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Resumen del trabajo presentado en el 25th Conference of European Comparative Endocrinologists, celebrada en Pécs (Hungría), del 31 de agosto al 4 de septiembre de 2010, Follicle-stimulating hormone (FSH) is essential to achieve follicular growth. Its action is exerted via interaction with its specific receptor, a transmembrane G-protein-coupled receptor. Activation of G proteins results in the regulation of a complex pattern of gene expression through different signaling cascades. In the present study the involvement of cAMP/PKA and MAP-kinase routes on FSH induced sea bass steroidogenesis was evaluated. Ovarian explants of one year old female sea bass were pre-incubated with different doses of the cAMP/PKA inhibitor Rp-cAMPs or the MAPK inhibitor PD-98059. Next, tissues were stimulated with sea bass recombinant FSH or the cAMP/PKA activator (8Br-cAMPs). After 20 hours culture at 21¿C the levels of estradiol (E2) and testosterone (T) were analyzed in the culture medium. Expression levels of StAR and CYP19A1 were as well evaluated by real-time PCR. Both, FSH and 8Br-cAMPs treatments significantly increased secretion of E2 and T to the culture medium. When the cAMP/PKA inhibitor Rp-cAMPs was added to the medium a marked decrease on T but not E2 levels was found. The MAPK inhibitor, PD-98059, either alone or in the presence of FSH or 8Br-cAMPs, was able to reduce T levels. In addition, E2 levels induced by the activators were also inhibited by PD-98059. Strong up-regulation effects on the expression of StAR and CYP19A1 were detected after FSH or 8Br-cAMPs exposure. The inhibitor Rp-cAMPs clearly blocked the expression of both genes in cultures treated with 8Br-cAMPs, but had no clear effect on gene expression in FSH treated tissue. These results confirm that FSH in sea bass exerts its action via the cAMP/PKA signaling pathway, but the action of MAP-kinases over the steroidogenic process is also relevant. Further research is necessary to elucidate the relation between the cAMP/PKA and MAP-kinase pathways in the steroidogenic., Research supported by MICINN (AGL2005-00796 and AGL2008-02937) MJ. Mazón received a FPI fellowship from the Spanish MICINN