Rat Uterine Estrogen Receptor Research Articles

Aromatization of 7α-Methyl-19-nortestosterone by human placental microsomes in vitro

Part of the biological effects of testosterone (T) are mediated by its enzymatic reduction to 5α-dihydrotestosterone (DHT) or aromatization to estradiol (E 2). 7α-Methyl-19-nortestosterone (MENT) is a synthetic androgen that is considerably more potent than T. Previous studies have shown that MENT is not 5α-reduced. The studies reported here were undertaken to determine whether MENT undergoes enzymatic aromatization in vitro. Human placental microsomes were used as the source of the aromatase. Radioactive or nonradioactive T or MENT was incubated with the microsomes in the presence of NADPH and the metabolites extracted out with ethyl ether. Following evaporation of ether, the residue was dissolved in benzene-petroleum ether and extracted with 0.4 N NaOH which selectively removes phenolic metabolites of the androgens. When either radioactive T or MENT was incubated with the aromatase in the presence of NADPH, there was a 20-fold increase in the amount of radioactivity extracted with NaOH. In contrast, if the incubation was carried out in the absence of NADPH or in the presence of R76713, an aromatase inhibitor, most of the radioactivity remained in the benzene-petroleum ether phase. To further identify the enzymatic reaction products, thin layer chromatography (TLC) was performed. The R f value for MENT was 0.22 while that of the major reaction product was 0.34, which corresponded with the RF value of the estrogen, 7α-methyl-estradiol (MeE 2). This was further verified by using a second solvent system for the chromatographic separation. In an effort to ascertain whether the metabolites bind to estrogen receptors (ER), rat uterine cytosol was used. NaOH extracts of medium following incubation of nonradioactive MENT with microsomes showed competitive inhibition of [ 3H]E 2 binding to rat uterine ER. Furthermore, after [ 3H]MENT was incubated with microsomes, the radioactive metabolite extracted in NaOH showed specific binding to the ER which could readily be displaced with E 2 or MeE 2. These results indicate that like T, MENT undergoes enzymatic aromatization.

Effect of 3-methylcholanthrene on rat uterus: Uterine growth and mechanism of action of 3-methylcholanthrene

This study has been undertaken to examine the effect of 3-methylcholanthrene (3MC) on rat uterine growth and to understand the mechanism of action of 3MC in rat uterus. After diethylstilbesterol(DES) or tamoxifen(TAM) or 3MC or DES plus TAM or DES plus 3MC was administered into immature female rats, uterine weight of each group was measured. DES treatment resulted in 4-fold increase in uterine weight over com oil-treated uteri. 3MC treatment had no effect on uterine weight but, DES stimulated uterine weight was inhibited by 3MC concomitant treatment. While TAM alone treatment showed slight increase in uterine weight, inhibited uterine growth stimulated by DES when it was administrated with DES concomitantly. Affinity of estradiol for estrogen receptor in the rat uterus was determined via direct binding assay with [3H]estradiol and the relative binding affinities of 3MC and TAM were estimated by competetion assay. Estradiol turned out to have high affinity for rat uterine estrogen receptor (Kd=0.4 nM). The relative binding affinities of TAM and 3MC were 1% and 4.7% that of DES for rat uterine estrogen receptor, respectively. 3MC was shown to have similar affinity for rat uterine estrogen receptor to that of TAM. Effects of DES, 3MC and TAM administration in vivo on rat uterine estrogen receptor level were examined. It was confirmed that the estrogen, DES and antiestrogen, TAM decreased estrogen receptor levels from rat uterus and also 3MC decreased rat uterine estrogen receptor level when rats were treated with DES, TAM and 3MC in vivo. Data indicates that 3MC acts as an antiestrogen mediated through estrogen receptor system.

Structural characterization of the trypsinized estrogen receptor.

