High serum concentration of total inhibin in polycystic ovary syndrome

To evaluate serum total inhibin (the sum of precursors, subunits, and mature molecules of inhibin) along with inhibin A and inhibin B in a large sample of women with polycystic ovary syndrome (PCOS) and to investigate whether these parameters differ between lean and overweight PCOS patients.

Cross-sectional, controlled study.

Academic health centers in Siena and Bologna, Italy.

A group of women with PCOS (n = 145) was divided according to body mass index (BMI) into "lean PCOS" (BMI 19-25 kg/m(2), n = 52) and "overweight PCOS" (BMI 26-51 kg/m(2), n = 93). A group of healthy women (n = 90) with BMI 19-24 kg/m(2) and a history of regular menstrual cycles and normal results on physical examination served as controls.

Blood samples were drawn between cycle days 3 and 5 in PCOS patients and controls.

Serum concentrations of total inhibin, inhibin A, inhibin B, FSH, and LH were measured using commercially available immunoassays.

Women with PCOS had serum total inhibin levels twice as high as in the control group (median = 115 vs. 47 pg/mL). Dimeric inhibin A concentration was lower in the PCOS group compared with controls (10 vs. 25 pg/mL), whereas inhibin B concentration did not differ significantly between PCOS and control groups. There was no difference of either total inhibin or inhibin A levels between lean and overweight women with PCOS, whereas the inhibin B level was higher in the lean PCOS subgroup compared with the overweight PCOS subgroup. Total inhibin did not show any linear correlation with inhibin B, inhibin A, or serum gonadotropins.

Women with PCOS have high serum concentration of total inhibin but not of inhibin A or inhibin B, thus suggesting that PCOS women have an impaired processing of alpha-inhibin precursor proteins.