Vascular inflammation was examined as a potential mechanism of aldosterone-mediated myocardial injury in uninephrectomized rats receiving 1% NaCl-0.3% KCl to drink for 1, 2, or 4 wk and 1) vehicle, 2) aldosterone infusion (0.75 microg/h), or 3) aldosterone infusion (0.75 microg/h) plus the selective aldosterone blocker eplerenone (100 mg. kg(-1). day(-1)). Aldosterone induced severe hypertension at 4 wk [systolic blood pressure (SBP), 210 +/- 3 mmHg vs. vehicle, 131 +/- 2 mmHg, P < 0.001], which was partially attenuated by eplerenone (SBP, 180 +/- 7 mmHg; P < 0.001 vs. aldosterone alone and vehicle). No significant increases in myocardial interstitial collagen fraction or hydroxyproline concentration were detected throughout the study. However, histopathological analysis of the heart revealed severe coronary inflammatory lesions, which were characterized by monocyte/macrophage infiltration and resulted in focal ischemic and necrotic changes. The histological evidence of coronary lesions was preceded by and associated with the elevation of cyclooxygenase-2 (up to approximately 4-fold), macrophage chemoattractant protein-1 (up to approximately 4-fold), and osteopontin (up to approximately 13-fold) mRNA expression. Eplerenone attenuated proinflammatory molecule expression in the rat heart and subsequent vascular and myocardial damage. Thus aldosterone and salt treatment in uninephrectomized rats led to severe hypertension and the development of a vascular inflammatory phenotype in the heart, which may represent one mechanism by which aldosterone contributes to myocardial disease.

We studied the role of aldosterone (aldo) in myocardial injury in a model of angiotensin (Ang) II-hypertension. Wistar rats were given 1% NaCl (salt) to drink and randomized into one of the following groups (n = 10; treatment, 21 d): 1) vehicle control (VEH); 2) Ang II infusion (25 ng/min, sc); 3) Ang II infusion plus the selective aldo blocker, eplerenone (epl, 100 mg/kg.d, orally); 4) Ang II infusion in adrenalectomized (ADX) rats; and 5) Ang II infusion in ADX rats with aldo treatment (20 micro g/kg.d, sc). ADX rats received also dexamethasone (12 micro g/kg.d, sc). Systolic blood pressure increased with time in all treatment groups except the VEH group (VEH, 136 +/- 6; Ang II/NaCl, 203 +/- 12; Ang II/NaCl/epl, 196 +/- 10; Ang II/NaCl/ADX, 181 +/- 7; Ang II/NaCl/ADX/aldo, 236 +/- 8 mm Hg). Despite similar levels of hypertension, epl and ADX attenuated the increase in heart weight/body weight induced by Ang II. Histological examination of the hearts evidenced myocardial and vascular injury in the Ang II/salt (7 of 10 hearts with damage, P < 0.05 vs. VEH) and Ang II/salt/ADX/aldo groups (10 of 10 hearts with damage, P < 0.05). Injury included arterial fibrinoid necrosis, perivascular inflammation (primarily macrophages), and focal infarctions. Vascular lesions were associated with expression of the inflammatory mediators cyclooxygenase 2 (COX-2) and osteopontin in the media of coronary arteries. Myocardial injury, COX-2, and osteopontin expression were markedly attenuated by epl treatment (1 of 10 hearts with damage, P < 0.05 vs. Ang II/salt) and adrenalectomy (2 of 10 hearts with damage, P < 0.05 vs. Ang II/salt). Our data indicate that aldo plays a major role in Ang II-induced vascular inflammation in the heart and implicate COX-2 and osteopontin as potential mediators of the damage.

