THE EFFECT OF RECOMBINANT FOLLICLE-STIMULATING-HORMONE (GONAL-F) ON ENDOGENOUS LUTEINIZING-HORMONE SECRETION IN WOMEN

Parenteral administration of follicle stimulating hormone (FSH) has be en shown to lower luteinizing hormone (LH) concentrations in women und ergoing ovulation induction. This study was designed to explore the ph ysiological mechanism of this effect. Seven healthy women were recruit ed into a double-blind placebo-controlled study. LH secretion, after t he administration of variable i.v. boluses (37.5, 75 and 150 IU) of re combinant FSH (Gonal-F), was evaluated. LH was measured at 10 min inte rvals for 2 h before and 4 h after the FSH/placebo infusion. LH pulse frequency and amplitude were evaluated and there was no significant di fference between control and trial cycles for each subject. A linear r egression analysis revealed that in the group receiving 150 IU FSH, th e mean plasma LH concentration decreased significantly due to a reduct ion tonic LH secretion. This could be a result of the suppression of s ecretion or an alteration of clearance. This decrease was not seen in the other dosage groups, revealing that above a dosage threshold, FSH reduced non-pulsatile-la secretion. Therefore the effect of FSH in thi s study exposed the likely presence of two components of LH concentrat ion: an FSH-sensitive, non-pulsatile tonic secretion and a gonadotroph in-releasing hormone-stimulated, pulsatile release that is unaffected by FSH. Although an indirect effect involving ovarian regulation is no t excluded, the rapidity of the effect suggests that FSH acts directly on the pituitary gland.