Evidence and characterization of the binding of two 3H-labeled androgens to the estrogen receptor

The physiological and biochemical basis of potency thresholds modeled using human estrogen receptor alpha: implications for identifying endocrine disruptors

The endocrine system functions by interactions between ligands and receptors. Ligands exhibit potency for binding to and interacting with receptors. Potency is the product of affinity and efficacy. Potency and physiological concentration determine the ability of a ligand to produce physiological effects. The kinetic behavior of ligand-receptor interactions conforms to the laws of mass action. The laws of mass action define the relationship between the affinity of a ligand and the fraction of cognate receptors that it occupies at any physiological concentration. We previously identified the minimum ligand potency required to produce clinically observable estrogenic agonist effects via the human estrogen receptor-alpha (ERα). By examining data on botanical estrogens and dietary supplements, we demonstrated that ERα ligands with potency lower than one one-thousandth that of the primary endogenous hormone 17β-estradiol (E2) do not produce clinically observable estrogenic effects. This allowed us to propose a Human-Relevant Potency Threshold (HRPT) for ERα ligands of 1 × 10-4 relative to E2. Here, we test the hypothesis that the HRPT for ERα arises from the receptor occupancy by the normal metabolic milieu of endogenous ERα ligands. The metabolic milieu comprises precursors to hormones, metabolites of hormones, and other normal products of metabolism. We have calculated fractional receptor occupancies for ERα ligands with potencies below and above the previously established HRPT when normal circulating levels of some endogenous ERα ligands and E2 were also present. Fractional receptor occupancy calculations showed that individual ERα ligands with potencies more than tenfold higher than the HRPT can compete for occupancy at ERα against individual components of the endogenous metabolic milieu and against mixtures of those components at concentrations found naturally in human blood. Ligands with potencies less than tenfold higher than the HRPT were unable to compete successfully for ERα. These results show that the HRPT for ERα agonism (10-4 relative to E2) proposed previously is quite conservative and should be considered strong evidence against the potential for disruption of the estrogenic pathway. For chemicals with potency 10-3 of E2, the potential for estrogenic endocrine disruption must be considered equivocal and subject to the presence of corroborative evidence. Most importantly, this work demonstrates that the endogenous metabolic milieu is responsible for the observed ERα agonist HRPT, that this HRPT applies also to ERα antagonists, and it provides a compelling mechanistic explanation for the HRPT that is grounded in basic principles of molecular kinetics using well characterized properties and concentrations of endogenous components of normal metabolism.

Brain-based sex differences in autism spectrum disorder across the lifespan: A systematic review of structural MRI, fMRI, and DTI findings

Females with autism spectrum disorder (ASD) have been long overlooked in neuroscience research, but emerging evidence suggests they show distinct phenotypic trajectories and age-related brain differences. Sex-related biological factors (e.g., hormones, genes) may play a role in ASD etiology and have been shown to influence neurodevelopmental trajectories. Thus, a lifespan approach is warranted to understand brain-based sex differences in ASD. This systematic review on MRI-based sex differences in ASD was conducted to elucidate variations across the lifespan and inform biomarker discovery of ASD in females We identified articles through two database searches. Fifty studies met criteria and underwent integrative review. We found that regions expressing replicable sex-by-diagnosis differences across studies overlapped with regions showing sex differences in neurotypical cohorts. Furthermore, studies investigating age-related brain differences across a broad age-span suggest distinct neurodevelopmental patterns in females with ASD. Qualitative comparison across youth and adult studies also supported this hypothesis. However, many studies collapsed across age, which may mask differences. Furthermore, accumulating evidence supports the female protective effect in ASD, although only one study examined brain circuits implicated in "protection." When synthesized with the broader literature, brain-based sex differences in ASD may come from various sources, including genetic and endocrine processes involved in brain "masculinization" and "feminization" across early development, puberty, and other lifespan windows of hormonal transition. Furthermore, sex-related biology may interact with peripheral processes, in particular the stress axis and brain arousal system, to produce distinct neurodevelopmental patterns in males and females with ASD. Future research on neuroimaging-based sex differences in ASD would benefit from a lifespan approach in well-controlled and multivariate studies. Possible relationships between behavior, sex hormones, and brain development in ASD remain largely unexamined.

The influence of microsatellite polymorphisms in sex steroid receptor genes ESR1, ESR2 and AR on sex differences in brain structure

The androgen receptor (AR), oestrogen receptor alpha (ESR1) and oestrogen receptor beta (ESR2) play essential roles in mediating the effect of sex hormones on sex differences in the brain. Using Voxel-based morphometry (VBM) and gene sizing in two independent samples (discovery n ​= ​173, replication ​= ​61), we determine the common and unique influences on brain sex differences in grey (GM) and white matter (WM) volume between repeat lengths (n) of microsatellite polymorphisms AR(CAG)n, ESR1(TA)n and ESR2(CA)n. In the hypothalamus, temporal lobes, anterior cingulate cortex, posterior insula and prefrontal cortex, we find increased GM volume with increasing AR(CAG)n across sexes, decreasing ESR1(TA)n across sexes and decreasing ESR2(CA)n in females. Uniquely, AR(CAG)n was positively associated with dorsolateral prefrontal and orbitofrontal GM volume and the anterior corona radiata, left superior fronto-occipital fasciculus, thalamus and internal capsule WM volume. ESR1(TA)n was negatively associated with the left superior corona radiata, left cingulum and left inferior longitudinal fasciculus WM volume uniquely. ESR2(CA)n was negatively associated with right fusiform and posterior cingulate cortex uniquely. We thus describe the neuroanatomical correlates of three microsatellite polymorphisms of steroid hormone receptors and their relationship to sex differences.

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Microsatellite polymorphisms in sex hormone receptor genes influence volume in regions of brain sex difference

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AR(CAG)n repeat length is positively associated with grey and white matter volume across males and females

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ESR1(TA)n repeat length is negatively associated with grey and white matter volume across males and females

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ESR2(CA)n repeat length is negatively associated with grey matter volume in females but not in males

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Repeat length was associated with volume in the hypothalamus, insula, temporal cortices, prefrontal cortices, inferior and superior longitudinal fasciculi in the three genes.

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These regions were largely replicated in an independent cohort acquired on a separate scanner.

The promiscuous estrogen receptor: Evolution of physiological estrogens and response to phytochemicals and endocrine disruptors

Many actions of estradiol (E2), the principal physiological estrogen in vertebrates, are mediated by estrogen receptor-α (ERα) and ERβ. An important physiological feature of vertebrate ERs is their promiscuous response to several physiological steroids, including estradiol (E2), Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol. A novel structural characteristic of Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol is the presence of a C19 methyl group, which precludes the presence of an aromatic A ring with a C3 phenolic group that is a defining property of E2. The structural diversity of these estrogens can explain the response of the ER to synthetic chemicals such as bisphenol A and DDT, which disrupt estrogen physiology in vertebrates, and the estrogenic activity of a variety of plant-derived chemicals such as genistein, coumestrol, and resveratrol. Diversity in the A ring of physiological estrogens also expands potential structures of industrial chemicals that can act as endocrine disruptors. Compared to E2, synthesis of 27-hydroxycholesterol and Δ⁵-androstenediol is simpler, leading us, based on parsimony, to propose that one or both of these steroids or a related metabolite was a physiological estrogen early in the evolution of the ER, with E2 assuming this role later as the canonical estrogen. In addition to the well-studied role of the ER in reproductive physiology, the ER also is an important transcription factor in non-reproductive tissues such as the cardiovascular system, kidney, bone, and brain. Some of these ER actions in non-reproductive tissues appeared early in vertebrate evolution, long before the emergence of mammals.

