Semester

Fall

Date of Graduation

2007

Document Type

Dissertation

Degree Type

PhD

College

School of Pharmacy

Department

Pharmaceutical Sciences

Committee Chair

Eisuke P Murono

Abstract

Methoxychlor, an organochlorine pesticide, is released into the environment as a result of its agricultural, home and veterinary use. Following in vivo administration, it is quickly metabolized by liver to the proposed active agent, HPTE. Both methoxychlor and HPTE have been shown to exhibit weak estrogenic and antiandrogenic activities, and they are thought to exert their effects through estrogen and androgen receptors. In vivo exposure to methoxychlor in laboratory animals causes ovarian atrophy and impaired ovarian steroid production. The effect of methoxychlor and its mechanism(s) of action on ovarian steroidogenesis are not clearly defined. The central hypothesis of these studies is that exposure to HPTE directly inhibits ovarian steroid biosynthesis, which is able to cause an imbalance in circulating progesterone and estradiol levels. The specific aims of the project are: (1) To pinpoint the potential effect of HPTE on ovarian steroidogenesis, (2) To examine the possible mechanism(s) of action of HPTE on ovarian steroidogenesis, (3) To evaluate the potential effect of HPTE on ovarian luteal steroidogenesis, (4) To determine whether in vivo exposure to methoxychlor lowers serum progesterone or estradiol levels and/or inhibits ex vivo ovarian steroidogenesis. Results obtained from the in vitro studies demonstrated that HPTE directly inhibits progesterone formation by PMSG-primed rat ovarian theca, granulosa and luteal cells, and this decline in progesterone corresponded to a decline in P450 cholesterol side-chain cleavage activity, which converts cholesterol to pregnenolone in the pathway of progesterone and estrogen biosynthesis. In addition, the percentage decrease in progesterone production was greater than the declines in estradiol and androgen formation suggesting that HPTE may increase the estrogen/progesterone ratio. Further, this effect of HPTE action could be observed at the environmentally relevant concentrations of 10-50 nM and does not appear to be mediated through ER or AR signaling pathways. Consistent with the HPTE action in the in vitro studies, in vivo exposure to methoxychlor lowers circulating progesterone levels in the immature rats not treated with gonadotropins; however, the exposure of animals to gonadotropins leads to an ex vivo increase in progesterone production by isolated ovarian theca cells and no change in circulating progesterone levels. This suggests that the pattern of active steroids secreted ex vivo by ovarian cells in response to methoxychlor exposure differs from that observed following in vitro exposure to methoxychlor/HPTE.

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