50th Anniversary of Aldosterone

Jonathan S. Williams and Gordon H. Williams

Endocrinology, Hypertension and Diabetes Division, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts 02115

Address all correspondence and requests for reprints to: Gordon H. Williams, M.D., Endocrinology, Hypertension and Diabetes Division, Brigham and Women’s Hospital, 221 Longwood Avenue, Boston, Massachusetts 02115. E-mail: gwilliams{at}partners.org.


    Introduction
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
This year marks the 50th anniversary of Simpson and Tait’s isolation of electrocortin (aldosterone) (Fig. 1Go). Five decades of research have yielded extensive insight into the biological actions mediated through this once elusive molecule, in particular, areas of sodium and potassium metabolism and the kidney. The history of discovery surrounding the mechanisms of regulation and action of aldosterone in the 1960s and 1970s provides a unique view of the birth of molecular biology and its consequent impact on the field of genomic research in the 1980s, 1990s, and the 21st century. Interestingly, recent areas of study have focused on the nongenomic effects of aldosterone and its involvement in inflammation and fibrosis in cardiovascular diseases. This has taken what might have at one time been considered a steroid hormone with a narrow pathological consequence into the realm of influencing widely prevalent diseases such as nephropathy, cardiomyopathy, and vasculopathy.



View larger version (151K):
[in this window]
[in a new window]
 
Figure 1. Contributors of the original manuscript describing the isolation of aldosterone. Left to right, Prof. Tadeus Reichstein, Dr. Sylvia A. Simpson, Dr. James F. Tait, Prof. Albert Wettstein, Dr. Robert Neher, and Dr. Joseph von Euw. (Reproduced with permission from J Steroid Biochem, vol 3. ©Elsevier Science, 1972.)

 
Here, we provide a historic review of the discovery of aldosterone, emphasizing its widely expanding involvement in human disease. We begin describing the early years of aldosterone discovery including mention of its involvement in fibrosis by Selye. Next, we explore how molecular biology and genetics yield novel mechanisms of action and regulation. Finally, we revisit the area of nonclassical effects and the expanding involvement of aldosterone in common cardiovascular diseases.


    The early years
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
The earliest recorded mention of the adrenal gland is Bartolomeo Eustacchio’s 1563 copper-etched depiction of "glandulae Renibus incumentes" (1). Several centuries later, Thomas Addison (1849) published his description of a lethal clinical syndrome resulting from destruction of the adrenal glands (2), thereby providing the stimulus for subsequent modern physiological investigations of the adrenal cortex. During the early part of the 20th century, focus turned to the role the adrenal cortex played in carbohydrate metabolism. By the late 1930s, most of the glucocorticoids produced by the adrenal cortex had been isolated and structures characterized. Whereas the discovery of glucocorticoids progressed relatively rapidly, bioassays developed to characterize adrenal cortical extracts proved remarkably insensitive for mineralocorticoid activity despite evidence that unfractionated extracts participated in Na+ and K+ metabolism. Additionally, controversy emerged over whether biologically important mineralocorticoids existed, with a majority of researchers maintaining that glucocorticoids were the major source of mineralocorticoid activity. For almost 20 yr these obstacles hampered attempts to crystallize what had been termed "electrocortin." Nevertheless, Kuizenga and Cartland (3) (1936-1939) had reported adrenocortical preparations containing "potent mineralocorticoid activity" in the amorphous unfractionated portion. Therefore, investigators—including Nobel Laureate Tadeus Reichstein and his colleagues in Basel, Switzerland; Simpson and Tait in London, United Kingdom; and Kendall and Mason in the United States—remained convinced that electrocortin was a clinically relevant hormone and could be isolated.

By 1948, Deane et al. (4), through anatomical and histological examination, determined that electrocortin was secreted from the zona glomerulosa of the adrenal cortex under provocation from a low sodium diet or potassium loading, providing early evidence of regulation. However, it wasn’t until 1953, when Simpson and Tait developed a landmark bioassay with high sensitivity for mineralocorticoid activity, that crystallization of 21 mg electrocortin from 500 kg beef adrenal glands was announced (5). Within months, groups in America and Basel confirmed these findings, and by 1954 the structure of aldosterone was reported (6). Highly specific and sensitive bioassays, such as the double isotope derivative assay by Kliman and Peterson (7), introduced a flood of investigations into the regulation and mechanisms of action of aldosterone in subsequent years. It was only 2 yr later that Conn (8) described hyperaldosteronism arising from an adrenal tumor, leading to the identification of the syndrome of hypertension and hypokalemia that bears his name. In 1956, Giroud et al. (9) reported production of aldosterone by the zona glomerulosa. Ganong and Mulrow established the limited role ACTH played in aldosterone regulation in 1962 with experiments in hypophysectomized higher animals, determining that although ACTH contributed to aldosterone secretion it was not a major stimulus in humans (10, 11).

Deane and Mason (12) in 1951 shed light on a major stimulus for electrocortin secretion when they hypothesized that the renin-angiotensin system directly stimulated aldosterone secretion and that this effect could be augmented with dietary sodium restriction. Paige and Helmer (13) a dozen years earlier had isolated a pressor agent, which they initially called angiotonin, also known as hypertenisin, and eventually angiotensin. Skeggs et al. (14) identified two forms of angiotensin: a decapeptide called angiotensin I and an octapeptide, angiotensin II. In 1958, Gross (15) suggested that the kidney secreted an aldosterone-stimulating factor largely responsible for aldosterone secretion. Three years later, Mulrow and Ganong (16) documented that angiotensin II stimulates aldosterone secretion. The other major stimulus for aldosterone secretion, potassium, was described by Giroud and colleagues (Refs. 17 and 18 ; Fig. 2Go). Sodium, calcium, magnesium, and hydrogen along with ACTH were found to play secondary roles in regulating aldosterone secretion.



View larger version (16K):
[in this window]
[in a new window]
 
Figure 2. Feedback loops regulating aldosterone secretion. (Reproduced with permission from G. Williams and R. G. Dluhy: Disorders of the Adrenal Cortex, McGraw-Hill, New York, 2001.)