Use of computational modeling approaches in studying the binding interactions of compounds with human estrogen receptors

Estrogens have a whole host of physiological functions in many human organs and systems, including the reproductive, cardiovascular, and central nervous systems. Many naturally-occurring compounds with estrogenic or antiestrogenic activity are present in our environment and food sources. Synthetic estrogens and antiestrogens are also important therapeutic agents. At the molecular level, estrogen receptors (ERs) mediate most of the well-known actions of estrogens. Given recent advances in computational modeling tools, it is now highly practical to use these tools to study the interaction of human ERs with various types of ligands. There are two common categories of modeling techniques: one is the quantitative structure activity relationship (QSAR) analysis, which uses the structural information of the interacting ligands to predict the binding site properties of a macromolecule, and the other one is molecular docking-based computational analysis, which uses the 3-dimensional structural information of both the ligands and the receptor to predict the binding interaction. In this review, we discuss recent results that employed these and other related computational modeling approaches to characterize the binding interaction of various estrogens and antiestrogens with the human ERs. These examples clearly demonstrate that the computational modeling approaches, when used in combination with other experimental methods, are powerful tools that can precisely predict the binding interaction of various estrogenic ligands and their derivatives with the human ERs.

Selective conversion by microglia of dehydroepiandrosterone to 5-androstenediol-A steroid with inherent estrogenic properties

The well-established neuroprotective effect of dehydroepiandrosterone (DHEA) has been attributed to its metabolism in the brain to provide estrogens known to be neuroprotective and to enhance memory and learning in humans and animals. However, our previous work showed that the conversion of DHEA to 4-androstenedione (AD), the precursor of estrone (E(1)) and estradiol (E(2)), is very low in several different types of neural cells, and that the main product is 7alpha-hydroxy-DHEA (7alpha-OH-DHEA). In this study, we found that microglia are an exception and produce mainly 5-androstene-3beta,17beta-diol (Delta(5)-Adiol), a C(19) steroid with estrogen-like activity from DHEA. Virtually, no other products, including testosterone (T) were detected by TLC or HPLC in incubations of (3)H-labeled DHEA with the BV2 microglial cell line. Microglia are important brain cells that are thought to play a house-keeping role during the steady state, and that are crucial to the brain's immune reaction to injury and the healing process. Our findings suggest that the microglia-produced Delta(5)-Adiol might have a role in modulating estrogen-sensitive neuroplastic events in the brain, in the absence of adequate local synthesis of estrone and estradiol.

Synthetic 19-nortestosterone derivatives as estrogen receptor alpha subtype-selective ligands induce similar receptor conformational changes and steroid receptor coactivator recruitment than natural estrogens

The binding of estradiol (E(2)) to estrogen receptors (ER) is followed by conformational changes resulting in coactivator or corepressor recruitment that influences gene transcription. A series of synthetic A-ring reduced 19-nortestosterone-derived progestins has the capacity to selectively bind and activate transcription through the ERalpha. Herein, the molecular mechanisms involved in ER subtype-selective interactions of these compounds as assessed by their effects upon both ERalpha and ERbeta structural conformation and their ability to induce recruitment of steroid receptor coactivator-1 (SRC-1) to ERalpha were investigated. The results demonstrated that all synthetic A-ring 3beta,5alpha-tetrahydro-reduced derivatives of 19-nortestosterone induced an ERalpha trypsin digestion pattern similar to that seen with E(2), without effects upon ERbeta. In addition, these compounds had the ability to recruit SRC-1 to the ligand-binding domain of ERalpha similar to E(2). Our data indicate that A-ring 3beta,5alpha-tetrahydro-reduced 19-nortestosterone-derived progestins behave as selective ERalpha agonists with ligand-receptor structural and functional responses similar to those induced with natural E(2).

C19‐5‐ene Steroids in Nature

Dehydroepiandrosterone (DHEA), produced from cholesterol in the adrenals, is the most abundant steroid in our circulation. It is present almost entirely as the sulfate ester, but the free steroid is the form that serves as a precursor of estrogens and androgens, as well as 7- and 16-oxygenated derivatives. Mammalian tissues reduce the 17-keto Group of DHEA to produce androstenediol-a weak estrogen and full-fledged androgen. Its androgen activity is not inhibited by the anti-androgens commonly used to treat prostate cancer. It is probably responsible for the growth of therapy-resistant prostate cancer. DHEA is hydroxylated at the 7 alpha position, and this derivative is oxidized by 11 beta-hydroxysteroid dehydrogenase to form 7-keto DHEA. The latter is reduced by the same dehydrogenase to form 7 beta-hydroxy DHEA. When fed to rats, each of the latter three steroids induce the formation of two thermogenic enzymes in the liver. The late-term human fetus produces relatively large amounts of 16 alphahydroxy DHEA, which serves the mother as a precursor of estriol.

Co-evolution of steroidogenic and steroid-inactivating enzymes and adrenal and sex steroid receptors

Receptors for the adrenal and sex steroids arose by a series of gene duplications from an ancestral nuclear receptor in a primitive vertebrate, at least 540 million years ago. Sequence analysis indicates many steroidogenic and steroid-inactivating enzymes, including cytochrome P450s and hydroxysteroid dehydrogenases (HSDs), arose at the same time. The estrogen receptor (ER) appears to be the ancestral steroid receptor. Initially, the redundant duplicated ER had a low specificity for its new ligand. This raises the question: "How was specificity for responses to different steroids regulated early in the evolution of steroid receptors?" Selective expression of these steroid-metabolizing enzymes provided specificity for different steroid responses in primitive vertebrates. 17 beta-Hydroxysteroid dehydrogenase-type 1 (17 beta-HSD-type 1) and 17 beta-HSD-type 2, which preferentially catalyze the reduction and oxidation at C17 of androgens and estrogens, respectively, provide an example of this mechanism. Selective expression of either 17 beta-HSD-type 1 or 17 beta-HSD-type 2 can regulate synthesis or inactivation of androgens or estrogens in specific cells. Steroids also were important in the evolution of land animals, which began about 400 million years ago. Steroidogenic and steroid-inactivating enzymes were recruited to regulate steroid-mediated responses as organ function became more complex. For example, in the kidney 11 beta-HSD-type 2 prevents binding of glucocorticoids to the mineralocorticoid receptor (MR), which is crucial for aldosterone-mediated regulation of electrolyte transport in the distal tubule. We propose that Delta 5 steroids, such as dehydroepiandrosterone and its metabolites, were the ligands for the ancestral ER. Understanding the actions of Delta 5 steroids in amphioxus and lamprey may shed light on adrenarche and neurosteroid actions in humans.

