Evidence that termination of the estradiol-induced luteinizing hormone surge in women is regulated by ovarian factors.

Background: The endogenous LH surge is the result of the estrogen-positive feedback effect. However, the factors that are responsible for the termination of LH surge are not known. Objective: The objective of the study was to investigate the mechanism that terminates the LH surge in women. Subjects and Methods: Eight normally cycling women (aged 42–48 yr) were investigated in two cycles, i.e. cycle 1 (control) and cycle 2. In cycle 2 total abdominal hysterectomy plus bilateral salpingooophorectomy was performed on d 3. In both cycles, estradiol was administered transdermally at the dose of 100 μg on d 3 and 150 μg on d 4 and 5. Blood samples were obtained every 12 h from d 3 to 5 and every 6 h thereafter until d 9. Results: In both cycles, after suppression of gonadotropins, the women displayed an endogenous LH surge. The time intervals between the commencement of estradiol treatment and the LH surge onset (73.5 ± 1.5 vs. 76.5 ± 2.5 h) and peak LH values (11.4 ± 1.9 vs. 12.4 ± 3.1 IU/liter) were comparabl...