Non-Steroidal Follicular Factors Attenuate the Self-Priming Action of Gonadotropin-Releasing Hormone on the Pituitary Gonadotroph

Abstract

Pituitary glands of pro-oestrous and oestrous rats were perifused in series with isolated ovarian follicles and the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to gonadotropin-releasing hormone (GnRH) were measured. Pituitary glands from pro-oestrous rats, perifused with the effluent medium from isolated preovulatory follicles, showed a significant reduction in the self-priming effect of GnRH as observed from the typical biphasic LH response to a continuous GnRH challenge. The initial FSH response to GnRH was also reduced. A similar trend was seen in the LH responses of pituitary glands from oestrous rats but results were not significant; there was no parallel reduction in FSH release. It is unlikely that the attenuation of GnRH self-priming was due to the steroids released by the isolated follicles. LH responses of pro-oestrous pituitaries, perifused with medium containing 200 pg oestradiol/ml, 5 ng progesterone/ml or 200 pg testosterone/ml were similar to paired controls as were the responses when all three steroids were added to the perifusing media at identical concentrations. Furthermore, when steroids were charcoal extracted from the effluent medium of perifused isolated follicles the biological activity of this medium in attenuating GnRH self-priming was not destroyed. Finally, the effects of purified bovine inhibin and steroid-free human follicular fluid (hFF) on LH responses were compared. Purified inhibin at a concentration of 20 or 50 ng/ml perifusing medium had no effect on GnRH-stimulated LH release although GnRH-stimulated FSH secretion was significantly reduced toward the end of an extended perifusing period.(ABSTRACT TRUNCATED AT 250 WORDS)