Ab initio electronic structure of the progestogen norethisterone and its 5 alpha-derivatives

The steroid 17 alpha-ethynyl-19-nor-4-androsten-17 beta-ol, 3-one (Norethisterone; NET) and its 5 alpha-dihydro (5 alpha-NET), 3 alpha- and 3 beta-tetrahydro derivatives (3 alpha,5 alpha- and 3 beta,5 alpha-NET), were comparatively studied by the ab initio quantum mechanics theory. Additionally, 5 alpha-androstan-3 beta,17 beta-diol (ADIOL) was also studied. The Hartree-Fock method and the 6-31G(*) basis set were used to obtain the lowest energy conformation, geometries, electronic structure and physicochemical properties of the steroids. The results showed bond distances and valence angles similar among all steroids, but some differences in dihedral angles in the A-B-ring system were observed. The electronic structure analysis showed that NET has both frontier orbitals that is, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) located at the C4-C5 pi-bond. In A-ring reduced derivatives, the HOMO was found at the 17 beta-OH and ethynyl groups. In the case of 5 alpha-NET, the LUMO was confined to the A-ring and its C3 carbonyl group while the two NET tetrahydro-reduced derivatives showed the LUMO at the 17 beta-OH and ethynyl groups. The energy changes of the rotational barrier of the 17 beta-OH group suggest that its movement is somewhat restricted by the 17 alpha-ethynyl group. Interestingly both groups at C17 form a single electrostatic potential with high electronic density. On the other side, the 19-nor condition increases the A-ring mobility. However, the 3 beta-OH group of 3 beta,5 alpha-NET may rotate without significant energy differences as compared to the same group in ADIOL. The electronic structure of NET and its A-ring reduced derivatives explains in some extent their interaction with androgen and progesterone receptors as well as their selectivity for the estrogen alpha-receptor.

The phenotype of the aromatase knockout mouse reveals dietary phytoestrogens impact significantly on testis function

Estrogen is synthesized in the testis, both in Leydig cells and seminiferous epithelium, and its importance in spermatogenesis is highlighted by the phenotype of the aromatase knockout (ArKO) mouse. These mice are unable to synthesize endogenous estrogens. The males develop postmeiotic defects by 18 wk of age. We hypothesized that maintenance of spermatogenesis in younger animals may be mediated by exogenous estrogenic substances. Dietary soy meal, contained in almost all commercial rodent diets, provides a source of estrogenic isoflavones. We thus investigated spermatogenesis in wild-type and ArKO mice raised on a diet containing soy, compared with a soy-free diet, to elucidate the biological action of phytoestrogens on the testis. In ArKO mice, dietary phytoestrogens could partially prevent disruptions to spermatogenesis, in that they prevented the decline in germ cell numbers. They also seemed to maintain Sertoli cell function, and they blocked elevations in FSH. The impairment of spermatogenesis seen in soy-free ArKOs occurred in the absence of a decreased gonadotropic stimulus, suggesting that the effects of dietary phytoestrogens are independent of changes to the pituitary-gonadal axis. Our study highlights the importance of estrogen in spermatogenesis and shows that relatively low levels of dietary phytoestrogens have a biological effect in the testis.

A estradiol-17beta receptor in the reproductive system of the female of Octopus vulgaris: characterization and immunolocalization

In this study, for the first time we have identified an estradiol-17beta receptor (ER) in the reproductive system of the female of Octopus vulgaris. Scatchard analysis revealed that one binding component with high affinity and low capacity for the ligand was present in the cytosol, but not in the nuclear extract of the ovary and the oviduct. A steroid specificity competition assay showed that 3H-estradiol-17beta binding activity showed a preference for estradiol-17beta. DNA-cellulose chromatography confirmed the presence of one 3H-estradiol-17beta binding component. By using antibodies anti ER (578-595), we have localized by Western blotting one band of about 70 kDa. ER immunoreactivity has been localized in the nuclei of the follicle cells of the ovary, in the nuclei of the epithelium lining the proximal portion of the oviduct and in the nuclei, and in the cytoplasm of the inner region of the oviducal gland and in the cytoplasm of the outer region of the oviducal gland. These data, taken together, provide evidence that in Octopus vulgaris the ER has biochemical and immunohistochemical characteristics resembling those of ER in vertebrates.

Impairment of spermatogenesis in mice lacking a functional aromatase (cyp 19) gene

It is well established that spermatogenesis is controlled by gonadotrophins and testosterone. However, a role for estrogens in male reproduction recently was suggested in adult mice deficient in estrogen receptor alpha. These mice became infertile primarily because of an interruption of fluid reabsorption by the efferent ductules of the epididymis, thus leading to a disruption of the seminiferous epithelium [Hess, R. A., Bunick, D., Lee, K. H., Bahr, J., Taylor, J. A., Korach, K. S., and Lubahn, D. B. (1997) Nature (London) 390, 509-512]. Despite the demonstration of the aromatase enzyme, which converts androgens to estrogens, and estrogen receptors within the rodent seminiferous epithelium, the role of aromatase and estrogen in germ cell development is unknown. We have investigated spermatogenesis in mice that lack aromatase because of the targeted disruption of the cyp19 gene (ArKO). Male mice deficient in aromatase were initially fertile but developed progressive infertility, until their ability to sire pups was severely impaired. The mice deficient in aromatase developed disruptions to spermatogenesis between 4.5 months and 1 year, despite no decreases in gonadotrophins or androgens. Spermatogenesis primarily was arrested at early spermiogenic stages, as characterized by an increase in apoptosis and the appearance of multinucleated cells, and there was a significant reduction in round and elongated spermatids, but no changes in Sertoli cells and earlier germ cells. In addition, Leydig cell hyperplasia/hypertrophy was evident, presumably as a consequence of increased circulating luteinizing hormone. Our findings indicate that local expression of aromatase is essential for spermatogenesis and provide evidence for a direct action of estrogen on male germ cell development and thus fertility.

The estrogen receptor beta subtype: a novel mediator of estrogen action in neuroendocrine systems

The recent discovery that an additional estrogen receptor (ERbeta) subtype is present in many rat, mouse, and human tissues has advanced our understanding of the mechanisms underlying estrogen signalling. Ligand-binding experiments have shown specific binding of 17beta-estradiol by ERbeta with an affinity similar to that of ERalpha. The rat tissue distribution and/or the relative level of ERalpha and ERbeta expression seems to be quite different, i.e., moderate to high expression in uterus, testis, pituitary, ovary, kidney, epididymis, and adrenal for ERalpha and prostate, ovary, lung, bladder, brain, bone, uterus, and testis for ERbeta. Within the same organ it often appears that the ER subtypes are expressed in different cell types, supporting the hypothesis that the ER's may have different biological functions. The cell type-specific expression of ERalpha and ERbeta in rat prostate, testis, uterus, ovary, and brain and the distribution of ERbeta mRNA in the ERalpha knock-out mouse brain are discussed. The discovery of ERbeta suggests the existence of two previously unrecognized pathways of estrogen signalling; via the ERbeta subtype in tissues exclusively expressing this subtype and via the formation of heterodimers in tissues expressing both ER subtypes. The existence of two ER subtypes, their differential expression pattern, and different actions on certain response elements could provide explanations for the striking species-, cell-, and promoter-specific actions of estrogens and antiestrogens. The challenge for the future is to unravel the detailed physiological role of each subtype and to use this knowledge to develop the next generation of ER-targeted drugs with improved therapeutic profiles in the treatment or prevention of osteoporosis, cardiovascular system disorders, Alzheimer's disease, breast cancer, and disorders of the urogenital tract.

