Effect of Estrone and Progesterone on the Nuclear Uptake of Estradiol by Slices of Human Endometrium

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Abstract
Slices of human endometrium were superfused with buffer solutions of tritiated estradiol (E2), alone or mixed with progesterone (P) or 14C-labeled estrone (E1). The concentrations of P and E1 in the medium were 10–50 times larger than the concentration of E2. P did not reduce the saturation level of nuclear E2. E1 was converted intracellularly to E2 and lowered the nuclear binding of 3H-E2. However, the total amount of E2 bound to the nuclei was not affected by the addition of E1 to the medium, as determined by measuring the amounts of 3H-E2 and 14C-E2 in nuclei. The levels of nuclear E2 obtained by superfusion of secretory endometrium with excess E2 were lower than the levels found when proliferative endometrium was used. Since neither P nor E1 compete directly with E2 for nuclear binding it is concluded that the concentration of E2 receptors in human endometrium declines significantly during the secretory phase of the menstrual cycle. (Endocrinology93: 245, 1973)

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