The effect of oestradiol-17β on the hypothalamo-pituitary axis of intact adult male rats was studied. A single injection of oestradiol did not change the serum LH response to gonadotrophin-releasing hormone (GnRH) 48 h or 7 days after the injection, while administration of oestrogen over 66 days suppressed basal serum LH to <3·1 μg/l and did not enhance the LH response to GnRH at any time.
Treatment of ovariectomized rats with oestradiol capsules, however, enhanced the LH response to GnRH on days 3 and 14 of the treatment as compared with the control group (P<0·02 and P<0·05 respectively). Long-term treatment with oestradiol suppressed intrapituitary LH and FSH contents as well as pituitary GnRH receptors (P<0·0004, P<0·005 and P<0·001 respectively), whereas serum and intrapituitary prolactin levels were increased. To exclude the possible inhibitory effect of hyperprolactinaemia on LH responsiveness to GnRH, oestradiol-implanted rats were treated with bromocriptine. This prevented the rise in serum prolactin, but failed to enhance the LH response to GnRH.
Neither short- nor long-term treatment with oestradiol given under conditions shown to be effective in female animals stimulated the hypothalamo-pituitary-gonadotrophin axis in adult male rats.
J. Endocr. (1987) 114,95–101