Effect of dehydroepiandrosterone on vaginal and uterine histomorphology in the rat

Dehydroepiandrosterone (DHEA) applied on the dorsal skin of ovariectomized animals, at the twice daily dose of 30 mg, resulted in a complete reversal of the vaginal atrophy seen 1, 3 and 6 months after ovariectomy, and induced proliferation and mucification of the vaginal epithelium. A similar mucification of the vaginal epithelium related to androgenic action was observed in intact rats treated with DHEA. While treatment of intact rats with DHEA resulted in a significant increase in uterine weight at 1 month, the value of the same parameter decreased by approximately 30% after 3 and 6 months of DHEA administration. In ovariectomized DHEA-treated animals, uterine weight was increased at all time intervals. At histopathological examination, following DHEA administration to intact animals, stimulation was seen in the myometrial layers of the uterus whereas atrophy, involving especially the endometrium, became apparent after 3 and 6 months of treatment. In ovariectomized animals, the endometrium remained atrophic at all time intervals during DHEA treatment and the uterine epithelium thus remained atrophic under DHEA treatment. Examination of the effect of DHEA on the vaginal epithelium indicates that local application of DHEA on the vaginal mucosa is approximately 10-fold more efficient than application at a distant site on the skin. Reversal of the ovariectomy-induced increase in serum LH levels was also observed after DHEA treatment. The present data suggest that DHEA possesses a tissue-specific action, through its local transformation into active estrogens in the vaginal epithelium while the uterine epithelium remains atrophic. In addition, the site of administration of DHEA appears to be a significant factor, at least for its stimulatory effect on the vaginal mucosa.

Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta

The rat estrogen receptor (ER) exists as two subtypes, ER alpha and ER beta, which differ in the C-terminal ligand binding domain and in the N-terminal transactivation domain. In this study we investigated the messenger RNA expression of both ER subtypes in rat tissues by RT-PCR and compared the ligand binding specificity of the ER subtypes. Saturation ligand binding analysis of in vitro synthesized human ER alpha and rat ER beta protein revealed a single binding component for 16 alpha-iodo-17 beta-estradiol with high affinity [dissociation constant (Kd) = 0.1 nM for ER alpha protein and 0.4 nM for ER beta protein]. Most estrogenic substances or estrogenic antagonists compete with 16 alpha-[125I]iodo-17 beta-estradiol for binding to both ER subtypes in a very similar preference and degree; that is, diethylstilbestrol > hexestrol > dienestrol > 4-OH-tamoxifen > 17 beta-estradiol > coumestrol, ICI-164384 > estrone, 17 alpha-estradiol > nafoxidine, moxestrol > clomifene > estriol, 4-OH-estradiol > tamoxifen, 2-OH-estradiol, 5-androstene-3 beta, 17 beta-diol, genistein for the ER alpha protein and dienestrol > 4-OH-tamoxifen > diethylstilbestrol > hexestrol > coumestrol, ICI-164384 > 17 beta-estradiol > estrone, genistein > estriol > nafoxidine, 5-androstene-3 beta, 17 beta-diol > 17 alpha-estradiol, clomifene, 2-OH-estradiol > 4-OH-estradiol, tamoxifen, moxestrol for the ER beta protein. The rat tissue distribution and/or the relative level of ER alpha and ER beta expression seems to be quite different, i.e. moderate to high expression in uterus, testis, pituitary, ovary, kidney, epididymis, and adrenal for ER alpha and prostate, ovary, lung, bladder, brain, uterus, and testis for ER beta. The described differences between the ER subtypes in relative ligand binding affinity and tissue distribution could contribute to the selective action of ER agonists and antagonists in different tissues.

Lack of estrogenic potential of progesterone- or 19-nor-progesterone-derived progestins as opposed to testosterone or 19-nor-testosterone derivatives on endometrial Ishikawa cells

Estrogen receptors of human endometrial cancer Ishikawa cells were found to be present in moderate amounts (160-200 fmol/mg protein), and to specifically bind moxestrol (R2858) with a very high affinity characterized by a Kd around 60 pM, when measured under equilibrium conditions. The binding specificity respected a decreasing order as follows: estradiol (E2: 100%) > 4-hydroxy-tamoxifen (4OHTAM: 52.7%) > estriol (E3: 5.7%) > estrone (E1: 2.1%) > TAM (0.2%). The induction of alkaline phosphatase activity (APase) used as an estrogen-specific response, confirmed the intrinsic estrogenicity of progestins derived from 19-nor-testosterone (19NT): norethindrone (NOR), norethynodrel and levonorgestrel, at concentrations ranging from 10(-8) to 10(-6) M. The effect of NOR was partially blocked by the antiestrogen 4OHTAM, which was also partially agonistic in this model, but neither by the antiprogestin mifepristone (RU486) nor by the aromatase inhibitor aminoglutethimide. A simulatory effect was also detected at 10(-7) or 10(-6) M with ethindrone, the testosterone- (T) derived progestin homologous to NOR, and with both androgenic parent-compounds, i.e. T and 19NT themselves. In contrast, progesterone (P) derivatives like medroxyprogesterone acetate (MPA) and chlormadinone acetate (CMA) remained totally inactive, as well as 19-nor-progesterone (19NP) itself or its progestagenic derivatives: ORG 2058 and nomegestrol acetate (NOM). Structure-activity relationships deduced from these studies suggest that it is not the absence of the 19-methyl group which can account for the estrogenic potential of the so-called "19-norprogestins", but rather their steroid structure derived from T in a broad sense (including the 19NT derivatives), as opposed to the non-estrogenic therapeutic progestins derived from P like MPA or CMA, or from 19NP like NOM.

Rainbow trout estrogen receptor presents an equal specificity but a differential sensitivity for estrogens than human estrogen receptor

The estrogen receptor is a transcription factor that mediates the actions of estrogens which plays a major role in salmonid vitellogenesis. Previously, we cloned and described the estradiol receptor in rainbow trout. To study the transactivation characteristics, the full length cDNA was inserted in an expression vector and tested by transfection on an estrogen-dependent promoter (pERE-TK-CAT). For the first time, direct comparison between the trout receptor (rtER) and human receptor (hER) in an analogous system has been possible. We demonstrate that rtER can, like hER, transactivate transcription in a strictly hormone-dependent manner. The specificity and sensitivity of the rtER response to different steroids have been studied. With rtER, the E2 concentration needed for half maximal activation is 10 times higher than with hER. In addition, we show that rtER has a weak affinity for androgens and transactivation could be induced using high testosterone concentration. Experiments show that both rtER and hER have an equal specificity for estrogens but that the rtER binds its ligand with a lower sensitivity than hER. Several hypotheses concerning the role of main amino acids within the receptor protein are proposed based on the different properties of the receptors and comparison of sequences.

