ER/Estrogen Receptor; Endogenous Metabolite

In vitro activity: Ethinyl Estradiol increases respiratory chain activity in both cultured rat hepatocytesand HepG2 cells. Ethinyl estradiol is a strong promoter of hepatocarcinogenesis. Ethinyl Estradiol enhances the transcript levels of nuclear genome- and mitochondrial genome-encoded genes and respiratory chain activity in female rat liver, and also inhibits transforming growth factor beta (TGFbeta)-induced apoptosis in cultured liver slices and hepatocytes from female rats. Ethinyl Estradiol increases the transcript levels of the mitochondrial genome-encoded genes cytochrome oxidase subunits I, II, and III in cultured female rathepatocytes. Ethinyl Estradiol significantly increases both the levels of glutathione (reduced [GSH] and oxidized [GSSG] forms) per mg protein in mitochondria and nuclei, while the percentage of total glutathione in the oxidized form is not affected.

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Ethinyl estradiol (EE) is a strong promoter of hepatocarcinogenesis. Treatment of rats with EE and other hepatic promoters induces a mitosuppressed state characterized by decreased hepatocyte turnover and reduced growth responsiveness. Previously, we identified several nuclear and mitochondrial genome-encoded mitochondrial genes whose transcripts were increased during EE-induced hepatic mitosuppression in rats and in EE-treated HepG2 cells (Chen et al. Carcinogenesis, 17, 2783-2786, 1996 and Carcinogenesis, 19, 101-107, 1998). In both cultured rat hepatocytes and HepG2 cells, EE increased respiratory chain activity (reflected by increased mitochondrial superoxide production detected as increased lucigenin-derived chemiluminescence (LDCL). In this paper, we provide additional characterizations of these effects. Increased LDCL was detected in mitochondria isolated from EE-treated rats, documenting that these estrogen effects on mitochondrial function are not confined to cells in culture. EE and estradiol (E2) increased LDCL in cultured rat hepatocytes and HepG2 cells in a dose- (beginning at 0.25 microM levels) and time-dependent response. Inhibition of P450-mediated estrogen metabolism inhibited, while direct exposure to E2 catechol metabolites enhanced LDCL. Co-treatment with glutathione ester or with the specific antiestrogen, ICI 182708 inhibited LDCL. In contrast, estrogen-induced LDCL was enhanced by glutathione depletion, and by inhibition of catechol-o-methyltransferase. These results support a working hypothesis that in liver cells, increased respiratory chain activity induced by estrogen treatment requires both metabolism to catechols and an estrogen receptor-mediated signal transduction pathway. [1]

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Ethinyl estradiol (EE) is a strong promoter and weak hepatocarcinogen in rats. Previously, we demonstrated that EE enhanced the transcript levels of nuclear genome- and mitochondrial genome-encoded genes and respiratory chain activity in female rat liver, and also inhibited transforming growth factor beta (TGFbeta)-induced apoptosis in cultured liver slices and hepatocytes from female rats. In this study, using cultured female rat hepatocytes, we observed that EE, within 24 h, increased the transcript levels of the mitochondrial genome-encoded genes cytochrome oxidase subunits I, II, and III. This effect was accompanied by increased mitochondrial respiratory chain activity, as reflected by increased mitochondrial superoxide generation, and detected by lucigenin-derived chemiluminescence and cellular ATP levels. EE also enhanced the levels of Bcl-2 protein. Biochemical analyses indicated that EE significantly increased both the levels of glutathione (reduced [GSH] and oxidized [GSSG] forms) per mg protein in mitochondria and nuclei, while the percentage of total glutathione in the oxidized form was not affected. This finding was supported by confocal microscopy. These effects caused by EE may contribute, at least in part, to the EE-mediated inhibition of hepatic apoptosis [2].

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The proton-coupled amino acid transporter, PAT1, is known to be responsible for intestinal absorption drug substances such as gaboxadol and vigabatrin. The aim of the present study was to investigate, if 17-α-ethinyl-estradiol (E-E2) and 17-β-estradiol (E) inhibit PAT1-mediated intestinal absorption of proline and taurine in vitro in Caco-2 cells and in vivo using Sprague-Dawley rats to assess the potential for taurine-drug interactions. E and E-E2 inhibited the PAT1-mediated uptake of proline and taurine in Caco-2 cells with IC50 values of 10.0-50.0 μM without major effect on other solute carriers such as the taurine transporter (TauT), di/tri-peptide transporter (PEPT1), and serotonin transporter (SERT1). In PAT1-expressing oocytes E and E-E2 were non-translocated inhibitors. In Caco-2 cells, E and E-E2 lowered the maximal uptake capacity of PAT1 in a non-competitive manner. Likewise, the transepithelial permeability of proline and taurine was reduced in presence of E and E-E2 [4].

