Temporal relationships between hormone receptor binding and biological responses in the uterus: studies with short- and long-acting derivatives of estriol.

The temporal relationships between hormone receptor binding and early and late biological responses in the uterus were examined using estriol (E3), a weak estrogen, and several more long-acting estriol derivatives, namely ethinyl estriol (EE3), estriol cyclopentyl ether (E3CPE), and ethinyl estriol cyclopentyl ether (EE3CPE). Dose-response curves of 3-day uterotrophic assays indicate that biological potency follows the order EE3CPE greater than EE3 or estradiol greater than E3CPE greater than E3. After a single injection of 5 mug of compound, E3 elicits the early uterotrophic responses (increased uterine wet weight and 2-deoxyglucose phosphorylation at 2-6 h) but gives only weak stimulation of later uterotrophic responses (enhanced rates of 2-deoxyglucose phosphorylation at 20-24 h and increased DNA synthesis rate and uterine weight over a 72 h period). E3, EE3, and estradiol all elicit a rapid (maximal by 1/2-1 h) uptake of receptor into the nucleus and show an equivalent wet weight response at 3 h. After E3, nuclear receptor levels and uterine weight decline rapidly; however, after EE3 or estradiol, nuclear receptor levels decline less rapidly remaining at least two-fold above the control until 24-48 hr, and uterine weight also remains elevated for at least 48-72 h. EE3CPE elicits both the early (4 h) and later (20-24 h) waves of glucose metabolism, shows a prolonged effect on DNA synthesis rate, and shows the most dramatic and prolonged (beyond 72 h) maintenance of elevated uterine weight and high nuclear receptor (beyond 24 h). Thus, chemical modifications of the estriol molecule which result in a prolonged stimulation of uterine growth and metabolism also result in a long-term maintenance of hormone-receptor complex in the uterine nucleus. These studies give strong support to the concept that true uterine growth requires the direct and prolonged influence of the nuclear estrogen-receptor complex.