Role of androgens in breast cancer

There is a vast amount of information on the concentration of different androgens in human breast cancer in pre- and post-menopausal women. Many years ago it was suggested that some androgens, in particular dehydroepiandrosterone (DHA), could be one of the parameters to establish whether these androgens can predict breast cancer. However, the enormous data available on the plasma and tissue concentrations, particularly DHA and DHA sulfate (DHA-S) allow confirmation that the quantitative values of these androgens are not significantly different in normal women from those with breast cancer. Another important aspect of androgens in breast cancer is their function as precursors of estrogens, hormones which play an important role in breast cancerization. However, it is not clear at present what the quantitative contribution of androgens "via aromatase" is to the formation of estrogens, because more recently it was found that estradiol in breast cancer tissues originates mainly "via sulfatase" using estrone sulfate as precursor. A point of further interest is that a series of authors have demonstrated that the administration of DHA to experimental animals with breast cancer significantly decreased the evolution of the disease. This part of the data is also contradictory because other experimental information has shown that administration of DHA can increase the incidence of granulosa cell tumors. Finally, it has been suggested that androgens, in their capacity as anti-estrogens, can be used to substitute anti-estrogens in cases where treatment with classical anti-estrogens has no response. In conclusion, more information concerning the plasma and tissular concentrations of androgens, their contribution as estrogen precursors and their biological response(s), is needed in order to have a clearer idea of the role of these steroids in breast cancer.

Estrogen receptor and C19-5-ene-steroid concentrations in the nuclear fraction from human breast carcinoma tissue

The adrenal-derived estrogen 5-androstene-3 beta,17 beta-diol (ADIOL) is estrogenic at the concentrations found in the blood of Western women. We have now measured the concentrations of both ADIOL and the estrogen receptor (ER) in the nuclear fraction (800 g pellet) of 89 primary human mammary tumors. No difference was found in nuclear ADIOL concentrations in tumors from 45 pre- and 44 postmenopausal women. Significantly higher nuclear ADIOL concentrations were found in 49 ER negative tumors compared to 40 ER positive tumors (P < 0.005). A similar relationship applied in the postmenopausal group (P = 0.01) and the premenopausal group, but in this latter instance failed to reach significance (P = 0.1). In ER positive tumors there was no correlation between ADIOL and ER nuclear levels. ADIOL was present in the total particulate fraction (100,000 g pellet) at twice the concentration found in the nuclear 800 g pellet and again no difference was found in its concentration in tumors from 20 pre- compared to 34 postmenopausal women. Dehydroepiandrosterone was also measured in the 800 g fraction of 45 tumors and its concentration, which was some 10-fold higher than ADIOL and significantly correlated with that steroid, was again independent of menopausal status. The higher concentration of C19-5-ene-steroids in ER negative cellular fractions could be due to differences in their metabolism; ER negative tumors either lack, or possess very low levels of, hydroxysteroid sulfotransferase which catalyzes formation of sulfate esters of C19-5-ene-steroids previously observed to be major metabolites produced by ER positive cells. Higher concentrations of free steroids in ER negative cells would then be available for combination with membranes and non-specific binding sites throughout the cell.

Contribution of aromatase to the deoxyribonucleic acid synthesis of MCF-7 human breast cancer cells and its suppression by aromatase inhibitors

We have studied the effects of various steroids on DNA synthesis in MCF-7 human breast carcinoma cells, which have aromatase activity and which exert an oestrogen receptor-mediated growth, to assess the significance of intracellular aromatase on growth stimulation as well as inhibition by aromatase inhibitors. The cells were cultured for 96 h in phenol red-free medium containing 10% charcoal-treated fetal bovine serum and test reagents and pulse-labelled with [3H]thymidine. Physiological concentrations of oestradiol, oestrone, testosterone (T) and androstenedione (AD) stimulated thymidine incorporation. However, oestrone-sulphate and dihydrotestosterone (DHT) only stimulated at concentrations greater than the physiological levels. T and DHT stimulation was blocked by tamoxifen, but not by cyproterone acetate, suggesting that the stimulation was mediated via the oestrogen receptor but not by the androgen receptor. Stimulation by T and AD was reduced by aminoglutethimide and 14 alpha-hydroxy-4-androstene-3,6,17-trione, both of which inhibit aromatase activity, however, stimulation by nonaromatizable DHT was not reduced by the inhibitors, suggesting that androgens were converted by the intracellular aromatase to oestrogens which stimulated the thymidine incorporation. It is suggested that intracellular aromatase significantly contributes to the stimulation of DNA synthesis and that aromatase inhibitors suppress the stimulation.

Differential effects of diethylstilbestrol and estradiol-17 beta in combination with testosterone on rat prostate lobes

Treatment of Noble rats with separate silastic implants containing testosterone (T) and estradiol-17 beta (E2) for 16 weeks has previously been shown to induce multifocal epithelial dysplasia, a putative preneoplastic lesion, consistently in the dorsolateral prostate (DLP) but not in the ventral prostate (VP). We now studied effects of diethylstilbestrol (DES) substituted for E2 on these prostate lobes under the same conditions of exogenous androgen support. Three-week treatments with one 1-cm-long silastic implant of E2 or DES were approximately equipotent in changing target-organ weights and plasma prolactin. Accordingly, rats received for 16 weeks one 1-cm-long E2 or DES implant and two 2-cm-long T implants. In contrast to T + E2, T + DES induced widespread multifocal VP dysplasia and less or no DLP dysplasia. A serum-free explant-culture assay was used to determine uptake and metabolic disposition of 3H-labeled 5 alpha-dihydrotestosterone (DHT), T, and E2. Dysplastic VP explants incubated with 1.7 microM 1 beta-3H-labeled DHT and T accumulated more 3H-labeled steroid, metabolized 69 and 50% less substrate to terminal hydroxylated metabolites, and thereby formed and retained up to eight times as much estrogenic metabolite 5 alpha-androstane-3 beta,17 beta-diol (3 beta-androstanediol) and its lipoidal derivative than control VP. Experimental DLP explants did not form or retain more 3 beta-[3H]androstanediol than control DLP irrespective of treatments. Control VP metabolized [2-3H]E2 more actively to estrone than DLP. Dysplastic VP, however, metabolized one-half and accumulated five times as much E2 as VP and did not release more 3H as a marker of the 2,3-catechol estrogen pathway. These data suggest that differential target-tissue bioavailability of the estrogen component of the protracted dual-hormone stimulus determines in which prostate lobe dysplasia develops.