 
Since the identification of aldosterone, it had been assumed that it promoted the excretion of potassium and retention of sodium, thereby influencing extracellular volume homeostasis and blood pressure. However, it wasn’t until 1958 when Leaf et al. (19) developed an isolated monolayer tissue system from toad bladder that a suitable model for the study of mineralocorticoid activity had been established. This enabled classic endocrinological studies of sodium and potassium transport in response to aldosterone and its antagonists.

By the late 1960s, the biosynthetic pathway from cholesterol to pregnenolone to progesterone to 11-deoxycorticosterone to corticosterone and finally 18-hydroxycorticosterone to aldosterone had been established with little controversy. Although all zones of the adrenal cortex contained most of these enzymes, in humans only the zona glomerulosa was found to demonstrate 18-hydroxycorticosterone activity, thus establishing a pivotal regulatory role for the last step in aldosterone synthesis.

Aldosterone antagonists.

Amphenone represents the first agent demonstrated to blunt mineralocorticoid action by inhibiting aldosterone biosynthesis (20). The ability of amphenone to alter urinary sodium excretion enabled study of secondary hyperaldosteronism in congestive heart failure and cirrhosis. Later, 17-spirolactone steroids or spirolactones were developed to antagonize aldosterone and the activity of other sodium-retaining hormones at the renal distal tubule. In the late 1950s, this lead to the development of spironolactone as a potassium-sparing diuretic in the treatment of volume overloaded states and primary hyperaldosteronism.

Genomic mechanisms of aldosterone activity.

Classic agonist/antagonist experiments in the toad bladder model in the 1960s revealed that a significant lag (30–90 min) existed between the time of aldosterone administration and alterations in Na/K flux (19, 22). Around this time, endocrinology entered the field of molecular biology, revealing the genomic actions of glucocorticoid-mediated, and eventually aldosterone-mediated, induction of RNA with subsequent protein synthesis (23). The delayed response in activity represented binding to cytosolic steroid receptors, translocation to the nucleus, interaction with DNA, and finally genomic transcription and translation of effector proteins.

Clinical significance of aldosteronism.

Since its structural identification in 1954, a great deal of information has accumulated about the contribution of aldosterone to several medically important diseases. In 1937, Steigler and Reichstein (24) synthesized desoxycorticosterone acetate, intending it to possess potent glucocorticoid activity. However, it was found to have only very weak glucocorticoid activity but surprisingly caused a syndrome of hypokalemia and hypertension. In 1955, Conn (8) described a clinical syndrome of hypertension with hypokalemia resulting from an autonomous aldosterone-secreting tumor of the adrenal cortex. These pathophysiological observations helped clarify the renin-aldosterone interaction. Two categories of hyperaldosteronism emerged: 1) primary hyperaldosteronism, conditions with suppressed plasma renin activity (PRA), and 2) secondary hyperaldosteronism, those diseases with elevated PRA (25). Therefore, increased aldosterone secretion was determined to contribute to some forms of arterial hypertension, disorders of sodium retention and edema, and syndromes of potassium wasting.

The contribution of aldosterone to hypertension, aside from overt primary hyperaldosteronism, remained obscure during this period although several groups, including Conn’s (25), felt that aldosterone activity/sensitivity either directly or indirectly contributed to a substantial portion of essential hypertension. In the late 1950s, increased aldosterone in edematous states was described (26). Rather than a primary event, the hyperaldosteronism was assumed to be secondary. The hyperaldosteronism was postulated to contribute to the sodium avid state of these edematous disorders (e.g. congestive heart failure). At the time, investigators assumed that the maladaptive response of aldosterone in these volume-overloaded states was secondary to the need to maintain intravascular volume. Curiously, edema was not a feature of primary hyperaldosteronism in which patients seem to "escape" the salt-retaining effects of aldosterone. Although several hypotheses have been proposed for the mechanism of escape, it still remains elusive (27) and it is likely that several mechanisms are involved.

Extrarenal effects of aldosterone: early description of cardiovascular remodeling.

In 1946, Selye (28) reported on "a state of chronic stress" that developed in rats fed deoxycorticosterone acetate, an intermediate in the biosynthetic pathway of aldosterone with mineralocorticoid activity. This state resulted in an "adaptation syndrome," leading to formation of perivascular granulomas visible in the coronary, renal, and systemic vasculature. A pathological consequence was the development of high blood pressure (28) and histological evidence of myocardial necrosis and fibrosis (29). Other investigators confirmed that administration of glucocorticoids reduced granuloma formation whereas mineralocorticoids induced inflammation and fibrosis in animal models in a yin/yang relationship (30, 31). Unfortunately, these observations remained essentially forgotten for 40 yr but clearly represent the groundwork on which future investigation of nonepithelial effects of aldosterone were formed.


    The middle years: 1970–1990
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
Regulation of aldosterone secretion.

The announcements of a sensitive RIA for plasma aldosterone (32) and a preparation of dispersed zona glomerulosa cells (33) were published in 1970. These two events marked a turning point in aldosterone physiological research, providing the necessary tools to perform detailed investigations of aldosterone biosynthesis and regulation. In the 1960s, theories of aldosterone formation divided biosynthesis into an "early pathway" preceding the production of pregnenolone and a "late pathway" in which corticosterone is converted to aldosterone (34). In the 1970s and 1980s, several inhibitors and stimulants of early-phase products were described, reinforcing the multifactorial complexity of aldosterone regulation; however, no substance had been reported to directly modify the late pathway enzyme, aldosterone synthase. Identified inhibitors of aldosterone biosynthesis included atrial natriuretic peptides, adrenal medullary inhibitor, somatostatin, dopamine, ouabain, androgens, glucocorticoids, and select prostaglandins. Direct simulators included angiotensin II and III, ACTH, {alpha}-MSH, prolactin, vasopressin, potassium, hydrogen, ammonium, serotonin, histamine, and select prostaglandins.

