1989) FSH synthesis and release respectively.
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Particularly, activins and inhibins, members of the transforming growth factor-β (TGF-β) superfamily, are able to stimulate ( Ling et al. While the LH secretion is mainly dependent of GnRH and gonadal steroids, additional factors are involved in regulation of FSH production. The hypothalamic GnRH is the major regulator of LH and FSH secretion. Synthesis and release of LH and FSH by gonadotrope cells are regulated by a complex interplay of hypothalamic, gonadal, and pituitary factors. In mammals, the gonadotropins FSH and LH are essential components for reproduction ( Morel et al. Collectively, our data showed that pituitary BMP4 would not play a crucial role in the regulation of FSH production during the estrous cycle, whereas local activin B would be a major stimulus of FSH synthesis necessary for the secondary FSH surge. In contrast, SB431542, an inhibitor of activin pathway, inhibited FSH release. Moreover, the in vitro FSH release was not modified by noggin, a BMP antagonist. E 2, but not GnRH, increased the level of activin βB mRNA. In ewe pituitary cell cultures, activin, GnRH, or estradiol-17β (E 2) did not significantly affect the levels of BMP4, BMP receptor, and Id2 mRNA. In contrast, the level of activin βB mRNA and the percentage of immunoreactive cells for activin βB-subunit were higher before the secondary surge of FSH compared to other groups. Using quantitative reverse transcription-PCR, we showed that the levels of mRNA for BMP4, BMP receptor, the inhibitor of differentiation 2 ( Id2), a target gene of BMP4, and noggin did not change significantly across the estrous cycle.
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Ewes were killed in late follicular stage ( n=5), before the secondary FSH surge ( n=4), and in luteal phase ( n=4). The estrous cycles of ewes were synchronized with progestagen sponges. This work aimed at determining whether BMP4 and/or BMP receptor mRNA as well as activin/inhibin subunit mRNA fluctuates during the estrous cycle when FSHβ mRNA and FSH release changed. The detection of BMP4 mRNA and BMP receptors in the pituitary suggests that BMP4 can exert paracrine actions on FSH production. Recently, bone morphogenetic protein (BMP) 4 has been shown to inhibit FSH secretion in ewe.