Structural differences between the unoccupied and ligand-occupied rat uterine estrogen receptors (ERs) were investigated using partial proteolysis followed by immunoblotting, affinity labeling, and gel filtration chromatography. Trypsin digestion of the unoccupied ER at 4 degrees C resulted in retention of 70-80% of high-affinity [3H]estradiol binding. Only two fragments of the rat ER were detected after prolonged trypsin treatment of the unoccupied ER followed by affinity labeling with [3H]tamoxifen aziridine. One fragment represents the intact steroid binding domain (28 kDa), and the other fragment is about 10 kDa. The small 10-kDa fragment of the ER detected by denaturing gel electrophoresis is shown to be held in a large oligomeric complex in solution using gel filtration chromatography. This oligomeric complex probably represents the steroid binding domain, which has its tertiary structure maintained predominantly by noncovalent interactions between the trypsin-generated fragments. The estrogen, anti-estrogen, and unoccupied trypsinized ERs all result in similar patterns of fragments after separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detection by immunoblotting. Although no new trypsin cleavage sites were exposed, the sensitivity of the available trypsin sites was altered by heating the ER and, to a lesser extent, by hormone treatment. Gel filtration chromatography of the trypsinized estradiol- and 4-hydroxytamoxifen-occupied ERs demonstrates similar, diffuse peaks centered at about the correct size for the intact steroid binding domain (28 kDa), whereas the trypsinized unoccupied ER results in a sharp, discrete peak centered at about 80 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)

The importance of long term developmental follow-up in the assessment of factors that may affect the development of the human fetal brain

There is growing concern that estrogenic chemicals, both natural and human-made, may be causing a variety of reproductive disorders in wildlife and human populations. Recent in vitro data suggest that the interaction between some weakly estrogenic organochlorines, dieldrin, endosulfan, toxaphene, and chlordane, causes a synergistic increase in their estrogenic potency, an effect due to joint action on estrogen receptors (ER). As these studies were conducted using models of estrogen action derived from cells that are not physiologically controlled by estrogens, the relevance of these findings to human health are not clear. The present studies were conducted to examine the interaction between endosulfan and dieldrin in the activation of ER in or extracted from mammalian cells. Endosulfan and dieldrin showed no synergism in displacing 3H-E2 from rat uterine ER or in inducing the proliferation of MCF-7 breast cancer cells, an estrogen-dependent response. Furthermore, endosulfan (0.1 mg per animal per d) or dieldrin (0.1 mg), alone or in combination, injected intraperitoneally daily for 3 d, did not stimulate any uterotrophic activity nor had any effect on pituitary prolactin or other endocrine-related endpoints in immature female rats. These studies demonstrate that these weakly estrogenic compounds do not interact in a synergistic fashion in binding to ER or in activating ER-dependent responses in mammalian tissues or cells. Thus, these results suggest that coexposure to these weakly estrogenic environmental contaminants likely will not cause human reproductive toxicity related to estrogen action.

Stimulation of estrogen receptor-mediated transcription and alteration in the phosphorylation state of the rat uterine estrogen receptor by estrogen, cyclic adenosine monophosphate, and insulin-like growth factor-I

Stimulation of estrogen receptor-mediated transcription and alteration in the phosphorylation state of the rat uterine estrogen receptor by estrogen, cyclic adenosine monophosphate, and insulin-like growth factor-I

Stimulation of estrogen receptor-mediated transcription and alteration in the phosphorylation state of the rat uterine estrogen receptor by estrogen, cyclic adenosine monophosphate, and insulin-like growth factor-I.

