Changes in pituitary response to gonadotropin releasing hormone following bilateral ovariectomy in women treated with follicle-stimulating hormone

Abstract

Superovulation induction in women attenuates the pituitary response to gonadotropin-releasing hormone (GnRH). The aim of this study was to assess the duration of the suppressing activity of the ovaries on the pituitary. Eighteen normally ovulating women received treatment with follicle-stimulating hormone (FSH, 225 IU/day) on cycle days 2, 3 and 4. On cycle day 4, six women underwent hysterectomy plus bilateral ovariectomy (group ), another six women underwent hysterectomy without ovariectomy (group B) and the remaining six women underwent no operation (group C). The women of group C were also investigated during a preceding untreated spontaneous cycle (group D). The response of luteinizing hormone (LH) to an intravenous injection of 10 μg GnRH was investigated on cycle days 2, 3, 4 (2 and 12 h after clamping of the infundibulopelvic and/or round ligaments), 5, 6, and 7 in all four groups. The response of LH to GnRH at 30 min (ΔLH) was significantly attenuated as early as 12 h from the onset of FSH treatment (groups A, B and C), while estradiol and inhibin concentrations started to increase later (group C). In group C (no operation), the attenuation of ΔLH values continued throughout the study period, while in groups A and B the initial attenuation was followed by a marked increase in ΔLH values within 2 h from the operation. The increase in group A was twice the value in group B. Following this, ΔLH values in group B were attenuated again within the next 24 h, while in group A the remained for the rest of the postoperative period significantly higher than in group B. In conclusion, it was found that factor that mediates the suppressing effect of superovulated ovaries on the pituitary has a short-lasting (< 2 h) attenuating activity in the circulation.