The purpose of this study was to examine the role of circulating 17β-estradiol in the regulation of pituitary gonadotropin secretion and, hence, ovarian maturation in immature female ferrets. The hypersensitive negative feedback relationship between the ovaries and the hypothalamo-pituitary axis in developing ferrets was disrupted by infusion of a specific antiserum to 17β-estradiol. The effect of this treatment on gonadotropin secretion and ovarian morphology was contrasted with that observed in intact age-matched control females treated with a nonimmune γglobulin preparation. Infusion of the antibody into intact immature ferrets caused, within 48 h, an increase in pulsatile secretion of LH to 0.67 ± 0.06 pulses/h over that observed in intact females treated with control γglobulin (0.13 ± 0.06 pulses/h). This increase in pulse frequency was similar to that observed 48 h after ovariectomy of young animals (0.70 ± 0.12 pulses/h). Furthermore, this level of gonadotropin secretion in antibody-treated animals resulted in stimulation of antral follicle growth in ovaries of these females. Ferrets treated with specific antiserum to 17β-estradiol showed a significant increase in numbers of ovarian follicles greater than 0.3 mm in diameter compared to those in ovaries of females treated with control γglobulin. These data strongly suggest that the limiting event at puberty in the ferret is the rise in gonadotropin secretion which is allowed by the pubertal decrease in efficacy of 17β- estradiol to inhibit gonadotropin secretion. (Endocrinology122: 1201–1207, 1988)

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