The effects of spironolactone monotherapy on blood pressure and myocardial remodeling in spontaneously hypertensive rats: a stereological study

Effects of spironolactone in spontaneously hypertensive adult rats subjected to high salt intake

OBJECTIVE

To evaluate the effect of spironolactone on ventricular stiffness in spontaneously hypertensive adult rats subjected to high salt intake.

INTRODUCTION

High salt intake leads to cardiac hypertrophy, collagen accumulation and diastolic dysfunction. These effects are partially mediated by cardiac activation of the renin-angiotensin-aldosterone system.

METHODS

Male spontaneously hypertensive rats (SHRs, 32 weeks) received drinking water (SHR), a 1% NaCl solution (SHR-Salt), or a 1% NaCl solution with a daily subcutaneous injection of spironolactone (80 mg.kg⁻¹) (SHRSalt- S). Age-matched normotensive Wistar rats were used as a control. Eight weeks later, the animals were anesthetized and catheterized to evaluate left ventricular and arterial blood pressure. After cardiac arrest, a double-lumen catheter was inserted into the left ventricle through the aorta to obtain in situ left ventricular pressure-volume curves.

RESULTS

The blood pressures of all the SHR groups were similar to each other but were different from the normotensive controls (Wistar = 109 ± 2; SHR = 118 ± 2; SHR-Salt = 117 ± 2; SHR-Salt-S = 116 ± 2 mmHg; P < 0.05). The cardiac hypertrophy observed in the SHR was enhanced by salt overload and abated by spironolactone (Wistar = 2.90 ± 0.06; SHR = 3.44 ± 0.07; SHR-Salt = 3.68 ± 0.07; SHR-Salt-S = 3.46 ± 0.05 mg/g; P < 0.05). Myocardial relaxation, as evaluated by left ventricular dP/dt, was impaired by salt overload and improved by spironolactone (Wistar = -3698 ± 92; SHR = -3729 ± 125; SHR-Salt = -3342 ± 80; SHR-Salt-S = -3647 ± 104 mmHg/s; P < 0.05). Ventricular stiffness was not altered by salt overload, but spironolactone treatment reduced the ventricular stiffness to levels observed in the normotensive controls (Wistar = 1.40 ± 0.04; SHR = 1.60 ± 0.05; SHR-Salt = 1.67 ± 0.12; SHR-Salt- S = 1.45 ± 0.03 mmHg/ml; P < 0.05).

CONCLUSION

Spironolactone reduces left ventricular hypertrophy secondary to high salt intake and ventricular stiffness in adult SHRs.

Effect of melatonin, captopril, spironolactone and simvastatin on blood pressure and left ventricular remodelling in spontaneously hypertensive rats

OBJECTIVE

Melatonin was shown to reduce blood pressure, oxidative load and to increase nitric oxide bioavailability predisposing melatonin to have antiremodelling potential.

DESIGN

The aim of this study was to show whether melatonin can reverse left ventricular remodelling in spontaneously hypertensive rats (SHR) and to compare this potential protective effect with captopril, spironolactone, or simvastatin.

METHODS

Six groups of 3-month old rats (eight per group) were treated for 5 weeks: control untreated Wistar rats, control SHR, SHR plus melatonin (10 mg/kg per 24 h), SHR plus captopril (100 mg/kg per 24 h), SHR plus spironolactone (200 mg/kg per 24 h) and SHR plus simvastatin (10 mg/kg per 24 h). Their systolic blood pressure (SBP) was measured by the tail-cuff method. The relative weights of the left ventricle, nitric oxide synthase (NOS) activity, endothelial NOS and nuclear factor kappa B (NF-kappaB) protein expression, conjugated dienes concentration, level of collagenous proteins and hydroxyproline were measured.

RESULTS

SBP was reduced by all drugs investigated but most prominently by captopril in SHR. The activity of NOS and endothelial NOS expression increased in the left ventricles of SHR compared with controls. Melatonin and spironolactone further increased NOS expression. Left ventricular oxidative load, estimated by NF-kappaB expression and conjugated dienes concentration, increased in SHR. Only melatonin reduced NF-kappaB expression and decreased conjugated diens concentration. Only captopril reduced left ventricular hypertrophy in SHR, whereas melatonin reduced collagenous protein concentration and hydroxyproline content in the left ventricle.

CONCLUSION

It is concluded that although melatonin, in comparison with captopril, did not reverse left ventricle hypertrophy, it reversed left ventricular fibrosis. This protection by melatonin may be caused by its prominent antioxidative effect.

Regression of left ventricular hypertrophy and aortic remodelling in NO-deficient hypertensive rats: effect of L-arginine and spironolactone

AIM

We investigated, whether the substrate for nitric oxide (NO) formation -L-arginine - and the aldosterone receptor antagonist - spironolactone - are able to reverse alterations of the left ventricle (LV) and aorta in N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension.

