Aldosterone and cardiovascular remodelling: focus on myocardial failure

Heart Failure With Preserved Ejection Fraction and Adipose Tissue: A Story of Two Tales

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of heart failure in the presence of a normal left ventricular ejection fraction. Although it accounts for up to 50% of all clinical presentations of heart failure, there are no evidence-based therapies for HFpEF to reduce morbidity and mortality. Additionally there is a lack of mechanistic understanding about the pathogenesis of HFpEF. HFpEF is associated with many comorbidities (such as obesity, hypertension, type 2 diabetes, atrial fibrillation, etc.) and is coupled with both cardiac and extra-cardiac abnormalities. Large outcome trials and registries reveal that being obese is a major risk factor for HFpEF. There is increasing focus on investigating the link between obesity and HFpEF, and the role that the adipose tissue and the heart, and the circulating milieu play in development and pathogenesis of HFpEF. This review discusses features of the obese-HFpEF phenotype and highlights proposed mechanisms implicated in the inter-tissue communication between adipose tissue and the heart in obesity-associated HFpEF.

Evaluation of the inhibitory effects of telmisartan on drug-induced renin-angiotensin-aldosterone system activation in normal dogs

INTRODUCTION

This study examined whether the angiotensin II receptor blocker telmisartan had inhibitory effects on drug-induced renin-angiotensin-aldosterone system (RAAS) activation in normal dogs.

ANIMALS

Five healthy laboratory beagles were used in this study.

METHODS

Each dog received amlodipine (0.5 mg/kg, q12h, PO) alone for 14 days. Starting on the next day, animals received both amlodipine and telmisartan (1.0 mg/kg, q24h, PO) for 84 days. Systolic blood pressure, heart rate, plasma biochemical variables (blood urea nitrogen, creatinine, and electrolytes), plasma renin activity, and 24-h urinary aldosterone elimination (U-Aldo) were measured before amlodipine administration; at day 0; and at days 1, 7, 14, 28, 56, and 84 of telmisartan treatment.

RESULTS

Telmisartan was associated with significant decreases in systolic blood pressure on day 56 (p=0.046), whereas heart rate did not significantly change during this treatment (p=0.061). Plasma renin activity was significantly increased on days 1, 7, 28, 56, and 84 during telmisartan administration (all p=0.04). No change in median U-Aldo was detected following telmisartan administration (p=0.241). When U-Aldo was evaluated in individual animals, two dogs displayed evidence of aldosterone breakthrough.

CONCLUSIONS

Telmisartan administration did not suppress RAAS activation. The appearance of aldosterone breakthrough supports the incomplete blockade of RAAS activation.

The SEISICAT study: a pilot study assessing efficacy and safety of spironolactone in cats with congestive heart failure secondary to cardiomyopathy

INTRODUCTION

The pathophysiology of heart failure involves activation of several neurohormonal systems including the renin-angiotensin-aldosterone system. The mineralocorticoid receptor antagonist spironolactone has been shown to be beneficial in humans and dogs with heart failure. The objective of this pilot study was to investigate the efficacy and safety of spironolactone in cats with heart failure secondary to cardiomyopathy already treated with furosemide and an angiotensin-converting enzyme inhibitor.

ANIMALS

Twenty cats with heart failure due to cardiomyopathy.

METHODS

The study was a double-blind, randomised, placebo-controlled, multicentre clinical study assessing the effect of spironolactone on survival and clinical parameters in cats with heart failure due to cardiomyopathy. The primary end point was mortality, defined as death (spontaneous or by euthanasia) due to cardiac causes.

RESULTS

Twenty cats were enrolled: 9 in the spironolactone group and 11 in the placebo group of which 56% (5/9) and 0% (0/11) completed the 15-month period respectively. At inclusion, differences in systemic blood pressure, body condition score, electrocardiographic abnormalities and LA/Ao ratio suggested that disease may be less severe in the spironolactone group. Twenty-two percent (2/9) of cats in the spironolactone group and 82% (9/11) in the control group reached the primary end point (Fisher's exact test, p = 0.0216). No safety issues were identified in either group.

CONCLUSIONS

This study suggests that spironolactone is well tolerated, and preliminary results support further investigation to evaluate the efficacy of spironolactone in the treatment of cats with cardiac failure due to cardiomyopathy.

