Recruitment of primordial follicles is essential for female fertility;
however, the exact mechanisms regulating this process are largely unknown.
Earlier studies using anti-Mullerian 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