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(97) EFFECT OF ESTROGEN AND PROGESTERONE ON PRIMORIDAL FOLLICLE ASSEMBLY AND EARLY PRIMORDIAL TO PRIMARY FOLLICLE TRANSITION IN THE NEONATAL RAT. Kezele, Phillip1, Skinner, Michael1, 1 Center for Reproductive Biology, Pullman, WA ABSTRACT- The assembly of the developmentally arrested primordial follicle and the subsequent transition of the primordial follicle to the primary follicle are critical processes for normal female reproduction that remain to be elucidated. Ovarian follicles do not proliferate, and the primordial follicles present in the neonate represent the total number of gametes available to a female throughout her reproductive life. Therefore abnormalities in primordial follicle assembly and the primordial to primary follicle transition can cause pathological conditions such as premature ovarian failure. In this study newborn rat ovaries were cultured for seven days. The rate of follicular assembly in vivo was identical to the rate in vitro. The rate of primordial to primary follicle transition was found to be around three times higher in culture. Newborn rat ovaries were cultured in the presence of progesterone (10-6 M), estrogen (10-6 M), and calf serum (10% by volume). Estrogen and calf serum appeared to significantly slow the degree of primordial to primary follicle transition. About 60% of follicles make the primordial to primary follicle in control ovaries and about 30% in treated ovaries. Progesterone appeared to slow the rate of follicular assembly. All viable oocytes assemble into follicles in control ovaries and about 40% remain unassembled in progesterone treated ovaries. Our hypothesis is that high levels of maternal steroids prevent follicular assembly and the primordial to primary follicle transition before birth in the rodent. After birth steroid levels fall dramatically and the follicles are free to assemble and begin development. These studies suggest a novel role for steroids in the control of early ovarian follicular development. KEY WORDS: primordial follicle, folliculogenesis, progesterone, estrogen |
