Uterotropic effects of dietary equol administration in ovariectomized Sprague-Dawley rats

Aim The aim of the present study was to evaluate the uterotropic effects of the administration of dietary equol, a metabolite of soy-derived daidzein or formononetin present in red clover, in an ovariectomized rat model of menopause. Method Two doses of racemic equol were used (50 mg kg of chow and 400 mg kg of chow) and the results were compared with two doses of estradiol-3 benzoate (E2B) (4.3 mg kg of chow and 17.3 mg kg of chow). After 3 months, animals were sacrificed and the uteri were removed, weighed and paraffin-embedded for morphometrical and immunohistochemical evaluation. The expression of selected uterine estrogen-responsive genes was also measured using real-time reverse transcription-polymerase chain reaction. Results Compared to controls, uterine weights in animals treated with high-dose equol were significantly higher, presented histologic features of mild estrogenic stimulation and had greater epithelial height and thickness of the uterine stroma and myometrium. Staining for the presence of the proliferating cell nuclear antigen (PCNA) also showed a greater prevalence of the PCNA-positive cells in the uterine stroma in animals treated with high-dose equol. Conversely, the percentage of PCNA-positive cells in the uterine epithelium was lower compared to the controls. Dietary high-dose equol treatment also increased significantly levels of uterine insulin-like growth factor 1, progesterone receptor and complement protein 3 mRNA. Although statistically significant, all these effects were, however, lower in magnitude compared to the effects of low- and high-dose E2B treatment. Low-dose equol did not have any effects on the above-studied parameters. Conclusion Long-term high-dose dietary equol administration to ovariectomized rats exerts uterotropic effects at the cellular and molecular level which question the safety of uncontrolled and unlimited consumption of soy or red clover supplements by postmenopausal women with intact uteri.