Effects of low-dose bisphenol AF on mammal testis development via complex mechanisms: alterations are detectable in both infancy and adulthood.

Despite growing concern about adverse effects of bisphenol AF (BPAF) due to its endocrine disrupting properties, there is a lack of toxicity data from low-dose studies and direct evidence linking its adverse effects to endocrine disrupting properties. Here, we investigated the effects of gestational and postnatal exposure to BPAF through drinking water (0.15-15 µg/mL, equivalent to the daily intake of ~ 50 and 5 mg/kg/day) on testis development in mice. We found that like mestranol, 5 mg/kg/day BPAF resulted in remarkable decreases in multiple male reproductive parameters in adulthood, such as the sperm number and serum testosterone level. Notably, 50 µg/kg/day BPAF also caused significant decreases in anogenital distance (AGD), the luteinizing hormone level and spermatocyte number, along with declining trends in sperm number and the serum levels of testosterone and follicle-stimulating hormone. In line with the adverse outcomes observed in adulthood, on postnatal day (PND) 9, we also observed BPAF-caused dose-dependent alterations, including reduced AGD, seminiferous tubule area and numbers of total germ cells, spermatocytes and Leydig cells, coupled with down-regulated expression of male-biased genes in testes. Even when exposure to 5 mg/kg/day BPAF as well as MES was initiated from PND 0, similar alterations in male reproductive parameters were also found on PND 9, along with a decrease in the GnRH content in the hypothalamus; moreover, testicular alterations and the reduction in AGD were partly antagonized by the estrogen receptor (ER) antagonist ICI 182,780, but the reduction of GnRH production was not done, showing that the effects of BPAF on testis development may be partially mediated by ER signaling. In conclusion, all the findings demonstrate that low-dose BPAF can partly disrupt mammal testis development and cause adverse testicular outcomes in adulthood, indicating a potential reproductive risk to mammals including humans. Importantly, our finding that developmental alterations elicited by BPAF have been detectable on PND 9 provides important motivation for the development of effective methods for early detection of adverse effects of estrogenic chemicals on testis development.

Effect of CYP2C9 Genetic Polymorphism in a Chinese Population on the Metabolism of Mestranol in vitro.

BACKGROUND: Mestranol is a widely used estrogen, which is converted into its active metabolite ethinyl estradiol by cytochrome P450 (CYP) 2C9. To comprehensively examine the enzymatic activity of reported CYP2C9 variants in Chinese individuals in response to mestranol, wild-type CYP2C9*1 and 35 allelic variants were highly expressed in Sf21 insect cell microsomes and used for the detection of their enzymatic values in vitro. These results showed that the majority of tested variants exhibited decreased clearance values compared to wild type, except for CYP2C9*40 and *36. METHOD: Insect microsomes expressing the 36 CYP2C9 variants were incubated with 0.25-8 µmol/l mestranol for 30 min at 37°C. Then, the production of the metabolite of mestranol, ethinyl estradiol, was analyzed using high-performance liquid chromatography. RESULTS: Most CYP-catalyzed reactions were sufficiently described by classical Michaelis-Menten kinetic parameters (e.g., Km and Vmax), while 9 variants exhibited atypical or non-Michaelis-Menten kinetic values, which were largely due to the self-inhibitory effect in response to mestranol. CONCLUSION: This is the first report of these rare alleles for mestranol metabolism, which provides fundamental data for further clinical studies on CYP2C9 alleles for mestranol metabolism.

A kinetic study on the lactoperoxidase catalyzed oxidation of estrogens.

Lactoperoxidase, which is produced in mammary glands, is proposed to be involved in carcinogenesis, because of its ability to react with estrogenic molecules, oxidizing them to free radicals. In the present study the reactivity towards six species (estradiol, ethynylestradiol, estriol, estrone, pregnenolone and mestranol) was investigated by means of a NADH-coupled system. The enzyme activity towards estradiol, ethynylestradiol, estriol and estrone did not vary much, suggesting that the different substituents in the D-ring of the steroid had little effect on the reaction. A somewhat higher K (m)-value was obtained with estriol; possibly because of a more effective splitting of the enzyme-substrate complex into products. Pregnenolone, without resonance in the A-ring, and a methyl group in 19-position, did not react with the enzyme, in spite of having the proposed essential hydroxyl group in 3-position. Mestranol, with a methoxy group in 3-position, did not react with the enzyme either, supporting the suggestion that lactoperoxidase reacts with the 3-hydroxyl group of the estrogens.

