[Study on serum inhibin concentrations in women during menopausal transition]

To investigate the changes of serum inhibin (Inh)-A, Inh-B concentrations during menopausal transition and the time relationship between changes of serum Inh-A, Inh-B and other reproductive hormone levels.

Serum Inh-A, Inh-B concentrations were measured by Serotec modified two-site enzyme immunoassay during different phases of normal menstrual cycle in 10 healthy reproductive women, any time of 10 postmenopausal women. So did the serum Inh-A on 5 - 9 days prior to next period (premenstrual phase) and Inh-B determinations on the 3rd day of menstrual cycle in 40 women of age 43 - 52 (menopausal transition group). In addition, serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E(2)), progesterone (P) levels were also determined when necessary for the purpose of analysis.

The fluctuation patterns of serum Inh-A, Inh-B concentrations during normal menstrual cycle were completely different. About 48% of women during menopausal transition had normal luteal function as shown by the P levels during the premenstrual phase. The only significant change in these women as compared with the young was decrease of Inh-A concentration [(24.7 +/- 13.0) ng/L Vs (42.9 +/- 12.1) ng/L, P = 0.017] in the same phase. Further significant declines of serum Inh-A levels were seen in the luteal phase defect (LPD) and anovulatory (AOV) groups [(12.4 +/- 10.2) ng/L and (5.3 +/- 3.8) ng/L, P = 0.033, P < 0.000 1 respectively], until undetectable in the postmenopausal group. The day 3 Inh-B levels tended to decrease in the normal luteal and LPD groups, became undetectable in the AOV and postmenopausal groups (P = 0.001). Day 3 Inh-B levels was significantly lower in women with day 3 FSH > or = 10 IU/L than those with < 10 IU/L [(16.2 +/- 4.0) ng/L Vs (62.0 +/- 43.8) ng/L]. The elevation of day 3 FSH, LH levels was not significant until the AOV group (P = 0.009, P = 0.027 respectively), and the drop of E(2) levels until the postmenopausal group (P < 0.001).

It is suggested that serum reproductive hormones should be measured in women of menopausal transition in order to know the stage of menopausal transition and to guide the clinical management. The decrease of serum Inh-A levels during the premenstrual phase is the earliest change of menopausal transition, and decrement of day 3 Inh-B levels a marker of decreased ovarian reserve.