Interactions between estrogens, androgens, progestins, and glucocorticoids in ZR-75-1 human breast cancer cells

The human breast cancer cell line ZR-75-1 possesses androgen, estrogen, progesterone, and glucocorticoid receptors, thus offering a good model to study the specific role of each class of steroids in the control of breast cancer growth. Although the stimulatory action of classical estrogens (E2 and estrone) is well known, we have found a potent mitogenic effect of the adrenal estrogen androst-5-ene-3 beta,17 beta-diol (delta 5-diol) at concentrations within the range of those found in the serum of adult women, thus suggesting that delta 5-diol might be the most important estrogen in women. Androgens, on the other hand, exert a potent inhibitory effect on basal ZR-75-1 cell growth and completely reverse the stimulatory effect of estrogens on the same parameter. The antiproliferative effect of androgens was completely prevented by the antiandrogen OH-FLU, thus suggesting an action mediated by the androgen receptor. Part of the effect of androgens can be explained by the marked inhibition of estrogen receptor binding and mRNA levels by androgens. The antiproliferative effect of androgens is additive to that exerted by antiestrogens. Progestins, on the other hand, exert a specific antiproliferative effect in the presence of estrogens, the effect of progestins being antagonized by the stimulatory action of insulin on cell growth. Medroxyprogesterone acetate (MPA), a compound frequently used in the treatment of breast cancer in women, exerts its main inhibitory action through an androgen receptor-mediated action, whereas its glucocorticoid-like activity could play an additional role at high concentrations. All four classes of steroids are present, to various extents, as lipophilic esters of long-chain fatty acids. It is of interest to mention that all steroids that inhibit ZR-75-1 breast cancer cell growth (androgens, progestins, and glucocorticoids) stimulate the secretion and mRNA levels of gross cystic disease fluid protein-15 (GCDFP-15), whereas estrogens have the opposite effects, thus suggesting that GCDFP-15 could well be a good marker for monitoring the response to androgens, progestins, and antiestrogens during the course of breast cancer therapy.

Wide spectrum of steroids serving as substrates for the formation of lipoidal derivatives in ZR-75-1 human breast cancer cells

Recently, several natural steroids have been found to be esterified to long-chain fatty acids (FAE) in various mammalian tissues. The purpose of the present study was to determine the ability of a series of 3H-labeled steroids to serve as substrates for the formation and accumulation of such non-polar derivatives in intact cells, using the hormone-responsive ZR-75-1 human breast cancer cell line as model. All 14 steroids tested were found to be converted, directly or following further metabolism, to lipoidal ester derivatives. The percentage of intracellular steroids recovered as FAE derivatives was usually substantial (14-90%), especially in the case of C-19 steroids (75-90%). The composition of the lipoidal steroid fractions recovered from the labeled cell extracts was characterized by chromatographic comparison with synthetic steroid FAEs and by saponification of the steroid FAEs and identification of the released steroidal moieties. Following metabolism, most steroid substrates were converted into multiple lipoidal esters. Furthermore, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol, as well as androst-5-ene-3 beta, 17 beta-diol formed lipoidal diesters in addition to the monoester form. The high level of intracellular steroid FAE accumulation reported in this study suggests that these yet poorly known steroid derivatives may play important functions in the regulation of steroid hormone metabolism and action.

Estrogen-like effect of 5-androstene-3 beta,17 beta-diol on the induction of fetal thymidine kinase in the rat uterus

The action of 5-androstene-3 beta,17 beta-diol (Adiol) on Thymidine Kinase (TK) was studied in the rat uterus. It appeared that Adiol, like 17 beta-estradiol (E2), could induce the synthesis of the fetal isoenzyme of TK. Its effects compared with those of E2, were delayed by 6 h and higher doses were required to reach the same levels of induction. The action of Adiol on TK was exclusively observed in tissues where E2 receptors were present. Moreover, Adiol could stimulate the activity of uterine DNA-polymerase alpha. These observations are additional evidence of the estrogen-like behaviour of Adiol. They suggest that it could participate in proliferative processes of tissues which are dependent on estrogens.

C19 adrenal steroids enhance prostaglandin F2 alpha output by human endometrium in vitro

Dehydroepiandrosterone sulfate significantly increased prostaglandin F2 alpha output by fragments of human secretory endometrium during the first and second 24-hour periods of incubation in Ham's F-10 medium containing 10% charcoal-treated calf bovine serum. The effects of dehydroepiandrosterone sulfate were noted at 10(-6) mol/L concentrations, which are close to the normal plasma levels of this compound. For the purpose of comparison, the effects of estradiol at 10(-8) mol/L and those of unconjugated dehydroepiandrosterone, dehydroepiandrosterone acetate, 5-androstene-3 beta, 17 beta-diol, or 5 alpha-dihydrotestosterone were evaluated at 10(-8) to 10(-8) mol/L concentrations in parallel experiments. All of the delta 5-C19 steroids tested enhanced prostaglandin F2 alpha output at 10(-6) mol/L but not at 10(-8) mol/L; 5 alpha-dihydrotestosterone was inactive at 10(-6) mol/L but showed a stimulatory effect at 10(-5) mol/L in two experiments. The stimulation of prostaglandin F2 alpha production by the adrenal steroids was significantly reduced by the antiestrogen 4-hydroxytamoxifen at 10(-6) mol/L (a finding consistent with the reported utilization of the estrogen receptor for their actions on other systems) but was not affected by the antiandrogen 4-hydroxyflutamide at 10(-6) mol/L. Progesterone (10(-7) mol/L) also lowered the effects of dehydroepiandrosterone (10(-6) mol/L) and 5-androstene-3 beta,17 beta-diol (10(-6) mol/L), as well as those of estradiol (10(-8) mol/L). delta 5-C19 steroids at 10(-6) mol/L levels did not antagonize the effect of 10(-8) mol/L estradiol, whereas 5 alpha-dihydrotestosterone reduced it by 50% at these concentrations. The significant effect of 5 alpha-dihydrotestosterone points to potential antiestrogenic effects of the C19 compounds that may be manifested in vivo at particular C19/estradiol concentration ratios. The demonstration of direct estrogenic effects of delta 5-C19 steroids, which are not significantly converted to estrogens in vivo, justifies their use in estrogen replacement preparations and indicates that aromatase inhibitors may not eliminate completely the stimulation of estrogen-responsive breast and endometrial tumors by the patient's adrenal steroids.

Full oestrogenic activity of C19-delta 5 adrenal steroids in rat pituitary lactotrophs and somatotrophs