Occurrence and photochemical degradation of 17alpha-ethinylestradiol in Acushnet River Estuary.

17alpha-Ethinylestradiol (EE2), a major constituent of common contraceptive pills, and three other estrogenic hormones, estrone (E1), 17beta-estradiol (E2) and mestranol (MeEE2) have been determined in Acushnet River Estuary seawater using a GC-MS technique. Among three estrogenic compounds detected, EE2 has the highest concentration, up to 4.7 ng/l, at which EE2 may affect lobster and other fish abundance in the coastal seawater due to its high biological activity on fish feminization. Two natural estrogenic hormones, E1 and E2 have also been found in the estuary at concentrations up to 1.2 ng/l and 0.83 ng/l, respectively. Although EE2 is persistent to microbial degradation, it can undergo a rapid photodegradation in estuarine seawater under natural sunlight irradiation, with a half-life of less than 1.5 days in spring sunny days.

Microbial transformation of mestranol by Cunninghamella elegans.

The microbial transformation of an oral contraceptive, mestranol (1) by Cunninghamella elegans yielded two hydroxylated metabolites, 6beta-hydroxymestranol (2) and 6beta,12beta-dihydroxymestranol (3). Metabolite 3 was found to be a new compound. These metabolites were structurally characterized on the basis of spectroscopic techniques.

Degradation of estradiol and ethinyl estradiol by activated sludge and by a defined mixed culture.

The aerobic degradation of the natural hormone 17-beta-estradiol (E2) and the synthetic hormone 17-alpha-ethinyl estradiol (EE2) was investigated in batch experiments with activated sludge from a conventional and a membrane sewage treatment plant. E2 was converted to estrone (E1), the well known metabolite, and further completely transformed within 3 days. The turnover rates of E2 did not differ greatly between conventional and membrane activated sludge. EE2 was persistent in both sludges. By several transfers into fresh E2-medium an enrichment culture could be selected that used E2 as growth substrate. Further enrichment and isolation led to a defined mixed culture consisting of two strains, which were identified by a polyphasic approach as Achromobacter xylosoxidans and Ralstonia sp., respectively. The culture used E2 and E1 as growth substrates and transformed estriol (E3) and 16-alpha-hydroxyestrone but not the xenoestrogens bisphenol A, alpha-zearalenol, mestranol or EE2. The turnover rates of E2 were 0.025-0.1 microg h(-1) cfu(-1) and did not depend on the steroid concentration.

The interaction between St John's wort and an oral contraceptive.

OBJECTIVES: The popular herbal remedy St John's wort is an inducer of cytochrome P450 (CYP) 3A enzymes and may reduce the efficacy of oral contraceptives. Therefore we evaluated the effect of St John's wort on the disposition and efficacy of Ortho-Novum 1/35 (Ortho-McNeil Pharmaceutical, Inc, Raritan, NJ), a popular combination oral contraceptive pill containing ethinyl estradiol (INN, ethinylestradiol) and norethindrone (INN, norethisterone). METHODS: Twelve healthy premenopausal women who were using oral contraception (>3 months) received a combination oral contraceptive pill (Ortho-Novum 1/35) for 3 consecutive 28-day menstrual cycles. During the second and third cycles, the participants received 300 mg St John's wort 3 times a day. The serum concentrations of ethinyl estradiol (day 7), norethindrone (day 7), follicle-stimulating hormone (days 12-16), luteinizing hormone (days 12-16), progesterone (day 21), and intravenous and oral midazolam (days 22 and 23) were determined in serial blood samples. The incidence of breakthrough bleeding was quantified during the first and third cycles. RESULTS: Concomitant use of St John's wort was associated with a significant (P <.05) increase in the oral clearance of norethindrone (8.2 +/- 2.7 L/h to 9.5 +/- 3.4 L/h, P =.042) and a significant reduction in the half-life of ethinyl estradiol (23.4 +/- 19.5 hours to 12.2 +/- 7.1 hours, P =.023). The oral clearance of midazolam was significantly increased (109.2 +/- 47.9 L/h to 166.7 +/- 81.3 L/h, P =.007) during St John's wort administration, but the systemic clearance of midazolam was unchanged (37.7 +/- 11.3 L/h to 39.0 +/- 10.3 L/h, P =.567). Serum concentrations of follicle-stimulating hormone, luteinizing hormone, and progesterone were not significantly affected by St John's wort dosing (P >.05). Breakthrough bleeding occurred in 2 of 12 women in the control phase compared with 7 of 12 women in the St John's wort phase. The oral clearance of midazolam after St John's wort dosing was greater in women who had breakthrough bleeding (215.9 +/- 66.5 L/h) than in those who did not (97.5 +/- 37.2 L/h) (P =.005). CONCLUSION: St John's wort causes an induction of ethinyl estradiol-norethindrone metabolism consistent with increased CYP3A activity. Women taking oral contraceptive pills should be counseled to expect breakthrough bleeding and should consider adding a barrier method of contraception when consuming St Johns wort.

