Inhibition of the 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2,2-trichloroethane (o,p'DDT)- and estradiol-mediated induction of rat uterine ornithine decarboxylase by prior treatment with o,p'DDT estradiol, and tamoxifen

Inactivation of the uterine estrogen receptor binding of estradiol during P-450 catalyzed metabolism of chlorotrianisene (TACE). Speculation that TACE antiestrogenic activity involves covalent binding to the estrogen receptor

Chlorotrianisene (TACE) exhibits in vitro little or no binding to the uterine estrogen receptor (ER) but demonstrates potent estrogenic activity in vivo, indicating that TACE is a proestrogen/proantiestrogen. Our earlier studies demonstrated that the incubation of TACE with rat liver microsomes and NADPH generates a reactive intermediate (T*) which binds covalently to proteins. The current study examined the possibility that T* may inactivate the uterine ER. The incubation of TACE with rat liver microsomes and NADPH in the presence of rat uteri, under conditions which generate T*, markedly decreased the binding capacity of the ER for [3H]estradiol (E2). The evidence indicates that ER inactivation was probably due to irreversible (covalent) binding of T* to the E2 binding site. The possibility that the antiestrogenic action of TACE and of other triphenylethylenes involves such a novel mechanism is discussed.

Relationships among uterine growth, ornithine decarboxylase activity and polyamine levels: studies with estradiol and antiestrogens

We have examined the effects of estradiol (E2) and antiestrogen (AE) on ornithine decarboxylase (ODC) activity and uterine polyamine concentrations as an aid to understanding the dissimilar effects of E2 and AE on uterine growth. ODC activity rises rapidly from very low levels in immature (day 20-23) rat uteri, showing two markedly (approximately 500-fold) increased peaks of activity at 5 h and 16 h after E2 (2 micrograms) injection. After AE (50 micrograms CI628 or U23469) treatment, the temporal increase in ODC activity is slow and only one major peak is found at 24 h. Daily injections of E2 over a 3-day period evoke continued stimulation of uterine ODC activity; however, the same daily treatment regimen with AE results in stimulation of ODC activity only during the first day. After pretreatment with AE, E2 can still elicit the early (5 h) peak of ODC activity, but the later (16 h) peak of ODC activity is blocked. Quantitation of uterine polyamines by high performance liquid chromatography reveals a 1.5-2-fold increase in the concentration of spermidine after 1 day of E2 or AE exposure, with little change in putrescine or spermine levels. After 3 days of E2, AE, or E2 plus AE treatment, spermidine concentrations are elevated 2-2.5-fold and spermine concentrations are elevated 1.5-fold. Putrescine concentrations are unchanged. Hence, regardless of the different degree to which the uterus is stimulated to grow in response to E2 and/or AE, there are corresponding changes in uterine ODC activity, such that polyamine concentrations are elevated to a similar extent in the E2- or AE-treated uterus.

Regulation of cytochrome P-450-dependent catechol estrogen formation in rat liver microsomes. Evidence for involvement of estrogen receptors

Experiments were conducted to evaluate whether estrogen 2-hydroxylase activity in liver microsomes, the main pathway for oxidative metabolism of estrogens in the rat, is regulated by administration of synthetic estrogens. Ovariectomized rats were treated with ethinylestradiol (EE), 100 micrograms s.c. for 3 days. Liver microsomes from EE-treated animals showed a 2-fold increase over control in estrogen 2-hydroxylase activity measured over a substrate concentration range of 0.5 to 50 microM. Double-reciprocal plots of enzyme activity as a function of substrate concentration were linear; apparent Vmax values were 2-fold greater in microsomes from EE-treated animals while apparent Km values for control and EE preparations were not different. Administration of the triphenylethylene antiestrogen tamoxifen (TAM), 100 micrograms s.c. for 3 days, did not affect microsomal catechol estrogen formation activity, and apparent Km and Vmax values were comparable with controls. When EE and TAM were co-administered, no increase in microsomal estrogen 2-hydroxylase was observed, and apparent Km and Vmax values were not different from either control of TAM-treated preparations. Thus, acute administration of EE was associated with a specific increase in the apparent Vmax of estrogen 2-OHase activity, and this effect was not observed when TAM was co-administered with the estrogen.

Effect of xenobiotic estrogens and structurally related compounds on 2-hydroxylation of estradiol and on other monooxygenase activities in rat liver

