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1 April 2002 Loss of Luteinizing Hormone Surges Induced by Chronic Estradiol Is Associated with Decreased Activation of Gonadotropin-Releasing Hormone Neurons
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Abstract

Chronic exposure of young ovariectomized rats to elevated circulating estradiol causes loss of steroid-induced LH surges. Such LH surges are associated with cFos-induced activation of GnRH neurons; therefore, we hypothesized that chronic estradiol treatment abolishes LH surges by decreasing activation of GnRH neurons. Regularly cycling rats were ovariectomized and immediately received an estradiol implant or remained untreated. Three days or 2 or 4 wk later, the estradiol-treated rats received vehicle or progesterone at 1200 h, and 7 hourly blood samples were collected for RIA of LH. Thereafter, all rats were perfused, and the brains were examined for immunocytochemical localization of cFos and GnRH. The GnRH neurons from untreated ovariectomized rats rarely expressed cFos. As reported, LH surges induced by 3 days of estradiol treatment were associated with a 30% increase in cFos-containing GnRH neurons, and progesterone enhanced both the amplitude of LH surges and the proportion of cFos-immunopositive GnRH neurons. As hypothesized, the abolition of LH surges caused by 2 or more weeks of estradiol was paralleled by a reduction in the percentage of cFos-containing GnRH neurons, and this effect was delayed by progesterone. These results suggest that chronic estradiol abolishes steroid-induced LH surges in part by inactivating GnRH neurons.

Houng-Wei Tsai and Sandra J. Legan "Loss of Luteinizing Hormone Surges Induced by Chronic Estradiol Is Associated with Decreased Activation of Gonadotropin-Releasing Hormone Neurons," Biology of Reproduction 66(4), 1104-1110, (1 April 2002). https://doi.org/10.1095/biolreprod66.4.1104
Received: 26 September 2001; Accepted: 1 November 2001; Published: 1 April 2002
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