Biotransformation of mestranol to ethinyl estradiol in vitro: the role of cytochrome P-450 2C9 and metabolic inhibitors.

Mestranol, the estrogen component of some oral contraceptive formulations, must be demethylated to its active metabolite, 17 alpha-ethinyl estradiol, to produce estrogenic activity. To investigate the transformation of mestranol to ethinyl estradiol, an in vitro assay was used with human liver microsomes from four different donors. Incubation of a fixed concentration of mestranol (3 mumol/L) with varying concentrations of CYP inhibitors revealed strong inhibition of ethinyl estradiol formation by sulfaphenazole, a specific CYP2C9 inhibitor, with an average inhibitor concentration at one half of Emax (IC50) of 3.6 mumol/L (range, 1.8-8.3 mumol/L) and an average maximal inhibitory capacity (Emax) of 75% (range, 60-91%). Troleandomycin (a CYP3A3/4 inhibitor) and quinidine (a CYP2D6 inhibitor), however, produced no substantial inhibitory activity. alpha-Naphthoflavone (a CYP1A1/2 inhibitor only at concentrations < 2 mumol/L and a CYP2C9 inhibitor at higher concentrations) had a weak inhibitory effect on ethinyl estradiol formation (< 20% decrease in mestranol demethylation activity). Of the three antifungal azoles tested, miconazole strongly inhibited mestranol demethylation, with an average IC50 of 1.5 mumol/L (range, 0.7-3.2 mumol/L) and an average Emax of 90% (range, 77-100%), whereas fluconazole displayed relatively weak inhibition only at the highest concentration of 50 mumol/L (mean reduction in demethylation activity was 29%). Itraconazole produced no meaningful inhibition. Strong inhibition of ethinyl estradiol formation by sulfaphenazole suggests a major contribution of CYP2C9 to this reaction.

Porphyria cutanea tarda: pregnancy versus estrogen effect.

We describe the worsening of porphyria cutanea tarda in a young woman while she was taking oral contraceptives. However, she did not have an exacerbation during two pregnancies. We conclude that estrogens produced during pregnancy do not exert the same effect as orally administered medications that contain estrogen. The pronounced effect of oral ethinyl estradiol on the liver may be attributed to its first-pass effect on that organ.

Selected aspects of the pharmacokinetics and metabolism of ethinyl estrogens and their clinical implications.

Careful studies in an adequate sample of subjects show a very marked degree of variability in the pharmacokinetics of ethinyl estradiol--specifically, in parameters such as area under the curve, half-life, and time to peak. This variability is seen in differences between different populations, as well as from one individual to another. These studies also show variability in area under the curve and other parameters in the same person from time to time. Such differences may equal or exceed the differences between low dose (35 micrograms) and high-dose (50 micrograms) formulations. The levels of plasma ethinyl estradiol produced by a 50 micrograms dose of mestranol are similar to those from 35 micrograms of ethinyl estradiol. Thus a high-dose pill may be no higher than a low-dose pill if the nature of the estrogen is not kept in mind. Qualitative differences in the oxidative metabolites of estrogens may be of significance with respect to oncogenic potential.