For more than 30 years after the discovery of aldosterone, scientists believed that its sole site of action was at epithelial tissues, most notably the kidney, where it mediated the transport of Na and K. It was soon recognized aldosterone contributed to several diseases by causing edema. Armed with this information, scientists set out more than 30 years ago to develop an antagonist of the mineralocorticoid receptor for the treatment of edematous states. From this effort, spironolactone (Aldactone was discovered. Spironolactone acts functionally as a competitive inhibitor of the mineralocorticoid (aldosterone) receptor, and although spironolactone is an effective mineralocorticoid receptor antagonist, it is not without limitations. These limitations include unwanted progestational and antiadrogenic side effects that limit its use in the chronic treatment of disease. In addition to its actions at the collecting tubule, aldosterone can participate in pathophysiology by actions at the heart, vasculature, and kidney, and it is likely that the most significant contributions to cardiovascular disease are due to actions at these sites rather than those related to Na and water retention. This is underscored by the recent clinical results from the RALES-004 Trial in which treatment with Aldactone demonstrated a significant benefit on mortality in patients with severe heart failure. The limited utility of spironolactone owing to the aforementioned steroid-related side effects has been especially frustrating, given the newly recognized role of aldosterone in cardiovascular disease. To obviate these limitations, eplerenone is currently being developed by Searle. Eplerenone is a competitive antagonist of the mineralocorticoid receptor that takes advantage of replacing the 17alpha-thoacetyl group of spironolactone with a carbomethoxy group, conferring excellent selectivity for the mineralocorticoid receptor over other steroid receptors. The pharmacological profile of eplerenone positions it to be an effective and selective mineralocorticoid receptor antagonist.

Aldosterone, the final product of the renin-angiotensin-aldosterone system (RAAS), is a mineralocorticoid hormone that classically acts, via the mineralocorticoid (aldosterone) receptor, on epithelia of the kidneys, colon, and sweat glands to maintain electrolyte homeostasis. Aldosterone has also been shown to act at nonepithelial sites where it can contribute to cardiovascular disease such as hypertension, stroke, malignant nephrosclerosis, cardiac fibrosis, ventricular hypertrophy, and myocardial necrosis. Although angiotensinconverting enzyme (ACE) inhibitors and angiotensin type 1 (AT 1 ) receptor antagonists act to suppress the RAAS, these agents do not adequately control plasma aldosterone levels -a phenomenon termed "aldosterone synthesis escape." Spironolactone, a nonselective aldosterone receptor antagonist, is an effective agent to suppress the actions of aldosterone; its use is, however, associated with progestational and antiandrogenic side effects due to its promiscuous binding to other steroid receptors. For these reasons, eplerenonethe first agent of a new class of drugs known as the selective aldosterone receptor antagonists (SARAs) -is under development. In rodent models, eplerenone provides marked protection against vascular injury in the kidney and heart. In phase II clinical trials, eplerenone demonstrates 24-h control of blood pressure with once or twice daily dosing, and is safe and well tolerated in patients with heart failure when given with standard of care agents. Pharmacokinetic studies reveal that eplerenone has good bioavailability with low protein binding, good plasma exposure, and is highly metabolized to inactive metabolites and excreted principally in the bile. Eplerenone is well tolerated in acute and chronic safety pharmacology studies. Ongoing phase III trials of eplerenone in the treatment of hypertension and heart failure are underway. These studies will extend our understanding 185

Myocardial infarction (MI) initiates adaptive tissue remodeling, which is essential for heart function (such as infarct healing) but is also important for maladaptive remodeling (for example, reactive fibrosis and left ventricular dilation). The effect of aldosterone receptor antagonism on these processes was evaluated in Sprague-Dawley rats using eplerenone, a selective aldosterone receptor antagonist. Infarct healing and left ventricular remodeling were evaluated at 3, 7, and 28 days after MI by determination of the diastolic pressure-volume relationship of the left ventricle, the infarct-thinning ratio, and the collagen-volume fraction. Eplerenone did not affect reparative collagen deposition as was evidenced by a similar collagen volume fraction in the infarcted myocardium between eplerenone and vehicle-treated groups at 7 and 28 days post-MI. In addition, the thinning ratio, which is an index of infarct expansion, was comparable between the eplerenone and vehicle-treated animals at 7 and 28 days post-MI. A protective effect of eplerenone was demonstrated at 28 days post-MI, where reactive fibrosis in the viable myocardium was reduced in eplerenone-treated animals compared with vehicle-treated animals. Thus aldosterone receptor antagonism does not retard infarct healing but rather protects against maladaptive responses after MI.