Estrogen receptors in different target tissues: similarities of form--dissimilarities of transformation

The time-related uptake, retention and intracellular distribution of estrogen by different target tissues of the intact immature female rat were studied. The cytoplasmic compartment of the uterus, hypothalamus and pituitary was shown to have a primary hormone receptor complex sedimenting as 8S by sucrose density gradient analysis. Nuclear extracts from all three target tissues contained two forms of estrogen receptor complex; a 5--6S form and a more slowly sedimenting 4S species. The heavier nuclear form accumulated subsequent to the 4S complex in a time-dependent manner which differed according to target tissue. The observed intranuclear differences in properties of the estrogen receptor system may be related to the physiologic responses which characterize dissimilar estrogen target tissues. The tissue content of such serum estrogen-binding proteins as alpha1-fetoprotein and albumin were also determined. The observed levels were evaluated as possible factors in tissue estrogen retention.