Anti-Müllerian hormone promotes pre-antral follicle growth, but inhibits antral follicle maturation and dominant follicle selection in primates

STUDY QUESTION: What are the direct effects and physiological role of anti-Müllerian hormone (AMH) during primate follicular development and function at specific stages of folliculogenesis? SUMMARY ANSWER: AMH actions in the primate ovary may be stage-dependent, directly promoting pre-antral follicle growth while inhibiting antral follicle maturation and dominant follicle selection. WHAT IS KNOWN ALREADY: AMH is expressed in the adult ovary, particularly in developing follicles. Studies in mice suggest that AMH suppresses pre-antral follicle growth in vitro, and inhibits primordial follicle recruitment and FSH-stimulated antral follicle steroidogenesis. STUDY DESIGN, SIZE, DURATION: For in vitro study, secondary follicles were isolated from ovaries of 12 rhesus macaques and cultured for 5 weeks. For in vivo study, intraovarian infusion was conducted on five monkeys for the entire follicular phase during two spontaneous menstrual cycles. PARTICIPANTS/MATERIALS, SETTING, METHODS: For in vitro study, individual follicles were cultured in a 5% O2 environment, in alpha minimum essential medium supplemented with recombinant human FSH. Follicles were randomly assigned to treatments of recombinant human AMH protein or neutralizing anti-human AMH antibody (AMH-Ab). Follicle survival, growth, steroid production, steroidogenic enzyme expression, and oocyte maturation were assessed. For in vivo study, ovaries were infused with control vehicle or AMH-Ab during the follicular phase of the menstrual cycle. Cycle length, serum steroid levels, and antral follicle growth were evaluated. MAIN RESULTS AND THE ROLE OF CHANCE: AMH exposure during culture weeks 0-3 (pre-antral stage) promoted, while AMH-Ab delayed, antrum formation of growing follicles compared with controls. AMH treatment during culture weeks 3-5 (antral stage) decreased (P < 0.05) estradiol (E2) production, as well as the mRNA expression of cytochrome P450 family 19 subfamily A polypeptide 1, by antral follicles relative to controls, whereas AMH-Ab increased (P < 0.05) follicular mRNA levels of the enzyme. Intraovarian infusion of AMH-Ab during the follicular phase of the menstrual cycle increased (P < 0.05) the average levels of serum E2 compared with those of the control cycles. Three of the five AMH-Ab-treated ovaries displayed multiple (n = 2-9) medium-to-large (2-8 mm) antral follicles at the mid-cycle E2 peak, whereas only one large (4-7 mm) antral follicle was observed in all monkeys during their control cycles. The average levels of serum progesterone were higher (P < 0.05) during the luteal phase of cycles following the AMH-Ab infusion relative to the vehicle infusion. LIMITATIONS, REASONS FOR CAUTION: The in vitro study of AMH actions on cultured individual macaque follicles was limited to the interval from the secondary to small antral stage. A sequential study design was used for in vivo experiments, which may limit the power of the study. WIDER IMPLICATIONS OF THE FINDINGS: The current study provides novel information on direct actions and role of AMH during primate follicular development, and selection of a dominant follicle by the late follicular phase of the menstrual cycle. We hypothesize that AMH acts positively on follicular growth during the pre-antral stage in primates, but negatively impacts antral follicle maturation, which is different from what is reported in the mouse model. STUDY FUNDING/COMPETING INTERESTS: NIH NICHD R01HD082208, NIH ORWH/NICHD K12HD043488 (BIRCWH), NIH OD P51OD011092 (ONPRC), Collins Medical Trust. There are no conflicts of interest. TRIAL REGISTRATION NUMBER: Not applicable.