Oestradiol-17β binding proteins in the rat uterus: Changes during postnatal development

Abstract

Changes in high affinity macromolecular binding of oestradiol-17β in uterine cytoplasm and nuclei from rats during postnatal development were investigated by sedimentation on sucrose density gradients. Cytoplasmic extracts of uteri from 5-day old rats, when analysed at low ionic strength, showed preponderantly a 4S oestradiol-binding component along with a small amount of 8S oestradiol-binding protein. With increasing age, the ratio of the two components altered, so that by the age of 20 days, uterine cytoplasm contained mainly an 8S oestradiol-binding protein while the 4S component had almost completely disappeared. Diethylstilbestrol was found to compete with oestradiol for the 8S cytoplasmic oestradiol receptor proteins but not for the 4S oestradiol binding components found in uterus and other organs of immature rats and in immature rat plasma. Therefore the cytoplasmic 4S oestradiol-binding component in uteri of immature rats was tentatively identified with the oestradiol binding protein found in plasma of foetal and immature rats. Nuclear 5S oestradiol-binding protein, which binds diethylstilbestrol as well, was found in uteri from untreated 10- and 15-day old rats, and in uteri from 5-day old rats that had received an injection of oestradiol. Nuclei isolated from untreated 5-day old rats showed no bound radioactivity in the 5S region when they were incubated with 3H-oestradiol in the absence of uterine cytosol. When such nuclei were incubated with 3H-oestradiol in the presence of cytoplasm from uteri of 20-day old rats, the 5S nuclear oestradiol receptor protein appeared; when cytoplasm was replaced by plasma from 5-day old rats, no 5S nuclear oestradiol complex was found. Spleen or kidney nuclei from 5-day old rats incubated with 3H-oestradiol in the presence of cytoplasm from 20-day old rat uteri did not yield the 5S oestradiol complex, showing that the nuclear interaction with oestradiol present on the 5th day after birth is organ specific.