PIP: The variability in the pharmacokinetics of ethinyl estradiol (EE) is pronounced, especially regarding such parameters as area under the curve, half-life, and time to peak. This variability shows up in different populations, different individuals, or in the same individual, and can even exceed the differences between low dose (35 mcg) and high- dose (50 mcg) formulations. 50 mcg of mestranol and 35 mcg of ethinyl estradiol both produce similar plasma EE levels. Qualitative differences in the oxidative metabolites of estrogens may be of significance with respect to oncogenic potential. The pharmacokinetic differences of EE whether caused by dietary, ethnic, or other factors are not merely differences in gastric absorption or renal excretion. Studies on kinetics and bioavailability showed that after oral administration of EE 3-sulfate only about 20% appeared as free EE in the blood, while EE 17-sulfate produced about half this amount. Individual variation showed a large spread both for plasma total EE sulfate levels and free EE. The pharmacokinetics of three 1 mg norethindrone/35 mcg EE and three 1 mg norethindrone/50 mcg mestranol formulations were analyzed and the mean values, standard deviations, and highest and lowest individual plasma patterns of the 3 EE preparations were indistinguishable. The administration of 50 mcg of mestranol resulted in an average area under the curve EE of 963 +- 544, whereas the dose 35 mcg of EE produced an area under the curve of 1036 +- 483, thus 35 mcg of EE proved to be a stronger dose than 50 mcg of mestranol. Inter- and intraindividual variability was demonstrated in a study: 24 patients received 35 mcg EE formulations and 27 others received 50 mcg mestranol agents. 3 identical formulations by different manufacturers proved to be bioequivalent. Extreme values ranged from -79% to +134% of the mean of the 3 determinations per individual. Clinical implications of these findings are that plasma EE levels engendered by 35 mcg EE may be indistinguishable from those produced by 50 mcg in another person. 2 to 3 mcg of moxestrol (the 11 beta-methoxy derivative of EE) is an effective contraceptive, as it is 10 times as potent as EE. Exposure of certain cell clones to estradiol, EE, and stilbestrol causes formation in vitro to foci of transformed (neoplastic) cells. However, moxestrol did not produce such cell transformation and these oxidative metabolites increased with estradiol or EE but not with moxestrol. This does not prove the oncogenic role of estrogens in humans, but it offers a new approach in the development of safer estrogens.

Metabolic profiles of endogenous and ethynyl steroids in plasma and urine from women during administration of oral contraceptives.

Conjugated ethynyl and endogenous steroids in plasma and urine from two women taking an oral contraceptive (Conlumin) containing 1 mg norethindrone and 50 micrograms mestranol have been analyzed by methods based on anion and ligand exchange chromatography and gas chromatography-mass spectrometry. Conjugated norethindrone and its reduced metabolites with 3 alpha,5 alpha, 3 alpha,5 beta, 3 beta,5 beta and 3 beta,5 alpha configurations were identified in the fluids. The quantitatively major metabolites in plasma were a disulphate of the 3 alpha,5 alpha isomer and a monosulphate of the 3 alpha,5 beta isomer. The renal clearance of the former compound was low. The major urinary metabolite of norethindrone was the 3 alpha,5 beta isomer conjugated with glucuronic or sulphuric acid. Disulphates constituted only a small portion of urinary ethynyl steroids. Metabolic profiles of endogenous neutral steroids in plasma and urine during the contraceptive cycle were compared with profiles during a physiological menstrual cycle. The concentrations of steroids in plasma during contraception were similar to those during the follicular and mid phases of the menstrual cycle, whereas levels of progesterone metabolites were higher in the luteal phase. The urinary excretion of steroids was 15-30% lower during the contraceptive cycle, due to a decrease in excretion of C21O5 steroids, 11-oxygenated androgens and etiocholanolone. The increase of urinary progesterone metabolites seen during the luteal phase was not observed during contraception, but the excretion of 5 beta-pregnane-3 alpha,20 alpha-diol glucuronide was higher than during the follicular and mid phases of the menstrual cycle.

Enhancement of the mutagenicity of carcinogenic arylamines by ethinyl estradiol.

