Mineralocorticoids, hypertension, and cardiac fibrosis

Aldosterone as a mediator of progressive renal disease: pathogenetic and clinical implications

End-stage renal disease is an enormous public health burden with an increasing incidence and prevalence. This escalating prevalence suggests that newer therapeutic interventions and strategies are needed to complement current antihypertensive approaches. Although much evidence shows that angiotensin II mediates progressive renal disease, recent evidence also implicates aldosterone as an important pathogenetic factor in progressive renal disease. Several lines of experimental evidence show that selective blockade of aldosterone, independent of renin-angiotensin blockade, reduces proteinuria and nephrosclerosis in the spontaneously hypertensive stroke-prone rat model and reduces proteinuria and glomerulosclerosis in the subtotally nephrectomized rat model (ie, remnant kidney). Although pharmacological blockade with angiotensin II-receptor blockers and angiotensin-converting enzyme inhibitors reduces proteinuria and nephrosclerosis and/or glomerulosclerosis, selective reinfusion of aldosterone restores these abnormalities despite continued renin-angiotensin blockade. Based on this theoretic construct, randomized clinical studies will be initiated to delineate the potential renal-protective effects of antihypertensive therapy using aldosterone-receptor blockade. This is a US government work. There are no restrictions on its use.

Mineralocorticoid and glucocorticoid receptors inhibit UCP expression and function in brown adipocytes

Uncoupling proteins (UCP), specific mitochondrial proton transporters that function by uncoupling oxidative metabolism from ATP synthesis, are involved in thermoregulation and control of energy expenditure. The hibernoma-derived T37i cells, which possess functional endogenous mineralocorticoid receptors (MR), can undergo differentiation into brown adipocytes. In differentiated T37i cells, UCP1 mRNA levels increased 10- to 20-fold after retinoic acid or beta-adrenergic treatment. Interestingly, UCP2 and UCP3 mRNA was also detected. Aldosterone treatment induced a drastic decrease in isoproterenol- and retinoic acid-stimulated UCP1 mRNA levels in a time- and dose-dependent manner (IC(50) approximately 1 nM aldosterone). This inhibition was unaffected by cycloheximide and did not modify UCP1 mRNA stability (half-life time = 5 h), indicating that it occurs at the transcriptional level. It involves both the MR and/or the glucocorticoid receptor (GR), depending on the retinoic or catecholamine induction pathway. Basal UCP3 expression was also significantly reduced by aldosterone, whereas UCP2 mRNA levels were not modified. Finally, as demonstrated by JC1 aggregate formation in living cells, aldosterone restored mitochondrial membrane potential abolished by isoproterenol or retinoic acid. Our results demonstrate that MR and GR inhibit expression of UCP1 and UCP3, thus participating in the control of energy expenditure.

Effects of high sodium intake on cardiovascular aldosterone synthesis in stroke-prone spontaneously hypertensive rats

OBJECTIVES

Aldosterone is synthesized in extra-adrenal tissues such as the vasculature, heart and brain. The mechanisms underlying the effect of high salt intake on the development and acceleration of vascular injury and cardiac hypertrophy in the stroke-prone spontaneously hypertensive rats (SHRSP) are still not clear. The goal of this study was to determine whether high salt intake increases cardiovascular aldosterone synthesis in SHRSP.

METHODS

Four-week-old SHRSP were given tap water or 0.9% NaCl solution for hydration for 4 weeks in addition to a normal salt diet. Isolated rat mesenteric arteries and hearts were perfused for 2 h, and the perfusate was analysed by high-performance liquid chromatography. The concentrations of aldosterone synthase gene (CYP11B2) mRNA and angiotensin II receptor (AT1R) mRNA were determined by competitive polymerase chain reaction.

RESULTS

Salt-loaded SHRSP had higher blood pressures than SHRSP with normal salt intake. Plasma aldosterone concentrations and plasma renin activity were decreased by high salt intake. Aldosterone production, the expression of CYP11B2 mRNA and AT1R mRNA in mesenteric arteries and hearts were significantly increased by high salt intake.

CONCLUSIONS

These results suggest that high salt intake increases aldosterone production and expression of the AT1R mRNA in the cardiovascular tissue in SHRSP, which may contribute to the development of malignant hypertension in salt-loaded SHRSP.

Arterial pressure, left ventricular mass, and aldosterone in essential hypertension

The purpose of the present study was to evaluate the relationship of aldosterone to blood pressure and left ventricular size in black American (n=109) and white French Canadian (n=73) patients with essential hypertension. Measurements were obtained with patients off antihypertensive medications and included 24-hour blood pressure monitoring, plasma renin activity and aldosterone, and an echocardiogram. Compared with the French Canadians, the black Americans had higher body mass indexes, higher systolic blood pressures, attenuated nighttime reduction of blood pressure, and lower serum potassium concentrations (P:<0.01 for each). Left ventricular mass index, posterior wall thickness, interventricular septal thickness, and relative wall thickness were also greater (P:<0.01 for each) in the black American patients. Supine and standing plasma renin activity was lower (P:<0.01 and P:<0.05, respectively) in the black Americans, whereas supine plasma aldosterone concentrations did not differ, and standing plasma aldosterone was greater (P:<0.05) in the black Americans (9.2+/-0.7 ng/dL) than in the French Canadians (7.3+/-0.6 ng/dL). In the black Americans, supine plasma aldosterone was positively correlated with nighttime systolic (r=0.30; P:<0.01) and diastolic (r=0.39; P:<0.001) blood pressures and inversely correlated with the nocturnal decline of systolic (r=-0.29; P:<0.01) and diastolic (r=-0.37; P:<0.001) blood pressures. In the black Americans, standing plasma aldosterone was positively correlated with left ventricular mass index (r=0.36; P:<0.001), posterior wall thickness (r=0.33; P:<0.01), and interventricular septal thickness (r=0.26; P:<0.05). When the black American patients were divided into obese and nonobese groups, significant correlations between plasma aldosterone and both blood pressure and cardiac mass were observed only in the obese. In the French Canadians, overall, plasma aldosterone did not correlate with either blood pressure or any measures of heart size. However, among obese French Canadians, supine plasma aldosterone correlated with nighttime diastolic (r=0.53, P:<0.02) and systolic (r=0.44, P:<0.01) blood pressures but not with cardiac mass. These results are consistent with the hypothesis that aldosterone contributes to elevated arterial pressure in obese black American and obese white French Canadian patients with essential hypertension and to the attenuated nocturnal decline of blood pressure and left ventricular hypertrophy in obese, hypertensive black Americans.

Effects of angiotensin-converting enzyme inhibitor and angiotensin type 1 receptor antagonist in deoxycorticosterone acetate-salt hypertensive mice lacking Ren-2 gene

We previously reported that inhibition of angiotensin-converting enzyme (ACE) prevented the hypertension and left ventricular hypertrophy induced by deoxycorticosterone acetate-salt (DOCA-salt) in 129/SvEvTac mice, which have 2 renin genes (Ren-1 and Ren-2). In the present study, we induced hypertension by uninephrectomy and DOCA-salt in mice having only the Ren-1 gene (C57BL/6J) and investigated the effect of an ACE inhibitor (ramipril, 4 mg. kg(-)(1). d(-)(1)) and an angiotensin type 1 (AT(1)) receptor antagonist (L-158809, 4 mg. kg(-)(1). d(-)(1)) on the development of hypertension, cardiac hypertrophy, and renal injury. After 4 weeks of treatment, systolic blood pressure in DOCA-salt mice was significantly increased (128+/-2 mm Hg) compared with controls (109+/-2 mm Hg) (P:<0.001), while plasma renin concentration was decreased by 97% (P:<0.001). DOCA-salt also induced left ventricular and renal hypertrophy and renal damage as manifested by proteinuria. Collagen content in the left ventricle and kidney was significantly higher in DOCA-salt mice (P:<0.001). Urinary albumin (P:<0.05) and proliferating cell nucleic antigen-positive cells in the tubules and interstitium of the renal cortex (P:<0.001) were significantly increased in the DOCA-salt group. Neither the ACE inhibitor nor the AT(1) antagonist had any antihypertensive effect; however, they partially prevented cardiac hypertrophy and completely inhibited left ventricular collagen deposition. In the kidney, both the ACE inhibitor and AT(1) antagonist partially reduced the increase in collagen but had no effect on hypertrophy. They also significantly prevented the effect of DOCA-salt on urinary albumin and proliferating cell nucleic antigen expression in the kidney. Despite the lack of an antihypertensive effect, both ACE inhibitor and AT(1) antagonist prevented cardiac remodeling and renal damage. Our results indicate that ACE inhibitors and AT(1) antagonists exert beneficial effects on the heart and kidney in DOCA-salt hypertensive mice independently of their effects on blood pressure.

