In vitro maturation of germinal vesicle stage oocytes

Many reproductive procedures require large numbers of mature oocytes, which are fertilized for embryo production, or are used in various fertility evaluations. The number of oocytes obtainable by the usual method of superovulation and oviduccal flushing, is a limiting factor in these procedures. A method is described for isolating large numbers of immature germinal vesicle stage oocytes from ovaries and culturing these ovarian oocytes to the same maturational stage as oviductal oocytes.

In the present study, bovine and murine ovaries were macerated and cumulus-free, germinal vesicle stage oocytes isolated and placed in culture for maturing. Oocytes were randomized into various treatment groups, including controls, and incubated with one or more of the following hormonal supplements; (1) 17-Estradiol-3-Benzoate, (2) Pregnant Mare's Serum Gonadotrophin, (3) Human Chorionic Gonadotrophin, or (4) Ovine Prolactin.

While all experimental groups exihibited increased maturation rates when compared to controls, groups treated with prolactin alone had the highest rates. Bovine and marine oocytes which were cultured with prolactin only had mean maturation rates of 27.2% and 41.1%. respectively. These data suggest that prolactin treatment alone is sufficient for increasing the rate of maturation of germinal vesicle stage oocytes and producing large numbers of oocytes at the second metaphase of meiosis. Implementation of this oocyte isolation procedure in conjunction with in vitro maturation with prolactin has the potential of greatly increasing the number of fertilizable oocytes which can be obtained from a single ovary.