Follicular stimulation versus ovulation induction in juvenile primates: importance of gonadotropin-releasing hormone dose.

We evaluated the dose of GnRH administered by 1-min pulsatile infusion necessary to achieve follicle growth vs. the dose needed for ovulation induction. Doses of 6.0, 0.6, and 0.06 micrograms GnRH were given to juvenile monkeys iv in 1 min once per h for 4 consecutive months. Monkeys receiving hourly 6.0-micrograms doses of GnRH had cyclic elevations of serum estradiol and had menses, but did not ovulate, as evidenced by lack of a corpus luteum at laparoscopy and consistently low progesterone concentrations. These monkeys ovulated only when hCG was administered near midcycle as a surrogate LH surge. In contrast, monkeys receiving 0.6-microgram doses of GnRH frequently had normal ovulatory menstrual cycles and characteristic elevations of progesterone during the luteal phase. Typically, juvenile monkeys receiving hourly 0.06-microgram doses of GnRH initially had development of a dominant follicle contemporaneous with a rise of serum estradiol, but never ovulated or had any subsequent follicular growth or elevated steroidogenic activity. In summary, ovarian follicular development and steroidogenesis in juvenile monkeys can be initiated by doses of GnRH ranging from 0.06-6.0 micrograms/h, although spontaneous ovulation and normal luteal function occurred frequently only with the 0.6 micrograms/h pulses of GnRH. Thus, the dose range of pulsatile GnRH needed for follicle growth is much broader than that required for induction of ovulatory menstrual cycles.