We have shown previously that exposure of rat uterine cells in primary culture to estradiol (E2), insulin-like growth factor-I (IGF-I), or agents which alter intracellular cAMP levels, such as cholera toxin plus isobutylmethylxanthine (CT + IBMX) and 8-Br-cAMP, results in the up-regulation of cellular levels of the progesterone receptor, an effect believed to be mediated through the activation of estrogen receptor (ER) and phosphorylation pathways. We have therefore undertaken studies using transient transfection of these uterine cell cultures with a simple estrogen-responsive reporter gene in order to determine the ability of these agents to stimulate ER-mediated gene transcription directly. We also compared the ability of these same agents to alter the phosphorylation state of the endogenous uterine ER protein. Plasmid DNA containing two tandem estrogen responsive elements and a TATA box linked to the chloramphenicol acetyl transferase (CAT) gene was introduced into immature rat uterine cells grown in primary culture. Treatment of transfected cells with 10(-9) M E2, CT (1 micrograms/ml) + IBMX (10(-4) M), 8-Br-cAMP (10(-4) M), or IGF-I (20 ng/ml) resulted in an 8- to 10-fold induction of CAT activity. CAT activity stimulated by all agents was nearly completely suppressed by coincubation with the antiestrogen ICI 164,384 (ICI) or the protein kinase (PK) inhibitor H8. CAT activity induced by 8-Br-cAMP was more readily suppressed by ICI than that induced by E2, indicating that ER in cells exposed to 8-Br-cAMP is either unoccupied or minimally occupied by ligand. The level of ER phosphorylation in uterine cells was increased 3- to 5-fold upon exposure to E2, CT + IBMX, 8-Br-cAMP, or IGF-I. Of interest, the antiestrogen ICI also elicited a similar increase in overall ER phosphorylation. The PK inhibitors H8 and PKI suppressed the increase in overall ER phosphorylation stimulated by these agents by 50-75%. The results of our study indicate that E2, IGF-I, and agents which raise intracellular cAMP are able to stimulate ER-mediated trans-activation and ER phosphorylation. The fact that antiestrogen (ICI) evokes a similar increase in ER phosphorylation without a similar increase in transcription activation indicates that an increase in overall ER phosphorylation does not necessarily result in increased transcriptional activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of rat uterine estrogen receptors in vivo

In vivo binding of [ 3H]estradiol ([ 3H]E 2) in the rat uterus was performed by an intraluminal perfusion of the ligand for different time periods. In this way the binding takes place in the intact organ before processing the tissue. In 10 min, with 10 nM [ 3H]E 2 apparent saturation or steady state incorporation of the [ 3H]E 2 was achieved with a similar distribution of the label between cytosol and nuclear fractions. In vitro, the subcellular localization of the estrogen receptor (ER) is influenced by the extent of tissue damage. With the intact organ the ER subcellular distribution approaches that of the in vivo perfusion. With increasing [ 3H 2 in the perfusate it was possible to obtain a “saturation” curve to derive the kinetic parameters. For cytosol: K d 16 nM; B max 235 fmol/mg prot. For nucleus: K d 2.7 nM; B max 103 fmol/mg prot. To follow the time course of the ER movement in vivo, “pulse and wait” experiments were designed. Both uterine horns were perfused for 1 min. One of the horns was immediately processed (0 time) and the other was left in place after the perfusion for different periods. At 0 time 90% of the bound label appeared in the cytosol. At 5, 15 and 30 min, the label in the cytosol decreased and that of the nucleus increased approx. to 50%. Thus, translocation of the bound label from cytosol to nucleus was apparent. The role of the cytoplasm-nucleus ER traffic in the regulation of gene transcription by estrogens is discussed.

Changes in Rat Uterine Estrogen Receptor Messenger Ribonucleic Acid Levels during Estrogen- and Progesterone-Induced Estrogen Receptor Depletion and Subsequent Replenishment1