Ethinyl estradiol, the estrogenic component of oral contraceptives, has been shown to enhance the mutagenicity of 2-aminofluorene, 2-acetylaminofluorene, N-hydroxy-2-acetylaminofluorene, and N-acetoxy-2-acetylaminofluorene with strain TA 98 of Salmonella typhimurium and various rat liver activating systems. The magnitude of the enhancement of mutation produced by ethinyl estradiol is dependent upon: the type of mixed-function oxidase inducer of the liver activating system; the structure and concentration of the arylamine; the concentration of ethinyl estradiol; and metabolism of ethinyl estradiol to its catechol, 2-hydroxyethinyl estradiol, by the activating system. Moxestrol, a biologically potent estrogenic derivative of ethinyl estradiol which is not metabolized effectively to its catechol by the mixed-function oxidases, does not enhance the mutagenicity of the above arylamines and related compounds. Both 2-hydroxyethinyl estradiol and 2-hydroxymoxestrol enhance the mutagenicity of 2-aminofluorene and 2-acetylaminofluorene. Neither the estrogens nor their catechols are mutagenic by themselves in this system. In the presence of ethinyl estradiol, a marked inhibition of ring hydroxylation of 2-acetylaminofluorene was demonstrated. Since ring hydroxylation is a well established detoxification pathway of arylamine and arylamide metabolism, the enhancement of mutagenicity by ethinyl estradiol may be the result of a net increase in N-hydroxylation of arylamines and arylamides.

The in vitro metabolism of ethinyloestradiol, mestranol and levonorgestrel by human jejunal mucosa.

1 Ethinyloestradiol was extensively metabolised in vitro by human jejunal mucosa to form ethinyloestradiol sulphate. 2 The amount of conjugation was directly related to the weight of biopsy tissue. 3 The degree of conjugation of mestranol and levonorgestrel was much lower than for ethinyloestradiol suggesting that the 17-position of the steroid nucleus is relatively inaccessible for conjugation. 4 No Phase I metabolism of ethinyloestradiol or levonorgestrel was apparent in the conditions used in these experiments.

PIP: In vitro studies were conducted on the metabolism of 3 steroids used in OCs (oral contraceptives) by small pieces of human jejunal mucosa. This was done because the gastrointestinal mucosa of humans is known to metabolise a number of drugs. Almost 40% of the ethinyl estradiol, 9.8% of the levonorgestrel, and 7% of the mestranol were metabolised after incubation. All these metabolic responses were significantly different from those in the control groups. Results of the study show that the metabolism of the ethinyl estradiol was related to the weight of the tissue used. These results are consistent with the known marked 1st pass effect of ethinyl estradiol. Norgestrel, known to have little or no 1st pass effect, did not show a high rate of gut metabolism. Under the experimental conditions employed, no Phase 1 metabolism of either ethinyl estradiol or levonorgestrel was apparent.

Properties of the estrogen receptor in the human oviduct and its interaction with ethinylestradiol and mestranol in vitro.

Biochemical properties of estrogen binding are investigated in the cytosol and nuclear fractions of the human Fallopian tube. Sucrose density ultracentrifugation and dextrancoated charcoal adsorption techniques are used for characterization of [3H]estradiol uptake in the human oviduct. There is indirect evidence for the presence of protease which can be inhibited by diisopropylfluorophosphate (DFP). When DFP is present in buffer of low ionic strength, the cytosol receptor sediments at 8S and 4S peaks. In the absence of DFP, the 4S peak alone is demonstrated. The proteolytic inhibitor does not alter the estrogen-binding capacity in the human oviduct. The dissociation constant (Kd) for [3H]estradiol in cytosol is 2 X 10(-10) M without DFP and 1.5 X 10(-10) M with DFP. The presence of protease in cytosol of human oviducts is confirmed by hydrolysis of benzoyl-arginine nitroanalide. The enzymatic activity is inhibited by DFP. Nuclear estrogen receptor sediments at 4S after extraction with 0.4 M KCL buffer. A rapid nuclear accumulation of [-3H]estradiol is seen at 25 C, with reciprocal depletion of cytoplasmic receptor in human oviduct tissue minces. The synthetic estrogens ethinylestradiol (17 alpha-ethynyl-1,3,5-estratriene-3,17 beta-diol) and mestranol [3-methoxy-17 alpha-ethinyl-1,3-5(10)-estratiene-17 beta-OL] are competitors for the estrogen receptor in the human Fallopian tube. Inhibition of oviductal estrogen binding is 500 times greater with ethinylestradiol than with mestranol (ki = 0.75 X 10(-9) M for ethinylestradiol; Ki = 3.74 X 10(-7) M for mestranol). The estrogen receptor in the human Fallopian tube shows properties similar to those of the estrogen receptor of the human uterus. However, the determination of the number of binding sites in the oviduct is not influenced by proteolytic enzyme activity.

