The effect of the traditional herbal medicine (TCM) on E
binding to estrogen receptor (ER)α and ERβ. The competition binding curves for ERα (a) and ERβ (b) were generated by exposing HELN-ERα and HELN-ERβ cells, respectively, to increasing dilutions of the TCM (1%-0.0003%) in the presence of radiolabeled 17β-estradiol (E2) (0.3 nM [3H]-E2) for 3 hours at 37°C in a 5% CO2 humidified atmosphere. The amount of binding was expressed as a percentage of the maximum ER binding (100%), which was defined when the cells were exposed to 100 nM unlabeled E2. The IC50 value was defined as the dilution at which E2 binding was 50%. Each value at each dilution in the binding curves is the mean of duplicate determination ± standard deviation from three separate experiments. * = p < 0.05 for IC50 ERα vs ERβ.