The overall objectives of this study were to determine whether the rapid decrease in estrogen receptor (ER) binding in the rat uterus after an injection of estradiol and subsequent recovery of ER levels was accompanied by similar changes in ER mRNA levels. Furthermore, the effect of progesterone administered under conditions known to decrease ER binding, in the rat uterus, on ER mRNA levels was also investigated. Ovariectomy for 14 days brought about a 3-fold increase in rat uterine ER mRNA levels, and these elevated levels were decreased by a 3-day treatment with 2 micrograms of estradiol in ethanol/saline injected i.p. In the ovariectomized rat, 1 and 5 micrograms of estradiol brought about small but significant decreases in ER mRNA levels in 1 h, which did not parallel the rapid decrease in ER binding at that time reported earlier. The 10-micrograms dose of estradiol brought about a bigger decrease in ER mRNA levels. In the ovariectomized rat primed with estradiol (2 micrograms/day in ethanol/saline), the administration of 2 micrograms of estradiol brought about no change in uterine ER mRNA levels at 6 h as compared to the 1-h time point if the values were not corrected for beta-actin, which was significantly increased at 6 h. A dramatic increase in ER mRNA levels 12 h after the estradiol injection preceded the increase in ER binding observed at 18 h. Progesterone (0.8 mg/kg body weight [BW]) in the absence of estrogen priming brought about minimal but significant inhibition of ER mRNA levels 12 and 18 h after administration, with no effects at 1 and 6 h. In the presence of estrogen priming, the 0.8-mg/kg BW dose of progesterone did not cause any changes in ER mRNA levels beyond those brought about by estrogen alone after 1 h, even though it has been shown to significantly decrease ER binding. This was also true when a larger dose of progesterone (2.0 mg/kg BW) was used, a dose that decreases ER binding to a significantly greater extent than the 0.8-mg/kg BW dose. However, the 4.0-mg/kg BW dose of progesterone decreased ER mRNA levels. Thus a single injection of estradiol appears to cause a decrease in ER binding primarily by accelerated receptor processing and degradation with small changes in ER mRNA within the first hour. A significant increase in uterine ER mRNA at 12 h precedes increased ER binding at 18 h. This indicates new synthesis of ER during the recovery period.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxidative dehalogenation of 2-fluoro-17α-ethynyloestradiol in vivo: A distal structure-metabolism relationship of 17α-ethynylation

Metabolic activation to catechols and their oxidation products is variously considered to contribute to the genotoxic, cytotoxic, transforming and tumour-promoting activities of exogenous steroidal oestrogens. 2-Fluoro-17α-ethynyloestradiol (2-FEE 2) was synthesized as a prototype of pharmacologically active derivatives of 17β-oestradiol which are resistant to metabolic activation in vivo. It possessed high affinity for the rat uterine oestrogen receptor and was oestrogenic in rats. Biliary metabolites of [6,7- 3H]2-FEE 2 (0.73 μmol/kg, 157 μg/kg, i.v.) in female rats were characterized: 87% of the radiolabel was excreted, principally as 2-FEE 2 glucuronide, over 6hr. Although 2-nuoro-17β-oestradiol is not metabolized to C-2 oxygenated products in vivo, 2-FEE 2 underwent rapid and appreciable oxidative defluorination. 2-Hydroxy-17α-ethynyloestradiol and 2-methoxy-17α-ethynyl-oestradiol represented, respectively, 8% and 13% of the dose. Fluorination nevertheless restricted C-2 oxygenation to ca. 28% of that which 17α-ethynyloestradiol undergoes in female rats. C-4 oxygenation of 2-FEE 2, resulting in catechol formation, occurred but to a lesser extent ( ca. 12% of dose). None of the major and identified minor biliary metabolites was a product of metabolic activation at the ethynyl function. A mechanistic rationalization of the long range enhancement by 17α-ethynylation of oxidative defluorination at C-2 is presented.

Estrogen platinum-diamine complexes: Preparation of a non-steroidal estrogen platinum—diamine complex labeled with platinum-191 and a study of its binding to the estrogen receptor in vitro and its tissue distribution in vivo

