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Regulação da função ovariana: caracterização estrutural e papel do hormônio anti-mülleriano (AMH) / Regulation of Ovarian Function: Structural Characterization and Role of Anti-Müllerian Hormone (AMH)

Rocha, Rebeca Magalhães Pedrosa; Alves, Anelise Maria Costa Vasconcelos; Lima, Laritza Ferreira de; Araújo, Valdevane Rocha; Bernuci, Marcelo Picinin; Rodrigues, Ana Paula Ribeiro; Figueiredo, José Ricardo de.
Acta sci. vet. (Impr.); 41: Pub. 1138, 2013. ilus
Artigo em Português | VETINDEX | ID: biblio-1372117

Resumo

Background: The anti-müllerian hormone (AMH) is a member of the transforming growth factor ß (TGF-ß) superfamily, which exerts important functions on local regulation of folliculogenesis. Although in vivo and in vitro studies suggest that AMH affects the primordial follicle assembly and activation, as well as the responsiveness of growing follicles to folliclestimulating hormone (FSH), the physiological mechanisms involved in these actions remain to be fully elucidated. Given the relevance of AMH in the folliculogenesis, this review aimed to describe the structural features, expression and the main biological effects of AMH on the follicular development. Review: Originally identified as a testicular product, AMH is responsible for regression of the Müllerian ducts during sexual differentiation of male embryos. In females, AMH is produced almost exclusively by granulosa cells of ovarian growing follicles, whose serum levels are positively related to the number of ovarian follicles, making AMH an excellent clinic marker of ovarian reserve. Along this work, it was shown aspects related to the structural characterization of AMH and its specific type II receptor (AMHRII). AMH is a glycoprotein dimer linked by disulfide bonds. The mature protein comprises two unequal domains: a long N-terminal domain (110-kDa) and a short C-terminal domain (25-kDa), responsible for the biological activity of the molecule. The AMHRII is an 82-kDa protein. Like others members of TGF-ß family, AMH signals through two types of serine/threonine kinase receptors called type I and type II, and two types of Smad proteins, receptor-regulated Smad (R-Smad) and common Smad, Smad4. However, the identity of the AMH type I receptor is not clear; three type I receptors of Bone Morphogenetic Proteins (BMPs), Alk2, Alk3 and Alk6 may transduce AMH signals. AMH expression was detected in granulosa cells of growing follicles and it decreases once FSH-dependent follicular growth has been initiated. Follicles showing signs of atresia also have decreased or no AMH expression, and expression is completely lost in corpora lutea. AMH is not found in primordial follicles, theca cells, oocytes or the interstitium. This specific expression pattern of AMH suggests a role in the two regulatory steps of folliculogenesis: the recruitment of primordial follicles and the sensitivity of large preantral and small antral follicles to FSH. Evidences obtained from studies with AMH-knockout mice suggest that AMH inhibits activation of primordial follicles into the growing pool, while at cyclic recruitment AMH lowers the FSH-sensitivity of follicles. In addition, AMH was recently implicated in the primordial follicle assembly. AMH was found to inhibit primordial follicle assembly and decrease the initial primordial follicle pool size in a rat ovarian organ culture. Conclusion: From this review, we can conclude that AMH plays a key role on the modulation of ovarian function in mammals. This substance is an important player in two checkpoints that regulate the efficiency of primordial follicle pool usage and the choice of the dominant follicle: activation and selection, respectively. However, it is necessary to perform additional studies that may provide a better understanding about the importance of AMH during folicullogenesis.
Biblioteca responsável: BR68.1