TOXICOLOGY AND APPLIED PHARMACOLOGY 113,284-292 (1992) Antiestrogenic Action of 2,3,7,8-Tetrachlorodibenzo-p-dioxin: Tissue- Specific Regulation of Estrogen Receptor in CD1 Mice’ M. J. DEVITO,*‘~ T. THOMAS, *,3 E. MARTIN,~ T. H. UMBREIT,* AND M. A. GALLO* Departments @Environmental dt Community Medicine and ff’athology, University ofMedicine and Dentistry of New Jersey- Robert Wood Johnson Medical School, Piscataway, New Jersey 08854 Received July 11, 1991; accepted December 20, 199 I Antiestrogenic Action of 2,3,7,8-Tetrachlorodibenzo-p-dioxin: Tissue-Specific Regulation of Estrogen Receptor in CD1 Mice. DEVITO, M.J., THOMAS, T., MARTIN, E., UMBREIT, T.H., AND GALLO, M. A. (1992). Toxicol. Appl. Pharmacol. 113,284-292. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a polychlo- rinated aromatic hydrocarbon with teratogenic and carcinogenic properties. Previous studies in our and other laboratories have demonstrated that TCDD has antiestrogenic properties. In order to elucidate the mechanism of action of TCDD on estrogen sen- sitive tissues, we studied its effects on serum estradiol and es- trogen receptor (ER) levels in liver and uteri of CD1 mice. Treatment with TCDD did not result in alterations of serum estradiol levels at any of the doses tested (1.0-30 pg/kg). In contrast, TCDD treatment induced a dose-dependent decrease in hepatic and uterine ER protein as determined by an enzyme immunoassay and equilibrium binding assays.A decrease in cy- tosolic and nuclear ER levels in uteri occurred as early as 24 hr after initial treatment with 30 pg/kg TCDD and recovery oc- curred by 14 days. Hepatic cytosolic and nuclear ER also de- creased at a dose of 30 rglkg TCDD at 24 hr after treatment, but recovery occurred only by 2 1 days. Studies in ovariectomized mice indicate that the regulation of hepatic ER by TCDD is independent of ovarian factors, but ovariectomy inhibited the downregulation of uterine ER by TCDD. Furthermore, deter- mination of TCDD-induced cytochrome P-450 levels indicates that the downregulation of uterine ER is uncoupled from in- duction of hepatic cytochrome P-450. This study indicates that the antiestrogenic effects of low doses of TCDD are mediated through its ability to decrease hepatic and uterine ER and are not due to alterations in serum estradiol levels. Our results on ovariectomized mice indicate that TCDD-induced downregu- lation of ER is tissue specific and may involve different mech- anisms at transcriptional or posttranscriptional levels. 0 1992 Academic Press. Inc. ’ This work was supported in part by National Institutes of Health Grant CA 42439 (T.T.) and ES05022 (NIEHS Center), General Research Support Program of Robert Wood Johnson Medical School (T.T.), the Environmental and Occupational Health SciencesInstitute (T.T., M.J.D.), NJDOJ (M.A.G.), and NJDEP (M.A.G. and T.H.U.). ’ This work forms part of the Ph.D. requirements of M.J.D. in the Joint Graduate Program in Toxicology, Rutgers the State University of New Jersey and UMDNJ-Robert Wood Johnson Medical School. 3 To whom correspondence should be addressed. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most potent toxicants (Poland and Knutson, 1982; Safe, 1986; Whitlock, 1987). The toxic effects of TCDD vary and are dependent upon the species, sex, and age of the animal studied. While the mechanisms by which the toxic effects occur are as yet unknown, it is possible that alterations in the endocrine system are involved in the toxicity and car- cinogenicity of TCDD. Antiestrogenic effects of TCDD have been described in several experimental paradigms. Mice are particularly sensitive to the antiestrogenic effects of TCDD. TCDD inhibits estrogen-induced uterine imbibition in weanling CD1 mice (Gal10 et al., 1986). C57BI/6 female mice treated with 6 pg/kg of TCDD three times a week for 25 weeks had greatly reduced uterine weights, histopatho- logical changes in the uterus, irregular estrus, and reproduc- tive failure (Umbreit et al., 1987). We have also demonstrated that TCDD suppressed the estrogen-induced uterine imbi- bition in three different strains of mice with progression to an anovulatory state (Umbreit et al., 1988). TCDD is not alone in its antiestrogenic activity. Com- pounds such as phenobarbital (Levin et al., 1968) and some of the polybrominated biphenyls (Bonhaus et al., 1981) in- duce hepatic cytochrome P-450, increase the metabolism of steroids, and inhibit the uterotropic action of 17gestradiol and estrone. It has been suggested that the antiestrogenic effect of TCDD is also due to altered metabolism of steroid hormones, because TCDD also induces the group of enzymes involved in the metabolism of steroids (Gierthy et al., 1988). In rhesus monkeys, TCDD-induced reproductive toxicity occurred at doses causing decreased serum estrogen and pro- gesterone levels (Barsotti et al., 1977). In contrast, in pregnant rats, nontoxic doses of TCDD increased cytochrome P-450 levels by two- to threefold but did not alter serum estradiol levels (Shiverick and Muther, 1982, 1983). TCDD also showed antiestrogenic effects in a human breast cancer cell line, MCF-7, in association with an increased metabolism of estradiol (Gierthy et al., 1988; Spink et al., 1990). Thus there is a controversy about the role of TCDD-induced es- tradiol metabolism in its antiestrogenic effects. An alternative mechanism by which TCDD could produce its antiestrogenic effects is through alterations of the estrogen 0041-008X/92 $3.00 Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. 284