We have prepared in radiolabeled form (platinum-191) a non-steroidal estrogen platinum—diamine complex (Pt—diamine complex) that is reported to have selective cytostatic activity in estrogen receptor positive mouse mammary tumors. We then studied the interaction of this metal radiolabeled complex with the estrogen receptor in vitro and its distribution in immature rats in vivo. The radiolabeled complex was prepared by incubation of the non-steroidal estrogen diamine with [ 191 Pt]( II)Cl 4 −2(t 1 2 = 2.96 days, sp. act. 7.54 Ci/mmol) in dimethylformamide (DMF)/H 2O, followed by purification by HPLC. The final radiolabeled product coeluted with an authentic standard of the unlabeled Pt—diamine complex, with a retention time distinct from those of the precursor diamine and chloroplatinate. In competitive radiometric receptor binding assays with rat uterine estrogen receptor, samples of the unlabeled diamine and Pt—diamine complex have apparent binding affinities of 53±3% and 32 ± 11%, respectively, relative to estradiol (RBA = 100% as standard). However, attempts to observe the binding of the 191Pt—diamine complex with the estrogen receptor were complicated by a very high level of non-receptor binding, an irreversible binding to proteins in the receptor preparation, and a degradation of the platinum complex that, in part, releases the diamine. As a result, it is difficult to be certain whether the binding affinity measured for the Pt—diamine complex in the competitive binding assays is due to the complex itself, or whether it arises from diamine released upon degradation of the complex. In tissue distribution studies in immature female rats, much of the 191Pt—diamine complex was deposited in the liver; there was no evidence of selective uptake of this compound by estrogen target tissues. Thus, it is not clear, from these studies, that the observed bioactivity of this complex arises from the interaction of the Pt complex or the diamine ligand with the estrogen receptor.

Nonsteroidal estrogens bearing acyl azide functions: potential electrophilic and photoaffinity labeling agents for the estrogen receptor

In an effort to develop novel affinity labeling agents for the estrogen receptor, we have synthesized two nonsteroidal ligands, a 1-aroyl-2-aryl tetralin system (1) and a 2-aryl-3-aroylbenzo[b]thiophene system (2). These agents, patterned after the Lilly antiestrogens trioxifene and LY 117018, respectively, embody acyl azide functions as part of a benzoyl chromophore. The acyl azide group has weak acylating activity, suitable for electrophilic affinity labeling, but this function is also photoreactive and, in its particular embodiment within these ligands, it could provide an efficient photochemical route to the highly reactive singlet acyl nitrene. The tetralin system (1) was prepared in nine steps from 6-methoxy-1-tetralone, and the benzothiophene system (2) was prepared in four steps from a known substituted benzo[b]thiophene precursor. In competitive binding assays, both compounds show reasonable binding affinity for the rat and lamb uterine estrogen receptor: estradiol = 100%, 1 = 3%, and 2 = 12%. When assayed by indirect receptor consumption assays, both compounds appear to have substantial capacity for irreversible binding (electrophilic reaction) with the receptor. This reactivity, which suggests that acylation of the receptor has occurred, is photoreversible. The nature of this ligand-receptor interaction is being investigated further.

Cellular variations in estrogen receptor mRNA translation in the developing brain: evidence from combined [ 125I]estrogen autoradiography and non-isotopic in situ hybridization histochemistry

