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a Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan, Republic of China
b National Museum of Marine Biology and Aquarium, Pingtung 944, Taiwan, Republic of China
c Laboratoire de Physiologie, UMR 8572 CNRS, Museum National d'Histoire Naturelle, Paris, France
We investigated the mechanism of estradiol-17ß (E2) action on stimulation of LH (=gonadotropin II) release in the black porgy fish (Acanthopagrus schlegeli Bleeker) using an in vivo approach and primary cultures of dispersed pituitary cells in vitro. In vivo, E2 but not androgens (testosterone [T] and 11-ketotestosterone [11-KT]) significantly stimulated plasma LH in a dose-dependent manner. Estradiol-17ß also increased brain content of seabream GnRH. GnRH antagonist prevented E2 stimulation of LH release in vivo, indicating that the effect of E2 on LH was mediated by GnRH. In vitro, sex steroids (E2, T, 11-KT) alone had no effect on basal LH release in the cultured pituitary cells, but GnRH significantly stimulated LH release. Estradiol-17ß potentiated GnRH stimulation of LH release, an effect that was inhibited by GnRH antagonist, and 11-KT, but not T, also potentiated GnRH stimulation of LH release. The potentiating effect of 11-KT on GnRH-induced LH release in vitro was stronger than that of E2. These data suggest that E2 triggers LH release in vivo by acting both on GnRH production at the hypothalamus and on GnRH action at the pituitary. In contrast, 11-KT may only stimulate GnRH action at the pituitary. The E2 induction of LH release, through multiple interactions with GnRH control, supports a possible central role of E2 in the sex change observed in the protandrous black porgy.
1 This work was supported in part by the National Science Council (NSC 91-2313-B019-058), Taiwan.
2 Correspondence. FAX: 886 2 2462 1579; b0044{at}mail.ntou.edu.tw
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