The effects of tanshinone VI (Tan), a diterpene extracted from Salvia miltiorrhiza, on insulin-like growth factor-1 (IGF-1)-induced hypertrophy of cardiomyocytes were examined. Cultured cardiomyocytes were isolated from neonatal rat hearts. The incorporation of [(3)H]-leucine into the trichloroacetic acid (TCA)-insoluble fraction was measured as a marker of protein synthesis, which revealed cardiomyocyte hypertrophy. Various concentrations of IGF-1, ranging from 0.1 nM to 10 nM, increased [(3)H]-leucine incorporation into the TCA-insoluble fraction of cardiomyocytes in a dose-dependent manner. IGF-1 induced an increase in phosphorylated extracellular signal-regulated kinase 1/2 (ERK), but did not change ERK protein content in cardiomyocytes. When the cells were incubated in the presence of Tan (0.1 muM to 10 muM), [(3)H]-leucine incorporation into IGF-1-untreated cells was unaltered. When the cells were incubated with 10 muM Tan, IGF-1-induced increases in [(3)H]-leucine incorporation into the TCA-insoluble fraction and phosphorylated ERK were attenuated. These results suggest that Tan is a possible agent for the suppression of IGF-1-induced hypertrophy of cardiomyocytes via an attenuation of ERK activation.