Perhaps one of the most intriguing aspects of the regulation of aldosterone biosynthesis are the roles of dietary sodium and, to a lesser extent, dietary potassium. In the early 1970s there was an extensive debate on whether sodium intake had an effect independent of its modulation of angiotensin II levels (30, 35, 36, 37). Several investigators as early as 1956 reported that angiotensin II-induced aldosterone secretion was modified by the level of sodium intake (38). A high salt diet blunted the aldosterone response to low-dose angiotensin II infusion as compared with low sodium diet in humans, but not in all experimental animal models. Alterations in aldosterone synthesis and secretion in response to dietary sodium maneuvers were considered to represent a tight link between aldosterone and the renin-angiotensin system activity. Additionally, short- and long-term effects of sodium depletion on aldosterone sensitivity could be replicated by exogenous administration of renin or angiotensin II, whereas in a bilaterally nephrectomized model aldosterone increase was not present. Finally, blockade of renin-angiotensin system activity abolished the aldosterone stimulatory effect of a low sodium diet (39, 40). However, the studies by Tait and Tait and their colleagues (33) and Williams et al. (41) clearly documented an independent role for sodium intake both in experimental animals and humans. Their results documented that sodium restriction and potassium loading enhanced the activity of the late pathway (aldosterone synthase) of aldosterone biosynthesis with consequent changes in the structure of the glomerulosa zone of the adrenal cortex and the acute response of aldosterone to angiotensin II and potassium administration. Hollenberg and Williams also documented that sodium intake had a reciprocal effect on the vascular (particularly renal vascular) response to angiotensin II but not to other pressors (31, 42). They proposed that effect of sodium intake on these two systems was designed to fine tune the organism’s response to sodium challenges to more precisely regulate sodium/volume homeostasis. Before these studies, it was generally assumed that the renin-angiotensin-aldosterone system was primarily involved in blood pressure regulation. With this new evidence, it was likely that its primary role was volume regulation. These findings in normal subjects provided the critical underpinnings for subsequent theories in human hypertension.

The discovery of secondary messenger systems removed the former "black box" of signal transduction at the adrenal cortex, thereby expanding the capabilities of cellular biology. The first step in the angiotensin II effect on aldosterone secretion is binding to the type I receptor (AT1). This is a G protein-coupled receptor that activates protein kinase C generating inositol triphosphate and 1,2 diacylglycerol. These then lead to an increase in calcium release, stimulating aldosterone synthesis (43). In contrast, ACTH activates adenylate cyclase, leading to production of cAMP (44), which in turn, as a secondary messenger, activates intracellular protein kinases (45), thereby leading to a cascade of calcium influx, further modulation of protein kinase activity, and subsequently aldosterone production. An elevation in extracellular potassium opens potential-dependent calcium channels. This increases intracellular calcium concentration and activates cAMP and protein kinases, leading to increased aldosterone synthesis (46, 47). Over the next 15 yr, these studies lead to an extensive evaluation of the interaction of several proteins, ions, and enzymes in the regulation of aldosterone secretion.

Aldosterone in essential hypertension.

In the 1960s, several groups maintained that aldosterone played an important role in human hypertension. In the early 1970s, a progressive hypothesis that altered target tissue sensitivity to angiotensin II, aldosterone, renin, and sodium intake together could contribute to the development of human hypertension. Efforts were made to categorize large heterogeneous populations of essential hypertension into homogeneous subsets by comparing hormonal responses to biological stimuli to facilitate investigation of pathophysiological candidates including aldosterone. One of the first substantial subsets identified was low renin hypertension. In this form of hypertension, patients display low PRA despite sodium restriction (48, 49). However, these subjects do not display unusually high aldosterone levels or hypokalemia and suppress aldosterone on high salt diet and are, therefore, distinct from primary hyperaldosteronism. An extensive search for other mineralocorticoids over the next decade identified many potential candidates, but in only a few low renin patients were any of them pathophysiologically involved (50).

Based on their earlier work in normal subjects, a second large subset of hypertension was described by Williams and Hollenberg and colleagues (51, 52) in the mid 1980s in which parallel alterations in both adrenal (aldosterone) and renal (renal blood flow) activity in response to angiotensin II and dietary sodium manipulation were described in 25% of the essential hypertensive population. In these normal/high renin individuals, changes in sodium intake failed to produce the reciprocal changes in adrenal and renal vascular responses to angiotensin II infusion; thus, was born the term "non-modulators." Over the ensuing 15 yr, it has been determined that these individuals have salt-sensitive hypertension (like low renin subjects), are insulin resistant (even if lean), and have a heritable form of hypertension that is associated with polymorphisms in the genes of the renin-angiotensin-aldosterone system. Most intriguingly, their pathophysiological defects are corrected by converting enzyme inhibitors (53, 54, 55, 56, 57). Thus, between the low renin and non-modulating hypertensive populations, nearly all of the salt-sensitive subgroups have been identified.

The mineralocorticoid receptor.

Historically, adrenal steroids had been classified according to their relative potency as a mineralocorticoid or a glucocorticoid. Similarly, receptors were categorized according to relative affinity. Mineralocorticoid (type I) receptors possessed high affinity for mineralocorticoids and glucocorticoid (type II) receptors possessed high affinity for glucocorticoids. Therefore, early studies using [3H]-labeled steroid-binding assays demonstrated high affinity for aldosterone and deoxycorticosterone but low affinity for dexamethasone and corticosterone for the mineralocorticoid receptor (58). However, contradictory models developed when attempts were made to explain aldosterone activity at the distal renal tubule in which varying concentrations of mineralocorticoid and glucocorticoid receptors were located and, at times, counterintuitive concentrations of aldosterone or cortisol (59). Clarifying this paradox were experiments performed in 1987 in which adrenalectomized rats were found to have equivalent renal cytosolic in vitro binding affinity for aldosterone and corticosterone. However, when these steroids were then injected into the animal in vivo significantly higher binding affinity for aldosterone was found in the kidney, parotid, and intestine but not in other tissues (60). The presence of 11ß-hydroxysteroid dehydrogenase (11ß-HSD) in these tissues conferred high aldosterone selectivity. Enzymatic conversion of cortisol to cortisone by this enzyme disabled the cortisol effect on the type I receptor. This observation explained the phenomenon of apparent mineralocorticosteroid excess in which deficiency of 11ß-HSD lead to a syndrome of cortisol-dependent type I receptor activation with ensuing hypertension and hypokalemia (61). This also explained licorice toxicity resulting in a similar syndrome in which glycyrrhizic acid was a potent inhibitor of 11ß-HSD production (62).

