Estrogen Receptor in Rat Adrenal Gland

Abstract

Specific binding of [3H]estradiol by the cytoplasmic fraction of rat adrenal gland was studied at 0.degree. C. The [3H]estradiol-binding component sedimented at 7 S on 5 to 20% sucrose gradients. Scatchard analysis of the cytosol binding reaction, measured by a charcoal-dextran assay, indicated a single class of estradiol binding sites of high affinity (Kd = 2.2 - 4.5 .times. 10-10 M) and limited number (5-22 fmol[femtomoles]/mg cytosol protein) (n = 7). Competition studies indicated specificity of the binding reaction for the biologically active estrogens, estradiol, estrone, estriol and diethylstilbestrol; binding of [3H]estradiol was unaffected by a 1000 fold excess of androgens, glucocorticoids, mineralocorticoids, or progesterone. The binding activity was temperature dependent (no binding was observed when incubations were performed at 25.degree. C or above) and appeared to be by a protein since binding was destroyed by trypsin and sulfhydryl reagents, but not by RNase or DNase. Kinetic studies indicated an apparent second order association rate constant of 3.3 .times. 105 M-1 s-1 and a Kd of 3.1 .times. 10-5 s-1 at 0.degree. C. Specific binding of [3H]estradiol by rat adrenal nuclei was also studied utilizing a nuclear exchange assay. One hour after estrogen injection in vivo, specific binding of [3H]estradiol by isolated adrenal nuclei in vitro increased more than 8 fold, suggesting nuclear translocation of the cytoplasmic adrenal estrogen receptor. Scatchard analysis of the specific nuclear binding indicated a single class of saturable high affinity sites with a dissociation equilibrium constant of 5 .times. 10-10 M. Since the specific [3H]estradiol-binding component of rat adrenal gland has the properties of a physiological estrogen receptor, the possibility of a direct effect of estrogens on rat adrenal cortical function is suggested.