Oestrogens are known to exert specific stimulatory effects on basal and dopamine (DA)-inhibited prolactin (PRL) release as well as on PRL cell content in rat adenohypophysial cells in primary culture. Recently, we have demonstrated that classical oestrogens increase growth hormone (GH) release and cellular GH content in rat pituitary somatotrophs. Since there is evidence that 5-androstene-3 beta, 17 beta-diol (delta 5-diol), a metabolite of dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S) can induce typical oestrogenic responses in target tissues, we have investigated the effect of C19 adrenal steroids and compared them to that of 17 beta-oestradiol (E2) on the above-indicated parameters. Following a 72-h incubation, maximal concentrations of E2, delta 5-diol and DHEA caused a similar increase in PRL cell content at respective EC50 values of 0.020, 14 and 115 nM. The sensitivity of lactotrophs to DA action was decreased by approximately 4-fold after a 48-h exposure to maximal concentrations of delta 5-diol or DHEA. The time course of the antidopaminergic effect of delta 5-diol and DHEA was almost superimposable to that of E2. A 72-h incubation with 5 microM DHEA-S, a concentration within the range of blood levels found in women, doubled (P less than or equal to 0.001) cellular PRL accumulation. On the other hand, androstenedione (delta 4-dione) was without effect on any of the parameters measured. All stimulatory effects induced by maximal effective concentrations of delta 5-diol, DHEA or DHEA-S were competitively inhibited by simultaneous incubation with the antioestrogen LY156758. The amplitude of the stimulatory effects of delta 5-diol and DHEA on GH cell content as well as on spontaneous GH-releasing factor (GRF)-induced GH release was superimposable to that observed with E2. The effect of the steroids on GH cell content was exerted at 0.016 nM (E2), 12 nM (delta 5-diol) and 250 nM (DHEA). Simultaneous incubation with LY156758 completely blocked the effect of maximally effective concentrations of E2, delta 5-diol and DHEA in somatotrophs. Furthermore, a physiological concentration of DHEA-S (5 microM) enhanced spontaneous as well as GRF-induced GH release. On the other hand, delta 4-dione as well as testosterone and dihydrotestosterone did not alter GH release. The present data demonstrate that delta 5-diol, DHEA and DHEA-S can exert full oestrogenic effects in lactotrophs and somatotrophs, thus supporting their potential oestrogenic role under both physiological and pathological conditions.

Adrenal C19-5-ene steroids induce full estrogenic responses in rat pituitary gonadotrophs

Previous studies have shown that the C19 adrenal steroid 5-androstene-3 beta, 17 beta-diol (5-ene-diol), a metabolite of dehydroepiandrosterone (DHEA), can stimulate typical estrogenic responses in target tissues. Since estrogens are known to cause a specific stimulatory effect on LHRH-induced LH release in rat anterior pituitary cells in culture, we have taken advantage of the precision of this system to study the effect of 5-ene-diol or DHEA on this precise estrogen-sensitive parameter. Pretreatment for 48 h with 17 beta-estradiol (E2), 5-ene-diol or DHEA induces a 2.4-, 2.7- and 2.6-fold stimulation of LH release induced by 0.3 nM LHRH, the effect being exerted at respective 50% maximally effective concentrations (ED50 values) of 0.015, 45 and 115 nM. Following a 48-h preincubation with 10 nM E2, 1 microM 5-ene-diol or 1 microM DHEA, the maximal LH and FSH responses to LHRH are increased by approx 50% above control. On the other hand, the sensitivities of the LH and FSH responses to LHRH as assessed by ED50 values of LHRH action are increased by 3.3- to 7.5-fold. As further proof of the estrogenic nature of the effect of 5-ene-diol and DHEA, the effects of E2, 5-ene-diol and DHEA are inhibited competitively by simultaneous incubation with the antiestrogen LY156758 (keoxifene). The 2-fold stimulation of LHRH-induced LH release caused by DHEA-S, at concentrations within the range found in the plasma of women, is also completely blocked by 120 nM LY156758. In direct binding studies, 5-ene-diol and DHEA or DHEA-S have approx 85- and greater than 10,000 lower affinities than E2, respectively, for the estrogen receptor in rat anterior pituitary homogenate and human breast carcinoma cytosol. The present data clearly show that 5-ene-diol, DHEA and DHEA-S can exert full estrogenic activity in rat gonadotrophs, thus supporting the potential estrogenic role of these C19 adrenal steroids in estrogen-dependent processes, especially breast cancer.

The metabolism of 19-nor contraceptive progestins modulates their biological activity at the neuroendocrine level

In this communication, a series of studies from our laboratory dealing with the mechanism of action of 17 alpha-ethinyl derivatives of 19-nor testosterone are reviewed. The administration of norethisterone (NET) to long-term castrated female rats induces the nuclear translocation of pituitary estradiol receptors and is followed by some estrogenic-like effects at the hypothalamic-pituitary unit. It is established that an A-ring reduced metabolite of NET, the 3 beta,5 alpha-tetrahydro NET derivative, is responsible for the observed in vivo estrogenic effects of the parent compound. 3 beta,5 alpha-NET binds to the estrogen receptor and is efficient in inducing the pituitary estrogen-dependent progesterone receptor and in increasing the uterine weight in long-term castrated rats. Furthermore, administration of 3 beta,5 alpha-NET and the 5 alpha-reduced metabolite of NET (5 alpha-NET) are able to inhibit the release of gonadotropins in the castrated animal to a greater extent than NET. Moreover, pretreatment with tamoxifen, an estrogen binding site competitor, results in a significant diminution of the antigonadotropic potency of 3 beta,5 alpha-NET but not of the 5 alpha-NET, which is only inhibited by the administration of cyproterone acetate. These findings underline the importance of the metabolic rate of NET for the expression of its biological effects at the hypothalamic-pituitary unit.

Induction of progesterone receptor by androgens in the mouse uterus

The comparative abilities of 3 naturally occurring androgens to compete for [3H]estradiol-17 beta ([3H]E2)-binding sites in uterine cytosol and to induce uterotrophic responses in immature female mice have been investigated. 5 alpha-Androstane-3 beta,17 beta-diol (3 beta-diol), 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-diol) and 5-androstene-3 beta,17 beta-diol (delta 5-diol) are all effective at diminishing cytoplasmic [3H]E2 binding. Their relative effectiveness are in the order of 3 beta-diol greater than delta 5-diol = 3 alpha-diol. When these steroids were injected intramuscularly (two 100-200 micrograms injections) into immature female mice (21 days old), they induced similar elevations of uterine dry weight, water content, cytosolic estrogen (ER) and progesterone (PR) receptor contents, and nuclear ER content as did estradiol-17 beta (E2). 3 beta-Diol was the most effective steroid at inducing cytosolic and nuclear ER, and PR production in mouse uterus. Followed in effectiveness was delta 5-diol and 3 alpha-diol. Unexpectedly, 3 beta-diol was found to be more potent than E2 in stimulating uterine ER and PR increases. Nonetheless, the androgens are poorer stimulators of uterine dry weight increase and water retention than E2 is. These results indicate that the androgens may interact with the ER system in the uterus to bring about the uterotrophic responses and 3 beta-diol is a more estrogenic steroid than delta 5-diol and 3 alpha-diol in the mouse uterus.

Changing concepts of active androgens in blood

We have provided a brief historical review of developments in our understanding of the endocrine mechanisms underlying the expression of androgen action in women. An alternative to the free hormone concept is considered which proposes that, at least in some target cells, androgens bound to SHBG are the biologically relevant molecules. In nearly every instance, the changes in blood levels of SHBG that have been observed are consistent with this idea. At present there are only bits of direct evidence to support the hypothetical mechanism proposed. As already mentioned, control of androgen action at the level of cellular uptake would provide obvious advantages as well as a potential mechanism to explain the antagonism between androgens and oestrogens which is still a mystery. It is important to note that the proposed mechanism is not obligatory for androgen or other steroid hormone action. Synthetic steroids which do not bind to SHBG or CBG clearly can gain access to target cells by simple diffusion and bind to intracellular receptors. Compounds such as methyltestosterone and dexamethasone are metabolized much more slowly than their natural counterparts and therefore are cleared slowly from the circulation. It is possible that the well-known difficulties in selecting appropriate therapeutic regimens with such compounds is related to the fact that they bypass an important regulatory step in steroid hormone action-modulated entry into target cells. Hopefully, the recent development of powerful new tools of molecular endocrinology will hasten the answer to the question: What is the active androgen in blood?

