Human preovulatory follicular fluid: inhibin and free steroids related to optimal follicular maturation in ovarian stimulation regimes and possible function in ovulation.

Abstract

Concentrations of inhibin, total and free oestradiol and progesterone were determined in preovulatory follicular fluid from 15 women undergoing in-vitro fertilization and embryo transfer treatment. The women underwent ovarian stimulation using clomiphene citrate and human menopausal gonadotrophin (HMG) (69 follicular fluid samples) in one cycle, and gonadotrophin-releasing hormone agonist (GnRHa) and HMG stimulation in the next treatment cycle (64 follicular fluid samples). The women thereby served as their own control. Inhibin, total oestradiol and progesterone were measured by radioimmunoassay. Concentrations of free steroid were calculated after quantitation of the steroid binding proteins, i.e. sex-hormone binding globulin (SHBG), cortisol binding protein (CBP) and albumin. Levels of inhibin and free and total progesterone were significantly higher in follicular fluids collected after stimulation with the GnRHa compared to the clomiphene regime (P less than 0.05, P less than 0.001, P less than 0.001, respectively). In contrast, levels of total and free oestradiol in follicular fluid were significantly lower after stimulation with GnRHa than after clomiphene stimulation (P less than 0.001). These results indicate that the follicles have achieved a more optimal maturation during the GnRHa regimen than during the clomiphene regime. It is suggested that the concentration of free biologically active steroids in follicular fluid, released into the peritoneal cavity during ovulation, may be physiologically important in stimulating the oviduct and the uterus in connection with ovulation, pre-embryo development and implantation.