The spatial distribution of cells in the adult rodent forebrain which express estrogen receptor mRNA, as shown by in situ hybridization histochemistry with isotopically-labeled probes, has been reported to overlap with regions that are known targets of estrogen and which bind estrogen. The extent to which detection of estrogen receptor mRNA within developing forebrain neurons of the postnatal day 10–12 female rat is accompanied by translation into estrogen binding sites was investigated by combining [ 125I]estrogen autoradiography with non-isotopic (digoxigenin) in situ hybridization, using a 48-base oligodeoxyribonucleotide probe encoding a sequence of the estrogen-binding domain of rat uterine estrogen receptor cDNA. Estrogen receptor mRNA and estrogen binding sites appeared to be restricted to neurons. No mRNA or binding was seen in ependymal cells. Cells expressing estrogen receptor mRNA were widely distributed in the developing rat forebrain and were found in brain regions generally corresponding to those previously shown in the adult, with the addition of some regions not previously described, such as the medial habenula and dorsal endopiriform nucleus. Although there was widespread overlapping of estrogen receptor mRNA expression with known estrogen binding sites, there were regional and cellular variations in the extent of receptor mRNA translation. This pattern was true for developing forebrain regions previously defined as estrogen receptor-containing (hypothalamus, preoptic area, medial and lateral septum, vertical and horizontal nuclei of the diagonal band, cerebral cortex, hippocampus and amygdala) as well as for regions heretofore not considered estrogen targets (the thalamus, dorsal endopiriform nucleus, claustrum, ventral pallidum/substantia innominata and the basal nucleus of Meynert) or characterized as estrogen-responsive in the adult without previously documented estrogen binding [caudate-putamen (striatum)]. While estrogen binding and receptor mRNA expression always co-localized, neurons expressing estrogen receptor mRNA did not always exhibit ligand binding and there was no clear-cut relationship between the intensity of the hybridization signal and estrogen binding. Little, however, is known about translational control of estrogen receptor expression in the brain. Localization of estrogen binding sites to regions not generally considered targets of estrogen would appear to reflect the greater sensitivity of the iodinated ligand than the tritiated estrogens more commonly used for autoradiography. Non-isotopic in situ hybridization histochemistry combined with [ 125I]estrogen autoradiography represents a very powerful tool with which to study regulation of estrogen receptor gene expression at the single cell level with an exceptional degree of cellular and anatomical resolution. These findings suggest that the extent of estrogen receptor mRNA translation in the developing brain has been underestimated. Differential patterns of translation may be related to regional differences in the ontogeny of the estrogen receptor and to developmentally-regulated differences in post-translational processing as well as to the autoradiographic method itself, particularly with respect to regional differences in the length of exposure required.

Protein purification using a soluble affinity matrix: Purification of estrogen receptor with estradiol-polylysine conjugate

A new strategy for protein purification using a soluble affinity matrix is described. The method was used for purification of estrogen receptor. Cytosols from rat uteri and human fibroid uterine tissue, after fractionation by ammonium sulfate, were treated with estradiol-polylysine conjugate. The highly basic affinity complex was separated from other proteins by DEAE-Sephacel chromatography. After dissociation of the eluted complex with excess estradiol, the receptor was recovered by CM-Sephadex chromatography. A 2000-fold purification of the rat uterine estrogen receptor was obtained with an activity recovery of 35%.

Developmental expression of estrogen receptor mRNA in the rat cerebral cortex: a nonisotopic in situ hybridization histochemistry study.

The distribution of estrogen receptor mRNA expression was studied in the developing rat cerebral cortex by in situ hybridization histochemistry. We used a specific, nonisotopically (digoxigenin) labeled, synthetic oligodeoxyribonucleotide complementary to a 48 base sequence in the region of the estrogen-binding domain of rat uterine estrogen receptor cDNA. During development, estrogen receptor mRNA was observed in all forebrain regions previously reported to bind estrogen, as determined by steroid autoradiography or nuclear binding assay. In the developing cerebral cortex, estrogen receptor mRNA was extensively expressed in the ventricular zone, primitive plexiform layer, and immature cortical plate at least as early as embryonic day 16. During the first 3 postnatal weeks, cortical mRNA expression was increasingly restricted to the upper third of the cerebral cortex and to the neurons of the cortical subplate (layer VIb/VII) and decreased to low levels by postnatal day 28. In the cerebral cortex, the spatial distribution of estrogen receptor mRNA expression overlapped that reported for the encoded protein. The extensive distribution of estrogen receptor mRNA throughout the late prenatal and early postnatal cerebral cortex points to an important role for estrogen in the differentiation and maturation of the cerebral cortex.

