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theses

Endocrine-disrupting chemicals (EDCs) are synthetic or natural compounds that can be found in the environment in various forms, such as pesticides [e.g., methoxychlor (MXC)], plasticizers [e.g., bisphenol A (BPA)], or pharmaceutical agents [e.g., diethylstilbestrol (DES), a potent synthetic estrogen that was prescribed to pregnant women between 1940s and 1970s. Previous studies indicated that the ovary is particularly vulnerable to estrogenic EDC exposures during fetal and neonatal periods. To investigate the effects of estrogenic EDCs in two critical developmental windows, we performed two experiments, using timed-pregnant Fisher CDF rats. In Experiment 1, we exposed the dams to 50 µg/kg/day (Low) BPA or 50 mg/kg/day (High) BPA, or vehicle from embryonic day (E) 18 to 21, and the pups from postnatal day (PND) 0 to 7. In Experiment 2, we exposed animals to 0.1µg/kg/day DES, 75 mg/kg/day MXC, 50 mg/kg/day BPA, or vehicle from E11 to PND7. We then examined reproductive parameters, including pubertal age, regularity of reproductive cycles, and follicular composition. Expression of critical ovarian markers, including estrogen receptor 1 (ESR1), Mullerian inhibiting substance (MIS), cytochrome P450 side chain cleavage (P450scc), luteinizing hormone receptor (LHR), and proliferating cell nuclear antigen (PCNA) were also examined. In Experiment 1, we found that there were no changes in age at puberty or estrous cyclicity in the both Low and High BPA-treated females. However, there was a decrease (p < 0.05) in primary follicles in High BPA-treated rats. In addition, there was an increase in atretic follicle numbers (p < 0.05) in the Low and High BPA-treated females suggesting that there was an effect on follicular dynamics. Moreover, a short window of ovarian exposure to BPA did not show any statistically significant effects on expression of ovarian markers except ESR1which was decreased in primary follicles in Low BPA-treated females. In Experiment 2, our results demonstrated that DES- and MXC-treated females had an accelerated onset of puberty and altered estrous cyclicity. Although there was no effect on the litter size, MXC-treated females showed a strong trend towards reduction in litter size (p = 0.07) as compared to control. MXC caused a decrease in steroid hormone levels. DES, MXC, and BPA exposures altered follicular dynamics. There was an increase in atretic follicles in DES and BPA-treated females. In addition, the number of corpora lutea (CL) was reduced (p < 0.01) in MXC-treated females while the total follicle numbers were not altered. There were alterations in ovarian molecular markers. Expression of MIS significantly increased in secondary and pre-antral follicles in MXC-treated group. Furthermore, expression of P450scc decreased in pre- and early-antral follicles in MXC-treated females while the expression increased in CL in BPA-treated females. Overall, the results show that developmental exposure to estrogenic-EDCs affects female reproduction and ovarian follicular dynamics. In addition, DES and MXC can alter the age of puberty, and regulatory of reproductive cycles, which may lead to female fertility problems.

ETD_7902

M.S.

Includes bibliographical references

by Seher Yirtici

doi:10.7282/T3FT8PZ8

ETD graduate

The author owns the copyright to this work.