Cytoplasmic and nuclear estradiol-17β binding in male and female rat brain: Regional distribution, temporal aspects and metabolism

Abstract

A study was conducted in which we simultaneously measured absolute levels of cell nuclear estradiol-17β (E 2) retention and cytosol E 2 saturation binding capacities in various neural tissues from adult gonadectomized-adrenalectomized (GX-ADX) male and female rats, at various times after a saturating dose of [ 3H]E 2. The results indicate that, with minor exceptions, the basic properties of E 2 metabolism and E 2 retention kinetics in target brain tissues and corresponding cell nuclear and cytosol fractions are quite similar in GX-ADX male and female rats. The results do not, however, rule out the possibility of subtle sex differences in estrogen binding in at least some brain regions which were studied. The present demonstration of E 2 binding in various regions of the male brain is consistent with a physiological role of estrogen in the male; however, the similarities in these E 2 binding parameters between the sexes unfortunately sheds little light on the marked neuroendocrine sex differences which have been documented. At times of maximal nuclear E 2 retention (2 h post-injection), pituitary cytosol was markedly depleted of E 2 binding sites, while cytosols obtained from the preoptic area, hypothalamus and amygdala were only moderately depleted. These observations suggest that within the brain the relationship between cytoplasmic and cell nuclear estrogen binding may be different from that observed in non-neural tissues. In all tissues, E 2 cytosol binding was replinished to normal levels 24 h after [ 3H]E 2 administration.