Additive amelioration of left ventricular remodeling and molecular alterations by combined aldosterone and angiotensin receptor blockade after myocardial infarction.

Objective: The mechanisms underlying the clinical benefits of mineralocorticoid receptor antagonism in patients with left ventricular (LV) dysfunction and heart failure (CHF) after myocardial infarction (MI) are poorly understood.

Methods: We investigated whether long-term (9 weeks) aldosterone antagonism with eplerenone (100 mg/kg/day) provides additional benefit to angiotensin II type 1 (AT1) receptor inhibition with irbesartan (50 mg/kg/day) on cardiac remodeling after MI in rats.

Results: Eplerenone monotherapy, like AT1 receptor blockade, significantly reduced LV end-diastolic pressure (LVEDP), end-systolic volume (LVESV) and end-diastolic volume (LVEDV) compared to placebo. Improvement of LV dilation by aldosterone antagonism was associated with a significant reduction of increased AT1 receptor, angiotensin-converting enzyme (ACE) and endothelin-1 gene expression in the noninfarcted LV myocardium. Combination therapy with irbesartan led to a substantial further leftward shift of the LV pressure-volume curve and decrease in LVEDP, LVESV and LVEDV. Moreover, combination therapy significantly improved LV systolic and diastolic function and reversed LV alterations of alpha- and beta-myosin heavy-chain isoforms, ANF and SERCA2 ATPase expression more effectively than monotherapies. LV collagen type I and type III expression as well as interstitial fibrosis were substantially increased in placebo CHF rats, similarly decreased by eplerenone and irbesartan, and further reduced by eplerenone/irbesartan. However, no additive effects of eplerenone/irbesartan on myocardial AT1 receptor, ACE and endothelin-1 mRNAs were observed.

Conclusions: Aldosterone receptor antagonism provides additional benefit to AT1 receptor blockade on LV function and remodeling associated with improvement of molecular alterations responsible for progressive contractile dysfunction post-MI.