SEXUAL-DIFFERENTIATION OF THE SURGE MODE OF GONADOTROPIN-SECRETION - PRENATAL ANDROGENS ABOLISH THE GONADOTROPIN-RELEASING-HORMONE SURGE INTHE SHEEP

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.