Cloning and sequencing techniques introduced in the mid 1980s greatly enhanced efforts to define physiology. The advances clarified how steroid hormones control gene function. By 1987 the mineralocorticoid receptor had been cloned (63) enabling detailed study of regulatory DNA sequences, hormone response elements, and the ability to influence transcription/translation of inducible protein elements. These studies also clarified the molecular mechanisms underlying the earlier in vitro studies. Corticosterone and aldosterone bind equally well to the type I glucocorticoid (i.e. mineralocorticoid receptor). Thus, the selectivity of the type I receptor for mineralocorticoids does not occur at the receptor level but at the level of 11ß-HSD type II—"the guardian of the gate" (64). In those tissues possessing this enzyme in close proximity to the receptor (e.g. epithelial cells in kidney, bladder, gastrointestinal tract, sweat and saliva glands, smooth muscle, and vascular endothelium), only mineralocorticoids can activate the receptor. In other tissues (e.g. brain and myocytes) that do not possess 11ß-HSD type II, glucocorticoids, because of their higher concentration, likely are the principle activators of the mineralocorticoid receptor.


    The later years: 1990–2000
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
Sodium transport at the distal renal tubule.

By 1990, substantial research reinforced aldosterone as the primary hormone of Na+ and K+ homeostasis, extracellular fluid volume, and blood pressure, yet still unidentified were the aldosterone-induced proteins that bridged aldosterone action at the nucleus and increased sodium transport. In the mid 1990s aldosterone was shown to exert its effect through the epithelial Na channel (ENaC) via latent transcriptional and translational regulation, leading to de novo synthesis of ENaC with selective insertion in the apical epithelial membrane effecting enhanced sodium transport (65, 66). Recently, the serum and glucocorticoid-induced kinase, a serine/threonine kinase, was identified as an aldosterone-induced protein that produced upregulation of EnaC (67), thereby completing a link between aldosterone introduction at the cell nucleus to the outcome of Na+ flux through the ENaC. Traditionally, it has been assumed that the reabsorption of sodium through ENaC modifies the electrochemical gradient for potassium producing an influx into the urine. However, whether this is the only mechanism responsible for potassium excretion is uncertain.

Nonepithelial effects of aldosterone.

For most of the past 50 yr the focus of aldosterone action resided in the classical target organ, the kidney. However, as noted previously, Selye and others in the 1950s realized that aldosterone exerted nonepithelial activity particularly relating to induction of inflammatory processes, collagen formation, fibrosis, and necrosis. In addition, steroid hormone biosynthesis had been described in several extra-adrenal tissues including brain, cardiac tissue (68), and blood vessels (69) in which paracrine and autocrine properties are assumed to exist. Studies have revealed the presence of mRNA for aldosterone synthase and aldosterone along with local tissue effects in these tissue beds. In the heart, this local production of aldosterone can be induced by angiotensin II or dietary sodium/potassium manipulations (70). By the early 1990s, interest in this aspect of aldosterone action resurfaced and reports of perivascular fibrosis and cardiac damage appeared in the literature again under various experimental models (71, 72). These nonclassical descriptions of aldosterone activity in nonepithelial target tissues have now been associated with various models of pathology in animals and in humans. Perhaps one of the most intriguing examples of a successful translational research endeavor involved the studies of Weber and Pitt. In the early 1990s, Weber and colleagues (73) studied the effects of aldosterone in cardiac remodeling documenting that chronic aldosterone excess in the presence of salt loading caused cardiac fibrosis in experimental animals. Additional animal studies demonstrated that uninephrectomized rats fed a high salt diet and aldosterone were protected from development of cardiac fibrosis with the administration of spironolactone (an aldosterone receptor antagonist), thus implicating the mineralocorticoid receptor in cardiac fibrosis. Similar studies in stroke-prone hypertensive rat support the notion that mineralocorticoid blockade reduces vascular injury (74). It should be pointed out that injury was not seen on low salt diet. Further clinical evidence that implicate the likely pathological influence of aldosterone in cardiac disease came from studies of patients with primary hyperaldosteronism. A study comparing severity of left ventricular hypertrophy (LVH), an independent risk factor of increased cardiovascular risk, in patients with primary hyperaldosteronism vs. those with essential hypertension found that primary hyperaldosteronism possessed a significantly higher severity of LVH despite controlling for age, duration of hypertension, gender, and severity of hypertension. Napoli et al. (75) demonstrated that patients with primary hyperaldosteronism had significantly more impairment in myocardial perfusion as measured by single photon emission computed tomography scan after exercise as compared with matched subjects with essential hypertension. These findings, along with the well documented observation of chronic renin-angiotensin-aldosterone system activation in congestive heart failure, and the finding that blockade of angiotensin was beneficial in this condition led Pitt and colleagues to devise the Randomized Aldactone Evaluation Study (RALES). This multicentered international clinical trial comparing standard therapy in moderate to severe heart failure vs. standard therapy plus low-dose spironolactone was terminated early when a 30% reduction in rate of death in the active drug arm was realized (Fig. 3Go; Ref. 76). Further supporting the role that both cardiac fibrosis and aldosterone effect had in this population was evidence from a substudy of RALES in which markers of collagen synthesis, associated with development of cardiac fibrosis, correlated with disease severity and increased cardiac risk. In the spironolactone-treated subjects, survival benefit correlated with reduced collagen synthesis markers at 6 months (77).



View larger version (21K):
[in this window]
[in a new window]
 
Figure 3. Survival curves among patients treated with placebo or spironolactone. Risk of death was 30% lower in the spironolactone-treated group in the RALES trial (P < 0.001). [Reproduced with permission from B. Pitt et al.: N Engl J Med 341:709, 1999 (76 ).]

 
Myocardial fibrosis seems to be a reparative process secondary to inflammatory necrosis (Fig. 4Go; Ref.s. 78 and 79). Animal models demonstrate alterations in Na,K-ATPase activity in cardiomyocytes treated with aldosterone lead to necrosis, recruitment and activation of macrophages, secretion of growth factors including TGF-ß, and subsequent reparative fibrosis and dysfunction. An important component of these events is the presence of dietary sodium. In low sodium environments, the negative effects of aldosterone administration were markedly blunted (80). Furthermore, although small increases in potassium may contribute to the beneficial effects of mineralocorticoid receptor blockade, animal studies have documented a protective effect of blockade independent of an increased potassium (80).



