Follicle stimulating hormone stimulates the production of gonadotrophin surge attenuating factor (GnSAF) in vivo.
To study the time-course production of gonadotrophin surge attenuating factor (GnSAF) after the onset of FSH treatment in women. Normally cycling women were treated with FSH injections (225 IU per day) starting on cycle day 2 (0800 h). The response of LH to an i.v. injection of 10 micrograms GnRH (GnSAF bioactivity) was investigated 12, 24, 36 and 48 hours after the first FSH injection, as well as during the early follicular phase of an untreated spontaneous cycle. Six normally ovulating women with long-standing unexplained infertility were studied. The women were used as their own controls during the spontaneous cycles. Pituitary response to GnRH was calculated as the net increase in LH at 30 min (delta LH30) above the basal value. delta LH30 was significantly attenuated 12, 24, 36 and 48 hours after the first FSH injection as compared to the spontaneous cycles. In the latter cycles, delta LH30 decreased significantly from day 2 (12 hours) to day 4 (48 hours). Serum oestradiol levels at 12 and 24 hours did not differ significantly between the FSH and the spontaneous cycles. These results demonstrate that in superovulated women, a marked attenuation in the pituitary response to GnRH occurs as early as 12 hours from a single injection of FSH before any significant increase in serum oestradiol levels. It is suggested that FSH is a potent stimulus of GnSAF production in women.