Ethinyl Estradiol (50 mg/kg/day) increases anogenital distance and reduces pup body weight at postnatal day 2, accelerates the age at vaginal opening, reduces F1 fertility and F2 litter sizes, and induces malformations of the external genitalia (5 mg/kg) in the female Long-Evans rat. Ethinyl Estradiol increases the number of low density lipoprotein (LDL) receptors in livers of rats, thereby producing a profound fall in plasma cholesterol levels. Ethinyl Estradiol exerts the same effect in livers of male and female rabbits and that the increase in receptor number is correlated with a 6- to 8-fold increase in the levels of receptor mRNA.

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Many chemicals released into the environment display estrogenic activity including the oral contraceptive Ethinyl estradiol (EE2) and the plastic monomer bisphenol A (BPA). Ethinyl estradiol (EE2) is present in some aquatic systems at concentrations sufficient to alter reproductive function of fishes. Many concerns have been raised about the potential effects of BPA. The National Toxicology Program rated the potential effects of low doses of BPA on behavior and central nervous system (CNS) as an area of "some concern," whereas most effects were rated as of "negligible" or "minimal" concern. However, the number of robust studies in this area was limited. The current study was designed to determine if maternal exposure to relatively low oral doses of EE2 or BPA in utero and during lactation would alter the expression of well-characterized sexually dimorphic behaviors or alter the age of puberty or reproductive function in the female Long-Evans rat offspring. Pregnant rats were gavaged with vehicle, EE2 (0.05-50 microg/kg/day), or BPA (2, 20, and 200 microg/kg/day) from day 7 of gestation to postnatal day (PND) 18, and the female offspring were studied. EE2 (50 microg/kg/day) increased anogenital distance and reduced pup body weight at PND2, accelerated the age at vaginal opening, reduced F1 fertility and F2 litter sizes, and induced malformations of the external genitalia (5 microg/kg). F1 females exposed to EE2 also displayed a reduced (male-like) saccharin preference (5 microg/kg) and absence of lordosis behavior (15 microg/kg), indications of defeminization of the CNS. BPA had no effect on any of the aforementioned measures. These results demonstrate that developmental exposure to pharmacologically relevant dosage levels of EE2 can permanently disrupt the reproductive morphology and function of the female rat [3].

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In male Sprague Dawley rats pre-dosed with Ethinyl estradiol (EE2) a decreased maximal plasma concentration (Cmax) of taurine and increased the time (tmax) to reach this was indicated, suggesting the possibility for an in vivo effect on the absorption of PAT1 substrates. In conclusion, 17-α-ethinyl-estradiol and 17-β-estradiol were identified as non-translocated and non-competitive inhibitors of PAT1 [4].

Estradiol and Ethinyl estradiol (EE2) Inhibit PAT1-Mediated Uptake of Taurine and Proline [4]
The uptake of solute carrier substrates such as taurine, proline, glycyl-sarcosine (Gly-Sar) and 5-hydroxytryptamine was investigated in Caco-2 cells in the presence of 100 μM E2 and E-E2 (Fig. 1). The uptake of both taurine and proline was higher under slightly acidic condition compared to neutral pH in the uptake buffer (Fig. 1 A and B), consistent with proton-coupled transport via PAT1. 100 μM E2 and E-E2 inhibited the uptake of proline and taurine at pH 6.0, but not at pH 7.4. Likewise, the ...

Dosage Levels and Administration of Chemicals [3]
Pregnant rat dams were randomly assigned to treatment groups on GD7 within each cohort prior to dosing. Laboratory-grade corn oil, Ethinyl estradiol (EE2), and BPA were used. Dams were dosed via oral gavage from GD7 through PND18 with 0 (corn oil, vehicle control), Ethinyl estradiol (EE2) at 0.05, 0.5, 1.5, 5, 15, or 50 μg/kg/day, or BPA at 2, 20, or 200 μg/kg/day. The doses were delivered in 0.5-ml corn oil/kg body weight; thus, all dams in the study received the same amount of vehicle per body weight. The dams were weighed daily during the dosing period to adjust the administered dose for body weight changes during pregnancy and lactation and to monitor their health.
This study was performed in two blocks. The first block involved 169 dams with 13–29 dams per treatment group: oil vehicle, Ethinyl estradiol (EE2) (0.05, 0.5, 5, or 50 μg/kg/day), or BPA (2, 20, or 200 μg/kg/day). The second block (block 2) was performed to expand the range of EE2 doses tested and involved 82 dams with 6–14 dams per treatment group: oil vehicle, EE2 (0.05, 0.15, 0.5, 1.5, 5, 15, or 50 μg/kg/day), or BPA (20 or 200 μg/kg/day).
The effects of Ethinyl estradiol (EE2) and BPA on the dams and the F1 male offspring were previously published by Howdeshell et al. (2008). Maternal body weight gain during pregnancy was calculated from inception of dosing (GD7) to GD20, and the analysis of these data included only those dams that were pregnant and survived through GD20. Maternal body weight gain during lactation was calculated from PND2 through the end of dosing (PND18) and included only those dams with pups surviving to weaning.

