IMMUNOREACTIVE INHIBIN IN HUMAN FOLLICULAR-FLUID IN AN OVARIAN HYPERSTIMULATION PROGRAM FOR INVITRO FERTILIZATION - CORRELATIONS AND DIFFERENT FORMS

The inhibin concentration in 131 samples of human follicular fluid obt ained from 31 women undergoing ovarian hyperstimulation for in vitro f ertilization was measured using specific double antibody radioimmunoas say. We used the synthetic 1-32-alpha-inhibin as standard and radioiod inated 1-32-Tyr-alpha-inhibin as tracer. Antibodies were raised in rab bits by immunization with the synthetic peptide. Estradiol and progest erone concentrations were measured using commercial radioimmunoassays. Results: The inhibin concentration correlated with the estradiol (r=0 .57, N=88, p<0.0001) and progesterone (r=0.82, N=88, p<0.0001) concent rations in human follicular fluid. The dosage of human menopausal gona dotropin given to individual patients correlated with the average inhi bin concentration measured in their follicles (r=0.72, N=23, p<0.0001) . Similarly, the size of follicles correlated with their inhibin conte nt (r=0.75, N=131, p<0.0001). Nineteen samples of human follicular flu id originating from follicles of different size and volume were examin ed using gel-chromatography. In each human follicular fluid the main f orm of inhibin (32 kDa) was recovered. In small follicles (3 ml) we fo und 12.8 +/- 9.1% (mean +/- SD) of the whole immunoreactive inhibin el uating in the area of V(o) (greater-than-or-equal-to 80 kDa). In the l arger follicles (4-7 ml), however, only 4.4 +/- 4.2% of this large inh ibin form could be found. Conclusions: Our data confirm that human men opausal gonadotropin stimulates ovarian inhibin production. In additio n to the estradiol and progesterone concentrations, the inhibin concen tration may be an index of granulosa cell function and follicular matu ration. The occurrence of large molecular weight forms of inhibin in s mall follicles remains unclear. They may represent large precursor mol ecules which are proteolytically cleaved in more mature follicles.