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Changes in Estrogen Receptor, DNA Ploidy, and Estrogen Metabolism in Rat Hepatocytes during a Two-Stage Model for Hepatocarcinogenesis Using 17-Ethinylestradiol as the Promoting Agent

Laboratory of Biochemical Risk Analysis, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709

17-Ethylestradiol (EE₂) was administered chronically to diethylnitrosamine (DEN)-initiated (200/mg/kg, i.p.) adult ovariectomized Sprague-Dawley rats, by means of Silastic implants at an estimated dose of 90 µg/kg/day. Isolated hepatocytes from DEN/EE₂-treated animals exhibited a 2- to 3-fold increase in nuclear estrogen receptor (ER) levels throughout the promotion period. Furthermore, approximately 30–40% of the receptor was occupied when quantified by an exchange assay. For all groups the ER had a sedimentation coefficient of approximately 8S for unoccupied ER and a binding affinity for 17ß-estradiol of 0.25 nM. An ER of lower affinity for estradiol was present in animals initiated with DEN and/or promoted with EE₂. The increase in hepatocyte ER was associated with a 5.2-fold increase in -glutamyl transpeptidase and 2.5-fold decrease in glucose-6-phosphatase activity at 20 weeks. EE₂ treatment caused a 50% increase in the maximal binding capacity (B_max) of hepatic epidermal growth factor receptors, but the equilibrium binding constant (K_d) did not change. Modulation of mitotic activity of hepatocyte subpopulations by EE₂ treatment was indicated by an increase in the proportion of diploid hepatocytes and an increase in the number of hepatocytes undergoing DNA synthesis. In general, effects on ER, epidermal growth factor receptor, -glutamyl transpeptidase and glucose-6-phosphatase were greater in DEN/EE₂-treated animals than in rats receiving only EE₂. Modification of receptor pathways associated with hepatocyte growth control, ER and epidermal growth factor receptor, may be contributing factors in the clonal expansion of preneoplastic cells during EE₂ promotion of hepatocarcinogenesis.

¹ To whom requests for reprints should be addressed, at National Institute of Environmental Health Sciences, P. O. Box 12233, MD A3-02, RTP, NC 27709.

Received 7/14/89. Accepted 8/25/89.

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