INVIVO AND INVITRO BINDING OF [H-3] ESTRADIOL IN BRAIN AND PITUITARY OF MONGOLIAN GERBILS, MERIONES-UNGUICULATUS

Following injection of [3H]estradiol in ovariectomized gerbils, the highest concentration of radioactivity was found in cell nuclei from the pituitary, followed by preoptic area, hypothalamus, amygdala, and midbrain, with very low levels in the olfactory bulbs and cerebral cortex. Cell nuclear binding was significantly reduced by pretreatment with unlabeled estradiol or nafoxidine but not by progesterone, 5α-dihydrotestosterone, or cortisol. The time course of estradiol binding in whole homogenate and cell nuclear fractions of brain and pituitary was determined by sacrificing animals 0.25, 1, 3, 6, or 12 hr after injection of [3H]estradiol and measuring hormone uptake into the respective cell components. While whole homogenate radioactivity was highest at 0.25 hr, cell nuclear uptake peaked at 1 hr. Radioactivity was still present in cell nuclei from pituitary, hypothalamus-preoptic area, and amygdala 12 hr after [3H]estradiol injection, although at a level only 2% of 1-hr peak values. Macromolecular binding of [3H]estradiol was found in the cytoplasmic fraction of pooled hypothalamus-preoptic area-amygdala. Scatchard analysis of this in vitro binding indicated a Kd of 5.0 × 10-10M. This binding was inhibited more by unlabeled estradiol or the synthetic estrogen, R2858, than by 5α-dihydrotestosterone, progesterone, or cortisol. Pronase almost totally inhibited binding, while DNase and RNase had little effect. The data indicate that the estradiol binding in female gerbil brain and pituitary is similar to that of other species previously studied, although some species differences were found. © 1979.