Abstract 3295: De-induction of the Maladaptive Fetal Gene Program During Chronic Monotherapy with Metoprolol Succinate is Retained Following Withdrawal of Therapy in Dogs with Chronic Heart Failure

Abstract

Background: Chronic therapy with extended release metoprolol succinate (MET), a selective β1 adrenergic receptor blocker, improves left ventricular (LV) function and attenuates global LV remodeling in dogs with chronic heart failure (HF). We previously showed that chronic therapy with β-blockade results in de-induction of the fetal gene program (FGP) in LV myocardium of dogs with HF. In this study, we tested the hypothesis that in dogs with HF withdrawal of chronic MET does not lead to re-induction of FGP. Methods: Studies were performed in 17 intracoronary microembolization-induced HF dogs randomized to 3 months oral therapy with MET (100 mg, once daily, n=11) or no therapy at all (Controls, n=6). In dogs randomized to MET, 6 were sacrificed after 3 months of therapy and in the remaining 5, MET was withdrawn after 3 months of therapy and dogs were observed for 6 weeks after withdrawal of MET (MET-W) and then sacrificed. LV tissue was also obtained from 6 normal (NL) dogs for comparison. mRNA expression of the FGP genes namely, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), sarcoplasmic reticulum calcium ATPase (CAA), cardiac β-1 adren-ergic receptor (AR) and α-myosin heavy chain isoform (α-MHC) was measured using reverse transcriptase polymerase chain reaction (RT-PCR) and bands were quantified in densitometric units (du). Results: In Controls, mRNA expression of ANP and BNP increased and expression of CAA, β 1-AR and α-MHC decreased. Treatment with MET decreased expression of ANP and BNP and increased expression of CAA, β 1-AR and α-MHC. Except for α-MHC, the improvement in FGP seen during MET treatment was preserved in MET-W dogs. Conclusions: Withdrawal of MET is associated with sustained de-induction of the FGP in LV myocardium of dogs with HF. This observation supports the concept that chronic β-blockade therapy in HF confers lasting reversal of LV remodeling and molecular recovery of the failing myocardium.