Effects of factors from ovarian follicular fluid and Sertoli cell culture medium on in-vivo and in-vitro release of pituitary gonadotrophins in the rat: an evaluation of systems for the assay of inhibin.

Inhibin-like activity is present both in testicular and ovarian fluids. Various methods can be used for the detection of this activity. Indirect methods, using organ weights as an endpoint, lack the specificity required for reliable estimation of inhibin-like activity. With in-vivo bioassay systems, using estimation of circulating concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in intact or gonadectomized, immature or adult, male or female rats, a suppression of FSH concentrations only is usually observed after injection of inhibin-like material. The largest suppression of FSH concentrations can be obtained in short-term gonadectomized adult female or 35-day-old male rats. Addition of inhibin-like activity to cultured pituitary cells specifically suppresses the spontaneous release of FSH from the cells. After stimulation of cultured pituitary cells with LH-releasing hormone (LH-RH), the release of both FSH and LH are suppressed when inhibin-like activity is present. From dialysis experiments it appears that the molecular weight of the inhibin-like material in follicular fluid is greater than 10 000. However, acid ethanol extracts of this fluid contain a factor with a molecular weight smaller than 10 000, which does not suppress the spontaneous release of FSH from cultured pituitary cells, but diminishes the LH-RH-stimulated release of both LH and FSH. Furthermore, both follicular fluid and Sertoli cell culture medium can stimulate the release of FSH and LH from pituitary cells when these are cultured without addition of fetal calf serum. These results suggest that gonadal fluids contain several non-steroidal factors which can influence the release of gonadotrophins from pituitary cells.