Increased oocyte degeneration and follicular atresia during the estrous cycle in anti-Müllerian hormone null mice.

Anti-Müllerian hormone (AMH) plays an important role in folliculogenesis. AMH null mice display an increased recruitment of primordial follicles. Nevertheless, these mice do not have proportionally more preovulatory follicles. Therefore, AMH null mice provide an interesting genetic model to study the regulation of species-specific number of preovulatory follicles. We studied the follicle pool throughout the estrous cycle at 4 months of age. Analysis of the follicle pool revealed that AMH null mice have an increased and earlier cyclic recruitment of growing follicles despite a blunted FSH surge at estrus. However, FSH levels at estrus were apparently too low to support growth to the preovulatory stage because an increased level of atresia was observed, which neutralized the increased cyclic recruitment. When AMH null mice were subjected to a superovulation scheme, the rise in FSH levels resulted in the rescue of the recruited cohort of growing follicles. Analysis of the follicle pool also revealed that the increased recruitment of primordial follicles in AMH null mice was neutralized by an increased loss of follicles during the transition from small preantral to large preantral follicle. This major loss of follicles was not completely reflected by a corresponding augmentation of atresia but did correspond with an increased number of oocyte remnants observed in AMH null mice. We conclude that a combination of increased oocyte degeneration and increased follicular atresia neutralizes the increased initial and cyclic recruitment in AMH null mice to a normal number of preovulatory follicles.

Anti-Müllerian hormone and its role in ovarian function.

Anti-Müllerian hormone (AMH) is expressed after birth in the ovary in the granulosa cells of healthy, small growing follicles. We have shown that AMH affects two important regulatory steps during folliculogenesis. At initial recruitment, AMH inhibits recruitment of primordial follicles into the growing pool, while at cyclic recruitment AMH lowers the FSH-sensitivity of follicles. In these ways, AMH plays an important role in regulation of ovarian follicle growth. AMH serum level is a strong candidate marker for ovarian reserve in women. In normo-ovulatory women, AMH serum levels correlated strongly with the number of antral follicles. In addition, AMH is a strong predictor for the number of oocytes retrieved in patients undergoing IVF treatment. The convenience of determination and its relative stable expression during the menstrual cycle indicate that further validation of the use of serum AMH is recommended as a clinical measure of ovarian reserve.

Regulation of ovarian function: the role of anti-Müllerian hormone.

Anti-Müllerian hormone (AMH), also known as Müllerian inhibiting substance, is a member of the transforming growth factor beta superfamily of growth and differentiation factors. In contrast to other members of the family, which exert a broad range of functions in multiple tissues, the principal function of AMH is to induce regression of the Müllerian ducts during male sex differentiation. However, the patterns of expression of AMH and its type II receptor in the postnatal ovary indicate that AMH may play an important role in ovarian folliculogenesis. This review describes several in vivo and in vitro studies showing that AMH participates in two critical selection points of follicle development: it inhibits the recruitment of primordial follicles into the pool of growing follicles and also decreases the responsiveness of growing follicles to FSH.

Anti-Müllerian hormone inhibits initiation of primordial follicle growth in the mouse ovary.

Recruitment of primordial follicles is essential for female fertility; however, the exact mechanisms regulating this process are largely unknown. Earlier studies using anti-Müllerian hormone (AMH)-deficient mice suggested that AMH is involved in the regulation of primordial follicle recruitment. We tested this hypothesis in a neonatal ovary culture system, in which ovaries from 2-d-old C57Bl/6J mice were cultured for 2 or 4 d in the absence or presence of AMH. Ovaries from 2-d-old mice contain multiple primordial follicles, some naked oocytes, and no follicles at later stages of development. We observed that in the cultured ovaries, either nontreated or AMH-treated, follicular development progressed to the same extent as in in vivo ovaries of comparable age, confirming the validity of our culture system. However, in the presence of AMH, cultured ovaries contained 40% fewer growing follicles compared with control ovaries. A similar reduction was found after 4 d of culture. Consistent with these findings, we noted lower inhibin alpha-subunit expression in AMH-treated ovaries compared with untreated ovaries. In contrast, expression of AMH ligand type II receptor and the expression of oocyte markers growth and differentiation factor 9 and zona pellucida protein 3 were not influenced by AMH. Based on the results, we suggest that AMH inhibits initiation of primordial follicle growth and therefore functions as an inhibitory growth factor in the ovary during these early stages of folliculogenesis.