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Pilot study with control male and female LE rats. [3]
Prior to the study of animals treated with Ethinyl estradiol (EE2) or BPA, a study of saccharin preference was conducted with untreated LE rats to confirm that the behavioral methods we were planning to use to assess the effects of in utero EE2 and BPA displayed the expected sexual dimorphism. This experiment also was designed to determine if female rats displayed a greater preference for either 0.50% wt/vol (5 g of saccharin was added to a liter of deionized, distilled water) or 0.25% wt/vol (2.5 g of saccharin was added to a liter of water) saccharin solutions. Adult male (n = 3–5 per dose group) and adult female intact (n = 4 per dose group) LE rats were purchased from Charles River Laboratories. Animals were housed individually upon receipt and allowed 2 weeks to acclimate before testing.

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Saccharin preference in experimental females. [3]
Following the pilot study, saccharin preference was measured in female rats exposed during gestation and lactation to varying doses of Ethinyl estradiol (EE2) or BPA in the first block of the study (sample sizes are shown in Fig. 5). Saccharin preference for 0.25% wt/vol saccharin solution versus deionized, distilled water was determined over a 5-day period, and the average saccharin preference over the 5-day period was then analyzed using litter means on PROC GLM.
Subsequently, females were ovariectomized and the activity levels measured a second time to determine if the removal of the ovaries and endogenous estrogens reduced the behavior to male levels. Females were then tested a third time after oral exposure to Ethinyl estradiol (EE2) at 0 (corn oil at 0.5 μl/g body weight), 175, or 275 μg/kg/day EE2 daily for 14 days. Based on the results of this experiment, we administered 275 μg EE2/kg daily for 14 days to restore activity levels in females developmentally exposed to EE2 and BPA.

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Assessment of Figure-8 maze activity in Ethinyl estradiol (EE2)- or BPA-treated females. [3]
Figure-8 maze activity was measured in ovariectomized females from the first block of the study. After recovering from surgery, Figure-8 maze activity levels were measured (trial 1), as above. Subsequently, females were treated orally by gavage for 14 days with 275 μg/kg Ethinyl estradiol (EE2) and retested in the Figure-8 mazes (trial 2; sample sizes are shown in Fig. 6).
Preliminary study of lordosis behavior and uterine weight in SD and LE rats after oral Ethinyl estradiol (EE2) treatment: dose-response to EE2. Lordosis behavior was studied using untreated adult ovariectomized females given Ethinyl estradiol (EE2) followed by progesterone to activate the behavior. Female rats that have been defeminized by neonatal estrogen exposures display low levels of lordosis behavior (Gorski, 1986).
Adult, ovariectomized SD and LE rats as well as adult, intact stimulus SD males were used. Female rats were housed two per cage in a room on a reversed light cycle (lights on from 9:00 P.M. to 11:00 A.M.) and given at least 2 weeks to recover from surgery and to acclimate to the altered light cycle prior used for behavioral testing. In this experiment, ovariectomized adult female LE rats were given varying doses of Ethinyl estradiol (EE2) by oral gavage in oil (0, 2.5, 5, 10, 12.5, 19, 25, 37.5, 50, 65, 80, 95, 110, 125, and 250 μg/kg) for 2 days, followed by 0.5 mg progesterone (sc) in oil on the third day in order to determine an optimal oral dose of EE2 that induces this behavior reliably in control females. Females were retested at different dosage levels two to three times. This experiment (Fig. 7) included both LE and SD female rats to determine if there was a strain difference in the dose-response to EE2.
A similar experiment compared the dose-related effects of Ethinyl estradiol (EE2) on uterine weight in LE and SD rats to determine which estrogen-dependent end point was more sensitive to low doses of Ethinyl estradiol (EE2), increased uterine weight, or induction of lordosis behavior. Ovariectomized female LE and SD rats were treated for 2 days by gavage with EE2 at 0, 0.5, 1, 2.5, 5, 10, 25, 50, or 250 μg/kg and necropsied on the third day, and the wet weight of the uterus was measured.
We used Ethinyl estradiol (EE2) to activate estrogen-dependent behaviors and uterine weight (Fig. 7) because our initial studies demonstrated that it can be used to induce female-like maze activity as well as lordosis behavior, whereas based upon unpublished studies, we suspected that a single daily dose of estradiol would not induce activity as effectively.