Aldosterone synthase (CYP11B2) -344 C/T polymorphism is associated with left ventricular structure in human arterial hypertension

OBJECTIVES

This study examined the association between the -344 C/T polymorphism of the human aldosterone synthase promoter and left ventricular structure in arterial hypertension.

BACKGROUND

Because of conflicting results from different studies, the mechanism of such an association, if any, has not been determined.

METHODS

We examined the aldosterone synthase promoter genotype in 120 young (age: 26 +/- 3 years) male, white subjects with normal or mildly elevated blood pressure. Left ventricular structural parameters and urinary sodium excretion over 24 h before and after additional oral sodium load (6 g/day over 1 week) were determined.

RESULTS

Hypertensive subjects with the CC genotype had a greater left ventricular end-diastolic diameter but smaller relative wall thickness than those with the TT genotype (54 +/- 2 vs. 50 +/- 4 mm, and 0.37 +/- 0.07 vs. 0.44 +/- 0.06 mm, respectively; p < 0.05). Hypertensive subjects with the TT genotype (n = 15) had a greater increase in urinary sodium excretion after oral sodium load than those with the CC genotype (n = 11) (135 +/- 95 vs. 24 +/- 133 mmol/liter/day; p < 0.05). Serum aldosterone levels were found to be decreased after oral sodium load in hypertensive subjects with the TT and CT genotypes only (-37 +/- 45 and -38 +/- 51 pg/ml, respectively; all p < 0.01) but not in those with the CC genotype (-12 +/- 30 pg/ml, n.s.). Such differences were not found in normotensive subjects.

CONCLUSIONS

Hypertensive subjects with the -344 CC genotype of the aldosterone synthase promoter are characterized by a pattern of early eccentric left ventricular hypertrophy. Differences in renal sodium handling across the genotypes might contribute to this finding.

Antifibrotic effects of N-acetyl-seryl-aspartyl-Lysyl-proline on the heart and kidney in aldosterone-salt hypertensive rats

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) inhibits not only hematopoietic cell proliferation but also fibroblast proliferation and collagen synthesis in vitro. Ac-SDKP also prevents collagen deposition and cell proliferation in the left ventricle (LV) in rats with renovascular hypertension (renin dependent). However, it is not clear whether Ac-SDKP has similar effects in a model of renin-independent hypertension (aldosterone-salt). Using a hypertensive rat model of cardiac and renal fibrosis created by chronic elevation of circulating aldosterone (ALDO) levels, we examined the effect of Ac-SDKP on blood pressure, cardiac and renal fibrosis and hypertrophy, and proliferating cell nuclear antigen (PCNA) expression in the LV and left kidney. Uninephrectomized rats were divided into 4 groups: (1) controls that received tap water, (2) rats that received ALDO (0.75 microgram/h SC) and 1% NaCl/0.2% KCl in drinking water (ALDO-salt), (3) rats that received ALDO-salt plus Ac-SDKP 400 microgram. kg(-1). day(-1) SC, and (4) rats that received ALDO-salt plus Ac-SDKP 800 microgram. kg(-1). d(-1) SC. After 6 weeks of treatment, the ALDO-salt group was found to have significantly increased blood pressure with decreased body weight and plasma renin concentration (P<0.05), LV and renal hypertrophy as well as renal injury, significantly increased collagen content in both ventricles and kidney as well as increased collagen volume fraction in the LV (P<0.0001), and significantly increased interstitial and perivascular PCNA-positive cells in the LV and kidney (P<0.0001). Ac-SDKP at 800 microgram. kg(-1). d(-1) markedly prevented cardiac and renal fibrosis (P<0.005) without affecting blood pressure or organ hypertrophy. It also suppressed PCNA expression in the LV and kidney in a dose-dependent manner. We concluded that Ac-SDKP prevents increased collagen deposition and cell proliferation in the heart and kidney in ALDO-salt hypertensive rats. Because ACE inhibitors increase plasma and tissue Ac-SDKP and decrease cardiac and renal fibrosis, we speculate that Ac-SDKP may participate in the antifibrotic effect of ACE inhibitors.

Effect of aldosterone on collagen steady state levels in primary and subcultured rat hepatic stellate cells

BACKGROUND/AIMS

Activation of the renin-angiotensin-aldosterone system can lead to collagen accumulation and reactive myocardial fibrosis. This study aims at evaluating the effect of aldosterone on extracellular matrix synthesis by rat hepatic stellate cells.

METHODS

Cultured cells were treated with different concentrations of aldosterone (10(-6)-10(-10) M) and metabolically labeled with 35S-methionine/35S-cysteine. Procollagen types I, III and IV, laminin and fibronectin were specifically immunoprecipitated and quantified by phosphor imaging. Using the reverse transcription-polymerase chain reaction, we investigated the expression of the mineralocorticoid receptor in hepatic stellate cells.

RESULTS

Quantitation showed that 10(-6) M aldosterone induced procollagen type I synthesis significantly, whereas procollagen type IV expression was significantly affected by 10(-9) and 10(-10) M aldosterone, both in primary hepatic stellate cells. RT-PCR experiments clearly demonstrated a lack of expression of the mineralocorticoid receptor in hepatic stellate cells.

CONCLUSION

We demonstrated that aldosterone altered moderately procollagen type I and IV synthesis by primary hepatic stellate cells, but not by activated stellate cells which are the principal cellular sources of extracellular matrix proteins in chronic liver disease. Moreover, hepatic stellate cells do not express the mineralocorticoid receptor, suggesting that the observed modest changes of extracellular matrix synthesis are probably due to mineralocorticoid receptor unrelated mechanisms.

Prevention of aortic and cardiac fibrosis by spironolactone in old normotensive rats

OBJECTIVES

Because the synthesis of aldosterone is mainly modulated by angiotensin II through type I receptor stimulation and because converting enzyme inhibition (CEI) does not modify aortic extracellular matrix in old normotensive rats, the aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in old Sprague-Dawley normotensive rats.

BACKGROUND

We have previously shown that long-term aldosterone antagonism prevents the age-related increase in aortic collagen accumulation in young spontaneously hypertensive rats, independent of blood pressure changes. In contrast, we reported that the positive effects of CEI in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type I receptors.

METHODS

For this purpose, we studied the histomorphometric and stiffness (echo-tracking technique) changes of an eight-week treatment with the aldosterone antagonist spironolactone by comparison with placebo.

RESULTS

At the end of treatment, spironolactone in conscious animals did not change intra-arterial blood pressure, aortic and carotid wall thickness, and cardiac weight. Cardiac collagen density and, to a lesser extent, carotid collagen and elastin densities and contents were significantly decreased in association with an increase of carotid distensibility.

CONCLUSIONS

These results show that in old normotensive rats, spironolactone can markedly prevent cardiac and, to a lesser extent, arterial fibrosis and improve arterial stiffness, despite a lack of hypotensive effect.