Derivatives of ethynylestradiol with oxygenated 17α-alkyl side chain: Synthesis and biological activity

The coupling reaction of an acetylide ion with alkyl bromide or δ-valerolactone was used to synthesize twelve 1 17α-derivatives of ethynylestradiol having various 17α-side chain lengths and, except one, having mono- or di-oxygenated function on the side chain. All compounds had low (0.01–1.79%) relative binding affinity (RBA) for the rat uterine estrogen receptor. The highest RBA were obtained for compounds 26 (1.79%), 30 (1.55%) and 19 (0.42%). The length and polarity of the side chain decreases the affinity for the estrogen receptor. The in vivo estrogenic activity was measured on mouse uterine weight and was found to range from 0 to 35%, except for compound 30 (100%). The antiuterotrophic activity was measured by inhibition of estradiol-induced stimulation of uterine weight and was found to be 39% for compound 19, 25% for compound 26 and 0% for all other compounds. These two compounds ( 19 and 26) possess mixed agonist and antagonist activity.

Effect of epostane, ZK 98299, and ZK 98734 on the interruption of pregnancy in the rat.

The objective of these studies was to determine whether treatment of 10-day pregnant rats with a combination of epostane (a progesterone biosynthesis inhibitor) and either ZK 98299 or ZK 98734 (progesterone receptor antagonists) would result in additive or synergistic effects on the interruption of pregnancy. When these compounds were tested individually, the order of potency in interrupting pregnancy was ZK 98734 greater than ZK 98299 greater than epostane (50% effective doses 1.3, 4.0, and 35 mg/kg, respectively). Epostane and ZK 98299 were then tested in combination. When epostane was given either 4 h prior to or concurrently with ZK 98299, the combined drug treatment resulted in a significant additive increase in interceptive activity compared to when ZK 98299 was administered alone. In vitro binding studies showed that ZK 98299 and ZK 98734 bound to the rat uterine progesterone receptor in vitro with approximately equal affinity. ZK 98734 bound to the rat thymus glucocorticoid receptor and to the rat ventral prostate androgen receptor with a greater affinity than ZK 98299. The affinity of ZK 98299 for the rat uterine estrogen receptor was weak while the binding of ZK 98734 was not detectable. Thus, the in vitro receptor binding profiles observed were consistent with the known progesterone and glucocorticoid antagonist activities of ZK 98299 and ZK 98734. Overall these findings show that the interceptive activity of epostane and ZK 98299, agents that exert their interceptive activity via different molecular mechanisms, is additive in the 10-day pregnant rat.

Effect of ether or ketamine anesthesia on rat uterine estrogen and progesterone receptors.

Rat uterine estrogen receptors (ER) and progesterone receptors (PR) have been used as controls in ER and PR assays of breast tumors. Stunning or decapitation of experimental animals without prior anesthesia is no longer acceptable as a method of killing. Thus, we compared the effects of two anesthetics on the concentration of rat uterine ER and PR. Rats were killed by one of three methods: (a) stunning, (b) ether anesthesia followed by decapitation, or (c) ketamine anesthesia followed by decapitation. ER and PR concentrations were determined by titration assay, with dextran-coated charcoal separation, and quantified by Scatchard analysis. No significant differences were found in mean receptor concentrations or dissociation constants for the three groups. The results indicate that there is no residual effect of diethyl ether or ketamine hydrochloride on the binding of either estrogen or progestin to their respective receptors. The use of decapitation after either ether or ketamine anesthesia is appropriate for measuring ER and PR receptors in rat uteri.

Bioflavonoid interaction with rat uterine type ii binding sites and cell growth inhibition

Competition analysis with a number of known bioflavonoids demonstrated that these compounds (luteolin, quercetin, pelargonin) compete for [ 3H]estradiol binding to cytosol and nuclear type II sites in rat uterine preparations. The inhibition of [ 3H]estradiol binding to type II sites was specific and these bioflavonoids did not interact with the rat uterine estrogen receptor. Since estradiol stimulation of nuclear type II sites in the rat uterus is highly correlated with cellular hypertrophy and hyperplasia, we assessed the effects of these compounds on the growth of MCF-7 human breast cancer cells in culture and on estradiol stimulation of uterine growth in the immature rat. The data demonstrated that addition of quercetin (5–10 μg/ml) to MCF-7 cell cultures resulted in a dose-dependent inhibition of cell growth (DNA/flask). This effect was reversible by removal of quercetin from the culture medium, or by the addition of 10 nM estradiol-17β to these cell cultures containing this bioflavonoid. Since estradiol-17β (10 nM) stimulated nuclear type II sites and proliferation of MCF-7 cells, we believe bioflavonoid inhibition of MCF-7 cell growth may be mediated through an interaction with nuclear type II sites. This hypothesis was confirmed by in vivo studies which demonstrated that injection of luteolin or quercetin blocked estradiol stimulation of nuclear type II sites in the immature rat uterus and this correlated with an inhibition of uterine growth (wet and dry weight). These studies suggest bioflavonoids, through an interaction with type II sites, may be involved in cell growth regulation.