View larger version (71K):
[in this window]
[in a new window]
 
Figure 4. Photomicrograph of myocardium in rats treated with aldosterone and salt with and without eplerenone. Note the presence of vasculopathy including perivascular inflammatory cell infiltrate in rats treated with aldosterone and the absence of these findings in rats treated with aldosterone and eplerenone [Reproduced with permission from R. Rocha et al.: Am J Physiol Heart Circ Physiol 283:H1802–H1810, 2002 (78 ).]

 
Nonclassical aldosterone action: rapid nongenomic effects of aldosterone.

Earlier studies demonstrated a lag between times of administration of aldosterone to increased cellular activity (~30–90 min). Subsequent research focused on revealing the cytosolic steroid receptors to which aldosterone binds. These receptors translocate to the nucleus and function as transcription factors through interaction with DNA regulatory elements (81, 82). As mentioned earlier, two distinct nuclear receptors were characterized: the mineralocorticoid and glucocorticoid receptors. The ENaC, K+ channels and Na+/K+-ATPase are the final effector elements of this genomic interaction. In general, this is described as classical genomic effect of aldosterone. However, research over the last 10 yr has led to the discovery of rapid, nongenomic or nonclassical effects of aldosterone. This has led to investigation of aldosterone action in tissues other than the kidney. In 1992, Wehling et al. (83) identified rapid (nongenomic) effects of aldosterone action in smooth muscle (83). Reports of rapid nongenomic effects of aldosterone have been described in skeletal muscle (84), colonic epithelial cells (85), and myocardial cells (86). These nongenomic effects have been linked to development of increased systemic vascular resistance (87) and might, therefore, participate in human hypertension and cardiovascular disease. However, it is uncertain whether these effects are secondary to activation of the classical mineralocorticoid receptor or not.


    The 21st century
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
It is only in the last 10 years that a flurry of academic interest has encircled the potential influence of aldosterone in a wide variety of diseases. Much of this excitement derives from the recently discovered nonclassical pathways of aldosterone action, the presence of extra-adrenal aldosterone production, and the rediscovery of mineralocorticoids as proinflammatory and profibrotic molecules (Fig. 5Go). Essentially, any tissue expressing the mineralocorticoid receptor is now a target of investigation. This also has lead to a renewed interest in the relative cardiovascular protective roles of blockade of angiotensin II formation or effect vs. blockade of aldosterone formation when angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers are administered. Two recently completed studies [The Eplerenone, Enalapril, Eplerenone and Enalapril (4E) studies] have addressed this question. Both studies had a similar design. In one, hypertensive subjects with LVH (4E-LVH) were enrolled (88). In the second, hypertensive subjects with diabetes and proteinuria (4E-DM) were studied (89). Subjects were randomized into maximum tolerated does of enalapril, eplerenone (a new selective aldosterone antagonist with virtually no effects on sex hormones), or the combination. The results on these cardiovascular target organs were nearly the same: blocking the mineralocorticoid receptor was as effective, if not more effective, in reducing LVH or proteinuria as blocking the formation of angiotensin II. Intriguingly, the combination produced a substantially greater reduction in target organ damage than either therapy alone suggesting both angiotensin II and aldosterone are involved in mediating damage. These studies suggest that aldosterone may be involved to a greater extent in human hypertension than what had been previously assumed. In addition, although still controversial, as many as 10% of the hypertensive population may have excess aldosterone production (i.e. primary aldosteronism; Ref. 90).



View larger version (28K):
[in this window]
[in a new window]
 
Figure 5. Suggested multistep process leading to organ dysfunction in individuals or animals in the presence of aldosterone and salt.

 
A recently completed mortality trial provides additional support for the hypothesis that aldosterone in the presence of salt is a cardiovascular risk hormone. In EPHESUS (Eplerenone Post-AMI Heart Failure Efficacy and Survival Study), patients who developed congestive heart failure acutely following a myocardial infarction were randomized into standard therapy with or without low-dose eplerenone. As with the RALES trial, there was a striking mortality reduction in those patients treated with eplerenone (91).


    Conclusions
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 
Fifty years of fruitful and exciting experimentation and discovery have elapsed since the isolation and characterization of aldosterone by Simpson and Tait. It seems ironic that considering the role of aldosterone teleologically as a relatively recent and advanced adaptive mechanism to assure sodium and volume homeostasis that it is implicated in maladaptive consequences in the setting of volume overload states such as hypertension, nephrosis, heart failure, and cirrhosis. The mechanisms by which this occurs are still being unraveled. Certainly, further study is needed to investigate what role functional polymorphisms might play in possible predisposition to developing this maladaptive response and critically how dietary sodium converts the effect of aldosterone from physiological to pathological. Regardless, the historical review of the discovery of aldosterone emphasizes the importance of recognizing early contributions to medical research in the setting of technological advances.


    Footnotes
 
Abbreviations: 11ß-HSD, 11ß-Hydroxysteroid dehydrogenase; ENaC, epithelial Na channel; LVH, left ventricular hypertrophy; PRA, plasma renin activity; RALES, Randomized Aldactone Evaluation Study.

Received March 19, 2003.

Accepted April 2, 2003.


    References
 Top
 Introduction
 The early years
 The middle years: 1970-1990
 The later years: 1990-2000
 The 21st century
 Conclusions
 References
 

