Cytoplasmic and nuclear estradiol-17 beta binding in male and female rat brain: regional distribution, temporal aspects and metabolism.

A study was conducted in which we simultaneously measured absolute levels of cell nuclear estradiol-17 beta (E2) retention and cytosol E2 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]E2. The results indicate that, with minor exceptions, the basic properties of E2 metabolism and E2 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 E2 binding in various regions of the male brain is consistent with a physiological role of estrogen in the male; however, the similarities in these E2 binding parameters between the sexes unfortunately shed little light on the marked neuroendocrine sex differences which have been documented. At times of maximal nuclear E2 retention (2 h post-injection), pituitary cytosol was markedly depleted of E2 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, E2 cytosol binding was replenished to normal levels 24 h after [3H]E2 administration.