Effects of Gonadotropin-Releasing Hormone Agonists on Meiotic Maturation of Follicle-Enclosed Oocytes in Rabbits

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Abstract
The effects of GnRH agonists on in vitro maturation of rabbit follicle-enclosed oocytes were studied. Rabbit preovulatory follicles were cultured with or without hCG (102 ng/ml), buserelin (102-105 ng/ml), or leuprolide (102-105 ng/ml) for 14 hours in vitro. GnRH agonists induced the resumption of meiosis in the follicle-enclosed oocytes in a dose-dependent manner. The percentage of oocytes achieving GVBD following treatment with 105 ng/ml buserelin (87.9 .+-. 6.3%) or 105 ng/ml leuprolide (86.0 .+-. 4.1%) did not differ significantly from hCG-treated control (87.3 .+-. 3.8%). Mature oocytes initial were detected within 2 hours of GnRH agonist exposure. Concomitant addition of a GnRH antagonist at 104 ng/ml significantly blocked the stimulatory effect of GnRH agonist on oocyte maturation. GnRH agonists significantly stimulated both prostaglandin (PG) E2 (PGE2) and PGF2.alpha. production by preovulatory follicles (p < 0.01), but secreted prostanoid levels did not differ significantly among different concentrations of GnRH agonists. Meiotic maturation of follicle-enclosed oocytes following GnRH agonist exposure began 2 hours earlier than production of PGs. PG production stimulated by GnRH agonists was reduced significantly by indomethacin. However, oocyte maturity in the presence of GnRH agonist plus indomethacin did not differ significantly from that of GnRH agonist alone. GnRH agonistic analogues induce the resumption of meiosis in follicle-enclosed oocytes in rabbits by a mechanism other than PG stimulation.