  1. Castiglioni A 1941 A history of medicine. New York: Alfred A. Knopf; 428
  2. Addison T 1855 On the constitutional local effects of disease of the suprarenal capsules. London: P. Highley
  3. Kuizinga MH, Cartland GF 1939 Fractionation studies on adrenal cortical extract with notes on the distribution of biological activity among the crystalline and amorphous fractions. Endocrinology 24:526–535
  4. Deane HW, Shaw JH, Greep RO 1948 The effect of altered sodium or potassium intake on the width and cytochemistry of the zona glomerulosa of the rat’s adrenal cortex. Endocrinology 43:133–153
  5. Simpson SA, Tait JF, Wettstein A, Neher R, von Euw J, Reichstein T 1953 Isolierung eines neuen kristallisierten Hormons aus Nebennerien mit besonders hoher Wirksamkeit auf den Mineralsoffwechsel. Experientia 9:333–335
  6. Simpson SA, Tait JF, Wettstein A. Neher R. Euw JV, Schindler O, Reichstein T 1954 Aldosteronisolierung und Eigenschaften über Bestandteile de Nebennierenrinde und verwandte Stoffe. Helv Chim Acta 37:1163–1200
  7. Kliman B, Peterson RE 1958 Isotope derivative assay of aldosterone in biological extracts. Fed Proc 17:255 (Abstract)
  8. Conn JW 1955 Primary aldosteronism: a new clinical syndrome. J Lab Clin Med 45:3–17
  9. Giroud CJP, Stachenko J, Venning EH 1956 Secretion of aldosterone by the zona glomerulosa of rat adrenal glands incubated in vitro. Proc Soc Exp Biol Med 92:154–158
  10. Ganong WF, Mulrow PJ 1962 Role of the kidney in adrenocortical response to hemorrhage in hypophysectomized dogs. Endocrinology 70:182–188[Medline]
  11. Mulrow PJ 1966 Neural and other mechanisms regulating aldosterone secretion. In: Martini L, Ganong WF, eds. Neuroendocrinology, vol. 1. New York: Academic Press; 407–444
  12. Deane HG, Mason GMC 1951 Adrenal cortical changes in rats with various types of experimental hypertension. J Clin Endocrinol 11:193–208[Medline]
  13. Paige IH, Helmer OM 1939 A crystalline pressor substance, angiotonin, resulting from the reaction between renin and renin activator. Proc Cent Soc Clin Invest 12:17
  14. Skeggs LT, Marsh WH, Kahn JR, Shumway NP 1954 The existence of two forms of hypertension. J Exp Med 99:275
  15. Gross F 1958 Renin und Hipertensin, physiologische oder pathologische Wirkstoffe? Klin Wochenschr 36:693–706
  16. Mulrow PJ, Ganong WF 1961 Stimulation of aldosterone secretion by angiotensin II. Yale J Biol Med 33:386–395[Medline]
  17. Giroud CJP, Saffran M, Schally AV, Stachenko J, Vinning EH 1956 Production of aldosterone by rat adrenal glands in vitro. Proc Soc Exp Biol Med 92:855
  18. Laragh JH, Stoerk HC 1957 A study of the mechanism of secretion of the sodium-retaining hormone (aldosterone). J Clin Invest 36:383[Medline]
  19. Leaf A, Anderson J, Page LB 1958 Active sodium transport by the isolated toad bladder. J Gen Physiol 41:657[Abstract/Free Full Text]
  20. Tullner WW, Graff MM 1956 Amphenone inhibition of adrenal corticosterone in the hypophysectomized dog. Endocrinology 58:280[Medline]
  21. Deleted in proof.
  22. Crabbe JJ 1961 Stimulation of active sodium transport by the isolated toad bladder with aldosterone in vitro. J Clin Invest 40:2103
  23. Feigelson, P, Feigelson M, Greengard O 1962 Comparison of the mechanisms of hormonal and substrate induction of rat liver tryptophan pyrrolase. Recent Prog Horm Res 18:491
  24. Steigler M, Reichstein T 1937 Desoxycorticosterone (21-oxyprogesterone aus 5–3-oxy-atio cholensaure). Helv Chim Acta 20:1164
  25. Conn JW 1964 Plasma renin activity in primary aldosteronism. JAMA 190:222–225[Medline]
  26. Duncun Jr LE, Liddle GW, Bartter FC 1956 The effect of changes in body sodium on extracellular fluid volume and aldosterone and sodium excretion by normal and edematous man. J Clin Invest 35:1299[Medline]
  27. Wolff HP, Koczorek KR, Buchborn E 1957 Lancet 2:63
  28. Selye H 1946 The general adaptation syndrome and the diseases of adaptation. J Clin Endocrinol 6:117–230
  29. Selye H 1960 Protection by a steroid-spirolactone against certain types of cardiac necrosis. Proc Soc Exp Biol Med 104:212–213
  30. Hall CE, Hall O 1965 Hypertension and hypersalimentation. I. Aldosterone hypertension. Lab Invest 14:285–294
  31. Gerarde HW, Jones M 1953 The effect of cortisone on collagen synthesis in vitro. J Biol Chem 201:553–560[Free Full Text]
  32. Mayes D, Furuyama D, Kem DC, Nugent CA 1970 A radioimmunoassay for plasma aldosterone. J Clin Endocrinol Metab 30:682–685[Medline]
  33. Haning R, Tait SAS, Tait JF 1970 In vitro effects of ACTH, angiotensins, serotonin, and potassium on steroid output and conversion of corticosterone to aldosterone by isolated adrenal cells. Endocrinology 87:1147–1167[Medline]
  34. Deleted in proof.
  35. Hollenberg NK, Chenitz WR, Adams DF, Williams GH 1974 Reciprocal influence of salt intake on adrenal glomerulosa and renal vascular responses to angiotensin II in normal man. J Clin Inves 54:34–42[Medline]
  36. Boyd GW, Adamson AR, Arnold M, James VH, Peart WS 1972 The role of angiotensin II in the control of aldosterone in man. Clin Sci 42:91–104[Medline]
  37. Oelkers W, Brown JJ, Fraser R, Lever AF, Morton JJ, Robertson JI 1974 Sensitization of the adrenal cortex to angiotensin II in sodium-deplete man. Circ Res 34:69–77
  38. Muller AF, Riondel AM, Manning EL 1956 Effect of corticotrophin on secretion of aldosterone. Lancet 2:1021–1024
  39. Williams GH, Dluhy RG 1972 Aldosterone biosynthesis. Interrelationship of regulatory factors. Am J Med 53:595–605[Medline]