Aldosterone production is activated in failing ventricle in humans

BACKGROUND

Recent reports have indicated that aldosterone is produced in extra-adrenal tissues in animals. The present study was designed to examine whether aldosterone is produced in human heart.

METHODS AND RESULTS

Plasma levels of aldosterone, BNP, and angiotensin-converting enzyme were measured in anterior interventricular vein (AIV), coronary sinus (CS), and aortic root (Ao), respectively, in 20 patients with left ventricular systolic dysfunction (LVSD), 25 patients with LV diastolic dysfunction (LVDD), and 23 control subjects. Aldosterone levels were significantly higher in AIV and CS than Ao in LVSD (98+/-10 versus 72+/-9 pg/mL, P:<0.001, and 97+/-11 versus 72+/-9 pg/mL, P:<0.001, respectively) and LVDD (87+/-10 versus 71+/-9 pg/mL, P:<0.01, and 84+/-10 versus 71+/-9 pg/mL, P:<0.01, respectively) groups, but no differences were observed in levels for these sites in the control group. Levels of ACE activity and BNP also were higher in AIV than Ao in both LV dysfunction groups. The difference in aldosterone levels between AIV and Ao and those in BNP and angiotensin-converting enzyme had a significant positive correlation with LVEDP and a significant negative correlation with LV ejection fraction in the LVSD group.

CONCLUSIONS

Production of aldosterone, angiotensin-converting enzyme, and BNP are activated in failing human ventricle in proportion to severity.

Aldosterone in renal disease

Blockade of the renin-angiotensin-aldosterone system has proved effective in retarding the progression of renal disease in the remnant kidney model, as well as other experimental diseases, and most importantly, in a range of progressive human renal diseases. Attention has focused on the role of angiotensin II in propagating progression both by its hemodynamic and non-hemodynamic actions. Recent evidence, predominantly in the remnant kidney model, indicates that the drugs used to block this hormone system, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, also lower aldosterone levels. Aldosterone as well as angiotensin II thus appears to be instrumental in sustaining the hypertension and fibroproliferative destruction of the residual kidney.

Aldosterone escape during angiotensin-converting enzyme inhibitor therapy in essential hypertensive patients with left ventricular hypertrophy

Continuous angiotensin-converting enzyme (ACE) inhibitor therapy does not necessarily produce significant decreases in plasma aldosterone levels (aldosterone escape). We examined the role of aldosterone escape in 75 essential hypertensive patients treated with an ACE inhibitor (enalapril maleate [34 patients], imidapril hydrochloride [24 patients] or trandolapril [17 patients]) for 40 weeks. With treatment, blood pressure decreased and plasma renin activity increased, while plasma aldosterone concentrations did not change. Aldosterone escape was observed in 38 of the 75 patients and in 17 of 37 patients with left ventricular hypertrophy before treatment. Left ventricular mass index did not change in patients with aldosterone escape but decreased significantly in patients without aldosterone escape. The present study demonstrated a high incidence of aldosterone escape in patients with essential hypertension despite the use of ACE inhibitors. The results also suggest that aldosterone escape may reverse the beneficial effects of an ACE inhibitor on left ventricular hypertrophy.

Limitation of excessive extracellular matrix turnover may contribute to survival benefit of spironolactone therapy in patients with congestive heart failure: insights from the randomized aldactone evaluation study (RALES). Rales Investigators

BACKGROUND

In congestive heart failure (CHF), extracellular matrix turnover is a major determinant of cardiac remodeling. It has been suggested that spironolactone may decrease cardiac fibrosis. We investigated the interactions between serum markers of cardiac fibrosis and the effect of spironolactone on outcome in patients with CHF.

METHODS AND RESULTS

A sample of 261 patients from the Randomized Aldactone Evaluation Study (RALES) were randomized to placebo or spironolactone (12.5 to 50 mg daily). Serum procollagen type I carboxy-terminal peptide, procollagen type I amino-terminal peptide, and procollagen type III amino-terminal peptide (PIIINP) were assessed at baseline and at 6 months. Baseline PIIINP >3.85 microgram/L was associated with an increased risk of death (relative risk [RR] 2.36, 95% CI 1.34 to 4.18) and of death+hospitalization (RR 1.83, 95% CI 1.18 to 2.83). At 6 months, markers decreased in the spironolactone group but remained unchanged in the placebo group. The spironolactone effect on outcome was significant only in patients with above-median baseline levels of markers. RR (95% CI) values for death among patients receiving spironolactone were 0.44 (0.26 to 0.75) and 1.11 (0.66 to 1.88) in subgroups of PIIINP levels above and below the median, respectively. Similarly, RR (95% CI) values for death+hospitalization among patients receiving spironolactone were 0.45 (0.29 to 0.71) and 0.85 (0.55 to 1.33), respectively.

CONCLUSIONS

In patients with CHF, high baseline serum levels of markers of cardiac fibrosis synthesis are significantly associated with poor outcome and decrease during spironolactone therapy. The benefit from spironolactone was associated with higher levels of collagen synthesis markers. These results suggest that limitation of the excessive extracellular matrix turnover may be one of the various extrarenal mechanisms contributing to the beneficial effect of spironolactone in patients with CHF.

Cardiac aldosterone production in genetically hypertensive rats

Aldosterone is synthesized in extra-adrenal tissues, both blood vessels and brain. We undertook the present study to determine whether the rat heart produces aldosterone and to investigate the effects of adrenalectomy, ACE inhibition, and angiotensin II on aldosterone synthesis in the heart. To clarify the pathophysiological role of cardiac aldosterone in the hypertensive heart, we compared the synthesis of aldosterone in the hearts of stroke-prone spontaneously hypertensive rats (SHRSP) with that in Wistar-Kyoto rats. The effects of the aldosterone antagonist spironolactone on myocardial hypertrophy in adrenalectomized SHRSP were also studied. Isolated rat hearts were perfused for 2 hours, and the perfusate was analyzed with HPLC and mass spectrometry. The activity of aldosterone synthase was estimated on the basis of the conversion of [(14)C]deoxycorticosterone to [(14)C]aldosterone. The levels of aldosterone synthase gene (CYP11B2) mRNA were determined with competitive polymerase chain reaction. Aldosterone production, the activity of aldosterone synthase, and the expression of CYP11B2 mRNA were increased in hearts from adrenalectomized rats and rats treated with angiotensin II. ACE inhibitors decreased cardiac aldosterone synthesis. Cardiac aldosterone, aldosterone synthase activity, and CYP11B2 mRNA levels in hearts from 2- and 4-week-old SHRSP were significantly greater than those of age-matched Wistar-Kyoto rats. Spironolactone prevented cardiac hypertrophy in adrenalectomized SHRSP. These results suggest that the rat heart produces aldosterone and that endogenous cardiac aldosterone may affect cardiac function and hypertrophy in hypertension in rats.

Spironolactone inhibits the transcardiac extraction of aldosterone in patients with congestive heart failure

OBJECTIVES

The study evaluated the transcardiac extraction or spillover of aldosterone (ALDO) in normal subjects and in patients with congestive heart failure (CHF).

BACKGROUND

Aldosterone promotes collagen synthesis and structural remodeling of target organs such as the heart. Spironolactone, an ALDO receptor antagonist, has recently been reported to reduce the mortality of patients with CHF; however, the effects of spironolactone on the transcardiac gradient of ALDO have not been clarified.

METHODS

We measured plasma ALDO in the aortic root (AO) and coronary sinus (CS) in normal subjects and 113 consecutive CHF patients and also measured plasma procollagen type III aminoterminal peptide (PIIINP) in CS, a biochemical marker of myocardial fibrosis.

