Exposure to dietary phytoestrogens such as genistein during early childhood is a growing public health concern. We examined the effect of early exposure to genistein on sexual maturation in immature rats.

Weaning (3wk-old) Sprague-Dawley female rats were assigned to three groups (n=6 for each): fed by high dose of genistein (100 mg/kg/d), low dose of genistein (10 mg/kg/d) and control group. First vaginal opening (VO) day was observed. Structural alterations in the ovary and uterus were assessed by histologically. Expression of genes of ERα, ERβ, and progesterone receptor (PR) in the ovary and uterus were investigated by RT-PCR.

High genistein group had earlier VO than control and low genistein group. Graafian follicle s and corpora lutea were observed from the ovary of genistein-treated groups, while primary, secondary follicles and small atretic follicles were observed in the control group. Hypertrophy of luminal and glandular uterine epithelia were found in the genistein-treated groups while poor development of gland and fewer myometrial cell layers were evident in control group. In ovary, the transcriptional activities of ERα and ERβ were higher in high genistein group than in controls. In uterus, the transcriptional activities of ERα, ERβ and PR were higher in low genistein group than in controls.

Acute exposure to genistein during the prepubertal period could activate the reproductive endocrine system resulting in the early onset of puberty in female rats. Further clinical investigation on the effect of genistein on the sexual maturation in children is warranted.