Effect of Estradiol Implants in the Hypothalamo-Hypophysial Region of the Rat on the Secretion of Luteinizing Hormone

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Abstract
Bilateral implants of estradiol or estradiol diluted with cholesterol were placed in various parts of the brain or pituitary of ovariectomized rats. Implants of estradiol in either the median eminence region or the anterior lobe of the pituitary prevented the post-castration rise of plasma luteinizing hormone (LH). The minimal effective dose of implanted estradiol to lower plasma LH was approximately the same whether the implant was located in the median eminence or pituitary gland. Median eminence implants lowered hypophysial LH content, whereas hypophysial implants did not. Implanted estradiol in both these loci also enlarged the anterior lobe of the hypophysis. Implants of cholesterol or corticosterone into the median eminence were without effect, as were control implants of estradiol which were located outside the median eminence region or the pituitary. Implants which were located in the globus pallidus or suprachiasmatic areas were also without effect. The negative feedback of estrogen on LH secretion may be mediated by sensitive cells located both in the median eminence region and in the anterior pituitary. (Endocrinology75: 243, 1964)