  40. Aguilera G, Catt KJ 1978 Regulation of aldosterone secretion by the renin-angiotensin system during sodium depletion in rats. Proc Natl Acad Sci USA 75:4057–4061[Abstract]
  41. Williams GH, Hollenberg NK, Braley LM 1976 Influence of sodium intake on vascular and adrenal angiotensin II receptors. Endocrinology 98:1343[Abstract]
  42. Braley LM, Menachery AI, Rystedt L, Williams GH 1989 Sodium-mediated modulation of aldosterone secretion: impact of converting enzyme inhibition on rat glomerulosa cell response to angiotensin II. Endocrinology 125:1310–1315[Abstract]
  43. Mortensen RM, Williams GH 1995 Aldosterone action. In: DeGroot LJ, ed. Endocrinology, 3rd ed. Philadelphia: WB Saunders Co.; 1668–1676
  44. Garren LD, Gill GN, Masui H, Walton GM 1971 On the mechanism of action of ACTH. Recent Prog Horm Res 27:433–478[Medline]
  45. Sala GB, Hayashi K, Catt KJ, Dufau ML 1979 Adrenocorticotropin action in isolated adrenal cells. The intermediate role of cyclic AMP in stimulation of corticosterone synthesis. J Biol Chem 254:3861–3865[Medline]
  46. Kojima I, Kojima K, Rasmussen H 1985 Intracellular calcium and adenosine 3',5'-cyclic monophosphate as mediators of potassium-induced aldosterone secretion. Biochem J 228:69–76[Medline]
  47. Hyatt PJ, Tait JF, Tait SAS 1986 The mechanism of the effect of K+ on the steroidogenesis of rat zona glomerulosa cells of the adrenal cortex: role of cyclic AMP. Proc R Soc Lond Biol 227:21–42[Medline]
  48. Streeten DHP, Schletter FE, Clift GV, Stevenson CT, Dalakos TG 1969 Studies of the renin-angiotensin-aldosterone system in patients with hypertension and in normal subjects. Am J Med 46:844–861[Medline]
  49. Baer L, Sommers SC, Krakoff LR, Newton MA, Laragh JH 1970 Pseudoprimary aldosteronism: an entity distinct from true primary hyperaldosteronism. Circ Res (Suppl 1) 27:203[Medline]
  50. Williams GH, Braley LM, Underwood RH 1976 The regulation of plasma 18-hydroxy 11-deoxycorticosterone in man. J Clin Invest 58:221–229[Medline]
  51. Shoback DM, Williams GH, Moore TJ, Dluhy RG, Podolsky S, Hollenberg NK 1983 Defect in the sodium-modulated tissue responsiveness to angiotensin II in essential hypertension. J Clin Invest 72:2115–2124[Medline]
  52. Hollenberg NK, Williams GH 1995 Abnormal renal function, sodium-volume homeostasis and renin system behavior in normal-renin essential hypertension: the evolution of the non-modulator concept. In: Laragh JH, Brenner BM, eds. Hypertension: pathophysiology, diagnosis, and management, ed 2. New York: Raven Press, Ltd.; 1837–1856
  53. Redgrave JE, Rabinowe SL, Hollenberg NK, Williams GH 1985 Correction of abnormal renal blood flow response to angiotensin II by converting-enzyme inhibition in essential hypertensives. J Clin Invest 75:1285–1290[Medline]
  54. Williams GH, Dluhy RG, Lifton RP, Moore TJ, Gleason R, Williams R, Hunt SC, Hopkins PN, Hollenberg NK 1992 Non-modulation as an intermediate phenotype in essential hypertension. Hypertension 20:788–796[Abstract]
  55. Hollenberg NK, Moore T, Shoback D, Redgrave J, Rabinowe S, Williams GH 1986 Abnormal renal sodium handling in essential hypertension: relation to failure of renal and adrenal modulation of responses to Ang II. Am J Med 81:412–418[Medline]
  56. Ferri C, Bellini C, Desideri G, Valenti M, De Mattia G, Santucci A, Hollenberg NK, Williams GH 1999 Relationship between insulin resistance and non-modulating hypertension: linkage of metabolic abnormalities and cardiovascular risk. Diabetes 48:1623–1630[Abstract]
  57. Hopkins PN, Hunt SC, Jeunemaitre X, Smith B, Solorio D, Fisher ND, Hollenberg NK, Williams GH 2002 Angiotensin genotype effect on renal and adrenal responses to angiotensin II in essential hypertension. Circulation 105:1921–1927[Abstract/Free Full Text]
  58. Rousseau G, Baxter JD, Funder JW, Edelman IS, Tomkins GM 1972 Glucocorticoid and mineralocorticoid receptors for aldosterone. J Steroid Biochem 3:219–227[CrossRef][Medline]
  59. Farman NA, Vandewalle A, Bonvalet JP 1982 Aldosterone binding in isolated tubules: 2. An autoradiographic study of concentration dependency in the rabbit nephron. Am J Physiol 242:F69
  60. Sheppard K, Funder JW 1987 Mineralocorticoid specificity of renal type I receptors: in vivo binding studies. Am J Physiol 252:E224
  61. Stewart PM, Corrie JE, Shackleton CH, Edwards CR 1988 Syndrome of apparent mineralocorticoid excess: A defect in the cortisol-cortisone shuttle. J Clin Invest 82:340–349[Medline]
  62. Stewart PM, Wallace AM, Valentino R, Burt D, Shackleton CH, Edwards CR 1987 Mineralocorticoid activity in licorice: 11 beta-hydroxysteroid dehydrogenase deficiency comes of age. Lancet 2:821[Medline]
  63. Arriza JL, Weinberger C, Cerelli G, Glaser TM, Handelin BL, Housman DE, Evans RM 1987 Cloning of human mineralocorticoid receptor complimentary DNA: structural and functional kinship with the glucocorticoid receptor. Science 237:268–275[Medline]
  64. Williams GH 1992 Guardian of the gate: receptors, enzymes, and mineralocorticoid function. J Clin Endocrinol Metab 74:961–962[Medline]
  65. Rossier BC 1997 The 1996 Homer Smith Award Lecture. Curn grano salis: the epithelial sodium channel and the control of blood pressure. J Am Soc Nephrol 8:980–992[Medline]
  66. Verrey F 1999 Early aldosterone action: toward filling the gap between transcription and transport. Am J Physiol 277:F319–F327
