Combinatorial effects of the phytoestrogen genistein and of estradiol in uterus and liver of female Wistar rats

In a previous study we showed that genistein (GEN) does not significantly stimulate proliferation in the endometrium of female ovariectomized (OVX) rats. Because of the relevance of this finding for menopausal applications of GEN we now extended our study to combinatorial effects of GEN and of estradiol (E2). Experimentally, we compared the effects of GEN (10mg/kg/d BW) on uterine proliferation and on uterine gene expression in intact female rats with those in OVX rats which were substituted with a low dose (1µg/kg/d BW) or a high dose (4µg/kg/d BW) of E2. In parallel we investigated effects of GEN in the liver of the same animals. Treatment of OVX animals with GEN verified its previously described weak uterotrophy. In combination with E2 no effects of GEN on uterine wet weight were detectable. In OVX animals GEN significantly reduced E2 induced stimulation of uterine epithelial height, an effect not detectable in intact animals. In intact animals GEN significantly down regulated the uterine mRNA expression of the proliferation marker PCNA and the number of PCNA stained nuclei. This effect was not detectable in OVX animals. In addition we investigated the uterine mRNA expression of six estrogen responsive genes. As a tendency GEN counteracted E2 mediated gene regulation pattern, although this effect was not detectable for all genes in each treatment group. GEN in combination with E2 strongly affected hepatic gene expression. In all combination experiments GEN down-regulated CaBP9K mRNA levels below the level of corresponding E2 groups, while effects on down-regulation of IGFBP1 expression was less pronounced. In conclusion, in view of our previous study, the results reported here strongly suggest that treatment with GEN either alone, or in combination with E2 is safe regarding stimulation of proliferation in the endometrium, although intact animals and OVX animals which were substituted with E2 responded different. Regarding the strong interaction of E2 and of GEN on hepatic gene expression it is important to rule out that these effects reflect toxic reactions.