Early life exposure to genistein and daidzein disrupts structural development of reproductive organs in female mice.

In mice, exposure to isoflavones (ISO), abundant in soy infant formula, during the first 5 d of life alters structural and functional development of reproductive organs. Effects of longer exposures are unknown. The study objective was to evaluate whether exposure to a combination of daidzein and genistein in the first 10 compared to 5 d of life results in greater adverse effects on ovarian and uterine structure in adult mice. Thirteen litters of 8-12 pups were cross-fostered and randomized to corn oil or ISO (2 mg daidzein + 5 mg genistein/kg body weight/d) for the first 5 or 10 d of life. The 10-d protocol mimicked the period when infants are fed soy protein formula (SPF) but avoids the time when suckling pups can consume mother's diet. Body and organ weights, and histology of ovaries and uteri were analyzed. There were no differences in the ovary or uterus weight, number of ovarian follicles, number of multiple oocyte follicles, or percent of ovarian cysts with 5 or 10 d ISO intervention compared to respective controls. The 10-d ISO group had higher body weights from 6 d to 4 mo of age and a higher percent of hyperplasia in the oviduct than the respective control. Lower number of ovarian corpus lutea and a higher incidence of abnormal changes were reported in the uteri of both ISO groups compared to their respective controls. Five and 10-d exposure to ISO had similar long-lasting adverse effects on the structure of ovaries and uterus in adult mice. Only the 10-d ISO exposure resulted in greater body weight gain at adulthood.