Effects of Intrahypothalamic and Intrahypophysial Estrogen Implants on Pituitary Prolactin and Lactation in the Rabbit

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Abstract
A minute amount of solid estradiol benzoate was implanted into the hypothalamus or pituitary gland in female rabbits. The prolactin content of each pituitary gland was assayed on White King squabs by the intradermal crop sac method. The pituitary prolactin content was elevated following estrogen implantation in the posterior median eminence area, but the mammary glands were not activated. In this group there was marked atrophy of the ovary and uterus, but hypertrophy of the adrenal cortex. Estrogen implantation into the anterior hypophysis was followed by activation of mammary glands and initiation of milk secretion, while the pituitary prolactin content was, if anything, depressed. No significant changes occurred in the ovary, uterus or adrenal. The results indicate that estrogen action on the posterior tuberal hypothalamus promotes synthesis and storage of prolactin in the pituitary gland, whereas the direct action of the steroid on hypophysial cells stimulates release of the lactogenic hormone.