Characterization of the maturational changes induced by a GnRH analogue in the rat ovarian follicle.
The GnRH analogue [D-Ser(t-Bu)6]des-Gly10-GnRH-N-ethylamide (GnRHa, 2 micrograms/rat) or hCG (4 i.u./rat) was administered to hypophysectomized, PMSG-primed immature female rats. Oocyte maturation was initially detected by 2 h after GnRHa administration but the response to hCG was observed only after 4 h. Initiation of GnRHa-induced ovulation also preceded the response to hCG by 2 h. Maximal response to both these hormones was obtained at 10 and 14 h after hormone administration for oocyte maturation and ovulation respectively. The number of oocytes ovulated after GnRHa was significantly lower than that with hCG (29 +/- 4 and 50 +/- 7 per rat respectively; P less than 0.05). Expansion of the cumulus mass and secretion of mucoid material, which are characteristic responses to LH, were also observed after GnRHa administration. However, while the action of 5 micrograms ovine LH/ml on the cumulus cells was mediated by cAMP, no accumulation of the nucleotide could be detected in follicles exposed to GnRHa (10(-7) M). We conclude that even though GnRHa and LH/hCG seem to elicit similar responses in the ovarian follicle they differ in their kinetics, their efficiency and the mediator of their action.
D000818:Animals; D002064:Buserelin / Q000494:pharmacology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology; D007016:Hypophysectomy; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D009865:Oocytes / Q000187:drug effects / Q000648:ultrastructure; D006080:Ovarian Follicle / Q000378:metabolism; D010053:Ovary / Q000187:drug effects*; D010060:Ovulation / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012741:Sexual Maturation; D013268:Stimulation, Chemical
D006063:Chorionic Gonadotropin; D006064:Gonadotropins, Equine; D000242:Cyclic AMP; D002064:Buserelin