RESULTS

Plasma ALDO was significantly lower in the CS than in the AO in normal subjects (n = 15; 61.2 +/- 9.3 vs. 83.1 +/- 11.8 pg/ml, p < 0.0001). In 96 CHF patients who did not receive spironolactone, plasma ALDO was significantly lower in the CS than in the AO (59.3 +/- 3.9 vs. 73.8 +/- 4.9 pg/ml, p < 0.0001). In contrast to the difference in these 96 patients, there was no significant difference in ALDO between the AO and CS in 17 patients who received spironolactone (127.4 +/- 20 vs. 124.0 +/- 19 pg/ml, p = 0.50). Stepwise multivariate analyses showed that spironolactone therapy had an independent and significant negative relationship with the transcardiac gradient of plasma ALDO in patients with CHF. In addition, significant positive correlations were seen between the transcardiac gradient of plasma ALDO and PIIINP (r = 0.565, p < 0.0001) and the left ventricular end-diastolic volume index (r = 0.484, p < 0.0001).

CONCLUSIONS

These results indicate that plasma ALDO is extracted through the heart in normal subjects and in CHF patients who do not receive spironolactone and that spironolactone inhibits the transcardiac extraction of ALDO in CHF patients, suggesting that spironolactone blocks the effects of ALDO on the failing heart in patients with CHF.

Aldosterone, a new appreciation of its role in heart failure

Understanding of the role, triggers, and impact of the renin-angiotensin-aldosterone system in cardiovascular disease has significantly broadened. In recent years substantial discoveries have been made regarding the pathophysiology of heart failure, particularly in the area of neurohormonal activation. New interest in therapy with aldosterone antagonists was stimulated by results of a 2-year study of 1663 patients with heart failure that showed a 30% relative risk reduction of death among patients given a subhemodynamic dosage of spironolactone, a nonselective aldosterone antagonist, compared with placebo, in addition to standard therapy of diuretics, angiotensin-converting enzyme inhibitors, beta-blockers, and digitalis.

Aldosterone and the heart

Classically, aldosterone is a steroid hormone secreted from the adrenal cortex, which acts on kidney, colon and sweat/salivary glands to promote unidirectional sodium transport. Currently, there is excellent experimental evidence for aldosterone acting directly on the central nervous system to raise blood pressure, and on the heart to cause cardiac hypertrophy and fibrosis. In addition, there is emerging evidence for aldosterone synthesis in the heart, and for as yet unexplained benefits of aldosterone antagonism in the treatment of cardiac failure.

Fibrosis and hypertensive heart disease

The normal myocardium is composed of a variety of cells: cardiac myocytes and noncardiomyocytes, which include endothelial and vascular smooth muscle cells and fibroblasts. Hypertensive heart disease involves a structural remodeling of muscular and nonmuscular compartments. It is not the quantity but rather the quality of myocardium that accounts for pathologic hypertrophy and predisposes to ventricular dysfunction and arrhythmias, which, in turn, confer increased risk of adverse cardiovascular events. Herein, factors regulating growth of these compartments are reviewed and in particular signals involved in promoting adverse remodeling of intramyocardial coronary arteries and arterioles by fibrous tissue.

Ventricular remodeling and the renin angiotensin aldosterone system

Ventricular remodeling in patients with left ventricular systolic dysfunction is an indolent process that is associated with a poor prognosis. Clinical and experimental data support the central role played by the renin-angiotensin-aldosterone system in the pathophysiology of remodeling. ACE inhibitors improve the natural history of ventricular remodeling and the syndrome of heart failure. Experimental and preliminary clinical data suggest that angiotensin II type I receptor blockade also impacts favorably on remodeling. Some experimental studies suggest a possible synergistic effect when combining ACE inhibitors and angiotensin II type I receptor antagonists. Aldosterone, the regulation of which, in part, is independent of angiotensin II, is a direct mediator of the interstitial component of remodeling, and its blockade has been found to improve clinical outcomes. Future research will more precisely define the mechanism for ventricular remodeling and will yield more effective means of achieving a clinically relevant impact on this process. (c)2000 by CHF, Inc.

Aldosterone and vascular damage

Although the aldosterone escape mechanism is well known, aldosterone has often been neglected in the pathophysiologic consequences of the activated renin-angiotensin-aldosterone system in arterial hypertension and chronic heart failure. There is now evidence for vascular synthesis of aldosterone aside from its secretion by the adrenal cortex. Moreover, aldosterone is involved in vascular smooth muscle cell hypertrophy and hyperplasia, as well as in vascular matrix impairment and endothelial dysfunction. The mechanisms of action of aldosterone may be either delayed (genomic) or rapid (nongenomic). Deleterious effects of aldosterone leading to vascular target-organ damage include (besides salt and water retention) decreased arterial and venous compliance, increased peripheral vascular resistance, and impaired autonomic vascular control due to baroreflex dysfunction.

Reversal of cardiac hypertrophy and fibrosis by S21402, a dual inhibitor of neutral endopeptidase and angiotensin converting enzyme in SHRs

OBJECTIVE

The major advantage of dual inhibitors of neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE) is their ability to lower blood pressure irrespective of renin or volume status. The aim of this study was to determine whether dual NEP/ACE inhibition produces different effects on cardiovascular structure and fibrosis, hormonal parameters and inhibition of tissue enzymes compared with selective inhibition of ACE and NEP in the spontaneously hypertensive rat (SHR).

METHODS

Male SHRs received the dual NEP/ACE inhibitor (S21402, 100 mg/kg per day), the ACE inhibitor (captopril, 50 mg/kg per day), the NEP inhibitor (SCH42495, 60 mg/kg per day) or vehicle for 2 weeks.

RESULTS

S21402 produced equivalent blood pressure lowering effects to captopril (vehicle, 220 +/- 1 mmHg; S21402, 189 +/- 2 mmHg; captopril, 187 +/- 3 mmHg), but was a more effective antihypertensive agent than SCH42495 (214 +/- 2 mmHg, P< 0.01). All treatments reduced left ventricular mass (P< 0.05) and cardiac fibrosis (P< 0.01). S21402 inhibited renal NEP and ACE (P< 0.01), SCH42495 inhibited renal NEP (P < 0.01), and captopril inhibited renal ACE (P< 0.01). Captopril and S21402 increased plasma renin activity (P< 0.05), but the rise with S21402 was attenuated compared with that caused by captopril (P< 0.01). All treatments reduced plasma aldosterone levels (P< 0.01), and NEP inhibition with SCH42495 and S21402 increased plasma atrial natriuretic peptide (ANP; P< 0.05).

CONCLUSIONS

These results indicate that selective NEP inhibition has major benefits in the regression of cardiac hypertrophy and reduction of fibrosis but has limited antihypertensive effects. The dual NEP/ACE inhibitor S21402 offered no advantage over the selective ACE inhibitor in terms of blood pressure reduction, or attenuation of cardiac hypertrophy and fibrosis, but did increase plasma ANP and blunted the reactive rise in renin with ACE inhibition. Further studies are needed to determine whether more complete blockade of the renin-angiotensin system with dual NEP/ACE inhibition results in additional benefits in terms of morbidity and mortality in cardiovascular disease.

