Objective:To investigate the effect of 17β-estradiol (E2) on cultured cardiomyocyte hypertrophy induced by mechanical stretch. Methods:Cardiomyocytes from neonatal rats were cultured in vitro and cardiomyocyte hypertrophy was induced by mechanical stretch. The effect of E2 on cardiomyocyte hypertrophy was evaluated by the surface areas of cardiomyocytes using immunocytochmistry and the β-MHC protein levels detected by Western blot. The integrin β1 protein levels were determined by Western blot. Results:Mechanical stretch for 24 h significantly increased cell surface areas and β-MHC protein levels, which suggested that mechanical stretch is a direct stimulus for isolated cardiomyocytes to develop hypertrophy. Mechanical stretch also significantly increased the expression of integrin β1 protein in cultured cardiomyocytes. Pretreatment with 100 nmol/L E2 for 30 min significantly attenuated the increases in cell surface areas and β-MHC protein levels induced by mechanical stretch which were attenuated by estrogen receptor antagonist ICI182780. Furthermore, E2 also decreased the levels of integrin β1 protein induced by mechanical stretch, and this was also attenuated by ICI182780. Conclusion:E2 prevents cardiomyocyte hypertrophy and the increase of integrin β1 protein induced by mechanical stretch in vitro.