Soy phytoestrogens improve radial arm maze performance in ovariectomized retired breeder rats and do not attenuate benefits of 17β-estradiol treatment

Objective: Soy phytoestrogens (SPEs) seem to have beneficial effects on the cardiovascular system with no adverse effects on the breast and uterus. Our objective was to examine the effects of oral estradiol alone, soy protein with phytoestrogens alone, and combinations of estradiol and SPEs on working memory of ovariectomized retired breeder female rats using the radial arm maze test. Design: Eighty-four bilaterally ovariectomized retired breeder female rats were randomized into 12 groups to examine the effects of chronic treatment (10 months) with oral micronized estradiol (0, 0.5, 1, and 2 mg/1,800 Cal), SPEs (0, 72, and 144 mg/1,800 Gal), and all combinations of these doses of estradiol and SPEs on working memory. Results: Oral administration of estradiol or SPEs resulted in a dose-dependent improvement in the performance of the radial arm maze tests. Zn addition, at each of the three doses of oral micronized estradiol tested, the performance of the radial arm tests was not significantly different in the presence or absence of SPEs. Conclusions: Our data suggest that SPEs may function as estrogen agonists in improving working memory in the ovariectomized retired breeder female rats and that SPEs do not antagonize the beneficial effects of estradiol on the working memory of these rats. No additional benefits on the radial arm maze test performance were observed with the tested combinations of estradiol and SPEs. (Menopause 2000;7:230-235. (C) 2000, The North American Menopause Society.).