Abstract
The bilateral stereotaxic implantation of estradiol into the brain of acutely ovariectomized rats was used to determine the hypothalamic sites of the positive feedback action of this steroid. The transport of estradiol from the site of implantation to the adenohypophysis was assessed by monitoring pituitary estradiol concentrations by radioimmunoassay. These concentrations were compared with the pituitary estradiol levels associated with LH release in the intact and estrogen-treated ovariectomized rat. The estradiol concentration in the pituitary increased gradually from 0.2 to 1.0 pg/mg during diestrus day 1 and day 2 of the estrous cycle and then showed a rapid rise to a plateau of 2.8 pg/mg on the morning of diestrus day 3. The pituitary estradiol concentration was maintained at this level until the initiation of the proestrous LH surge and then fell rapidly to diestrous levels. A similar concentration of estradiol in the pituitary (2.9–3.4 pg/mg) was associated with LH release in ovariectomized animal...
Published Version
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