Luteinizing hormone regulation in the monkey (Macaca nemestrina): failure of testosterone and dihydrotestosterone to block the estrogen-induced gonadotropin surge.

Abstract

In contrast to females, intact male monkeys do not release luteinizing hormone (LH) after an acute estrogen challenge; orchidectomized males, on the other hand, do release LH in response to estrogen. To examine whether physiological levels of testosterone (T) or dihydrotestosterone (DHT) could effect a blockade of the estrogen-induced LH surge in the female monkey, we treated 4 long term oophorectomized female pigtailed macaques (Mocaca nemestrina) for 10 days with Silastic capsules containing T. These capsules produced T blood levels of 6.80 ± 0.97 ng/ml, which approximated the normal range (3.44-15.75 ng/ml). In addition to T or DHT, in this and subsequent experiments all gonadectomized animals received a long term (> 1 week) pretreatment with a 1.5 cm Silastic capsule containing estradiol-1 7j3. This treatment, designed to titrate the high postgonadectomy levels of LH into approximately the intact range, was continued throughout the entire experimental period. The monkeys were then challenged with estradiol benzoate (EB) (50 pg/kg, s.c.) and bled twice daily for 6 days; each responded with a typical LH surge. In a second trial, the animals were treated with T for 6 weeks and then challenged with EB; again, each responded with an LH surge. In a third trial, each monkey was treated with T for 8 weeks combined with DHT for the final 2 weeks. This treatment also failed to block the EB-induced LH surge. We then treated 3 long term orchidectomized male pigtailed macaques with T for 10 days and then challenged them with EB; each animal responded with a normal LH surge. These data demonstrate that 1) neither T nor DHT can block the EB-induced LH surge in the oophorectomized female and 2) T in the physiological range can not effect a blockade of the EB-induced surge in the orchidectomized male.