INTRACELLULAR ANTAGONISTIC INTERACTION BETWEEN GNRH AND GONADOTROPIN SURGE-INHIBITING ATTENUATING FACTOR BIOACTIVITY DOWNSTREAM OF 2ND-MESSENGER INVOLVED IN THE SELF-PRIMING PROCESS/
Ami. Tijssen et al., INTRACELLULAR ANTAGONISTIC INTERACTION BETWEEN GNRH AND GONADOTROPIN SURGE-INHIBITING ATTENUATING FACTOR BIOACTIVITY DOWNSTREAM OF 2ND-MESSENGER INVOLVED IN THE SELF-PRIMING PROCESS/, Journal of Reproduction and Fertility, 111(2), 1997, pp. 235-242
The antagonistic control of LH concentrations by GnRH and the putative
ovarian factor gonadotrophin surge-inhibiting or -attenuating factor
(GnSIF/AF) was studied by perifusion of female rat pituitary glands in
vitro. LH release and GnRH self-priming were measured in response to
five (0.32-10 nmol l(-1)) or three (10 nmol l(-1)) 10 min pulses of Gn
RH. In the latter case, pulses were preceded by five 10 min pulses of
either I mmol 8-bromo-cAMP l(-1) plus 10 mmol theophylline l(-1) or I
mu mol phorbol 12-myristate 13-acetate l(-1) The stimulations were car
ried out in the presence or absence of steroid-free bovine follicular
fluid, which possesses GnSIF/AF bioactivity, to study the effect of Gn
SIF/AF on the self-priming process during successive stimulations by G
nRH. First, the effect of follicular fluid was studied on GnRH-induced
LH release from pituitary glands collected during the ovarian cycle.
Only when a clear self-priming effect was evident, as on day 2 of dioe
strus and the day of pro-oestrus, follicular fluid antagonized the sel
f-priming effect of GnRH. Second, when,glands on day 2 of dioestrus we
re used, self-priming was displayed by various combinations of GnRH an
d follicular fluid. The pulses with the lowest concentrations of GnRH
together with a high concentration of follicular fluid, however, led t
o stable low amplitude LH pulses. Finally, priming of the pituitary LH
response to GnRH with 8-bromo-cAMP plus theophylline or phorbol 12-my
ristate 13-acetate was inhibited by follicular fluid. These results co
nfirm the control of LH release by GnRH and GnSIF/AF bioactivity. The
effect of GnSIF/AF in follicular fluid is most pronounced on the days
before the LH surge, showing evidence of its important role in maintai
ning low LH concentrations during this period. GnSIF/AF neutralizes do
wnstream actions of second messengers involved in GnRH self-priming.