METHODS

Six groups of male adult Wistar rats were investigated: controls after 4 and 7 weeks of experiment, rats treated with L-NAME for 4 weeks and three recovery groups: spontaneous-reversion (4 weeks L-NAME + 3 weeks placebo), spironolactone-induced reversion (4 weeks L-NAME + 3 weeks spironolactone) and L-arginine-induced reversion (4 weeks L-NAME+ 3 weeks L-arginine). Blood pressure was measured by tail-cuff plethysmography. Relative weight of the LV, myocardial fibrosis (based upon histomorphometry and hydroxyproline determination) and conjugated dienes in the LV and aortic cross-sectional area, inner diameter and wall thickness were determined. NO-synthase activity was investigated in the LV and aorta.

RESULTS

L-NAME administration induced hypertension, left ventricular hypertrophy (LVH), LV fibrosis, aortic thickening and diminution of NO-synthase activity in the LV and aorta. Reduction in blood pressure and regression of LVH were observed in all recovery groups, yet reduction in LV fibrosis and aortic thickening were not. NO-synthase activity was restored only in the L-arginine and spironolactone group.

CONCLUSION

In our study, the reversion of hypertension and LVH was not dependent on the restoration of NO-synthase activity. Moreover, LV fibrosis and aortic remodelling seem to be more resistant to conditions resulting in regression of LVH. Preserved level of fibrosis in the initial period of LVH regression might result in loss of structural homogeneity and possible functional alterations of the LV.

Adenovirus-mediated delivery of relaxin reverses cardiac fibrosis

We have evaluated the effectiveness of systemic adenovirally delivered mouse relaxin on reversing fibrosis in a transgenic murine model of fibrotic cardiomyopathy due to beta(2)-adrenergic receptor (beta(2)AR) overexpression. Recombinant adenoviruses expressing green fluorescent protein (Ad-GFP), rat relaxin (Ad-rRLN) and mouse relaxin (Ad-mRLN) were generated and Ad-rRLN and Ad-mRLN were demonstrated to direct the expression of bioactive relaxin peptides in vitro. A single systemic injection of Ad-mRLN resulted in transgene expression in the liver and bioactive relaxin peptide in the plasma. Ad-mRLN, but not Ad-GFP, treatment reversed the increased left ventricular collagen content in beta(2)AR mice to control levels without affecting collagen levels in other heart chambers or in the lung and kidney. Hence a single systemic injection of adenovirus producing mouse relaxin reverses cardiac fibrosis without adversely affecting normal collagen levels in other organs and establishes the potential for the use of relaxin gene therapy for the treatment of cardiac fibrosis.

Eplerenone offsets cardiac and aortic adverse remodeling in spontaneously hypertensive rats

BACKGROUND

Several studies have shown beneficial effects of eplerenone in hypertension and left ventricular dysfunction, but its action on cardiac and vascular changes secondary to blood pressure elevation are not clear yet.

METHODS

Twenty-five male spontaneously hypertensive rats (SHR) were assigned into five groups: young SHR (16 weeks), control SHR (22 weeks), and SHR treated by eplerenone (50 mg/kg/day), enalapril (10 mg/kg/day) or eplerenone+enalapril during 6 weeks. Five Wistar male rats were used as reference group. Cardiac structure and aorta were analyzed by stereology and image analysis.

RESULTS

The raise of blood pressure (202+/-3 mm Hg in control SHR) was significantly attenuated by eplerenone (169+/-2 mm Hg) or enalapril (170+/-2 mm Hg, P<0.001 versus control SHR), and more intensely by combined therapy (160+/-2 mm Hg, P<0.01 versus eplerenone or enalapril). The number of cardiomyocytes in left ventricle was preserved in enalapril group (35,660+/-910 versus 16,220+/-730x10(3) in control SHR, P<0.01) but more significantly in eplerenone, alone or combined, groups (38,380+/-439 and 38,660+/-374x10(3), respectively, P<0.001 versus control). The increased connective tissue volume density (35.8+/-1.2%) noted in the left ventricle of control SHR was significantly attenuated by eplerenone (7.4+/-0.8%), enalapril (8.0+/-0.6%) or eplerenone+enalapril (6.0+/-1.1%, P<0.01 treated versus control SHR). Media-to-lumen ratio of intramyocardial arteries was reduced by enalapril, but more significantly by eplerenone alone or combined with enalapril. The increase of media cross-sectional area of aorta in control SHR was attenuated by eplerenone and/or enalapril.

CONCLUSIONS

Eplerenone is effective in attenuating cardiovascular remodeling in SHR, confirming the important role of aldosterone in this process.

