2,3,7,8-Tetrachlorodibenzo-p-dioxin Decreases Responsiveness of the Hypothalamus to Estradiol as a Feedback Inducer of Preovulatory Gonadotropin Secretion in the Immature Gonadotropin-Primed Rat

Short-Term Hormone Release from Adult Female Rat Hypothalamic and Pituitary Explants is not Altered by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

“…Apparently TCDD changes the estrogen threshold such that the concentration o f s e r u m e s t r o g e n r e q u i r e d t o e l i c i t t h e gonadotropin surge is ten times greater than normal [17]. Our data would suggest that the reduced ability of the pituitary to respond to estrogen following TCDD exposure observed by Gao et al [17] is mediated via a mechanism other than the ERα. On the other hand, we were also una ble to detect any changes in ERα as a consequence of day of the estrous cycle.…”

“…TCDD could alter feedback of estrogen at the pituitary by altering either ERα or ERβ. Gao et al [17] observed that the ovulatory rate, which is typically reduced by TCDD exposure, returned to normal in rats that were also treated with high doses of estrogen. The addition of estrogen triggered the release of the FSH and LH surge [17].…”

“…Gao et al [17] observed that the ovulatory rate, which is typically reduced by TCDD exposure, returned to normal in rats that were also treated with high doses of estrogen. The addition of estrogen triggered the release of the FSH and LH surge [17]. Apparently TCDD changes the estrogen threshold such that the concentration o f s e r u m e s t r o g e n r e q u i r e d t o e l i c i t t h e gonadotropin surge is ten times greater than normal [17].…”

“…The addition of estrogen triggered the release of the FSH and LH surge [17]. Apparently TCDD changes the estrogen threshold such that the concentration o f s e r u m e s t r o g e n r e q u i r e d t o e l i c i t t h e gonadotropin surge is ten times greater than normal [17]. Our data would suggest that the reduced ability of the pituitary to respond to estrogen following TCDD exposure observed by Gao et al [17] is mediated via a mechanism other than the ERα.…”

“…It was concluded that TCDD was able to increase the potency of sex-steroids as feedback inhibitors of LH [15,16] by altering pituitary GnRH receptor number and responsiveness to GnRH [16]. Similarly, Gao et al [17] reported that exposure to TCDD blocks ovulation in female rat.…”