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50 mg/kg

Rats

Absorption, Distribution and Excretion
A 30µg oral dose of ethinylestradiol reaches a Cmax of 74.1±35.6pg/mL, with a Tmax of 1.5±0.5h, and an AUC of 487.4±166.6pg\*h/mL. A 1.2mg dose delivered via a patch reaches a Cmax of 28.8±10.3pg/mL, with a Tmax of 86±31h, and an AUC of3895±1423pg\*h/mL.
Ethinylestradiol is 59.2% eliminated in the urine and bile, while 2-3% is eliminated in the feces. Over 90% of ethinylestradiol is eliminated as the unchanged parent drug.
A 30µg oral dose has an apparent volume of distribution of 625.3±228.7L and a 1.2mg topical dose has an apparent volume of distribution of 11745.3±15934.8L.
Ethinylestradiol has an intravenous clearance of 16.47L/h, and an estimated renal clearance of approximately 2.1L/h. A 30µg oral dose has a clearance of 58.0±19.8L/h and a 1.2mg topical dose has a clearance of 303.5±100.5L/h.
Ethinyl estradiol is rapidly and almost completely absorbed. When the lowest and highest tablet strengths, 0.100 mg desogestrel/0.025 mg ethinyl estradiol and 0.150 mg desogestrel/0.025 mg ethinyl estradiol, were compared to solution, the relative bioavailability of ethinyl estradiol was 92% and 98%, respectively.
The distribution of exogenous estrogens is similar to that of endogenous estrogens. Estrogens are widely distributed in the body and are generally found in higher concentrations in the sex hormone target organs. Ethinyl estradiol circulates in the blood largely bound to ... albumin. ... Although ethinyl estradiol does not bind to SHBG, it induces SHBG synthesis.
Estradiol, estrone, and estriol are excreted in the urine along with glucuronide and sulfate conjugates.
25 healthy women of reproductive age who had not previously used oral contraceptive steroids, were each given a single tablet containing 50, 80, or 100 ug of mestranol or 50 or 80 ug of ethinyl estradiol. Blood samples were obtained before taking the tablets and at intervals of 1, 2, 4, and 24 hours afterward. Anti-ethinyl-estradiol antibody in 1 to 100,000 initial dilution was used. Details of techniques employed are given. With ethinyl estradiol, the 1-hour sampling yielded the maximum plasma levels. At 24 hours, the plasma level was not detectable in 4 of 5 subjects given 50 ug or in 1 of 5 given 80 ug. With mestranol, the disappearance curve was more variable with the peak levels usually at 2 hours but occasionally at 4 hours. At all 3 dose levels of mestranol, measurable serum ethinyl estradiol levels were found at 24 hours. These levels were reached more slowly and were lower than when ethinyl estradiol was given. In contrast to natural estrogens ethinyl, estrogens are bound to plasma proteins chiefly by nonspecific binding and are therefore less likely to affect the metabolism of the ethinyl estrogens than are the endogenous steroids. Also, significant amounts of ethinyl estradiol are was given. In contrast to natural estrogens ethinyl, estrogens are bound di-ethynylated in vitro. The pharmacokinetics of ethinyl estrogens differ from those of natural estrogens. This complicates interpretation of plasma or urinary estrone and estradiol measurements.
For more Absorption, Distribution and Excretion (Complete) data for ETHINYLESTRADIOL (7 total), please visit the HSDB record page.

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Metabolism / Metabolites
Ethinylestradiol can be glucuronidated by UGT1A1, UGT1A3, UGT1A4, UGT1A9, and UGT2B7. Ethinylestradiol is also sulfated by SULT1A1, SULT1A3, and SULT1E1. Ethinylestradiol can also be hydroxylated at positions 2, 4, 6, 7, and 16 by CYP3A4, CYP3A5, CYP2C8, CYP2C9, and CYP1A2. These hydroxylated metabolites can be methylated by catechol-O-methyltransferase. The methoxy metabolites can in turn be sulfated or glucuronidated.
Exogenous estrogens are metabolized in the same manner as endogenous estrogens. Circulating estrogens exist in a dynamic equilibrium of metabolic interconversions. These transformations take place mainly in the liver. Estradiol is converted reversibly to estrone, and both can be converted to estriol, which is the major urinary metabolite. Estrogens also undergo enterohepatic recirculation via sulfate and glucuronide conjugation in the liver, biliary secretion of conjugates into the intestine, and hydrolysis in the gut followed by reabsorption. In postmenopausal women, a significant proportion of the circulating estrogens exist as sulfate conjugates, especially estrone sulfate, which serves as a circulating reservoir for the formation of more active estrogens.
Ethinyl estradiol is extensively metabolized, both by oxidation and by conjugation with sulfate and glucuronide. Sulfates are the major circulating conjugates of ethinyl estradiol and glucuronides predominate in urine. The primary oxidative metabolite is 2-hydroxy ethinyl estradiol, formed by the CYP3A4 isoform of cytochrome P450. Part of the first-pass metabolism of ethinyl estradiol is believed to occur in gastrointestinal mucosa. Ethinyl estradiol may undergo enterohepatic circulation.
Ethinyl estradiol is cleared much more slowly ... due to decreased hepatic metabolism.
Studies on the metabolism of ethinylestradiol have been carried out in rats, rabbits, guinea-pigs, dogs and monkeys. It is very rapidly and effectively absorbed from rat intestine; no appreciable metabolic transformation is reported to take place during the absorption process. The main metabolic pathway of ethinylestradiol in rats is by aromatic 2-hydroxylation; hydroxylations at ring B (C-6/C-7) are of only minor importance. Rat liver forms 2-hydroxyethinylestradiol and the methyl ethers thereof, 2-methoxyethinylestradiol and 2-hydroxyethinylestradiol-3-methy1 ether, as its major metabolic products. This pathway is also important in humans. Metabolites of ethinylestradiol in rats are excreted almost exclusively in the feces.
For more Metabolism/Metabolites (Complete) data for ETHINYLESTRADIOL (10 total), please visit the HSDB record page.
Ethinylestradiol has known human metabolites that include 17-Ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-3,4,17-triol and 17-Ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-2,3,17-triol.
Ethinylestradiol is a known human metabolite of Mestranol.
Hepatic. Quantitatively, the major metabolic pathway for ethinyl estradiol, both in rats and in humans, is aromatic hydroxylation, as it is for the natural estrogens.
Half Life: 36 +/- 13 hours