  67. Chen SY, Bhargava A, Mastroberardino L, Meijer OC, Wang J, Buse P, Firestone GL, Verrey F, Pearce D 1999 Epithelial sodium channel regulated by aldosterone-induced protein sgk. Proc Natl Acad Sci USA 96:2514–2519[Abstract/Free Full Text]
  68. Silvestre J-S, Robert V, Heymes C, Aupetit-Faisant B, Mouas C, Moalic JM, Swynghedauw B, Delcayre C 1998 Myocardial production of aldosterone and corticosterone in the rat: physiological regulation. J Biol Chem 273:4883–4891[Abstract/Free Full Text]
  69. Takeda Y, Miyamori I, Yoneda T, Iki K, Hatakeyama H, Blair IA, Hsieh FY, Takeda R 1995 Production of aldosterone in isolated rat blood vessels. Hypertension 25:170–173[Abstract/Free Full Text]
  70. Silvestre J-S, Heymes C, Oubénaïssa A, Robert V, Aupetit-Faisant B, Carayon A, Swynghedauw B, Delcayre C 1999 Activation of cardiac aldosterone production in rat myocardial infarction: effect of angiotensin II receptor blockade and role in cardiac fibrosis. Circulation 99:2694–2701[Abstract/Free Full Text]
  71. Brilla CG, Pick R, Tan LB, Janicki JS, Weber KT 1990 Remodeling of the rat right and left ventricle in experimental hypertension. Circ Res 67:1355–1364[Abstract]
  72. Brilla CG, Weber KT 1992 Reactive and reparative myocardial fibrosis in arterial hypertension in the rat. Cardiovasc Res 26:671–677[Medline]
  73. Brilla CG, Pick R, Tan LP, Janicki JS, Weber KT 1990 Remodeling of the rat right and left ventricle in experimental hypertension. Circ Res 67:1355–1364[Abstract]
  74. Rocha R, Chander PN, Khanna K, Zuckerman A, Stier Jr CT 1998 Mineralocorticoid blockade reduces vascular injury in stroke-prone hypertensive rats. Hypertension 31:451–458[Abstract/Free Full Text]
  75. Napoli C, DiGregorio F, Leccese M, Abete P, Ambrosio G, Giusti R, Casini A, Ferrara N, DeMatteis C, Sibilio G, Donzelli R, Montemarano A, Mazzo C, Rengo F, Mansi L, Liguori A 1999 Evidence of exercise-induced myocardial ischemia in patients with primary aldosteronism: the Cross-sectional Primary Aldosteronism and Hear Italian Multicenter Study. J Invest Med 47:212–221[Medline]
  76. Pitt B, Zannad F, Remme WJ 1999 The effect of spironolactone on morbidity and mortality in patients with severe heart failure. N Engl J Med 341:709–717[Abstract/Free Full Text]
  77. Zannad F, Alla F, Dousset B, Perez A, Pitt B, RALES Investigators 2000 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. Circulation 102:2700–2706[Abstract/Free Full Text]
  78. Rocha R, Rudolph AE, Frierdich GE, Nachowiak DA Kekec BK, Blomme EA, McMahon EG, Delyani JA 2002 Aldosterone induces a vascular inflammatory phenotype in the rat heart. Am J Physiol–Heart and Circ Physiol. 283:H1802–H1810
  79. Rocha R, Stier Jr CT, Kifor I, Ochoa-Maya MR, Rennke HG, Williams GH, Adler GK 2000 Aldosterone: a mediator of myocardial necrosis and renal arteriopathy. Endocrinology 141:3871–3878[Abstract/Free Full Text]
  80. Martinez DV, Rocha R, Matsumura M, Oestreicher E, Ochoa-Maya M, Roubsanthisuk W, Williams GH, Adler GK 2002 Cardiac damage prevention by eplerenone: comparison with low sodium diet or potassium loading. Hypertension 39:614–618[Abstract/Free Full Text]
  81. Farman N, Rafestin-Oblin ME 2001 Multiple aspects of mineralocorticoid selectivity. Am J Physiol Renal Physiol 280:F181–F192
  82. Funder JW 1997 Glucocorticoid and mineralocorticoid receptors: biology and clinical relevance. Annu Rev Med 48:231–240[CrossRef][Medline]
  83. Wehling M, Eisen C, Christ M 1992 Aldosterone-specific membrane receptors and rapid non-genomic actions of mineralocorticoids. Mol Cell Endocrinol 90:C5–C9
  84. Passaquin AC, Lhote P, Ruegg UT 1998 Calcium influx inhibition by steroids and analogs in C2C12 skeletal muscle cells. Br J Pharmacol 124:1751–1759[Abstract]
  85. Doolan CM, Condliffe SB, Harvey BJ 2000 Rapid non-genomic activation of cytosolic cyclic AMP-dependent protein kinase activity and [Ca(2+)](i) by 17-ß-estradiol in female rat distal colon. Br J Pharmacol 129:1375–1386[Abstract/Free Full Text]
  86. Barbato JC, Mulrow PJ, Shapiro JI, Franco-Saenz R 2002 Rapid effects of aldosterone and spironolactone in the isolated working rat heart. Hypertension 40:130–135[Abstract/Free Full Text]
  87. Wehling M, Spes CH, Win N, Janson C, Schmidt BMW, Theisen K, Christ M 1998 Rapid cardiovascular action of aldosterone in man. J Clin Endocrinol Metab 83:3517–3522[Abstract/Free Full Text]
  88. Pitt B, Reichek N, Metscher R, Phillips R, Roniker B, Kleiman J, Burns D 2002 Efficacy and safety of eplerenone, enalapril, and eplerenone/enalapril combination therapy in patients with left ventricular hypertrophy. Am J Hypertens 15:24A (Abstract)[CrossRef][Medline]
  89. Epstein M, Buckalew V, Martinez F, Altamisano J, Roniker B, Kleiman J, Krausse S 2002 Antiproteinuric efficacy of eplerenone, enalapril, and eplerenone/enalapril combination in diabetic hypertensives with microalbuminuria. Am J Hypertens 15:24A (Abstract)[CrossRef][Medline]
  90. Gordon RD, Ziesak MD, Tunny TJ, Stowasser M, Klemm SA 1993 Evidence that primary aldosteronism may not be uncommon: twelve percent incidence among anti-hypertensive drug trial volunteers. Clin Exp Pharmacol Physiol 20:296–298[Medline]
  91. Pitt B, Remme W, Zannad F, Neaton J, Martinez F, Roniker B, Bittman R, Hurley S, Kleiman J, Gatlin M, Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study Investigators 2003 Eplerenone, a selective aldosterone blocker, in patients with left ventricular dysfunction after myocardial infarction. N Engl J Med 348:1309–1321[Abstract/Free Full Text]