Effects of Copper on Cytoplasmic and Nuclear Binding of 17β-Estradiol in the Rat Uterus 1

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Abstract
Interference of Cu2+ with the initial events in estrogen action was tested by determining Cu2+ effects on estradiol-receptor interactions. When immature rat uteri were incubated in vitro with [3H]estradiol ([3H]E2), steroid was bound in cytoplasmic fractions and rapidly accumulated in the nuclear fraction in a manner which was dependent upon time and hormone concentration. Uteri which were preincubated with 2 .times. 10-4 M CuCl2 for 40-60 min and then exposed to [3H]E2 had a 30-50% decrease in the amount of steroid bound in the cytoplasmic and nuclear fractions. When Cu-treated uteri were exposed to [3H]E2 for variable times, the quantity of steroid bound in the cytoplasmic fraction was markedly depressed and the rate of nuclear accumulation of [3H]E2 was significantly decreased. Cu2+ can inhibit [3H]E2 binding to tissue cytoplasmic receptors in vitro and thereby interfere with hormone delivery to target cell nuclei. [The mode of action of copper intrauterine contraceptive devices is considered.].