Inhibin A and inhibin B in women with polycystic ovarian syndrome during treatment with FSH to induce mono-ovulation.

OBJECTIVE

Polycystic ovary syndrome (PCOS) is characterized by the presence of numerous small antral follicles arrested at a diameter of less than 10 mm. As development of large antral follicle(s) can be stimulated by the administration of FSH, it has been suggested that the arrest of follicle development is due to a relative lack of or resistance to FSH. We have measured the concentration of FSH and LH and the ovarian hormones oestradiol, inhibin A and B, in relation to the dynamics of follicular development in women with PCOS under basal conditions and during treatment with FSH.

DESIGN

The concentrations of FSH, LH, oestradiol, inhibin A and B were measured in women with PCOS who were untreated (n = 9) or following progesterone-induced menses (10 cycles in six women) and control women on day 3 of a normal cycle (n = 10). Serial measurements of the same hormones were made during induction of ovulation with low dose of exogenous FSH in the women with PCOS who had been treated with progesterone. The dynamics of follicle development were measured by serial pelvic ultrasound examinations during treatment with FSH in PCOS and in the follicular phase of control cycles.

PATIENTS

Nine anovulatory untreated women with PCOS were compared with 10 normal women and six women with PCOS undergoing FSH treatment.

RESULTS

The concentrations of inhibin B and LH were higher in both groups of women with PCOS than in normal control women on day 3. In untreated women with PCOS the concentration of inhibin A was also significantly elevated compared to control women (P < 0.01) but not in women pretreated with progesterone. Basal concentrations of oestradiol were also significantly higher in women with PCOS than in the early follicular phase of the normal cycle. There were no significant differences in the concentration of FSH between the groups. Treatment of women with PCOS with low doses of FSH stimulated the development of a single dominant follicle which had an identical rate of growth and secretion of oestradiol and inhibin A to that observed in spontaneous cycles in normal women. In contrast to normal women, the concentration of inhibin B rose 7-fold following FSH treatment and remained elevated until the luteal phase.

CONCLUSIONS

The raised concentrations of inhibin A and B in women with PCOS probably reflects the increased number of small antral follicles characteristically present in that condition. The striking similarity in the dynamics of growth of the dominant follicle and the pattern in concentration of oestradiol and inhibin A in normal women and in women with PCOS treated with modest amounts of FSH, suggests that the arrest of follicle development in PCOS may be due to a relative deficiency of FSH which may in turn be secondary to increased secretion of either or both inhibin forms.