Abstract: AIM To investigate the effect of genistein (Gen) on the expression of interleukin 6 (IL-6), an important inflammatory cytokine, in cultured cardiomyocytes and the role of reactive oxygen species (ROS) in signal transduction mechanisms. METHODSCardiomyocytes were isolated and cultured from neonatal Sprague Dawley rats, which were divided into four groups: control group, AngII group, AngII+Gen group and Gen group. Expression of IL-6 mRNA and protein level were determined by RT-PCR and ELISA. ROS generation in cardiomyocytes was determined by peroxide-specific probe 2,7-dichlorofluorescein diacetate (DCF-DA). Activity of NADPH oxidase in cardiomyocytes was measured by superoxide dismutase inhibitable cytochrome C reduction assay. RESULTSIn cardiomyocytes stimulated with angiotensin II (AngII), expression of IL-6 mRNA was higher than in untreated cells (P<0.05), which was markedly attenuated by pretreatment with 1×10-7 mol/L Gen (P<0.05). Similarly, compared with blank group, IL-6 content in culture medium significantly increased in LPS group (P<0.05). Pretreatment with Gen decreased IL-6 content induced by AngII (P<0.05). Furthermore, AngII increased ROS generation and activity of NADPH oxidase in myocytes in comparison with that in blank control group, which was also attenuated by pretreatment with Gen (P<0.05). CONCLUSIONGenistein inhibits expression of IL-6 in cultured cardiomyocytes induced by AngII. ROS is probably an important downstream signaling molecule in the molecular mechanism.