Endocrine mechanisms governing transition into adulthood: a marked decrease in inhibitory feedback action of estradiol on tonic secretion of luteinizing hormone in the lamb during puberty.

Abstract

The hypothesis was tested that a decrease in response to the inhibitory feedback action of estradiol on tonic LH secretion occurs in the female lamb during puberty. Ovaries were removed from 10 female lambs at 19 weeks of age, which was approximately 11 weeks before the expected first ovulation. At ovariectomy, Silastic implants containing crystalline estradiol were inserted sc in 6 lambs to maintain chronic low levels of circulating estradiol. In estradiol-treated ovariectomized lambs, serum LH was suppressed to undetectable concentrations until the age when first ovulations were initiated in untreated intact lambs. At this time, circulating LH increased dramatically to castrate levels in 5 of 6 estradiol-treated ovariectomized females despite maintenance of constant levels of serum estradiol. The ”escape“ from estradiol negative feedback on tonic LH secretion in ovariectomized lambs and the first ovulation in intact lambs occurred over a wide range of body weights. In the slowest growing estradiol-treat...