Gonadotroph and corpus luteum responses to two successive intranasal doses of a luteinizing hormone-releasing hormone agonist at different days after the midcycle luteinizing hormone surge.

Two successive intranasal doses (300 micrograms at 8:00 A.M. and 6:00 P.M.) of the luteinizing hormone-releasing hormone (LH-RH) agonist (D-Ser[TBU]6-des-Gly-NH2(10))LH-RH ethylamide (Buserelin) were administered on days 1 to 10 after the midcycle luteinizing hormone (LH) surge in 33 normally cycling women. Maximal stimulation of gonadotropins was observed at 4 hours and was of higher amplitude in the first 2 days after the LH surge. The response to the second dose was markedly blunted, showing pituitary refractoriness. On each day of treatment there was a progressive increase of serum estradiol, which was maximal (threefold) 4 hours after the second dose of Buserelin. Serum progesterone (P) levels were not significantly changed on days 1 to 4, but they were increased by 50% at 10 hours on days 5 to 10. Daily blood samples revealed that following treatment on days 1 to 4 after the midcycle LH surge, serum P profiles were lower than in control cycles, without change in the length of the luteal phase. Starting on treatment day 5, a precocious luteolysis was induced, as illustrated by an early fall in serum P levels and shortening of the luteal phase (1 to 4 days). All posttreatment control cycles were normal. The results of this time study indicate that an appropriate treatment with an intranasal Buserelin administered at any time between days 1 to 10 after the midcycle LH surge impair luteal function and could lead to a new postcoital contraceptive approach.