Sex-hormone-binding globulin in human follicular fluid and serum at the time of oocyte recovery

Androgen binding activity, indistinguishable from sex-hormone-binding globulin (SHBG) in serum, has been identified in human follicular fluid by binding analyses (saturation and Scatchard analyses and binding specificity), immunoradiometric assay and Con-A Sepharose chromatography. Follicular fluid was obtained at the time of oocyte recovery from either individual follicles (range 2-7) from seven patients, or as a pool obtained from follicles of several patients who had received a Clomid-human menopausal gonadotrophin treatment to stimulate follicular growth as part of an in vitro fertilization program. Concentrations of SHBG in follicular fluid varied between individual follicles (750 +/- 202 fmol mg-1 protein; mean +/- s.d.; n = 14) and ranged above and below concentrations of SHBG in serum (948 +/- 171 fmol mg-1 protein; n = 5) taken 4 h before oocyte recovery and harvest of follicular fluid. There were strong correlations (r = 0.7-0.9) between the steroid and SHBG contents in individual follicular fluids of two patients. However, the concentration of SHBG in follicular fluid was generally 100-fold lower than that of oestradiol or progesterone, suggesting that SHBG may play some role other than determining the concentration of unbound steroid in the follicle.