Structural analysis of covalently labeled estrogen receptors by limited proteolysis and monoclonal antibody reactivity.

We have used limited proteolysis of affinity-labeled estrogen receptors (ER), coupled with antireceptor antibody immunoreactivity, to assess structural features of ER and the relatedness of ER from MCF-7 human breast cancer and rat uterine cells. MCF-7 ER preparations covalently labeled with [3H]tamoxifen aziridine [( 3H]TAZ) were treated with trypsin (T), alpha-chymotrypsin (C), or Staphylococcus aureus V8 protease prior to electrophoresis on sodium dodecyl sulfate gels. Fluorography revealed a distinctive ladder of ER fragments containing TAZ for each protease generated from the Mr 66,000 ER: for T, fragments of 50K, 38K, 36K, 31K, 29K, and 28K that with longer exposure generated a 6K fragment; for C, fragments of 50K, 38K, 35K, 33K, 31K, 19K, and 18K that with longer exposure generated 14K and 6K fragments; and for V8, ca. 10 fragments between 62K and 28K. Two-dimensional gels revealed charge heterogeneity (two to three spots between pI 5.5 and 6.2) of the 66K ER and the T-generated 28K meroreceptor form. Immunoblot detection with the primate-specific antibody D75P3 gamma revealed that all immunoreactive fragments corresponded to TAZ-labeled fragments but that some small TAZ-labeled fragments (V8-generated forms less than 47K and T-generated forms less than 31K) were no longer immunoreactive. In contrast, use of the antibody H222Sp gamma revealed a correspondence between TAZ-labeled and immunoreactive fragments down to the smallest fragments generated, ca. 6K for T and C and 28K for V8. MCF-7 nuclear and cytosol ER showed very similar digest patterns, and there was a remarkable similarity in the TAZ-labeled and H222-immunoreactive fragments generated by proteolysis of both MCF-7 and rat uterine ER. These findings reveal great structural similarities between the human (breast cancer) and rat (uterine) ER and between nuclear and cytosol ER, indicate charge heterogeneity of ER, and allow a comparison of the immunoreactive and hormone attachment site domains of the ER. The observation that T and C generate a ca. 6K TAZ-labeled fragment that is also detectable with the H222 antibody should be of interest in studies determining the hormone binding domain of the ER and in amino acid sequencing of this region.

The antiestrogen LY117018 is estrogenic in the fetal rat.

LY117018 (LY) has high affinity for the adult rat uterine estrogen receptor, has little uterotrophic activity, and inhibits many estradiol (E2)-induced responses in the adult or immature uterus. In these studies, LY was injected into day 19 rat fetuses, with and without diethylstilbestrol (DES) or E2, to determine whether it could block the estrogen-induced teratogenesis. LY at 1, 25, or 50 micrograms/fetus failed to decrease the 15-70% incidences of oviduct malformation and cleft phallus induced by DES (2.5 micrograms/fetus) or E2 (50 micrograms/fetus). However, LY alone (1-50 micrograms/fetus) was more potent than E2 in eliciting these same urogenital malformations. LY also failed to compete in vitro for plasma protein-bound 3H-E2, and therefore, like DES, is more available than E2 for uptake into fetal tissues. Thus, in the fetus, unlike the adult, LY was an estrogen agonist, which indicates that the fetus has a very different sensitivity than the adult to estrogenic compounds.