Gonadotropin releasing hormone agonists stimulate oocyte meiosis and ovulation in hypophysectomized rats.

The acute effects in vivo of gonadotropin releasing hormone (GnRH) and a potent agonistic analogue (GnRHa) were tested in PMSG-treated immature female rats, hypophysectomized on the morning of proestrus. The rats were injected once with either LH, GnRH, or GnRHa 3-4 h after surgery, and the effects on oocyte meiosis, ovulation, and plasma progesterone were investigated. LH (25 microgram) and GnRHa (12.0 and 1.2 microgram) caused a high rate of meiosis, while GnRH (100 microgram) or GnRHa (0.12 microgram) caused a partial response. LH and GnRHa produced ovulation in all of the treated rats and caused a prolonged increase in plasma progesterone levels. It is concluded that GnRH agonists exert acute stimulatory effects in the ovarian follicle, independent of pituitary factors.