The antihypertensive effect of ethyl acetate extract of radish leaves in spontaneously hypertensive rats

Radish (Raphanus sativus L.) is a cruciferous vegetable, and its leaves have antioxidant and anticancer properties. This study was conducted to evaluate the effects of ethyl acetate extracts from radish leaves on hypertension in 11-week-old spontaneously hypertensive rats (SHRs). The SHRs were randomly divided into 3 groups of 6 rats each on the basis of initial systolic blood pressure (SBP) and were treated with oral administration of radish leaf extract (0, 30, or 90 mg/kg body weight [bw], respectively) for 5 weeks. Six Wistar rats were used as normotensive controls. The amount of the radish leaf extract had no effect on body weight. The SBP of the SHRs showed a decreasing trend with the consumption of the radish leaf extract. In the third week, the SBP of the group fed 90 mg extract/kg bw reduced from 214 mmHg to 166 mmHg and was significantly lower than that of the normotensive and hypertensive controls. The extract did not show a significant effect on the angiotensin-converting enzyme (ACE) activity in the serum, kidney, and lung. The extract increased the concentration of NO in serum and the activities of antioxidant enzymes such as glutathione peroxidase and catalase in red blood cells (RBCs). The serum concentrations of Na(+) and K(+) were not significantly different between all groups. However, the fecal concentrations of Na(+) and K(+) increased; the fecal concentrations of Na(+) and K(+) for the normotensive and hypertensive controls were not different. Urinary excretion of Na(+) was higher in the normotensive Wistar rats than in the SHRs, while that of K(+) was not significantly different. These findings indicate that consumption of radish leaves might have had antihypertensive effects in SHRs by increasing the serum concentration of NO and fecal concentration of Na(+) and enhancing antioxidant activities.

Neuronal nitric oxide synthase inhibition improves diastolic function and reduces oxidative stress in ovariectomized mRen2.Lewis rats

OBJECTIVE

The loss of estrogen in mRen2.Lewis rats leads to an exacerbation of diastolic dysfunction. Because specific neuronal nitric oxide synthase (nNOS) inhibition reverses renal damage in the same model, we assessed the effects of inhibiting neuronal nitric oxide on diastolic function, left ventricular remodeling, and the components of the cardiac nitric oxide system in ovariectomized (OVX) and sham-operated mRen2.Lewis rats treated with N5-(1-imino-3-butenyl)-L-ornithine (L-VNIO; 0.5 mg/kg per day for 28 d) or vehicle (saline).

METHODS

Female mRen2.Lewis rats underwent either bilateral oophorectomy (OVX; n = 15) or sham operation (or surgical procedure) (sham; n = 19) at 4 weeks of age. Beginning at 11 weeks of age, the rats were randomized to receive either L-VNIO or vehicle.

RESULTS

The surgical loss of ovarian hormones, particularly estrogen, led to exacerbated hypertension, impaired myocardial relaxation, diminished diastolic compliance, increased perivascular fibrosis, and increased relative wall thickness. The cardiac tetrahydrobiopterin-to-dihydrobiopterin levels were lower among OVX rats compared with sham-operated rats, and this altered cardiac biopterin profile was associated with enhanced myocardial superoxide production and decreased nitric oxide release. L-VNIO decreased myocardial reactive oxygen species production, increased nitrite concentrations, attenuated cardiac remodeling, and improved diastolic function.

CONCLUSIONS

Impaired relaxation, diastolic stiffness, and cardiac remodeling were found among OVX mRen2.Lewis rats. A possible mechanism for this unfavorable cardiac phenotype may have resulted from a deficiency in available tetrahydrobiopterin and subsequent increase in nNOS-derived superoxide and reduction in nitric oxide synthase metabolites within the heart. Selective nNOS inhibition with L-VNIO attenuated cardiac superoxide production and limited remodeling, leading to improved diastolic function in OVX mRen2.Lewis rats.

Cardiac hypertrophy and fibrosis in the metabolic syndrome: a role for aldosterone and the mineralocorticoid receptor

Obesity and hypertension, major risk factors for the metabolic syndrome, render individuals susceptible to an increased risk of cardiovascular complications, such as adverse cardiac remodeling and heart failure. There has been much investigation into the role that an increase in the renin-angiotensin-aldosterone system (RAAS) plays in the pathogenesis of metabolic syndrome and in particular, how aldosterone mediates left ventricular hypertrophy and increased cardiac fibrosis via its interaction with the mineralocorticoid receptor (MR). Here, we review the pertinent findings that link obesity with elevated aldosterone and the development of cardiac hypertrophy and fibrosis associated with the metabolic syndrome. These studies illustrate a complex cross-talk between adipose tissue, the heart, and the adrenal cortex. Furthermore, we discuss findings from our laboratory that suggest that cardiac hypertrophy and fibrosis in the metabolic syndrome may involve cross-talk between aldosterone and adipokines (such as adiponectin).

Efficacy of spironolactone on survival in dogs with naturally occurring mitral regurgitation caused by myxomatous mitral valve disease

BACKGROUND

Spironolactone, an aldosterone antagonist, has been demonstrated to decrease mortality in human patients when added to other cardiac therapies.

HYPOTHESIS

Spironolactone in addition to conventional therapy increases survival compared with conventional therapy in dogs with naturally occurring myxomatous mitral valve disease (MMVD).

ANIMALS

Between February 2003 and March 2005, 221 dogs were recruited in Europe. Nine dogs were excluded from analysis, leaving 212 dogs with moderate to severe mitral regurgitation (MR) caused by MMVD (International Small Animal Cardiac Health Council classification classes II [n = 190] and III [n = 21]).

