e53 Letter to the Editor Response to Letter Regarding “Myostatin Regulates Energy Homeostasis in the Heart

In the article1 referred to in Drs McLean and Oudit’s letter,2 we ana lyzed the effects of inactivation of myostatin in adult cardiomy-ocytes. Drs McLean and Oudit correctly point out that treatment of mice with tamoxifen to induce activation of cre recombinase estrogen receptor fusion proteins causes transient systolic dys-functions.3 They expressed concern that the relatively high dos-age of tamoxifen administered in our experiments (100 mg/kg daily for up to 5 days) contributed to decreased survival, transient impairment of contractility, and cardiomyocyte hypertrophy in adult cardiomyocyte-specific myostatin mutants.1 In our experi-ments, we always directly compared tamoxifen-treated αMyHC-MCM/Mstnfl/fl with tamoxifen-treated αMyHC-MCM mice, which in our view is the best possible control. In tamoxifen-treat-ed αMyHC-MCM mice, we only observed a mild depression of cardiac function without any effect on lethality while tamoxifen