Actions of estradiol on the gonadotropic axis and spermatogenesis in male european sea bass (Dicentrarchus labrax)

Póster presentado en el XII Congress of Iberian Association for Comparative Endocrinology, celebrado en Faro (Portugal) del 26 al 28 de septiembre de 2019.The follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) are central endocrine regulators of gametogenesis in vertebrates, and gonadotropin-releasing hormones (Gnrh) have been postulated as the main regulators of their synthesis and secretion. In addition, gonadal sex steroids have a feedback effect modulating the availability of gonadotropins. All these effects at the level of pituitary have a direct impact in gametogenesis progression. Previous in vivo studies in sea bass, during the sexual resting period, showed that Gnrh injections stimulated Lh synthesis and release, but had no effect on the expression of the Fsh beta-subunit gene. At the same time, different steroid implants repressed fsh beta expression, but activated the expression of lh-beta in the pituitary. In this study we have focused on the action of estradiol in males in different moments of gametogenesis. To elucidate how this system is organized in the pituitary of sea bass, we analysed in a first step the annual profile of male pituitary expression of the three nuclear estrogen receptors, in relation with the different stages of spermatogenesis, the pituitary gonadotropin content and the circulating levels of estradiol. In addition, immunohistochemistry studies have been performed to identify the pituitary cells containing steroid receptors and their relation with gonadotrophs and GnRh1 fibers. Next, we have used an in vitro pituitary primary cell cultures stimulated with estradiol to study its direct action on gonadotrophs, and estradiol implants to study its in vivo effect on the pituitary and the gonad. We have concluded that estradiol has a general an inhibitory effect on the gonadotropins, although with different specific actions, which is also reflected in the distribution of the estradiol receptors in the gonadotrophs, while Gnrh differentially regulates Lh and Fsh cells in male seabass.Funded by MICINN (AGL2015-67477-C2-1-R, RTI2018-094667-B-C22) and CSIC (201640E073