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Biology of Reproduction, Vol 10, 438-446, Copyright © 1974 by Society for the Study of Reproduction
1 Department of Endocrinology, Medical College of Georgia, Augusta, Georgia 30902 The intricate relationship between the gonads and pituitary gonadotropin secretion
has been studied in the immature, 26-day-old rat. In male rats orchidectomized at this
age, serum FSH and LH rose to significantly higher levels at 8 h postcastration. A
much later response was seen in ovariectomized females: at 24 h and 48 h for FSH
and LH, respectively. When groups of rats castrated at 26 days of age were treated
with pharmacologic dosages of various steroids for 6 and 15 days postoperative, it was
found that testosterone, 5
-dihydrotestosterone, and estradiol prevented the rise of both
FSH and LH, in both sexes. A steroid-derived drug, 17
-ethinyl-testosterone-2,3-isoxazol, was also effective, while progesterone alone was unable to suppress gonadotropins
in either sex. Results reaffirm that the gonadalhypophyseal relationship is sensitive before
puberty. The marked sex difference in the response to castration is undoubtedly due to
different gonadal hormones (androgen or estrogen) present at the time of castration,
and their contributions to this feedback process. However, it appears that hormones of
either type can suppress both gonadotropins in both sexes. Results with 17
-ethinyl-testosterone-2,3-isoxazol were particularly encouraging with respect to its clinical usefulness
as a gonadotropin inhibitor with little or no biologic activity as a sex steroid.
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