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Biological Half-Life
A 30µg oral dose has a half life of 8.4±4.8h and a 1.2mg topical dose has a half life of 27.7±34.2h.
The pharmacokinetics of 19-nor-17 alpha-pregna-1,3,5(10)-trien-20-yne-3,17-diol (ethinylestradiol, Progynon C) (EE2) has been studied after intravenous administration of 0.1 or 0.01 mg/kg and after intragastric administration of 1 mg/kg in female rats, rabbits, beagle dogs, rhesus monkeys and baboons. After intravenous administration disposition of unchanged drug in the plasma was biphasic with initial half-lives between 0.3 and 0.5 hr and terminal half-lives between 2.3 and 3.0 hr. Total plasma clearance was of the same magnitude as total plasma liver flow or even higher rat) indicating a rapid biotransformation of the estrogen in the liver. Systemic availability of intragastric EE2 amounted to 3% in the rat, 0.3% in the rabbit, 9% in the dog, 0.6% in rhesus monkeys and 2% in the baboon and was considerably lower than in humans (40%). Differences in the pharmacokinetics and in the systemic availability of EE2 between laboratory animals and man should be taken into account in the retrospective interpretation of pharmacological and toxicological data and in the design of new studies.
... The elimination phase half-life has been reported ... to be 13 to 27 hours.

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
This record contains information specific to ethinyl estradiol used alone. Users with an interest in an oral contraceptive should consult the record entitled, record entitled, Contraceptives, Oral, Combined.
There is little information available on the use of ethinyl estradiol alone during breastfeeding. Levels in milk appear to be low. Based on studies on oral contraceptives that contain ethinyl estradiol, immediate side effects such as breast enlargement appear to occur rarely. It seems likely that doses of 30 mcg daily or greater can suppress lactation. The magnitude of the effect on lactation likely depends on the dose and the time of introduction postpartum. It is most likely to occur if the estrogen is started before the milk supply is well established at about 6 weeks postpartum. The decrease can happen over the first few days of estrogen exposure.
◉ Effects in Breastfed Infants
Published information was not found as of the revision date on the effects of ethinyl estradiol alone on breastfed infants. However, case reports exist of breast enlargement in the infants of mothers taking combination oral contraceptives that contained ethinyl estradiol or its prodrug, mestranol.
◉ Effects on Lactation and Breastmilk
Published information was not found as of the revision date on the effects of ethinyl estradiol on milk production. However, numerous studies on combination contraceptives containing ethinyl estradiol or its prodrug mestranol indicate that doses of 30 mcg daily or greater might interfere with lactation. One study that used a contraceptive containing 10 mcg of ethinyl estradiol found no effect on lactation.
A retrospective cohort study compared 371 women who received high-dose estrogen (either 3 mg of diethylstilbestrol or 150 mcg of ethinyl estradiol daily)during adolescence for adult height reduction to 409 women who did not receive estrogen. No difference in breastfeeding duration was found between the two groups, indicating that high-dose estrogen during adolescence has no effect on later breastfeeding.

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Protein Binding
Enthinylestradiol is 98.3-98.5% bound to albumin in serum but also exhibits binding to sex hormone binding globulin.

