[Combined estrogenic activity of soybean extract used in a dietary supplement and ethinyl estradiol].

We examined the combined estrogenic activity of soybean extract used in a dietary supplement and ethinyl estradiol (EE) contained in an oral contraceptive. Olive oil (control), soybean extract (0.0036 or 0.36 g/kg corresponding to doses of total isoflavone of 0.83 or 83 mg/kg respectively), EE (1 or 10 microg/kg), and soybean extract+EE were administered to ovariectomized CD-1 mice by oral gavage for 4 consecutive days. Soybean extract (0.0036 or 0.36 g/kg) and EE (1 microg/kg) did not increase the relative uterine weight. The relative uterine weight of the soybean extract (0.0036 or 0.36 g/kg)+EE (10 microg/kg) group was significantly higher than that of the control. The relative uterine weight of the soybean extract (0.36 g/kg)+EE (10 microg/kg) group was also significantly higher than that of the EE (10 microg/kg) group. Soybean extract showed estrogenic activity for human estrogen receptor (hER)-alpha and -beta. Coadministration of EE with soybean extract increased the estrogenic activity for hER-alpha and -beta.