Abstract 19439: Melatonin Blunts Pressure-overload Left Ventricular Hypertrophy and Improves Cardiac Performance in Pathologic and PPhysiologic Cardiac Hypertrophy

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Introduction: Reactive oxygen species (ROS) has been established as key mediators in cardiac hypertrophy and function through activation of redox-sensitive kinases, by stimulating NADPH oxidase. Melatonin has been described as having potent antioxidant properties in different tissues. Hypothesis: The hormone melatonin, would prevent pressure-overload (pathologic) hypertrophy, Methods: Mice (C57Bl6) were subjected to transverse aortic constriction (TAC), and treated with melatonin (MEL, 10 mg/Kg/day) in water (“TAC+MEL”) or placebo (TAC). A second group underwent intense treadmill exercise for 8 weeks and also received melatonin (EX-MEL) or water (EX). A sham operated group served as control (“sham”). After 7 weeks of TAC and 8 weeks of exercise, cardiac function was assessed by echocardiography and pressure –volumetric analysis. Cardiac ROS activity (TBARS, NRF2, Keap-1) was determined. Results: TAC promoted LVH in mice (LVMI: 6.38±0.38 mg/mm tibia length (sham), 8.11±0.63 (TAC) which was blunted by melatonin (LVMI: 6.34±0.31 (TAC+MEL) mg/mm, P<0.05). Increased LVH was associated with decreased endocardial shortening measured by echocardiography, from 61±2 (sham) to 54±1.8 % (TAC + placebo), P <0.05. This decrease in fractional shortening was less pronounced in the TAC+ MEL group (58±2.9%) as well as in PV loop analysis. The antioxidant action of MEL was evidenced by the decrease in myocardial lipid peroxidation (TBARS) from 0.35±0.02 (TAC) to 0.25±0.02 (TAC+MEL) nmol/mg of protein, P<0.05. Adult mice isolated myocyte studies revealed that Ang 2 (20nM) increased sarcomere shortening and calcium transient, both of which were blunted when cells were pre-incubated with melatonin (p< 0.005, Ang2 vs MEL + Ang2). In the exercise group, melatonin had only a small, non-significant reduction in LVMI, but a marked improvement in cardiac performance (PV loop analysis). Conclusion: Melatonin prevents pressure-overload LVH and improves contractility due to its antioxidant action. In physiologic LVH (exercise), melatonin does not affect hypertrophy, but exerts a positive effect on cardiac performance. These effects seem to be, at least in part, mediated through melatonin interfering with the Keap-1- Nrf2 antioxidant pathway.