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Toxicity Summary
IDENTIFICATION: Ethinylestradiol is a synthetic steroid, prepared from estrone. It is a white to creamy or slightly yellowish-white powder or crystals. It is insoluble in water, soluble in ethanol. Indications: The most frequent use is as the estrogen component of combined oral contraceptives. Also used for the treatment of menopausal and post menopausal symptoms, especially the vasomotor effects. Used in the treatment of female hypogonadism and as a palliative treatment in malignant neoplasm of breast and prostate. Also used in the treatment of some women with acne, and in Turner's syndrome. HUMAN EXPOSURE: Main risks and target organs: Acute poisoning with ethinylestradiol results in mild, self limiting effects, usually involving the gastrointestinal tract. Chronic toxicity increases the risk of cardiovascular disease, including myocardial infarction, cerebrovascular disease, thromboembolic disease, gallbladder disease, and certain cancers in some people. Summary of clinical effects: Acute poisoning with ethinylestradiol is mild and self limiting. Nausea, vomiting and occasionally vaginal breakthrough bleeding may occur. Chronic toxicity from ethinylestradiol, like other estrogens, increases the risk for stroke, myocardial infarction and thromboembolic disease in certain populations. Jaundice, hypertension, nasal congestion, headache, dizziness and fluid retention may occur. Endometrial, breast, and certain liver cancers may occur at a higher incidence than the general population. Contraindications: Contraindications are those of the use of estrogens in general, and include the following: Known or suspected carcinoma of the breast, except in selected patients being treated for metastatic disease. Known or suspected estrogen dependent neoplasia. Known or suspected pregnancy. Undiagnosed abnormal genital bleeding. Active thrombophlebitis or thromboembolic disease. A past history of thrombophlebitis, thrombosis or thromboembolic disease associated with the previous use of estrogen containing compounds. Absorption by route of exposure: Ethinylestradiol is rapidly and completely absorbed from the gastrointestinal tract. The ethinyl substitution in the C17 position inhibits first-pass metabolism. Bioavailability is reported at 40%. Distribution by route of exposure: Extensively plasma protein bound, mainly to albumin. Unbound molecules distribute widely in the tissues due to their lipophilic nature. Peak plasma concentrations occur initially at 2 to 3 hours after oral ingestion. A second, 12 hour peak, is thought to represent extensive enterohepatic circulation. Biological half-life by route of exposure: Biological half life is approximately 7.7 hours following a single oral therapeutic dose. Elimination phase half life is reported between 13 and 27 hours. Metabolism: Compared to other estrogens, metabolism is slow. Primary route of biotransformation is via 2-hydroxylation and the formation of 2- and 3-methyl ethers. First-pass metabolism occurs primarily in the gut wall. Elimination by route of exposure: Some enterohepatic circulation of sulfate and glucuronide metabolites does occur, hence some is excreted via the feces. Excretion is also via the kidneys. Mode of action: Toxicodynamics: 2 to 3 fold increase in the incidence of gallbladder disease is reported with the use of estrogens. This is thought due to an increased saturation of bile with cholesterol and a reduction of bile acid secretion. Also, many studies have been performed investigating the adverse effects of estrogens, including ethinylestradiol, on coagulation. These have used estrogens alone, and estrogens in combination with progestins. However a consensus of the net outcome of physiologic or pharmacological doses has not occurred as yet. Pharmacodynamics: Like other steroid hormones, ethinylestradiol is thought to act primarily through the regulation of gene expression. As a lipophilic hormone, it diffuses readily through cellular membranes to bind to estrogen receptors situated in the nucleus. Estrogen receptors are found in the female reproductive tract, breast, pituitary, hypothalamus, bone, liver and other tissues. The receptor interacts with a specialized nucleotide sequence, resulting in either an increase or decrease in the transcription of hormone regulated genes. Tissues may vary in the way in which they respond to receptor activation. Desirable therapeutic effects, include its action on the female reproductive tract, (usually in combination with a progesterone), where ethinylestradiol stimulates proliferation and differentiation in the fallopian tube, and increase the tubal muscular activity. Ethinylestradiol also increases the water content of cervical mucus and favors contraction of the uterine myometrium. Estrogens, including ethinylestradiol, block resorption of bone, resulting in a positive effect on bone mass. It is well established that the risk of endometrial hyperplasia and cancer is increased in women receiving unopposed estrogen replacement therapy, including ethinylestradiol. Data from the 1970's and 1980's reported a 2 to 15 fold increase in the risk of endometrial carcinoma. The higher the dose and the longer the length of therapy the greater the risk. However, the addition of progestogen to estrogen replacement therapy was protective. More research is needed before a conclusion can be drawn on whether ethinylestradiol therapy, and other estrogens, increase the risk of breast carcinoma. Conflicting findings have been reported. A review of data from the 1970's and 1980's suggests that there is a moderate increase in the risk of breast carcinoma, but this did not occur until after 5 years of therapy. Teratogenicity: No specific data available for ethinylestradiol. Reports suggest a link between fetal exposure to female sex hormones and congenital abnormalities. These include heart defects, and limb defects. Other estrogens, namely diethylstilbestrol, have been associated with the development of vaginal and cervical adenocarcinoma in female offspring of mothers who had taken this drug during the first trimester. Diethylstilbestrol ingestion during pregnancy is also associated with a number of other abnormalities in male offspring, including, smaller testes and urogenital abnormalities. Although no studies relating ethinylestradiol directly to these findings were identified, the pharmacological similarities in this class of compounds suggest caution should be used. Main adverse effects: The main adverse effects of ethinylestradiol given in therapeutic dose are directly related to its estrogenic and metabolic effects. They include water and sodium retention, which may result in edema, weight gain and tender breast enlargement. Changes in libido, and withdrawal vaginal bleeding is also reported. Liver function impairment, jaundice and gallstones may occur. Headache, depression, dizziness, glucose intolerance, and a sensitivity to contact lenses are described. Large doses may produce hypercalcemia when used in the treatment of metastatic carcinoma. Nausea, vomiting and diarrhea are not uncommon. Dermatological effects include chloasma, melasma, rashes and urticaria. Erythema multiforme and erythema nodosum occur. Hypertension and thromboembolic disease are reported. Acute poisoning: Ingestion: Acute poisoning effects are mild and self limiting. Nausea, vomiting and break through vaginal bleeding have been reported following oral contraceptive overdose. Nasal congestion, visual disturbances, headache and hypertension have also been reported in association with estrogen overdose. ANIMAL/PLANT STUDIES: Relevant animal data: A correlation between the prolonged use of oral contraceptives and the development of liver cancer was demonstrated in rats. Induced DNA breaks in hamster kidneys, but not in livers, following 2 weeks of treatment with a single estradiol implant. Tumors of kidney, bone, testis, uterus and breast, were induced in animals exposed to estrogens. Mutagenicity: Estradiol induced DNA breaks in hamster renal cells, but not in hepatocytes. International Programme on Chemical Safety; Poisons Information Monograph: Ethambutol (PIM 221) (1997) Available from, as of May 19, 2005: https://www.inchem.org/pages/pims.html

