Effect of equol on oestrogen receptors and on synthesis of DNA and protein in the immature rat uterus.

In immature, 3-week-old female rats, 5 mg equol given by subcutaneous injection increased uterine wet weight 24 h later to the same degree as did 5 microgram oestradiol-17 beta. At this dose there was more receptor complex binding to the nucleus in the equol-injected rats than in the rats injected with oestradiol-17 beta even after 6 h. However, the equol-receptor complex that bound to the nucleus was more extractable with 0 x 3 M-KCl. In the equol-injected rats the duration of uterine growth was shorter and there was less receptor replenishment and synthesis of protein and DNA than in the rats injected with oestradiol-17 beta 30 h after either injection. It was concluded that equol is a weakly oestrogenic compound which is antagonistic to oestradiol-17 beta by competing with oestradiol-receptor complex for nuclear binding and yet fails to initiate the replenishment of oestrogen receptors effectively in the cytoplasm.