Estrogen-mediated cytoplasmic and nuclear distribution of rat cardiovascular estrogen receptors

Abstract

We used either the synthetic estrogen R2858 (moxestrol) or estradiol-17 beta to characterize estrogen receptors in cytoplasmic (R2858) and nuclear (estradiol-17 beta) preparations from rat aorta and myocardium. Relative steroid specificity studies showed that only estrogens were effective inhibitors of R2858 or estradiol-17 beta binding to aortic and myocardial estrogen receptors, whereas androgens, progestins, and cortisol were ineffective inhibitors. Low ionic strength sucrose density gradient analyses showed that myocardial estrogen receptors that localized in the cytoplasmic fraction migrated as macromolecules with sedimentation coefficients of 8S to 9S. In contrast, two binding components of sedimentation coefficients 8S to 9S and 10S to 11S were characteristic of the estrogen receptors localized in aortic cytoplasmic preparations. High ionic strength sucrose density gradient analysis showed that aortic and myocardial estrogen receptors localized in the nuclear fraction migrated as macromolecules with sedimentation coefficients of 4S to 6S. Saturation analyses showed that aortic and myocardial cytoplasmic preparations from intact young mature male rats contained 50.6 +/- 12.9 (mean +/- SD) and 51.0 +/- 14.1 fmol receptor/mg DNA, respectively. The respective R2858 dissociation constants were 0.42 and 0.15 nM. Estrogen receptors could not be demonstrated in nuclear preparations from cardiovasculature of intact males. Estradiol-17 beta injection of intact young mature male rats caused "depletion" of aortic and myocardial cytoplasmic fraction estrogen receptors and resulted in the appearance of 51.9 +/- 21.0 and 36.9 +/- 9.5 fmol receptor/mg DNA in the corresponding nuclear fractions. The respective estradiol-17 beta dissociation constants were 1.56 and 0.71 nM. Increased estrogen receptor content of cardiovascular nuclear fractions of estradiol-17 beta injected male rats correlated well with the concomitant decreased cytoplasmic fraction receptor content. The ability of estradiol-17 beta to affect localization of cardiovascular estrogen receptors between cytoplasmic and nuclear fractions suggests these estrogen receptors are physiologically functional and indicates that estrogen may directly regulate cardiovascular cell function.