Estrogens diffuse into their target cells and interact with a protein receptor. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Estrogens increase the hepatic synthesis of sex hormone binding globulin (SHBG), thyroid-binding globulin (TBG), and other serum proteins and suppress follicle-stimulating hormone (FSH) from the anterior pituitary. This cascade is initiated by initially binding to the estrogen receptors. The combination of an estrogen with a progestin suppresses the hypothalamic-pituitary system, decreasing the secretion of gonadotropin-releasing hormone (GnRH).

[1]. Increased mitochondrial superoxide production in rat liver mitochondria, rat hepatocytes, and HepG2 cells following ethinyl estradiol treatment. Toxicol Sci. 1999;51(2):224-35;
[2]. Enhanced mitochondrial gene transcript, ATP, bcl-2 protein levels, and altered glutathione distribution in ethinyl estradiol-treated cultured female rat hepatocytes. Toxicol Sci.2003;75(2):271-8. 2003;
[3]. In utero and lactational exposure to bisphenol A, in contrast to ethinyl estradiol, does not alter sexually dimorphic behavior, puberty, fertility, and anatomy of female LE rats. Toxicol Sci. 2010;114(1):133-48.
[4]. Inhibitory Effects of 17-α-Ethinyl-Estradiol and 17-β-Estradiol on Transport Via the Intestinal Proton-Coupled Amino Acid Transporter (PAT1) Investigated In Vitro and In Vivo. J Pharm Sci . 2021 Jan;110(1):354-364. .

Ethinylestradiol can cause cancer according to an independent committee of scientific and health experts.
Ethinylestradiol is a fine white to creamy white powder. A synthetic steroid. Used in combination with progestogen as an oral contraceptive.
17alpha-ethynylestradiol is a 3-hydroxy steroid that is estradiol substituted by a ethynyl group at position 17. It is a xenoestrogen synthesized from estradiol and has been shown to exhibit high estrogenic potency on oral administration. It has a role as a xenoestrogen. It is a 17-hydroxy steroid, a terminal acetylenic compound and a 3-hydroxy steroid. It is functionally related to a 17beta-estradiol and an estradiol.
Ethinylestradiol was first synthesized in 1938 by Hans Herloff Inhoffen and Walter Hohlweg at Schering. It was developed in an effort to create an estrogen with greater oral bioavailability. These properties were achieved by the substitution of an ethinyl group at carbon 17 of [estradiol]. Ethinylestradiol soon replaced [mestranol] in contraceptive pills. Ethinylestradiol was granted FDA approval on 25 June 1943.
Ethinyl estradiol is an Estrogen. The mechanism of action of ethinyl estradiol is as an Estrogen Receptor Agonist.
Ethinyl estradiol has been reported in Minthostachys mollis, Elsholtzia eriostachya, and other organisms with data available.
Ethinyl Estradiol is a semisynthetic estrogen. Ethinyl estradiol binds to the estrogen receptor complex and enters the nucleus, activating DNA transcription of genes involved in estrogenic cellular responses. This agent also inhibits 5-alpha reductase in epididymal tissue, which lowers testosterone levels and may delay progression of prostatic cancer. In addition to its antineoplastic effects, ethinyl estradiol protects against osteoporosis. In animal models, short-term therapy with this agent has been shown to provide long-term protection against breast cancer, mimicking the antitumor effects of pregnancy. (NCI04)
A semisynthetic alkylated estradiol with a 17-alpha-ethinyl substitution. It has high estrogenic potency when administered orally and is often used as the estrogenic component in oral contraceptives . Ethinyl estradiol is marketed mostly as a combination oral contraceptive under several brand names such as Alesse, Tri-Cyclen, Triphasil, and Yasmin. The FDA label includes a black box warning that states that combination oral contraceptives should not be used in women over 35 years old who smoke due to the increased risk of serious cardiovascular side effects.
A semisynthetic alkylated ESTRADIOL with a 17-alpha-ethinyl substitution. It has high estrogenic potency when administered orally, and is often used as the estrogenic component in ORAL CONTRACEPTIVES.
See also: Ethinyl estradiol; norgestrel (component of); Ethinyl estradiol; ethynodiol diacetate (component of); Ethinyl estradiol; etonogestrel (component of) ... View More ...