Induction of cardiac fibrosis by aldosterone

An intracardiac aldosterone system which responds to short- and long-term physiological stimuli has been described. This cardiac generated aldosterone has possibly autocrine or paracrine actions. Normal cardiac tissue contains mineralocorticoid receptors (MR) and cardiac high affinity MR are localized in cardiac myocytes and endothelial cells. Data concerning the presence of MR in cardiac fibroblasts are, however, controversial. MR are not specific for aldosterone but they also bind glucocorticoids. Cardiac fibroblasts however contain the enzyme 11beta-hydroxy-steroid dehydrogenase II which converts these glucocorticoids to inactive metabolites. Discordant findings on the in vitro effect of aldosterone on the collagen synthesis in cardiac fibroblasts are reported and can at least partly attributed to the presence of various fibroblasts phenotypes. During chronic aldosterone infusion in uninephrectomized rats on a high-salt diet, a marked accumulation of interstitial and to a lesser extent perivascular collagen occurs in the heart in both ventricles. This cardiac fibrosis in this aldosteronism model is prevented by spironolactone. This effect of aldosterone is crucially dependent on the salt status of the rat. Indeed, rats on a restricted salt intake infused with aldosterone had no cardiac fibrosis above control levels. During the continuous infusion of aldosterone in the rat the appearance of fibrosis was delayed and starts 4 weeks after the beginning of the infusion which argues against a direct effect of aldosterone. The mechanism of aldosterone-salt induced cardiac fibrosis possibly involves angiotensin II acting through upregulated AT1 receptors and the cardiac AT1 receptor is the target for aldosterone. An accumulation of collagen in the heart has also been found in patients with adrenal adenomas and during chronic activation of the renin-angiotensin-aldosterone system such as in surgically induced unilateral renal ischemia, unilateral renal artery banding or renovascular hypertension. Spironolactone prevents aortic collagen accumulation in spontaneously hypertensive rats. In patients with stable chronic heart failure spironolactone treatment in addition to diuretics and angiotensin-converting enzyme (ACE) inhibition reduced circulating levels of procollagen type III N-terminal aminopeptide. Also, in the Randomized Aldactone Evaluation Study spironolactone coadministered with conventional therapy of ACE inhibitors, loop diuretics and digitalis in patients with symptomatic heart failure defined as NYHA classes III-IV reduces total mortality by 30%.

Inverse relation between aldosterone and venous capacitance in chronically treated congestive heart failure

The purpose of this study was to examine if there is a relation between the aldosterone escape phenomenon and venous capacitance of the upper and lower limbs in patients with long-term congestive heart failure (CHF) receiving chronic treatment with angiotensin-converting enzyme (ACE) inhibitors. The study group consisted of 16 subjects with ischemic CHF in New York Heart Association functional class II (age 59 +/-2 years, ejection fraction 24+/-4%), stabilized under a constant drug regimen comprising furosemide, captopril 50 mg 3 times daily, and digoxin for at least 3 months. Thirteen apparently healthy volunteers, aged 50+/-4 years acted as controls. Forearm and calf venous capacitances were measured simultaneously by venous occlusion plethysmography using mercury-in-silastic strain gauges. The equilibration technique was used to derive venous capacitance from the recorded pressure-volume curves. Active renin, angiotensin II, and aldosterone levels were determined on venous blood samples obtained in the supine position. Angiotensin II (p<0.05) and aldosterone (p<0.01) were statistically significantly higher in patients with CHF under long-term ACE inhibition than in controls (aldosterone escape phenomenon). In CHF, forearm venous capacitance was 2.19+/-0.18 ml/100 ml; calf venous capacitance was 2.83+/-0.27 ml/100 ml. Aldosterone significantly and inversely correlated with venous capacitance in both upper (r = -0.586; p = 0.017) and lower (r = -0.625; p = 0.01) limbs. No correlations were found between forearm or calf venous capacitance and renin or angiotensin II. In patients with heart failure chronically treated with diuretics and full ACE inhibition, venous capacitance is inversely correlated with aldosterone through the mechanism of aldosterone escape, creating the potential for further deterioration of the CHF process.

Cardiac aldosterone production and ventricular remodeling

An intracardiac production of aldosterone has been recently reported in rat. This production is increased both acutely and chronically by angiotensin II, observations suggesting that the heart contains a steroidogenic system that is regulated similarly to the adrenal one. Cardiac production of aldosterone is small compared with that of the adrenal, raising the question of its function in normal conditions. Moreover, the regulation of this synthesis in pathophysiologic states remains unknown. In an analysis of the effects of a one-month myocardial infarction (MI) on the cardiac steroidogenic system, it was observed that aldosterone-synthase mRNA and the aldosterone concentration were increased by 2- and 3.5-fold, respectively, in the noninfarcted part of the rat left ventricle. MI also induced a 1. 9-fold increase in the cardiac angiotensin II level. Losartan prevented these changes, and the MI-induced collagen deposition in noninfarcted area of the left ventricle was reduced by 1.6- and 2. 5-fold by both spironolactone and losartan treatments, respectively. Thus, these observations indicate that MI is associated with tissue-specific activation of myocardial aldosterone synthesis. This activation is mediated by cardiac angiotensin II via the angiotensin II type 1 (AT1) receptor, and the resultant increase of intracardiac aldosterone level may be involved in post-MI ventricular remodeling.

Aldosterone and mineralocorticoid receptors: orphan questions

Classically, mineralocorticoid receptors (MR) are activated by aldosterone to promote unidirectional transepithelial sodium transport. Activation of MR in nonepithelial tissues has been shown to elevate blood pressure (central nervous system; CNS) and to cause hypertrophy and fibrosis (heart). For both epithelial and nonepithelial tissues, there remain a variety of questions regarding MR which are not only unanswered but also essentially not addressed. Seven such questions include: (1) how the physiologic glucocorticoids (cortisol and corticosterone) can mimic aldosterone action in epithelial MR, but act as antagonists in the heart and AV3V region; (2) how salt facilitates the nonepithelial, pathophysiologic effects of aldosterone; (3) how aldosterone activates unprotected AV3V MR in the face of orders of magnitude higher circulating glucocorticoid concentrations; (4) how unprotected nonepithelial MR act as "always occupied" receptors in guinea pigs and other species; (5) how, when 11beta hydroxysteroid dehydrogenase type 2 is active, epithelial MR occupied by physiologic glucocorticoids appear transcriptionally inactive; (6) how aldosterone activates epithelial MR in the face of approximately 103-fold higher glucocorticoid levels, plasma binding and 11beta hydroxysteroid dehydrogenase type 2 activity notwithstanding; and (7) how aldosterone produces changes in urinary [K+] before [Na+].

beta(2)-adrenergic receptor overexpression exacerbates development of heart failure after aortic stenosis

BACKGROUND

Beta-adrenergic signaling is downregulated in the failing heart, and the significance of such change remains unclear.

METHODS AND RESULTS

To address the role of beta-adrenergic dysfunction in heart failure (HF), aortic stenosis (AS) was induced in wild-type (WT) and transgenic (TG) mice with cardiac targeted overexpression of beta(2)-adrenergic receptors (ARs), and animals were studied 9 weeks later. The extents of increase in systolic arterial pressure (P<0.01 versus controls), left ventricular (LV) hypertrophy (TG, 94+/-6 to 175+/-7 mg; WT, 110+/-6 to 168+/-10 mg; both P<0.01), and expression of ANP mRNA were similar between TG and WT mice with AS. TG mice had higher incidences of premature death and critical illness due to heart failure (75% versus 23%), pleural effusion (81% versus 45%), and left atrial thrombosis (81% versus 36%, all P<0.05). A more extensive focal fibrosis was found in the hypertrophied LV of TG mice (P<0.05). These findings indicate a more severe LV dysfunction in TG mice. In sham-operated mice, LV dP/dt(max) and heart rate were markedly higher in TG than WT mice (both P<0.01). dP/dt(max) was lower in both AS groups than in sham-operated controls, and this tended to be more pronounced in TG than WT mice (-32+/-5% versus -16+/-6%, P=0.059), although dP/dt(max) remained higher in TG than WT groups (P<0.05).

CONCLUSIONS

Elevated cardiac beta-adrenergic activity by beta(2)-AR overexpression leads to functional deterioration after pressure overload.

Lack of association between polymorphisms of eight candidate genes and idiopathic dilated cardiomyopathy: the CARDIGENE study

OBJECTIVES

The study investigated the potential role of eight candidate genes in the susceptibility to idiopathic dilated cardiomyopathy (IDC).

BACKGROUND

Idiopathic dilated cardiomyopathy has a familial origin in 20% to 25% of cases, and several genetic loci have been identified in rare monogenic forms of the disease. These findings led to the hypothesis that genetic factors might also be involved in sporadic forms of the disease. In complex diseases that do not exhibit a clear pattern of familial aggregation, the candidate gene approach is a strategy widely used to identify susceptibility genes. All genes coding for proteins involved in biochemical or physiological abnormalities of cardiac function are potential candidates for IDC.

