Rapid inhibitory effects of an LHRH agonist implant on the oestrogen-induced LH surge and the induction of a defective luteal phase after an agonist-induced ovulation in the macaque.

Three experiments were performed to evaluate in detail pituitary--ovarian function during the first 21 days after treatment with a luteinizing hormone releasing hormone (LHRH) agonist implant. First, six adult macaques with normal menstrual cycles received an LHRH agonist implant during the late luteal or early follicular phase. To investigate the rapidly of effects on pituitary responsiveness the macaques were treated with 50 micrograms LHRH at the time of implant (day 0) and at days 4, 10 and 21. Effects on serum LH and FSH were determined on basal samples and at 30 and 60 min. At 4 days, LH and FSH were elevated as a result of the implant and no further response to LHRH challenge was observed. By 10 days, LH had returned to the pretreatment range but was unresponsive to the LHRH challenge; by 21 days, LH was lower than the pretreatment range and again LHRH failed to induce a significant response. Serum FSH concentrations also declined during treatment, but in contrast to LH, a significant response to LHRH was observed on day 10. Secondly, the ability to respond to an oestrogen provocation test was examined in six macaques with normal menstrual cycles treated with the LHRH agonist implant during the late luteal or early follicular phase and 7 days later with 50 micrograms/kg oestradiol benzoate in oil s.c. to induce an LH/FSH surge. In control animals, oestrogen treatment resulted in a positive feedback surge, reaching a maximum at 48 h post-injection. In contrast, agonist-treated animals showed complete abolition of the expected increase in LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)