Nuclear Receptor Estrogen Complex: Accumulation, Retention and Localization in the Hypothalamus and Pituitary1

The effect of estradiol injection on the quantity of estrogen receptors in the nuclear fraction of the hypothalamus and the anterior pituitary was examined by the 3H-estradiol exchange assay. The accumulation of the receptor estradiol complex (RE) in the nuclear fraction of both tissues in the female rat reached a maximum one hour after an injection of 25 μg of estradiol. Between 1 and 12 hr after treatment, parallel declines in hypothalamic and hypophyseal nuclear RE were observed. The quantity of receptor in the pituitary is several-fold greater than the quantity in the hypothalamus. However, hypothalamic receptors are confined to the basal medial region, and the concentration in this region (1.1 fmole/μg DNA) is similar to the concentration in the pituitary (1.3 fmole/μg DNA). The increases in nuclear RE in both tissues are equally dependent on the quantity of estrogen administered. One hr after an injection of a physiological dose (0.5 μg) of estradiol the amount of receptor in the nuclei in both tissues is -50–60% of maximum. Estradiol injection also increases the quantity of nuclear RE in the hypothalamus and pituitary of 21-day-old male rats. Further, the accumulation of nuclear RE in male and female rats is equally dependent on estradiol dose. The results of this investigation are consistent with the proposal that the presence of the estrogen receptor in the nucleus of hypothalamic and pituitary cells is important in the regulation of reproductive processes. (Endocrinology93: 711, 1973)