METHODS

We studied 433 patients with IDC and 401 gender- and age-matched controls. Polymorphisms investigated were the I/D polymorphism of the angiotensin I-converting enzyme (ACE) gene, the T174M and M235T polymorphisms of the angiotensinogen (AGT) gene, the A-153G and A+39C polymorphisms of the angiotensin-II type 1 receptor (AGTR1) gene, the T-344C polymorphism of the aldosterone synthase (CYP11B2) gene, the G-308A polymorphism of the tumor necrosis factor-alpha (TNF) gene, the R25P polymorphism of the transforming growth factor beta1 (TGFB1) gene, the G+11/in23T polymorphism of the endothelial nitric oxide synthase (NOS3) gene and the C-1563T polymorphism of the brain natriuretic peptide (BNP) gene.

RESULTS

None of the polymorphisms were significantly associated with the risk or the severity of the disease.

CONCLUSIONS

We did not find evidence for an involvement of any of the 10 investigated polymorphisms in the susceptibility to IDC.

Joint effects of an aldosterone synthase (CYP11B2) gene polymorphism and classic risk factors on risk of myocardial infarction

BACKGROUND

The -344C allele of a 2-allele (C or T) polymorphism in the promoter of the gene encoding aldosterone synthase (CYP11B2) is associated with increased left ventricular size and mass and with decreased baroreflex sensitivity, known risk factors for morbidity and mortality associated with myocardial infarction (MI). We hypothesized that this polymorphism was a risk factor for MI.

METHODS AND RESULTS

We used a nested case-control design to investigate the relationships between this polymorphism and the risk of nonfatal MI in 141 cases and 270 matched controls from the Helsinki Heart Study, a coronary primary prevention trial in dyslipidemic, middle-aged men. There was a nonsignificant trend of increasing risk of MI with number of copies of the -344C allele. However, this allele was associated in a gene dosage-dependent manner with markedly increased MI risk conferred by classic risk factors. Whereas smoking conferred a relative risk of MI of 2.50 (P=0.0001) compared with nonsmokers in the entire study population, the relative risk increased to 4.67 in -344CC homozygous smokers (relative to nonsmokers with the same genotype, P=0.003) and decreased to 1.09 in -344TT homozygotes relative to nonsmokers with this genotype. Similar joint effects were noted with genotype and decreased HDL cholesterol level as combined risk factors.

CONCLUSIONS

Smoking and dyslipidemia are more potent risk factors for nonfatal MI in males who have the -344C allele of CYP11B2.

Epidermal growth factor as a local mediator of the neurotrophic action of vitamin B(12) (cobalamin) in the rat central nervous system

We have recently demonstrated that the myelinolytic lesions in the spinal cord (SC) of rats made deficient in vitamin B(12) (cobalamin) (Cbl) through total gastrectomy (TG) are tumor necrosis factor-alpha (TNF-alpha)-mediated. We investigate whether or not permanent Cbl deficiency, induced in the rat either through TG or by chronic feeding of a Cbl-deficient diet, might modify the levels of three physiological neurotrophic factors-epidermal growth factor (EGF), vasoactive intestinal peptide (VIP), and somatostatin (SS)-in the cerebrospinal fluid (CSF) of these rats. We also investigated the ability of the central nervous system (CNS) in these Cbl-deficient rats to synthesize EGF mRNA and of the SC to take up labeled Cbl in vivo. Cbl-deficient rats, however the vitamin deficiency is induced, show a selective decrease in EGF CSF levels and an absence of EGF mRNA in neurons and glia in various CNS areas. In contrast, radiolabeled Cbl is almost exclusively taken up by the SC white matter, but to a much higher degree in totally gastrectomized (TGX) rats. Chronic administration of Cbl to TGX rats restores to normal both the EGF CSF level and EGF mRNA expression in the various CNS areas examined. This in vivo study presents the first evidence that the neurotrophic action of Cbl in the CNS of TGX rats is mediated by stimulation of the EGF synthesis in the CNS itself. It thus appears that Cbl inversely regulates the expression of EGF and TNF-alpha genes in the CNS of TGX rats.

Recent insight into therapy of congestive heart failure: focus on ACE inhibition and angiotensin-II antagonism

One possible intervention to interrupt the deleterious effects of the renin-angiotensin system is suppression of angiotensin II (Ang II) formation by inhibition of angiotensin-converting enzyme (ACE). However, ACE inhibition incompletely suppresses Ang II formation and also leads to accumulation of bradykinin. Angiotensin II type 1 (AT1) receptors are believed to promote the known deleterious effects of Ang II. Therefore, AT1 receptor antagonists have been recently introduced into therapy for hypertension and congestive heart failure (CHF). Although there are significant differences between the effects of AT1 receptor antagonists and ACE inhibitors including the unopposed stimulation of angiotensin II type 2 (AT2) receptors by AT1 receptor antagonists, the discussion of whether ACE inhibitors, AT1 receptor antagonists or the combination of both are superior in the pharmacotherapy of CHF is still largely theoretical. Accordingly, AT1 receptor antagonists are still investigational. Angiotensin-converting enzyme inhibitors remain first line therapy in patients with CHF due to systolic dysfunction. However, in patients not able to tolerate ACE inhibitor induced side effects, in particular cough, AT1 receptor antagonism is a good alternative. In clinical practice, emphasis should be placed on increasing the utilization of ACE inhibitors, as more than 50% of patients with CHF do not receive ACE inhibitors. In addition, the majority of those on ACE inhibitors receive doses lower than the dosage used in the large clinical trials. Although not yet completely proved, it is likely that high doses of ACE inhibition are superior to low doses with respect to prognosis and symptoms.

Angiotensin AT1 receptor subtype as a cardiac target of aldosterone: role in aldosterone-salt-induced fibrosis

This study tests the hypothesis that aldosterone induces cardiac fibrosis through an increase of cardiac angiotensin II (Ang II) AT1 receptor levels, thereby potentiating the fibrotic effect of Ang II by determining the effects of spironolactone and losartan on cardiac fibrosis, AT1 density, and gene expression in aldosterone-salt-treated rats. Fibrosis was quantified by slot blots of collagen I and III mRNA levels and videomorphometry of Sirius red-stained collagen. AT1 receptor density was determined by (125I-Sar1-Ile8)-Ang II competition binding, and AT1 mRNA levels were analyzed by quantitative reverse transcriptase polymerase chain reaction. One month of aldosterone-salt treatment induced a decrease in plasma Ang II and an increase in blood pressure, left ventricular hypertrophy, and ventricular fibrosis. Spironolactone (20 mg/kg per day) and losartan spironolactone (10 mg/kg per day) had no effect on the first 3 parameters. Losartan was as effective as spironolactone in preventing ventricular collagen mRNA increase and fibrosis. Ventricular density of AT1 receptors increased 2-fold and was accompanied by a 3-fold increase in the corresponding mRNA in aldosterone-salt compared with sham-operated rats. Both spironolactone and losartan prevented the elevation of ventricular AT1 density and that of right ventricular AT1 mRNA levels. These results demonstrate that the mechanism by which aldosterone-salt induces cardiac fibrosis involves Ang II acting through AT1 receptors. They also suggest that the cardiac AT1 receptor is a target for aldosterone.

Aldosterone synthase (CYP11B2) polymorphisms and cardiovascular function

In addition to regulating renal sodium resorption and, thus, intravascular volume, aldosterone may have direct effects on the cardiovascular system. We previously identified a polymorphism (-344C/T) in the promoter of the aldosterone synthase (CYP11B2) gene that affects binding of the SF-1 transcription factor and thus might influence gene expression. We found that, whereas this polymorphism has inconsistent associations with levels of aldosterone secretion and blood pressure, the -344C allele is strongly associated with increased left ventricular size and decreased baroreflex sensitivity in healthy individuals. These physiological parameters are cardiovascular risk factors. Indeed, preliminary studies suggest that the -344C allele is also associated with increased risk of myocardial infarction in high risk dyslipidemic males.

