Timed Analysis of the Nuclear Maturation of Oocytes in Early Preantral Mouse Follicle Culture Supplemented with Recombinant Gonadotropin

Objective: To analyze the effects of combined FSH and variable doses of LH on the nuclear maturity and capacity to resume meiosis in oocytes from preantral follicles from prepubertal mice.

Design: Prospective, randomized, and controlled in vitro laboratory experiment.

Setting: Academic research environment.

Intervention(s): Meiosis was studied after somatic cell removal or after stimulation with hCG plus epidermal growth factor in three culture conditions: maturation medium with FSH alone and with two different doses of LH.

Main Outcome Measure(s): The nuclear maturation of the oocytes and the E2, progesterone, and alpha-specific inhibin content of the conditioned medium.

Result(s): Somatic cell removal and hormonal stimulation were equally effective in inducing germinal vesicle breakdown, but the hormonal stimulus was essential for the completion of meiosis, which was maximal (70%) on day 13 of culture. Continuous addition of LH to FSH during the oocytes' growth made them more prone to spontaneous resumption of meiosis I but resulted in a higher proportion of oocytes reaching the completion of meiosis. Estradiol and progesterone measurements demonstrated that the presence of LH influences luteinization.

Conclusion(s): In contrast to oocytes grown in vivo, cumulus cell removal by itself is an insufficient stimulus for oocytes cultured in vitro to complete meiosis. Timed stimulation with hCG and epidermal growth factor increases nuclear maturation rates. A maximum number of metaphase II oocytes are obtained after a 13-day in vitro growth period when LH is added to the maturation medium.