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Drug Indication
Ethinylestradiol is combined with other drugs for use as a contraceptive, premenstrual dysphoric disorder, moderate acne, moderate to severe vasomotor symptoms of menopause, prevention of postmenopausal osteoporosis.
FDA Label

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Mechanism of Action
Ethinylestradiol is a synthetic estrogenic compound. Use of estrogens have a number of effects on the body including reduced bone density. Combined oral contraceptives suppress ovulation by suppressing gonadotrophic hormone, thickening cervical mucus to prevent the travel of sperm, and preventing changes in the endometrium required for implantation of a fertilized egg. Ethinylestradiol decreases luteinizing hormone, decreasing vascularity in the endometrium. It also increases sex hormone binding globulin.
Endogenous estrogens are largely responsible for the development and maintenance of the female reproductive system and secondary sexual characteristics. Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, estradiol is the principal intracellular human estrogen and is substantially more potent than its metabolites estrone and estriol at the receptor level. ... After menopause, most endogenous estrogen is produced by conversion of androstenedione, secreted by the adrenal cortex, to estrone by peripheral tissues. Thus, estrone and the sulfate conjugated form, estrone sulfate, are the most abundant circulating estrogens in postmenopausal women. The pharmacologic effects of ethinyl estradiol are similar to those of endogenous estrogens. Estrogens act through binding to nuclear receptors in estrogen-responsive tissues. To date, two estrogen receptors have been identified. These vary in proportion from tissue to tissue. Circulating estrogens modulate the pituitary secretion of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH) through a negative feedback mechanism. Estrogens act to reduce the elevated levels of these hormones seen in postmenopausal women.
Estrogens have an important role in the reproductive, skeletal, cardiovascular, and central nervous systems in women, and act principally by regulating gene expression. Biologic response is initiated when estrogen binds to a ligand-binding domain of the estrogen receptor resulting in a conformational change that leads to gene transcription through specific estrogen response elements (ERE) of target gene promoters; subsequent activation or repression of the target gene is mediated through 2 distinct transactivation domains (ie, AF-1 and AF-2) of the receptor. The estrogen receptor also mediates gene transcription using different response elements (ie, AP-1) and other signal pathways. Recent advances in the molecular pharmacology of estrogen and estrogen receptors have resulted in the development of selective estrogen receptor modulators (eg, clomiphene, raloxifene, tamoxifen, toremifene), agents that bind and activate the estrogen receptor but that exhibit tissue-specific effects distinct from estrogen. Tissue-specific estrogen-agonist or -antagonist activity of these drugs appears to be related to structural differences in their estrogen receptor complex (eg, specifically the surface topography of AF-2 for raloxifene) compared with the estrogen (estradiol)-estrogen receptor complex. A second estrogen receptor also has been identified, and existence of at least 2 estrogen receptors (ER-alpha, ER-beta) may contribute to the tissue-specific activity of selective modulators. While the role of the estrogen receptor in bone, cardiovascular tissue, and the CNS continues to be studied, emerging evidence indicates that the mechanism of action of estrogen receptors in these tissues differs from the manner in which estrogen receptors function in reproductive tissue. /Estrogen General Statement/
Intracellular cytosol-binding proteins for estrogens have been identified in estrogen-responsive tissues including the female genital organs, breasts, pituitary, and hypothalamus. The estrogen-binding protein complex (ie, cytosol-binding protein and estrogen) distributes into the cell nucleus where it stimulates DNA, RNA, and protein synthesis. The presence of these receptor proteins is responsible for the palliative response to estrogen therapy in women with metastatic carcinoma of the breast. /Estrogen General Statement/
Estrogens have generally favorable effects on blood cholesterol and phospholipid concentrations. Estrogens reduce LDL-cholesterol and increase HDL-cholesterol concentrations in a dose-related manner. The decrease in LDL-cholesterol concentrations associated with estrogen therapy appears to result from increased LDL catabolism, while the increase in triglyceride concentrations is caused by increased production of large, triglyceride-rich, very-low-density lipoproteins (VLDLs); changes in serum HDL-cholesterol concentrations appear to result principally from an increase in the cholesterol and apolipoprotein A-1 content of HDL2- and a slight increase in HDL3-cholesterol. /Estrogen General Statement/
For more Mechanism of Action (Complete) data for ETHINYLESTRADIOL (7 total), please visit the HSDB record page.

C20H24O2

296.4

296.177

C, 81.04; H, 8.16; O, 10.80

57-63-6

313-06-4 (cypionate) ; 57-63-6 (ethinyl) ; 3571-53-7 (undecylate); 50-28-2; 172377-52-5 (sulfamate); 50-50-0 (benzoate); 979-32-8 (valerate); 113-38-2 (dipropionate); 57-63-6

5991

White to off-white solid powder

1.2±0.1 g/cm3

457.2±45.0 °C at 760 mmHg

182-183 °C(lit.)

211.2±23.3 °C

0.0±1.2 mmHg at 25°C

1.624

4.52

2

2

1

22

505

5

C[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@]2(C#C)O)CCC4=C3C=CC(=C4)O

BFPYWIDHMRZLRN-SLHNCBLASA-N

InChI=1S/C20H24O2/c1-3-20(22)11-9-18-17-6-4-13-12-14(21)5-7-15(13)16(17)8-10-19(18,20)2/h1,5,7,12,16-18,21-22H,4,6,8-11H2,2H3/t16-,17-,18+,19+,20+/m1/s1

(8R,9S,13S,14S,17R)-17-ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-3,17-diol

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)