Specific, high-affinity binding of 17β-estradiol in cytosols from several brain regions and pituitary of intact and castrated adult male rats

Abstract

Specific 17β-estradiol binding capacities of cytosols from several brain regions and pituitary were determined in intact and castrated adult male rats. The binding capacity of the pituitary was approximately 10 times higher than that of any of the 5 brain regions studied. Of these brain regions, the highest 17β-estradiol binding capacities were present in the anterior hypothalamus followed by progressively lower capacities in the posterior hypothalamus, amygdala, midbrain, and cerebral cortex. The specific 17β-estradiol binding capacity of cytosol from the anterior hypothalamus was significantly higher in castrated males than in intact rats. No such difference was found in any of the other tissues studied. Using sucrose gradient ultracentrifugation, an 8S sedimentation coefficient was found for the specific estradiol binding macromolecules present in cytosols from pituitary as well as anterior and posterior hypothalamus of castrated rats. The affinity for estradiol of cytosols from anterior and posterior hypothalamus was very high, with the mean association constants being 2.9 and 2.4 × 1010 M-1, respectively. In competition experiments the 17β-estradiol binding molecules present in cytosols from pituitary and anterior hypothalamus showed a higher affinity for 17β-estradiol than for either estrone or estriol. In both tissues these 17β-estradiol binding molecules showed a moderate affinity for the anti-estrogens MER-25 and cis-clomiphene citrate as well as for the androgen 3β-androstanediol, but almost no affinity for 3×-androstanediol, 5α-dihydrotestosterone, testosterone, or corticosterone. These findings suggest that a true cytoplasmic receptor for estradiol exists in the male rat brain and pituitary which may play an important role in regulating reproductive function. © 1975 by The Endocrine Society.