Abstract
Aldosterone is a mineralocorticoid primarily produced in the zona glomerulosa of the adrenal gland. For many years, aldosterone (Aldo) was thought to have its sole site of action in the kidney, where it regulated sodium excretion and potassium reabsorption. It is now known that Aldo is produced in cardiovascular tissues, and has been implicated in the development of ventricular hypertrophy and cardiac fibrosis. The precise mechanisms whereby Aldo acts in cardiac tissues are diverse. It was assumed that Aldo production could be limited by angiotensin-converting enzyme (ACE) inhibition, but serial measurements during therapy reveal only a transient decrease in Aldo levels. Moreover, the effects of Aldo on cardiac tissues occur even when angiotensin II (Ang II) has been suppressed or eliminated. Multiple investigators have examined effects of Aldo receptor blockade in human subjects and various animal models using the two Aldo receptor antagonists (ARAs), spironolactone and eplerenone. Major clinical trials involving spironolactone (RALES) and eplerenone (EPHESUS) ARAs have shown significant benefits in the treatment of congestive heart failure (CHF). In RALES, patients with New York Heart Association (NYHA) Class III or IV systolic heart failure treated with spironolactone had a 30% relative risk decrease in mortality. Although spironolactone is an effective competitive inhibitor of the mineralocorticoid receptor (MR), progestational and antiandrogenic side effects limit its use in some patients. Eplerenone, a more selective ARA, lacks these undesirable side effects. Although eplerenone is 20-fold less potent at the MR, it demonstrates efficacy similar to spironolactone, possibly due to decreased protein binding. Eplerenone has fewer side effects than spironolactone, which has been attributed to the low cross-reactivity with androgen and progesterone receptors. In EPHESUS, patients with left ventricular systolic dysfunction [Ejection Fraction (EF) < 40%] and CHF following an acute myocardial infarction (AMI), were treated with eplerenone, resulting in a 17% reduction in cardiovascular mortality. However, these studies were limited in that diastolic function was not evaluated, although approximately 1/2 of CHF is due to diastolic dysfunction alone. To date, neither ARA has been studied for the treatment of diastolic dysfunction in a major clinical trial. However, numerous animal studies employing ARAs have shown a decrease in cardiac hypertrophy and fibrosis, indicating the potential benefits of these agents in the treatment of diastolic heart failure. In this review, we discuss possible underlying mechanisms responsible for Aldo effects on cardiovascular function and compare the beneficial effects of spironolactone and eplerenone in the treatment of heart disease.
Keywords: Renin-Angiotensin-Aldosterone System, cytochrome P450, phospholipase C (PLC), adenylate cyclase (AC) system, Blood pressure, Spironolactone
5