Genetic polymorphism of CYP11B2 gene and hypertension in Japanese

Low-renin hypertension is characterized by a high ratio of aldosterone to plasma renin activity (ALD/PRA), which may suggest inappropriately increased aldosterone biosynthesis. The genes for the enzymes involved in aldosterone synthesis may contribute to low-renin hypertension. We investigated the associations between genetic variations of CYP11B2 (aldosterone synthase) T(-344)C and hypertension in 482 Japanese subjects. Subjects older than 50 years with a blood pressure <140/85 mm Hg were considered normotensive (n=227 subjects), and subjects younger than 65 years old with a BP >160/95 mm Hg were considered hypertensive (n=255 subjects). The frequency of the TC+CC genotypes in the normotensive group was significantly lower than in the hypertensive group. Logistic analysis on 482 subjects revealed that body mass index, gender, and the genotype of CYP11B2 T(-344)C were significantly associated with hypertension. ALD and PRA were assessed in 97 subjects with hypertension, and the TC+CC genotypes were significantly associated with higher ALD/PRA. Sixty-five subjects with hypertension were assessed by 24-hour ambulatory blood pressure monitoring, and the frequency of nondippers (a difference in mean blood pressure of <10% between the daytime [6 AM to 9 PM] and nighttime [9 PM to 6 AM] hours) was significantly higher in subjects with the TC+CC (hetero+homo mutation) genotype than in subjects with the TT (wild-type) genotype. Echocardiographic assessment (n=136) revealed that the ratio of left ventricular end-diastolic dimension to height tended to be higher in subjects with the TC+CC genotype than in subjects with the TT genotype. The present study suggests that the (-344)C allele of the CYP11B2 gene may be a genetic marker for low-renin hypertension in Japanese.

Molecular mechanisms of myocardial remodeling

"Remodeling" implies changes that result in rearrangement of normally existing structures. This review focuses only on permanent modifications in relation to clinical dysfunction in cardiac remodeling (CR) secondary to myocardial infarction (MI) and/or arterial hypertension and includes a special section on the senescent heart, since CR is mainly a disease of the elderly. From a biological point of view, CR is determined by 1 ) the general process of adaptation which allows both the myocyte and the collagen network to adapt to new working conditions; 2) ventricular fibrosis, i.e., increased collagen concentration, which is multifactorial and caused by senescence, ischemia, various hormones, and/or inflammatory processes; 3) cell death, a parameter linked to fibrosis, which is usually due to necrosis and apoptosis and occurs in nearly all models of CR. The process of adaptation is associated with various changes in genetic expression, including a general activation that causes hypertrophy, isogenic shifts which result in the appearance of a slow isomyosin, and a new Na+-K+-ATPase with a low affinity for sodium, reactivation of genes encoding for atrial natriuretic factor and the renin-angiotensin system, and a diminished concentration of sarcoplasmic reticulum Ca2+-ATPase, beta-adrenergic receptors, and the potassium channel responsible for transient outward current. From a clinical point of view, fibrosis is for the moment a major marker for cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, and the propensity for reentry arrhythmias. In addition, systolic dysfunction is facilitated by slowing of the calcium transient and the downregulation of the entire adrenergic system. Modifications of intracellular calcium movements are the main determinants of the triggered activity and automaticity that cause arrhythmias and alterations in relaxation.

Salt induces myocardial and renal fibrosis in normotensive and hypertensive rats

BACKGROUND

The detrimental effects of high dietary salt intake may not only involve effects on blood pressure and organ hypertrophy but also lead to tissue fibrosis independently of these factors.

METHODS AND RESULTS

The effect of a normal (1%) or high (8%) sodium chloride diet on myocardial and renal fibrosis was assessed by quantitative histomorphometry in spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto rats (WKYs). The effect of salt on transforming growth factor-beta1 (TGF-beta1) gene expression was assessed by Northern blot hybridization. A high-salt diet from 8 to 16 weeks of age resulted in increased blood pressure and left ventricular and renal hypertrophy in both WKYs and SHRs. Marked interstitial fibrosis was demonstrated in the left ventricle (LV), glomeruli, and renal tubules and in intramyocardial arteries and arterioles but not in the right ventricle. The collagen volume fraction increased significantly after high-salt diet in the LV, intramyocardial arteries and arterioles, glomeruli, and peritubular areas in both WKYs and SHRs. In the kidneys, glomerular and peritubular type IV collagen was also increased. There was overexpression of TGF-beta1 mRNA in the LV and kidneys in both rat strains after a high-salt diet (all P<0.001).

CONCLUSIONS

High dietary salt led to widespread fibrosis and increased TGF-beta1 in the heart and kidney in normotensive and hypertensive rats. These results suggest a specific effect of dietary salt on fibrosis, possibly via TGF-beta1-dependent pathways, and further suggest that excessive salt intake may be an important direct pathogenic factor for cardiovascular disease.

Inhibition of tissue repair by spironolactone: role of mineralocorticoids in fibrous tissue formation

Mineralocorticoids have been implicated in promoting fibrous tissue formation in various organs. In the present study, we sought to address the potential contribution of mineralocorticoids to fibrous tissue formation using a skin pouch model which has proved valuable for the analysis of inflammatory and wound healing responses. Skin pouches were induced in rats by administration of a phorbol ester, croton oil (0.5 ml of a 1% solution). After 2 weeks, rats were killed and intact pouch tissue collected. Pouch weights of control and aldosterone-treated (0.75 microg/h via osmotic minipump) rats were similar (3.33 +/- 0.44 g vs. 3.70 +/- 0.28 g respectively). However, pouch weights were reduced by more than 50% in spironolactone-treated (25 mg/day powdered in food) animals (1.62 +/- 0.22 g and 1.27 +/- 0.23 g respectively in aldosterone and spironolactone alone groups). To ascertain the effects of different treatments on collagen accumulation, hydroxyproline concentration was measured. Compared with controls, hydroxyproline concentration was significantly reduced following spironolactone treatment (17.1 +/- 0.08 vs. 7.5 +/- 2.0 microg/mg dry wt, respectively, p < 0.01). This response to spironolactone was negated by coadministration of aldosterone (hydroxyproline concentration was 18.6 +/- 2.1 microg/mg dry wt). Following bilateral adrenalectomy, spironolactone reduced pouch weight and hydroxyproline concentration, which was not the case for adrenalectomy alone. Two week aldosterone administration in uninephrectomized rats on high salt diet was deemed ineffective in modulating pouch development (pouch wet wts were 3.48 +/- 0.4 g vs. 3.00 +/- 0.19 g in controls and aldosterone-treated rats, respectively). Mineralocorticoid receptor expression in pouch tissue was demonstrated by RT/PCR. Furthermore, NADP+-dependent 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) activity was detected in pouch tissue, together with lower levels of NAD+-dependent 11beta-HSD2. Spironolactone (p < 0.05) significantly reduced 11beta-HSD1 activity compared with controls. Thus, fibrous tissue possesses requisite components of MC action, and antagonism of mineralocorticoid receptors by spironolactone attenuates its formation. Pouch formation is under the influence of circulating MC and, we would like to propose, is also mediated through corticosteroids generated de novo at the site of tissue repair.

