Cg. Herbosa et al., SEXUAL-DIFFERENTIATION OF THE SURGE MODE OF GONADOTROPIN-SECRETION - PRENATAL ANDROGENS ABOLISH THE GONADOTROPIN-RELEASING-HORMONE SURGE INTHE SHEEP, Journal of neuroendocrinology, 8(8), 1996, pp. 627-633
In sheep, the surge mode of gonadotropin secretion is sexually differe
ntiated, i.e. the LH surge is present in the female, but not in the ma
le. The present study tested the hypothesis that sexual differentiatio
n of the FH surge mechanism reflects a sex difference in the pattern o
f GnRH, and that prenatal androgens abolish the surge mode of GnRH sec
retion, We monitored the pattern of GnRH secretion in pituitary portal
blood after acute treatment with estradiol in gonadectomized postpube
rtal males (n = 6), females (n = 6), and androgenized females (exposed
prenatally to testosterone from day 30-90 in gestation, n = 7). Four
capsules, each containing a 30-mm column of estradiol were implanted s
.c. into each lamb to produce high physiologic concentrations of the h
ormone. Beginning 7 h later, portal and peripheral blood samples were
collected hourly for 48 h for measurement of GnRH and LH, respectively
, All females exhibited a GnRH surge beginning 13.0 +/- 0.4 h after es
tradiol treatment; this was accompanied by an LH surge. By contrast, o
nly one male produced a small surge in GnRH (1.7 pg/min) with a latenc
y of 32 h; a corresponding increase in LH occurred in this male. Likew
ise, among the androgenized females, only one exhibited GnRH and LH su
rges which began at about 22 h after estradiol treatment. Some of the
androgenized females had sporadic increases in GnRH which were of lowe
r amplitude than in the control females, and were unaccompanied by ris
es in LH. These findings provide the first direct evidence that the se
x difference in the surge mode of LH secretion results from the sexual
differentiation of the pattern of GnRH release, The study also sugges
ts that androgens during prenatal development abolish the GnRH surge a
nd subsequently, the generation of the LH surge.