METHODS

Double-blinded, field study conducted with dogs randomized to receive either spironolactone (2 mg/kg once a day) or placebo in addition to conventional therapy (angiotensin converting enzyme inhibitor, plus furosemide and digoxin if needed). Primary endpoint was a composite of cardiac-related death, euthanasia, or severe worsening of MR.

RESULTS

Primary endpoint reached by 11/102 dogs (10.8%) in the spironolactone group (6 deaths, 5 worsening) versus 28/110 (25.5%) in control group (14 deaths, 8 euthanasia, 6 worsening). Risk of reaching the composite endpoint significantly decreased by 55% (hazard ratio [HR] = 0.45; 95% confidence limits [CL], 0.22-0.90; log rank test, P = .017). Risk of cardiac-related death or euthanasia significantly reduced by 69% (HR = 0.31; 95% CL, 0.13-0.76; P = .0071). Number of dogs not completing the study for cardiac and other miscellaneous reasons similar in spironolactone (67/102) and control groups (66/110).

CONCLUSION AND CLINICAL IMPORTANCE

Spironolactone added to conventional cardiac therapy decreases the risk of reaching the primary endpoint (ie, cardiac-related death, euthanasia, or severe worsening) in dogs with moderate to severe MR caused by MMVD.

Beneficial effects of add-on hydrochlorothiazide in rats with myocardial infarction optimally treated with quinapril

BACKGROUND

The antihypertensive and renoprotective effects of ACE inhibitor (ACEi) therapy are enhanced by inducing a negative sodium balance. Whether this strategy also improves outcome of chronic ACEi treatment after myocardial infarction (MI) is unknown. Therefore, we investigated whether hydrochlorothiazide (HCTZ) or dietary sodium restriction further improves survival in ACEi-treated rats with MI.

METHODS

MI was induced by coronary ligation. After 2 weeks rats were randomised to quinapril (QUI), HCTZ added to quinapril (QUI+HCTZ), or low sodium diet added to quinapril (QUI+LS). Survival was monitored for 62 weeks, after which left ventricular (LV) pressures were measured and blood for neurohumoral characterisation was collected. A separate group of rats, subjected to the same procedure, was evaluated after 35 weeks.

RESULTS

After 62 weeks, mortality was comparable in all groups. However, survival was improved by HCTZ until 35 weeks. This effect on survival was paralleled by decreased proteinuria and LV end-diastolic pressures in QUI+HCTZ rats at 35, but not 62 weeks. Plasma renin activity was significantly decreased in QUI+HCTZ rats at 35 weeks. Contrary to HCTZ, LS added to QUI caused no benefit.

CONCLUSIONS

Adding HCTZ, but not LS, to quinapril improved survival, neurohumoral status, and proteinuria during the early chronic phase of experimental post-MI LV dysfunction. Since no adverse effects were observed, HCTZ may safely be used to improve ACEi therapy.

Participation of prostacyclin in endothelial dysfunction induced by aldosterone in normotensive and hypertensive rats

The aim of the present study was to analyze the possible involvement of vasoconstrictors prostanoids on the reduced endothelium-dependent relaxations produced by chronic administration of aldosterone in Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). For this purpose, acetylcholine (ACh) relaxations in aortic segments from both strains were analyzed in absence and presence of the cyclooxygenase-1 (COX-1) and COX-2 inhibitor indomethacin, the specific COX-2 inhibitor NS-398, the TP receptor antagonist (SQ 29 548), the thromboxane A2 (TXA2) synthase inhibitor furegrelate, and the prostacyclin (PGI2) synthesis inhibitor tranylcypromine (TCP). In addition, COX-2 protein expression was studied by Western blot analysis. Release of prostaglandin E2 (PGE2) and the metabolites of PGF2alpha, TXA2, and PGI2, 13,14-dihydro-15-keto PGF2a, TXB2, and 6-keto-PGF1alpha, respectively, were measured. Treatment with aldosterone did not modify blood pressure levels in any strain. However, aldosterone markedly reduced (P<0.05) ACh-induced relaxations in segments from both strains in a similar extent. Indomethacin, NS-398, SQ 29 548, and TCP enhanced (P<0.05) ACh relaxations in both strains treated with aldosterone. Aortic COX-2 protein expression was higher in both strains of rats treated with aldosterone. In normotensive animals, aldosterone increases the ACh-stimulated aortic production of 13,14-dihydro-15-keto PGF2a, PGE2, and 6-keto-PGF1alpha (P<0.05). In SHR, ACh only increased the 6-keto-PGF1alpha production (P<0.05). It could be concluded that chronic treatment with aldosterone was able to produce endothelial dysfunction through COX-2 activation in normotensive and hypertensive conditions. PGI2 seems to be the main factor accounting for endothelial dysfunction in hypertensive rats, whereas other prostanoids besides PGI2 appear to be involved in endothelial dysfunction under normotensive conditions.