Anti-Müllerian Hormone (AMH) is a TGFβ
superfamily member with multiple roles in reproductive biology. AMH induces regression of the Müllerian duct
in male foetuses and has roles in testicular development. AMH negatively regulates ovarian follicular
development in females. We have
determined that AMH in blood consists of a precursor form (proAMH) and the
receptor-competent form (AMHN,C).
Commercially available assays do not differentiate the two forms and
most AMH measurements are an aggregate of proAMH and AMHN,C (total
AMH) concentrations. We have developed a
proAMH-specific assay to generate the first description of the relative quantities
of proAMH and AMHN,C in the normal population. An AMH prohormone index has been calculated
from this data (API, [proAMH]/[total AMH] x 100) which represents proAMH as a
percentage of total AMH. ProAMH
concentrations were significantly higher in prepubertal boys (n=131) relative
to men (n=80) (p = 0.000). Prepubertal
girls (n=14) also had higher proAMH concentrations relative to women (n=18) (p
= 0.032). The mean API of boys was
approximately 2-fold higher than in men with no overlap between the ranges of
each group (p = 0.000). The total AMH
levels in girls and women were not significantly different but the mean API in
girls was significantly greater than in women (p = 0.000). These data suggest that there is increased
processing of proAMH into receptor-competent AMHN,C after puberty,
implying a greater proportion of AMH is active.
The cleavage enzymes for AMH facilitate activation of multiple gonadal
regulators, hence these findings may have wider implications for gonadal
regulation during development.