Relaxin Reverses Cardiac and Renal Fibrosis in Spontaneously Hypertensive Rats

The antifibrotic effects of the peptide hormone relaxin on cardiac and renal fibrosis were studied in 9- to 10-month-old male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Rats (n=8 to 9 per group) were allocated into 3 groups: WKY controls, vehicle-treated SHR (SHR-V), and relaxin-treated SHR (SHR-R). Relaxin (0.5 mg/kg per day) was administered via subcutaneously implanted osmotic mini-pumps over 2 weeks before hearts and kidneys were harvested for analysis. Collagen content was analyzed by hydroxyproline assay, gel electrophoresis, and quantitative histology. Zymography was used to determine matrix metalloproteinase (MMP) expression and Western blotting to determine proliferating cell nuclear antigen (PCNA) expression and α-smooth muscle actin (α-SMA)/myofibroblast expression, whereas cardiac hypertrophy was assessed by myocyte size and real-time polymerase chain reaction of associated genes. The left ventricular (LV) myocardium of SHR-V contained increased collagen levels (by 25±1%, P <0.01 using biochemical analysis and 3-fold; P <0.01 using quantitative histology), enhanced expression of PCNA (by 70±8%; P <0.01), α-SMA (by 32±2%; P <0.05), and the collagen-degrading enzyme MMP-9 (by 70±6%; P <0.05) versus respective levels measured in WKY controls. The kidneys of SHR-V also contained increased collagen (25±2%, P <0.05 using biochemical analysis and 2.4-fold; P <0.01 using quantitative histology). Relaxin treatment significantly normalized collagen content in the LV ( P <0.01) and kidney ( P <0.05), completely inhibited cell proliferation ( P <0.01) and fibroblast differentiation ( P <0.05) in the LV, and increased MMP-2 expression (by 25±1%; P <0.05) without affecting MMP-9 in the LV compared with that measured in SHR-V. Thus, relaxin is a potent antifibrotic hormone with a rapid-occurring efficacy that may have therapeutic potential for hypertensive disease.

Alpha-tocopherol supplementation favorable effects on blood pressure, blood viscosity and cardiac remodeling of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were separated into two groups (n = 6 per group) and, since 5 months old, received alpha-tocopherol (alpha-tocopherol acetate120 IU) or vehicle by daily gavage for 2 weeks. Blood viscosity, blood pressure (BP) and myocardial remodeling were analyzed. The SHRs treated with alpha-tocopherol showed a significant reduction of BP and a major reduction of blood viscosity in comparison with the control SHRs. The cardiac hypertrophy indices showed some differences when the two SHR groups were compared, the LV mass index was not different between the groups; however, the cardiomyocyte size was more than 20% smaller in SHRs treated with alpha-tocopherol than in control SHRs (P < .05). The intramyocardial vessels distribution was more than 45% greater in alpha-tocopherol-treated SHRs than in control rats, significantly improving the vessels-to-myocytes ratio in treated SHRs than in control SHRs (P < .05). In conclusion, present findings strongly suggest a beneficial effect of alpha-tocopherol supplementation to genetically hypertensive rats. This was observed by a reduction of both blood viscosity and BP, and a consequent cardiomyocyte hypertrophy in treated SHRs; an improvement of vessels-to-myocytes ratio in these rats was also observed.

Effects of spironolactone on rat liver fibrosis and expression of transforming growth factor β1 and tissue inhibitor of metalloproteinase-1

AIM: To identify the effects of spironolactone on expressions of transforming growth factor β₁ and tissue inhibitor of metalloproteinase-1 and to evaluate the curative effect of spironolactone.

METHODS: Thirty four male SD rats were randomly divided into 3 groups: Hepatic fibrosis model group: the rats were injected with 400 mL/L CCl₄ 3 mL/kg subcutaneously two times a week; Spironolactone group: the rats were injected with 400 mL/L CCl₄ 3 mL/kg subcutaneously two times a week; Spironolactone equivalent to 20 mg/kg per day was given intragastrically; Normal control group: normal chow. Hepatic tissue was observed with light microscopy to compare histological alterations dynamically. The expression of transforming growth factor β₁ and tissue inhibitor of metalloproteinase-1 was detected by RT-PCR.

RESULTS: The grades of fibrosis in spironolactone group were less than those in hepatic fibrosis model group at the end of the week 10 (P < 0.05). However, at the end of week 13, there was no significant difference between the two groups. The expression of TGFβ₁ and TIMP-1 mRNA was up-regulated when fibrogenesis occurred (P < 0.05). Although at the end of week 10 there was an inclination that the levels of TGFβ₁ and TIMP-1 mRNA in spironolactone group were less than those in hepatic fibrosis model group, there was no significant difference between two groups.

CONCLUSION: The expression of TGFβ₁ and TIMP-1 mRNA is up-regulated significantly when fibrogenesis occurs. Spironolactone may have a fibrogenesis-inhibiting effect on CCl₄ -induced hepatic fibrosis in some degree. Spironolactone has no significant effect on the expression of TGFβ₁ and TIMP-1 mRNA