PIP: The biochemical properties of estrogen binding are investigated in the cytosol and nuclear fractions of the human fallopian tube. Sucrose density ultracentrifugation and dextrancoated charcoal absorption techniques are used for characterization of estradiol uptake in the human oviduct. There is indirect evidence for the presence of protease which can be inhibited by (DFP) diisopropylfluorophosphate. When DFP is present in buffer of low ionic strength, the cytosol receptor sediments at 8S and 4S peak. In the absence of DFP, the 4S peak alone is demonstrated. The proteolytic inhibitor does not alter the estrogen-binding capacity in the human oviduct. The presence of protease in cytosol of human oviducts is confirmed by hydrolysis of benzoyl-arginine nitroanalide. The enzymatic activity is inhibited by DFP. Nuclear estrogen receptor sediments at 4S after extraction with 0.4M KCL buffer. A rapid nuclear accumulation of estradiol is seen at 25 C, with reciprocal depletion of cytoplasmic receptor in human oviduct tissue minces. The synthetic estrogens ethinyl estradiol (17alpha-ethynyl-1,3,5-estratriene-3,17 beta-diol) and mestranol (3-methoxy-17alpha-ethinyl-1,3,5(10)-3stratriene-17beta-OL) are competitors for the estrogen receptor in the human fallopian tube. Inhibition of oviductal estrogen binding is 500 times greater with ethinyl estradiol than with mestranol. The estrogen receptor in the human fallopian tube shows properties similar to those of the estrogen receptor of the human uterus. However, the determination of the number of binding sites in the oviduct is not influenced by proteolytic enzyme activity.

Variation of ethinylestradiol blood levels among healthy women using oral contraceptives.

Data concerning ethinylestradiol (EE) blood levels among 93 healthy women using oral contraceptives are presented. Seventy-two per cent of the observed variation in EE blood levels was unexplainable on the basis of time since ingestion of the last oral contraceptive, day of menstrual cycle, race, age, weight, height, blood pressure, cigarette consumption, alcohol consumption, diurnal variation, or lifetime use of oral contraceptives.

PIP: This 2-fold investigation studied 1) the extent to which women vary in blood levels of ethinylestradiol (EE) after ingesting oral contraceptives (OCs) containing similar amounts of EE or mestranol (ME), which is metabolized to EE; and 2) whatever variations might be accountable on the basis of physical, behavioral, or other characteristics. 93 healthy OC users were given either OCs with 50 mcg of ME (84 subjects) of 50 mcg of EE (9 subjects). Linear regression was used to determine relevance of variation in EE blood levels based on hours since pill ingestion, day of menstrual cycle, or any other variables. Hours since OC showed the strongest relationship to log EE, accounting for 25% of the variation. Another 3% could be accounted for by day of menstrual cycle. The remaining 72% of observed variation in EE levels could not be explained in terms of time since ingestion of last OC, day of menstrual cycle, race, age, weight, height, or use-duration of OCs.

[Cellular estrogen receptors]. / Receptory komórkowe estrogenów.

PIP: The mechanism of hormone activity, especially that of estrogens presents an important link in the body of knowledge concerning the cyclical changes in a woman's life. The understanding of the individual stages of this mechanism is especially interesting in relation to hormonal therapy. This paper presents a review of actual knowledge in the field of cell response and cellular receptors of estrogen. The effect of estrogen activity on the tissues is discussed. The effect of estrogens can be well-demonstrated in hormone dependent cells and tissues (target cells and tissues). (Author's modified)^ieng

Synthesis and estrogenic properties of 17-epi-ethynylestradiol and its ether derivatives epimestranol and epiquinestrol.

The synthesis of 17-epi-ethynylestradiol (10), the 17 beta-ethynyl-17 alpha-ol epimer of the well-known orally active estrogen, ethynylestradiol (1), was achieved by LiA1H4 reduction of epoxide 9, as well as by demethylating epimestranol (11) with CH3MgI. Compound 11 was obtained by the unusual 17 beta-ethynylation of estrone 3-methyl ether 22 under equilibrating conditions. The in vitro estrogen receptor-binding affinity and the oral estrogenicity in the rat for the 17-epi compounds 10, 11 and 20 (epiquinestrol) was evaluated. Despite moderate estrogen receptor-binding affinity, compound 10 was devoid of measurable estrogenicity at 10 mg/kg or antiestrogenicity at 3 mg/kg.