomitant high salt-loading attenuated the blood pressure (BP) elevation. LVH was also not attenuated significantly by these treatments. [Experiment 2] After 8 wk of 8% salt-loading, the rats were given a 0.3% NaCl diet and concurrently received candesartan, enalapril, or vehicle for 5 wk. Switching from the high-salt to low-salt diet significantly decreased BP and left ventricular mass in the vehicle-treated animals. Both candesartan and enalapril normalized BP during salt-depletion; the blockade of the renin-angiotensin system produced an additive reduction in LVH. These findings suggest that sodium intake and hemodynamic load, but not the renin-angiotensin system, may be major determinants of the development of LVH in DS rats.

AT1 receptor antagonist, TCV 116, does not prevent cardiac hypertrophy in salt-loaded Dahl salt-sensitive rats.

1. We investigated the effects of direct blockade of angiotensin II (AngII) by a potent, non-peptide angiotensin II toff 1 (AT1) receptor antagonist, TCV 116, on the development of cardiac hypertrophy in salt-loaded Dahl salt-sensitive rats. 2. Six week old male Dahl salt-sensitive rats (n = 44) were fed a 4% salt diet and were simultaneously given various doses of TCV 116 orally for 7 weeks. Each control group received vehicle alone. 3. Dietary high salt intake elevated blood pressure continuously and caused left ventricular hypertrophy in rats treated with vehicle. TCV 116 had a minor effect on the rise in blood pressure. Left ventricular mass (left ventricular weight/body-weight) decreased slightly but not significantly, in rats treated with 3 mg/kg per day of TCV 116 (n = 8). Higher doses of TCV 116 (6 and 10 mg/kg per day; n = 8 each) did not show a decrease in left ventricular mass compared with the vehicle control. 4. These results suggest that AngII blockade has only minor effects on hypertension and on cardiac hypertrophy in salt-loaded Dahl salt-sensitive rats and that the renin-angiotensin system may not contribute to the development of cardiac hypertrophy in Dahl salt-sensitive rats on a moderately high-salt diet.

Cardiac Hypertrophy and the Blockade of Angiotensin II Receptors by Losartan in Salt-Loaded Dahl Salt-Sensitive Rats.

We studied the effects of direct blockade of angiotensin II by a non-peptide angiotensin II receptor (AT1) antagonist, losartan, on development of cardiovascular hypertrophy in salt-loaded Dahl salt-sensitive (DS) rats. Six-week-old male DS rats were fed a 4% NaCl diet and were simultaneously treated with one of two doses of oral losartan for 7 weeks. Vehicle-treated rats were given tap water alone. Blood pressure and body weight were monitored. The low-dose of losartan (30 mg/kg/day; n=12) blunted the rise in tail-cuff systolic blood pressure only transiently and did not reduce the left ventricular mass (ratio of left ventricular weight/body weight), when compared to the vehicle control (n=12). The high dose of losartan (100mg/kg/day; n=6) blunted the rise in blood pressure; however, left ventricular mass was not significantly lower in rats given the high dose of losartan than in those given vehicle (n= 12). The pressor response to intravenous angiotensin II was greatly suppressed in salt-loaded DS rats treated with 30mg/kg/day of losartan. These results suggest that losartan has minor hypotensive effects without reducing cardiovascular hypertrophy in DS rats fed a 4 % NaCl diet. We conclude that angiotensin II blockade has only minor effects on hypertension and cardiovascular hypertrophy in salt- loaded DS rats, and that the renin-angiotensin system may play no major role in the development of cardiovascular hypertrophy in DS rats on a moderately high-salt diet. (Hypertens Res 1994; 17: 199-203)

Angiotensin II-induced protein phosphorylation in the hypertrophic heart of the Dahl rat.

Angiotensin II-induced phosphorylation of proteins was examined in isolated myocytes from hearts of Dahl rats. A high salt diet induced cardiac hypertrophy in Dahl salt-sensitive rats. Angiotensin II-induced phosphorylation of a 42-kd protein (pp42) was detected by two-dimensional electrophoresis in hypertrophic but not normal ventricular myocytes. Angiotensin II stimulation was time-dependent, with a peak effect at 30 minutes. The half-maximal and maximal concentrations of angiotensin II that stimulated pp42 phosphorylation were 1 and 10 nM, respectively. Phosphorylation of pp42 was a function of cardiac hypertrophy. Phorbol 12-myristate 13-acetate-induced phosphorylation of pp42 indicates the possibility of an association between protein kinase C and the signal transduction pathway of angiotensin II-induced pp42 phosphorylation. Ionomycin and A23187 (both at 1 microM) did not stimulate phosphorylation of pp42. Angiotensin II produced a small increase in the synthesis of myocyte proteins in both normal and hypertrophic cells as shown by [35S]methionine incorporation. However, this increase could not account for the increase in the phosphate content of pp42. This protein was not an isoform of actin nor was it of platelet origin. These results raise the possibility that angiotensin II may play a role in the activation of factors in hypertrophic myocytes; however, further study is required to define a link between phosphorylation of pp42 and the hypertrophic process.

P-442 - Effects of Y-27152, a new K channel opener with gradual onset of action and less tachycardia, on the development of hypertension and cardiac hypertrophy in Dahl salt-sensitive rats

P-442 - Effects of Y-27152, a new K channel opener with gradual onset of action and less tachycardia, on the development of hypertension and cardiac hypertrophy in Dahl salt-sensitive rats