Previous study demonstrated that the administration for several days of 1-(o-chlorphenyl)-1-(p-chlorophenyl)-2,2,2-trichloroethane (o,p'DDT) (estrogenic DDT derivative) or of tamoxifen (antiestrogen), but not of 2,2-bis-(p-chlorophenyl)-1,1-dichloroethylene (p,p'DDE) (nonestrogen), to ovariectomized female rats dramatically diminished the induction of uterine ornithine decarboxylase (ODC) by subsequently administered estradiol [W. H. Bulger and D. Kupfer, Archs Biochem, Biophys. 182, 138 (1977)]. The present investigation examines whether the inhibition of ODC induction by o,p'DDT and tamoxifen may have been due to enhanced hydroxylation of estradiol by the hepatic monooxygenase system. Additionally, the effects of other estrogenic and nonestrogenic xenobiotics on the major route of estradiol metabolism (2-hydroxylation) were examined. Treatment of ovariectomized (ovex) rats with o,p'DDT or p,p'DDE caused induction of hepatic estradiol-2-hydroxylation and increased demethylase activities of several substrates. Administration of Kepone (estrogenic) and Mirex (nonestrogenic), both inducers of hepatic monooxygenase, also increased 2-hydroxylation of estradiol. For comparative purposes, the effects on estradiol-2-hydroxylation of administration of classical estrogens (estradiol and diethylstilbestrol) and antiestrogen (tamoxifen) and inducers of monooxygenase activity (phenobarbital and 3-methylcholanthrene) were also studied. Treatment of ovariectomized and adrenalectomized (ovex/adx) or intact female rats with estradiol or ovex/adx animals with diethylstilbestrol had no effect on estradiol-2-hydroxylation. Similarly, tamoxifen did not alter the rate of estradiol-2-hydroxylation. The treatment of ovex/adx rats with 3-methylcholanthrene did not affect the rate of estradiol-2-hydroxylation. By contrast, ovex/adx female or intact male rats treated with phenobarbital exhibited induction of estradiol-2-hydroxylase activity. In the above studies only 2-hydroxyestradiol was found; there was no evidence for the formation of primary metabolites hydroxylated at other sites on estradiol. The current findings exclude the possibility that the previously observed inhibition of estradiol-mediated induction of ODC by pretreatment with o,p'DDT or tamoxifen (see article cited above) was due to enhanced hydroxylation of estradiol by liver monooxygenases. Also, it was concluded that there is no correlation between the ability to induce hepatic microsomal estradiol-2-hydroxylase activity and estrogenic (or antiestrogenic) properties of a given compound.

Inhibition of ornithine decarboxylase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the activity of rat liver ornithine decarboxylase (ODC) were investigated. Sixteen hours after partial hepatectomy, rats that had been pretreated with TCDD for 1 week exhibited a 3- to 4-fold increase in ODC activity, while vehicle controls exhibited to 8- to 10-fold increase. This inhibition of ODC induction by TCDD was time dependent since TCDD administration at the time of partial hepatectomy did not produce inhibitory effects on the subsequent ODC induction. ODC induction after either aminophylline or dexamethasone administration, agents which act via cAMP-mediated and direct nuclear events, respectively, also was inhibited by pretreatment with TCDD. It was concluded that TCDD pretreatment decreased the ability of the liver to respond to hormonal stimulation as reflected in the attenuation of ODC induction. RNA polymerase I activity, which positively correlates with ODC activity in growth and development, decreased concomitantly with decreased induction of ODC. In unstimulated liver RNA polymerase I activity, as well as protein, DNA, and RNA levels, remained unchanged 1 week after TCDD. However, TCDD administration resulted in decreased liver concentrations of putrescine and spermidine, but not spermine. This suggests that TCDD pretreatment results in a time-dependent decrease in hormone responsivity.

The binding of [3H]-oestradiol-17 beta in the immature rat uterus during the sequential administration of non-steroidal anti-oestrogens

1 The binding of [(3)H]-oestradiol-17beta (0.08 mug) in the uterus, vagina, liver and heart of immature female rats has been studied in vivo and the effect of daily administrations of the non-steroidal anti-oestrogens, tamoxifen and monohydroxytamoxifen, on the 2 h accumulation of [(3)H]-oestradiol-17beta in the uterus has been determined.2 Doses of tamoxifen (8 mug daily) or monohydroxytamoxifen (1.28 mug daily), which have previously been found to antagonize completely the uterotrophic activity of oestradiol-17beta (0.08 mug daily), did not significantly reduce the total uterine binding of 0.08 mug [(3)H]-oestradiol-17beta administered on day 4 of a 3-day uterine weight test.3 The simultaneous administration of tamoxifen (8 mug) or monohydroxytamoxifen (1.28 mug) with [(3)H]-oestradiol-17beta (0.08 mug) on day 3 of a uterine weight test did not significantly reduce the total uterine binding of oestradiol-17beta. The binding of [(3)H]-oestradiol-17beta was reduced if monohydroxytamoxifen or tamoxifen was administered 4 h before the oestradiol.4 Tamoxifen (8 mug daily) or monohydroxytamoxifen (1.28 mug daily) did not prevent the translocation of [(3)H]-oestradiol (0.08 mug) to the uterine cell nucleus on day 3 of a 3-day uterine weight test.5 The measurement of total nuclear oestrogen receptors by an exchange assay technique demonstrated a higher concentration of oestrogen receptors in anti-oestrogen-treated animals compared with controls.6 Since the administration of anti-oestrogenic doses of non-steroidal anti-oestrogens during a 3-day uterine weight test did not inhibit the total binding of oestradiol in the uterus, or affect the translocation of the steroid to the nucleus, the mechanism of action of non-steroidal anti-oestrogens over the range of the partial agonist dose-response curve must involve an interaction, or competition of oestradiol-17beta- and anti-oestrogen-oestrogen receptor complexes for sites within the nucleus.