EFFECT OF FOLLICLE-STIMULATING-HORMONE OR HUMAN CHORIONIC-GONADOTROPIN TREATMENT ON THE PRODUCTION OF GONADOTROPIN SURGE ATTENUATING FACTOR(GNSAF) DURING THE LUTEAL-PHASE OF THE HUMAN MENSTRUAL-CYCLE

OBJECTIVE Although there is much in-vivo evidence for the existence of a gonadotrophin surge attenuating factor (GnSAF), its source and iden tity remain unknown. We have studied the control of GnSAF production b y FSH and hCG during the luteal phase of the cycle. DESIGN Normally cy cling women were investigated in three cycle. Starting on day 5 after the midcycle LH peak, the women received i.m. injections of placebo (I st cycle control), hCG at a dose of 750 IU per day (2nd cycle) and FSH at a dose of 225 IU per day (3rd cycle) for five consecutive days. Th e response of LH to a single i.v. dose of 10 mu g GnRH (GnSAF bioactiv ity) was investigated several times during the experimental period. PA TIENTS Six normally ovulating women with long-standing unexplained inf ertility were studied. The women were used as their own controls durin g the cycle treated with placebo. MEASUREMEMTS Pituitary response to G nRH was calculated as the net increase in LH at 30 minutes (Delta LH) above the basal value. RESULTS Serum concentrations of FSH and hCG inc reased significantly during the second and 3rd cycles respectively. Co mpared with the control cycles, Delta LH was significantly attenuated as early as 12 hours from the onset of FSH injections. In contrast, ba sal concentrations of oestradiol (E(2)) and immunoreactive inhibin sta rted to increase 48 hours after the first injection of FSH, while prog esterone values remained similar to those in the controls. During trea tment with hCG, no attenuation was seen in Delta LH values, while thos e of E(2), progesterone and inhibin showed a significant increase. CON CLUSIONS These results demonstrate that during the luteal phase of the human menstrual cycle, FSH, but not LH, stimulates the production of gonadotrophin surge attenuating factor. It is suggested that the sourc e of gonadotrophin surge attenuating factor at that stage of the cycle is a cohort of small follicles rather than the corpus luteum.