Endocrine Abstracts

Anti-Mullerian hormone (AMH) has an important regulatory role both in early folliculogenesis (inhibiting the recruitment of follicles from the primordial pool into the growing phase) and at the antral stage (where it inhibits the action of FSH). In the mouse, AMH action appears to be mediated by a heterodimeric receptor complex comprising a type I receptor and the specific AMH receptor AMHRII, which is essential for AMH signalling in the murine ovary. Post-receptor signalling involves Smad proteins 1, 5 & 8. AMHRII is expressed in the primordial follicle onwards in mouse ovary. In the human ovary AMH protein is also expressed in preantral follicles and recent studies have shown reduced AMH expression in early preantral follicles from ovaries from women with polycystic ovary syndrome (PCOS). In this study we examined the expression of AMHRII and Smad1, 5 & 8 by immunohistochemistry in archived human ovarian tissue taken from women with normal ovaries and PCOS. A total of 465 follicles were analysed in sections from 9 ovaries. AMHRII protein was not found in preantral follicles but was present (mainly in granulosa but also in theca cells) in all antral follicles. Smad1, 5 & 8 were expressed in the oocyte in preantral follicles and in somatic cells of antral follicles. In normal ovaries, Smad 8 was found in the nucleus of the oocytes of 98% of primordial, 74% of transitional and 63% of primary follicles (Chi-square=79, P<0.0001), suggesting reduced activation with follicle development. There were no significant differences in AMHRII or Smad expression between normal and PCOS tissue. The ability of AMH to inhibit growth of human preantral follicles suggests that AMH receptors are present at these stages. The absence of immunostaining for AMHRII may reflect low, and therefore undetectable, receptor protein levels but is conceivable that AMH acts via an alternative receptor in the human ovary.