Inhibin A and B in peri- and postmenopause

Objective: The aim of the study was to investigate the origin of inhibin A and B during the last years of the reproductive age and after menopause by measuring their levels in the ovarian and peripheral venous blood. Methods: The study population consisted of 43 women, aged 42-69 years (mean 50), who underwent hysterectomy with ovarian removal for a benign disease. A total of 24 of them were in follicular phase, 11 in luteal phase, and eight were postmenopausal. Peripheral and ovarian venous blood was collected for measurement of inhibin A and B. In addition, sex steroid hormone and gonadotropin levels were measured. Results: Ovarian venous inhibin B correlated significantly with ovarian estradiol secretion (r = 0.5, P = 0.001). The levels of inhibin B were significantly higher in the ovarian vein than in the peripheral vein (P = 0.006). The highest inhibin B concentrations were detected in the mid-proliferative (mid-follicular) phase (median 31.6 pg/ml range 25.9-47.9). In postmenopausal women, inhibin B was not detectable. No correlation between FSH and ovarian inhibin B was found. Inhibin A rose rapidly in late proliferative (late follicular) phase (median 28.5, range < 2-51.8) and dominated in the circulation throughout the luteal phase (median 20.9, range 8.8-60). For inhibin A, no concentration gradient existed between the ovarian and peripheral vein. Unlike inhibin B, inhibin A was detectable in ovarian and peripheral blood in postmenopausal women. A significant negative correlation between ovarian and peripheral inhibin A and FSH was found (r = 0.386, P = 0.015; r = -0.345, P = 0.034, respectively). Conclusion: Inhibin B correlates with ovarian estradiol secretion and seems to reflect follicular function. Inhibin A dominates in circulation during the luteal phase but is detectable at low concentrations both in follicular phase and even in postmenopause. Our findings suggest that inhibin A may play a role in FSH suppression in the female reproduction. In addition to the ovary, there may be extragondal source(s) of inhibin A. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.