Ovarian fertility reserve, present in form of
primordial follicles, which represent the longevity and quality of reproductive activity. Complete depletion of
fertility reserve with age due to high rate of consumption will lead to the
cessation of ovarian function in mammals and specifically menopause in women.
The initial transition from primordial to primary follicle is the key limiting
step of follicle development and consumption. Folliculogenesis is primarily a gonadotropin-dependent
process in addition to the role of several other factors such as the bone
morphogenetic proteins (BMPs). However, the regulation of initial follicle
development is generally known as gonadotropin-independent but other
conflicting reports indicate otherwise and this discrepancy needs to be
unequivocally clarified. Using a computerised stereological analysis the
aim of this study was to investigate the role of BMPs in the regulation of
primordial follicle depletion and rate of primary follicle survival in
different ages of passively immunized mice against BMP receptor 1B (BMPR1B) and
BMP-4 with and without treatment with the gonadotropin PMSG. The mean total
numbers of primordial follicles in immunized mice with anti-BMPR1B and anti-BMP-4
were significantly (p<0.0001) increased with ratios up to 205% to the
numbers present in control animals of the same age. Treatment with PMSG alone
has no effect on the numbers of primordial follicles. However, PMSG treatment
of immunized mice abolished the increase in numbers of primordial follicles
resulted from immunization. The mean total numbers of primary follicles in
immunized mice were also significantly (p<0.0001) increased with ratios up
to 175% to those present in control animals of the same age. In contrast to the
case of primordial follicles, treatment with PMSG alone or as a supplement with
antibodies significantly reduced the number of primary follicles to a minimum
ratio of 59% of follicles in control animals. The rates of primary follicle survival
were decreased after puberty with age and particularly significant in treated
animals. However, there was no significant difference in the survival rates of
primary follicles between the different treatment groups within a given age.