Acute and Chronic Exposure to Phytoestrogens Disrupts Ovarian Follicle Maturation in Sprague-Dawley Rats.

Abstract

The consumption of dietary phytoestrogens, such as isoflavones, has grown increasingly popular due to their potential health benefits. These soy products contain the isoflavones genistein, diadzein, and glycitein, which belong to a class of non-steroidal estrogen-like compounds called phytoestrogens. These naturally occurring plant estrogens may provide health-related benefits in some tissues; however, they may present deleterious side effects on estrogen-sensitive reproductive tissue such as the developing ovary. Several studies have documented that an in-utero and lactational exposure to estrogenic chemicals alters normal reproductive tissue development. This study was designed to determine (1) if an in-utero, lactational and chronic exposure to a low or high dose of a mixed isoflavone supplement (LSup and HSup) or a low dose of pure genistein (Gen) exerts detrimental effects on ovarian follicle maturation in the Sprague-Dawley rat; (2) whether estrogen concentrations are altered following acute or chronic exposure; and (3) whether estrous cycles are modulated during chronic exposure. Animals receiving an acute exposure were treated in utero and lactationally from gestational day 7 through postnatal day 28 (weaning). Animals receiving a chronic exposure were treated directly for an additional 65 days. Acute- and chronic-exposure groups were treated daily via oral gavage (LSup, HSup) or subcutaneous injection (Gen). LSup and HSup treatment groups received 2.4 mg/kg/day or 24 mg/kg/day, respectively. The Gen treatment group received 0.2 mg/kg/day. Acutely exposed pups were sacrificed on postnatal day 28 (chosen in order to follow the pups' exposure through lactation). Chronically exposed rats were sacrificed on postnatal day 93. Following sacrifice, the ovaries were excised, fixed for histology, and analyzed. The analysis included a count, and measurement and classification of preantral and antral follicles in the greatest cross-sectional area of the ovary. Blood samples collected at the time of sacrifice were analyzed for estrogen concentrations via radioimmunoassay. No statistical change in estrogen concentrations was noted among acute-treatment groups. Radioimmunoassay results for the chronically exposured groups indicated a significant difference in estrogen concentration between the control group and the other three treatment groups (p<0.001). For both the acute- and chronic-treatment groups, atresia levels and follicular count remained consistent in the control, LSup, and Gen treatment groups; however, increased atresia and decreased follicles were observed in the HSup treatment groups (p<0.05). Modulation of estrous cycles was noted in all four chronic treatment groups. These data support the hypothesis that isoflavones reduce the number of follicles of certain size classes in rats exposed during the critical period of development and during chronic exposure after birth. Atresia of antral follicles may constitute one of the underlying mechanisms by which folliculogenesis is modulated by phytoestrogens. The results of this study begin to elucidate the acute and chronic effects of a soy phytoestrogen on reproductive parameters in the female Sprague-Dawley rat. (platform)