Ml. Hull et al., THE EFFECT OF RECOMBINANT FOLLICLE-STIMULATING-HORMONE (GONAL-F) ON ENDOGENOUS LUTEINIZING-HORMONE SECRETION IN WOMEN, Human reproduction, 13(5), 1998, pp. 1139-1143
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.