In vivo left ventricular function and collagen expression in aldosterone/salt-induced hypertension

Cardiac fibrosis is linked to aldosterone-induced hypertension, but the effects on in vivo left ventricular (LV) function are not established. We studied the relations between in vivo LV function and aldosterone/salt cardiac fibrosis. Adult guinea pigs (GPs) were treated for 3 months with an aldosterone infusion and high-salt diet. This treatment induced arterial hypertension (+35%) and moderate LV hypertrophy (LVH; +60%) without right ventricular (RV) hypertrophy. Echo-Doppler LV assessment demonstrated unaltered cardiac output, stroke volume, or LV relaxation. Type I collagen messenger RNA (mRNA) was significantly increased in both ventricles (LV, +48%; RV, +77%) and accompanied by a significant increase in total collagen deposition (LV, from 0.52% in controls to 4.4% in treated GPs; RV, from 0.82 to 5.5% in treated GPs). Plasma norepinephrine levels increased 2.6-fold (p < 0.01) and correlated with the increase in collagen deposition in both ventricles. Collagen content was not correlated with hypertension or LVH. We conclude that aldosterone administration induces cardiac collagen accumulation and a sympathetic stimulation, which might preserve systolic and diastolic function.

Aldosterone action: fact, failure and the future

1. It is now 45 years since aldosterone was isolated and 25 years since its genomic action, via mineralocorticoid receptors (MR), was first described. 2. Although the classic physiological role of aldosterone is to promote unidirectional transepithelial sodium transport, our ignorance of the mechanisms involved remains profound. 3. Unanswered questions include: (i) the physiological significance of the equivalent, high affinity of MR for aldosterone, progesterone, corticosterone and cortisol; (ii) the protein(s) induced as a direct transcriptional response to aldosterone; (iii) the physiological roles of MR in non-epithelial tissues where aldosterone, in concert with salt loading, produces direct pathophysiological effects; (iv) how aldosterone occupies epithelial MR, despite the 100-fold 'advantage' it enjoys over cortisol/corticosterone due to transcortin binding/11 beta-hydroxysteroid dehydrogenase activity, as plasma glucocorticoid levels are approximately 2000-fold higher; and (v) how epithelial MR, normally overwhelmingly occupied by glucocorticoids, are not transcriptionally active under normal circumstances in vivo, in contrast with transfection systems or the syndrome of apparent mineralocorticoid excess. 4. Possible avenues for consideration of the last two of these questions are briefly proposed.

Relations between cardiac and vascular structure in patients with primary and secondary hypertension

BACKGROUND

Data on cardiac and vascular structure in secondary hypertension are generally scarce, and no data on the interrelations between cardiac mass and structural characteristics of the vessel wall, both in large and in small resistance arteries, are presently available.

OBJECTIVES

The aim of this study was to investigate the relation between structural changes in subcutaneous small arteries, left ventricular mass and wall thickness of the common carotid artery in patients with primary and secondary hypertension.

METHODS

Seventy-four subjects were included in the study: 11 patients with pheochromocytoma, 14 with primary aldosteronism (PA), 19 with renovascular hypertension (RVH), 18 with essential hypertension (EH) and 12 normotensive (NT) control subjects. All subjects were submitted to a biopsy of subcutaneous fat. Morphologic characteristics of subcutaneous small resistance arteries (relaxed diameter <300 microm) were directly evaluated using a micromyographic technique. All subjects were submitted to calculation of left ventricular mass index (LVMI) and common carotid artery intima-media thickness (CCIMT), using ultrasound technique.

RESULTS

The correlation coefficients between the media to lumen ratio in subcutaneous small arteries (M/L) and LVMI or between M/L and CCIMT were closer in RVH than in pheochromocytoma, EH or NT; in PA the correlation coefficients were slightly less close than those in RVH. An excess prevalence of carotid plaques in RVH was observed.

CONCLUSIONS

A close relation between small resistance artery morphology and cardiac or carotid artery structure may be observed in those hypertensive patients in whom the renin-angiotensin-aldosterone system is activated. In constrast, in NT, EH and pheochromocytoma no significant correlation between M/L and LVMI or CCIMT was observed.

Regulation of angiotensin II receptor expression by nitric oxide in rat adrenal gland

We recently reported that administration of Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) production, activates the vascular and cardiac renin-angiotensin systems and causes vascular thickening and myocardial hypertrophy in rats with perivascular and myocardial fibrosis. It has been reported that aldosterone may contribute to the development of cardiac fibrosis, but it is not known whether inhibition of NO synthesis affects angiotensin II (Ang II) receptor gene expression and aldosterone secretion. The aim of this study was to investigate the effect of NO inhibition on the expression of Ang II receptors in the adrenal gland and on aldosterone secretion in rats. Wistar King A rats received normal water, L-NAME alone (1 mg/mL in the drinking water), or L-NAME and the alpha1-adrenergic receptor blocker bunazosin (0.1 mg/mL in the drinking water) for 1 week. After 1 week of treatment with L-NAME, systolic blood pressure, plasma aldosterone concentration (PAC), and mRNA level and number of Ang II type 1 receptor (AT1-R) were increased. Plasma renin activity, serum angiotensin-converting enzyme activity, and the number of AT2-R were unchanged. Although addition of bunazosin to L-NAME restored systolic blood pressure to the control level, PAC and AT1-R numbers remained significantly higher than those of control level. These results suggest that the increased AT1-R number and PAC induced by the inhibition of NO synthesis were independent of blood pressure and systemic renin-angiotensin system. Therefore, hypertension and myocardial fibrosis induced by NO blockade may be due in part to an elevation of PAC caused by increased AT1-R in the adrenal gland.

Aldosterone synthase (CYP11B2) polymorphisms and cardiovascular function

In addition to regulating renal sodium resorption and, thus, intravascular volume, aldosterone may have direct effects on the cardiovascular system. We previously identified a polymorphism (-344C/T) in the promoter of the aldosterone synthase (CYP11B2) gene that affects binding of the SF-1 transcription factor and thus might influence gene expression. We found that, whereas this polymorphism has inconsistent associations with levels of aldosterone secretion and blood pressure, the -344C allele is strongly associated with increased left ventricular size and decreased baroreflex sensitivity in healthy individuals. These physiological parameters are cardiovascular risk factors. Indeed, preliminary studies suggest that the -344C allele is also associated with increased risk of myocardial infarction in high risk dyslipidemic males.

Decreased blood pressure variability at rest in patients with primary aldosteronism

Increased blood pressure (BP) variability in essential hypertension (EH) is attributed in part to a reduction in baroreflex sensitivity. We previously showed that baroreflex sensitivity is not reduced in hypertension associated with primary aldosteronism (PA) compared with normotensive (NT) subjects. This study examined whether the preservation of baroreflex function in patients with PA would prevent an increase in BP variability. The beat-to-beat BP (measured with Finapres) and RR interval (from electrocardiograms) were monitored for 10 min in the supine and standing positions in 34 patients with PA, 60 patients with EH, and 45 NT subjects. Recordings were also performed during mild ergometer exercise in 7 PA patients, 8 EH patients, and 9 NT subjects. Blood pressure variability was assessed by both standard deviation (SD) and coefficient of variation (CV). Baroreflex sensitivity (BRS) was assessed by the closed-loop gain between systolic BP and RR interval variability. The SD and the CV of systolic BP (SBP) and the CV of diastolic (DBP) BP were significantly smaller in patients with PA than in patients with EH in both supine and standing positions. The SD of SBP and DBP were similar in patients with PA and NT subjects, although the CV were significantly smaller in patients with PA. The BRS was inversely correlated with both the SD and CV for SBP in the supine (r = -0.397 and -0.440, P < .05, respectively) and standing (r = -0.457 and -0.412, P < .05, respectively) positions in patients with PA. Exercise reduced the BRS in all groups (70%, 26%, and 64% for PA, EH, and NT, respectively, P < .01). Blood pressure variability did not change significantly during exercise, compared with rest, in the PA and NT groups but was decreased (P < .05) in the patients with EH. In conclusion, primary aldosteronism is characterized by decreased supine and standing BP variability, which is due in part to the preservation of baroreflex function. Our data further showed that BP variability is minimized by nonbaroreflex mechanisms during mild exercise.