Response to Estradiol Inhibition of Tonic Luteinizing Hormone Secretion Decreases during the Final Stage of Puberty in the Rhesus Monkey*

Abstract

This investigation was conducted to determine if a decrease in responsiveness to estradiol inhibition of tonic LH secretion occurs in the female rhesus monkey during the late stages of sexual maturation. The study was conducted during the several month period between menarche and first ovulation. Serum LH was measured in postmenarchial females (n = 8) before and after ovariectomy and insertion of estradiol implants that achieved subadult concentrations (10–30 pg/ml) of the steroid. Removal of the ovaries 1–4 months after menarche (31 ± 1 months) produced a prompt 3- to 5-fold rise in circulating LH. This was prevented by estradiol replacement therapy beginning at ovariectomy. Similarly, insertion of estradiol implants after the castration response was established decreased the high concentrations of circulating LH to preoperative levels where they remained for several months. At 42± 1 months of age, and in the face of unchanging peripheral estradiol, circulating LH rose severalfold in the ovariectomized females (n = 7). At a similar age (44 ± 2 months, n = 4), ovulations began in untreated females. The results indicate that subadult concentrations of peripheral estradiol which are capable of suppressing LH secretion before the age of first ovulation are ineffective in this regard afterward. This provides compelling evidence for a decrease in estradiol inhibition of tonic LH secretion during puberty in the primate female.