Medlock K L, Lyttle C R, Kelepouris N, Newman E D, Sheehan D M
Division of Reproductive and Developmental Toxicology, Food and Drug Administration, National Center for Toxicological Research, Jefferson, Arkansas 72079.
Proc Soc Exp Biol Med. 1991 Mar;196(3):293-300. doi: 10.3181/00379727-196-43191.
We have previously shown that neonatal exposure of rats to pharmacologic doses of diethylstilbestrol via daily injections resulted in a significant decrease in the estrogen-binding capacity of the uterine estrogen receptor (ER). In this study, we examined the effects of physiologic and pharmacologic doses of estradiol (E2) administered to adult ovariectomized rats via Silastic implants. Two days after implantation, uteri were removed, weighted, and homogenized, and ER levels were determined in the supernatant (hydroxylapatite assay) and low-speed pellet (nuclear exchange assay). Implants containing E2 concentrations of 0.005 or 0.05 mg/ml increased cytosolic but not total ER-binding capacity, whereas 0.5 or 5.0 mg of E2/ml implants decreased the binding capacity of cytosol ER to 40% and total ER to 50% of control values. The 0.005-mg/ml dose increased cytosol ER without increasing uterine weight; all higher doses significantly increased uterine weight. Determination of ER protein by an ER radioimmunoassay showed the same extent of reduction of ER concentration as the binding assays, demonstrating that the loss in E2 binding capacity is homologous down-regulation. The down-regulation of ER was maximal at 24 hr and was completely reversible after implant removal, although the time required to recover from down-regulation was dose dependent. Uterine weight also returned to control levels slowly after implant removal. Neither the sedimentation rate of the down-regulated ER nor the Kd of the cytosolic ER changed following long-term implantation; however, the Kd of the nuclear ER decreased significantly. This is the first demonstration of in vivo homologous down-regulation of uterine ER. ER down-regulation may play a role in several biologic processes.
我们之前已经表明，通过每日注射给予大鼠药理学剂量的己烯雌酚，会导致子宫雌激素受体（ER）的雌激素结合能力显著下降。在本研究中，我们研究了通过硅胶植入物向成年去卵巢大鼠给予生理剂量和药理剂量的雌二醇（E2）的效果。植入后两天，取出子宫，称重并匀浆，然后通过上清液（羟基磷灰石测定法）和低速沉淀（核交换测定法）测定ER水平。含有0.005或0.05mg/ml E2浓度的植入物增加了胞质溶胶中而非总的ER结合能力，而含有0.5或5.0mg/ml E2的植入物使胞质溶胶ER的结合能力降至对照值的40%，总ER降至50%。0.005mg/ml的剂量增加了胞质溶胶ER，但未增加子宫重量；所有更高剂量均显著增加了子宫重量。通过ER放射免疫测定法测定ER蛋白显示，ER浓度降低的程度与结合测定法相同，表明E2结合能力的丧失是同源性下调。ER的下调在24小时时达到最大，并且在取出植入物后完全可逆，尽管从下调中恢复所需的时间取决于剂量。取出植入物后，子宫重量也缓慢恢复到对照水平。长期植入后，下调的ER的沉降率和胞质溶胶ER的解离常数（Kd）均未改变；然而，核ER的Kd显著降低。这是子宫ER在体内同源性下调的首次证明。ER下调可能在多个生物学过程中起作用。
