Effects of hypothalamic estrogen implants on pituitary LH and prolactin in rabbits

¹ Department of Anatomy and Brain Research Institute, University of California, Los Angeles, California

A minute amount of estradiol benzoate was implanted into the posterior median eminence-basal tuberal region of the hypothalamus or hypophysis in female rabbits. Pituitary LH was measured by the ovarian ascorbic acid depletion method. Prolactin assays were performed on the same hypophyses by the intradermal pigeon crop sac method. Pituitary LH content was 0.47 µg/mg wet wt. following implantation of estrogen into parts of the brain other than the posterior median eminence-basal tuberal area. However, when estrogen was implanted into the posterior median eminence-basal tuberal area the pituitary LH content decreased markedly to less than 0.05 µg/mg and this decline was associated with ovarian atrophy. The prolactin content was significantly elevated (P < 0.01) but the mammary glands were not activated. Estrogen implantation into the adenohypophysis appeared to cause release of prolactin but failed to affect the LH content (0.50 µg/mg) or to induce ovarian atrophy. The results indicate that estrogen acts on the posterior median eminence-basal tuberal area to stimulate production but not release of prolactin and, simultaneously, to inhibit synthesis of LH.

Key Words: gonadotrophin • hormonal feedback • adenohypophysis ovary • mammary gland • lactation • uterus

Submitted on April 15, 1963