Clinical Endocrinology (2004) 60, 120–124 doi: 10.1046/j.1365-2265.2003.01948.x 120 © 2004 Blackwell Publishing Ltd Blackwell Publishing, Ltd. FSH and LH responses to GnRH after ovariectomy in postmenopausal women K. C. Dafopoulos*†, C. P. Kotsovassilis‡, S. D. Milingos*, A. T. Kallitsaris*, G. S. Georgadakis†, P. G. Sotiros‡ and I. E. Messinis* * Department of Obstetrics and Gynaecology, University of Thessalia, Larissa, † State Department of Obstetrics and Gynaecology, General Hospital of Volos, Volos, and ‡ State Department of Clinical Chemistry, General Hospital of Athens, Athens, Greece (Received 3 February 2003; returned for revision 24 February 2003; finally revised 13 May 2003; accepted 6 October 2003) Summary OBJECTIVE Whether the postmenopausal ovary is still playing a role in the control of gonadotrophin secretion in response to GnRH has not been investigated. The aim of the present study was to test this hypothesis by examining changes in basal and GnRH-induced gonadotrophin secretion in postmenopausal women after bilateral ovariectomy. DESIGN The responses of LH and FSH to GnRH [10 μg intravenously (i.v.)] were investigated in postmenopau- sal women from 2 days before to 8 days after total abdominal hysterectomy plus bilateral ovariectomy. PATIENTS Nine postmenopausal women aged 52– 67 years and between 5 and 15 years after menopause. In all cases the ovaries were histologically normal. MEASUREMENTS Pituitary responses to GnRH were calculated every 12–24 h as the net increases in LH (∆LH) and FSH (∆FSH) at 30 min above the basal val- ues. Basal values of oestradiol (E2) and testosterone were also measured. RESULTS Basal values of FSH showed a significant decrease on postoperative days 2 ( P < 0·01) and 8 ( P = 0·03) as compared to day 0, while at the same time points after the operation LH values were marginally lower than on day 2 ( P = 0·05). Serum E2 values showed a gradual increase up to postoperative day 1 ( P = 0·04) and a gradual decline thereafter. Basal testosterone concentrations decreased gradually and significantly after ovariectomy and were significantly lower on day 8 than on day 0 ( P < 0·01). ∆ FSH and ∆ LH responses to GnRH did not change significantly with time. A temporary increase at 12 h after the operation was not significant. CONCLUSIONS These results demonstrate for the first time that the removal of the ovaries in postmenopausal women does not affect GnRH-induced gonadotrophin secretion in the short term. It is suggested that the postmenopausal ovary is not a dominant regulator of hypothalamic–pituitary interactions. During the normal menstrual cycle, ovarian steroids are im- portant regulators of pituitary function. Oestradiol (E2) exerts a negative effect on basal gonadotrophin secretion, while at the same time sensitizes the pituitary to GnRH (Lasley et al ., 1975; Wang et al ., 1976; Messinis et al ., 1998). The interaction between E2 and GnRH during the follicular phase of the cycle results in the positive feedback effect which results in the midcycle endogenous LH surge (Hoff et al ., 1977). Following the menopause, serum concentrations of ovarian hormones become very low, while those of FSH and LH increase markedly (Burger, 1996). In terms of stimulation by GnRH, an enhanced response of LH and FSH to this peptide has been reported in postmenopausal women (Siler & Yen, 1973) that can be modulated by the admin- istration of exogenous oestrogen (Yen et al ., 1974; Lasley et al ., 1975). Although this denotes the crucial role of the ovaries on hypothalamic–pituitary interaction during the reproductive years, no studies have been performed to investigate if GnRH- induced gonadotrophin secretion after menopause is still under the ovarian control. In premenopausal women, the use of the model of ovariectomy has provided useful information regarding the relationships between the ovaries and the hypothalamic– pituitary system during the normal menstrual cycle (Yen & Tsai, 1971; Alexandris et al ., 1997; Messinis et al ., 2002). So far in postmenopausal women, only basal gonadotrophin secretion has been sporadically examined following ovariectomy (Heinonen et al ., 1986; Hughes et al ., 1991). The present study was undertaken to investigate changes in basal and GnRH-stimulated gonadotrophin secretion during the immediate period after ovariectomy in postmenopausal women in order to clarify whether their ovaries are still playing an endo- crine role within the reproductive axis. Correspondence: Professor I. E. Messinis, Department of Obstetrics and Gynaecology, University of Thessalia, 22 Papakiriazi Street, 41222 Larissa, Greece. Tel.: + 302410682795; Fax: + 302410670096; E-mail: messinis@med.uth.gr