Cardioprotection by Aldosterone Receptor Antagonism in Heart Failure: 1. The Role of Aldosterone in Heart Failure

In recent years, understanding of the role of aldosterone has expanded beyond the known classic effects of promoting renal sodium retention and potassium and magnesium loss. It is now well documented that aldosterone causes myocardial and perivascular fibrosis, blocks the myocardial uptake of norepinephrine, and increases plasminogen activator inhibitor levels. In conjunction with angiotensin II, aldosterone causes vascular damage, endothelial dysfunction, and decreased vascular compliance. Thus, the renin-angiotensin-aldosterone system (RAAS) plays a major role in the development of both hypertension and heart failure and is, therefore, a key target for therapeutic interventions. Commonly prescribed medications for control of hypertension and congestive heart failure are inhibitors of the RAAS, including angiotensin converting enzyme inhibitors (ACE-Is) and angiotensin II (A-II) receptor antagonists. A well-documented increase in aldosterone levels occurs over several months during chronic treatment with an ACE-I or an A-II receptor antagonist. Such suppression of circulating aldosterone, however, is transient, as exemplified by the term “escape” used to describe the phenomenon. This rebound of aldosterone even occurs when patients receive both an ACE-I and an A-II receptor antagonist. In addition, ACE-Is and A-II receptor antagonists are less effective in controlling blood pressure in the estimated 60% of hypertensive patients who are salt- (volume-) sensitive and more prone to hypertension-associated morbidity, such as black patients and type 2 diabetics. Thus, chronic and complete blockade of aldosterone action requires an aldosterone receptor antagonist. The Randomized Aldactone Evaluation Study (RALES) trial results in patients with severe heart failure (New York Heart Association class III or IV) and a left ventricular ejection fraction of no more than 35% showed that administration of a subhemodynamic dose of spironolactone (25 mg/day) as an add-on therapy to ACE-Is plus standard treatment resulted in a significant mortality reduction due to decreases in both death from progressive heart failure and sudden cardiac death. These findings support the pivotal role of aldosterone in the pathophysiology of progressive heart failure. Although it is an effective antialdosterone agent, widespread use of spironolactone in humans is limited by its tendency to produce undesirable sexual side effects. At standard doses, impotence and gynecomastia can be induced in men, whereas premenopausal women may experience menstrual disturbances. Data on a selective aldosterone receptor antagonist, eplerenone, show that it appears promising for the effective blockade of aldosterone and its harmful effects without the sexual disturbances of spironolactone. Recently, eplerenone was successfully introduced for the treatment of hypertension and heart failure. A growing number of experimental studies are finding a broader role for aldosterone in driving the pathophysiology of both heart failure and hypertension. When added to conventional therapy, aldosterone receptor blockers show benefits in addition to those conferred by ACE-Is and/or A-II receptor blockers.