Slowly exchangeable pool of estradiol in the rat uterus

Abstract

Chase experiments, alternating infusions with 14C and 3H labelled estradiol, were performed in adult rats. After infusion, purified nuclei were extracted from uterine homogenates and the 3H/ 14C ratio was determined in cytosol and nuclear fractions. It was shown that {4 14C}estradiol exchanged progressively with {6,7 3H}estradiol in all subcellular fractions, but at a much slower rate than in the plasma. The retardation was more evident in the Tris-EDTA-KCl extract (S III) of the nuclear preparations than in other soluble “receptors” from the cyctosol (S I) or the particulate fraction (S II). The final residual precipitate of the nuclear fraction contained a limited pool of estradiol, more slowly exchangeable than in other fractions. These data confirm the extensive recycling of estradiol within the uterine cell. They also show in the nucleus, the existence of a more slowly exchangeable pool, of limited capacity, which appears to be possibly a final but still reversible step in the hormone distribution within the cell. The implication of this limited pool in the hormonal activity is briefly discussed.