Evidence that a non-aromatizable metabolite of norethisterone induces estrogen-dependent pituitary progestin receptors

Neutral reduced metabolites of norethisterone (NET) specifically interact with intracellular estrogen receptors in target organs. To determine if this interaction can effectively initiate estrogen-dependent cellular responses, the effects of an A-ring-reduced NET derivative upon the induction of cytosol-located pituitary progestin receptors (PR) and uterine growth were studied in adult castrated female rats. Different doses of 17 alpha-ethynyl-5 alpha-estran-3 beta, 17 beta-diol (3 beta, 5 alpha-NET) were s.c. administered to ovariectomized animals for 6 days. 17 beta-Estradiol (E2) and oil-treated rats served as experimental controls. Pituitary PR were labeled in vitro by a post-gradient technique using [3H]ORG-2058 as the ligand. PR binding specificity was determined by the use of an excess of radioinert steroids. The results demonstrated that administration of 3 beta, 5 alpha-NET induced specific 8-9S pituitary cytosol PR in a dose-dependent manner. Binding properties of the 3 beta, 5 alpha-NET-induced progestin binding sites (Kd = 1.0 X 10(-9) M; NBS = 1.2 X 10(-9) M) appear indistinguishable from those induced by E2. In addition, 3 beta, 5 alpha-NET administration resulted in a significant increase in uterine weight at the expense of myometrium and endometrium growth in a similar fashion to that observed in the E2-treated group. When 3 alpha, 5 alpha-epimeric alcohol (3 alpha, 5 alpha-NET) was administered, induction of pituitary PR and uterine growth were also observed although to a lesser extent. Inasmuch as the results demonstrate that neutral non-aromatizable NET metabolites induce biochemical and morphological estrogenic responses, they offer an alternative explanation for the mechanism of estrogen-like action of this synthetic contraceptive progestin.

Concentrations of 3 beta-hydroxy androgens in epithelium and stroma of benign hyperplastic and normal human prostate

Androgen metabolites with 3 beta-hydroxy configuration--ie, dehydroepiandrosterone (3 beta-hydroxy-5-androsten-17-one, DHEA), 5-androstene-3 beta-17 beta-diol (A-Diol), and 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-Diol)--were measured by radioimmunoassay in the homogenate, in the mechanically separated epithelium and stroma, and in the nuclear fractions of epithelium and stroma of benign hyperplastic (BPH) and normal human prostatic tissue, in muscle homogenates and in plasma. The main results were: 1) Mean prostatic DHEA, A-Diol and 3 beta-Diol were 6-7 times as high as plasma values (1 g = 1 ml). Compared to muscle, prostatic values were more than tenfold higher. 2) The values in homogenates of BPH and normal prostate were not statistically different (pmol/mg DNA, mean +/- SEM, BPH: DHEA 46.8 +/- 7.2, n = 11; A-Diol 5.7 +/- 1.2, n = 12; 3 beta-Diol 3.7 +/- 0.6, n = 13; normal prostate: DHEA 56.0 +/- 5.5, n = 2; A-Diol 7.4 +/- 2.4, n = 5; 3 beta-Diol 5.8 +/- 1.7, n = 5). 3) In the nuclear fractions of epithelium and stroma the values were low compared to the homogenates and could not be discriminated from unspecific retention. Although we could not demonstrate either a specific retention of the 3 beta-hydroxysteroids in the nuclei or conclusive differences in steroid accumulation between epithelium and stroma of BPH and normal prostate, which could explain the development of the disease, the high levels in the tissue particularly of A-Diol would be compatible with estrogenic action at the prostate level.

Effect of dextran-coated charcoal treatment on 17 beta-estradiol receptor in human benign prostatic hyperplasia

Using glycerol density gradient centrifugation technique, single saturation dose assay, and Scatchard plot, the effect of dextran-coated charcoal (DCC) treatment of homogenate or crude cytosol on estradiol binding protein in human benign prostatic hyperplasia was investigated. Receptor binding is increased after thirty minutes DCC treatment of homogenate or cytosol. Increase in estradiol binding is accompanied by loss in cytosolic protein. A 75 per cent increase in binding of estradiol to its receptor was observed after two hours incubation of DCC with homogenate. The concomitant increase in estradiol binding and decrease in protein concentration in both homogenate or cytosol after DCC treatment indicate the possible removal of some protein(s) which inactivate(s) the estradiol receptor. Removal of cofactors required for activation of proteases and removal of endogenous steroids which could be occupying the estradiol sites also are possible. This simple experimental procedure has improved significantly the methodology for the measurement and characterization of estrogen receptor in human BPH.

Hormonal effects on the estrogen receptor system in the epididymis and accessory sex organs of sexually immature rabbits

The epididymis and male accessory sex organs (vesicular gland, prostate, and bulbourethral gland) of sexually immature rabbits contain a functional estrogen receptor system which is regulated in an organ-specific manner by various hormones. In both intact and castrated animals, acute estrogen challenge causes depletion of estrogen receptor from the cytosolic fraction and its appearance in the nuclear fraction of these tissues. A considerable amount of unoccupied nuclear receptor was detected both before and after estrogen challenge. An estrogen-activated, receptor-processing mechanism is operable in these organs since chronic treatment (daily for 14 days) with estradiol benzoate modified the levels of total estrogen receptor, and altered the relative amounts of occupied to unoccupied nuclear receptor present following estrogen challenge. Chronic treatment with estradiol benzoate, Tamoxifen, and testosterone propionate (alone and in combination) had differential, organ-specific effects on the ability of subsequent estrogen challenge to cause accumulation of nuclear receptor. The vesicular gland was the most responsive to estrogen treatment and the bulbourethral gland the least responsive.

Studies on the effects of dehydroepiandrosterone and its metabolites on attack by castrated mice on lactating intruders

Triads of castrated male mice (residents) were injected each day for 2 weeks with oil vehicle or 280 nmol of dehydroepiandrosterone (D). They were tested for their attack on a lactating female (intruder) introduced in their home-cage 2,24 or 48 hr after their last injection. D significantly reduced male aggressive behavior for at least 24 hr. Other groups of castrated males were injected each day with vehicle or 280 nmol of D, dehydroepiandrosterone sulfate (DS) or androstenediol (ADIOL). D, but neither DS nor ADIOL, significantly reduced their aggressive responses to intruders. Neural levels of D, DS and testosterone (T) were measured in intact males injected with vehicle or D. The concentration of D in brain was unchanged by castration and was increased about 20 fold in D injected males. The concentration of neural T was 10 nmol/g of tissue in intact males, was almost undetectable in castrated males, and was slightly increased in D injected males. Further work will be needed to identify the steroid molecule(s) responsible for this behavioral effect of D.

Stimulation by estradiol-17 beta of thymidine kinase activity in the rat uterus

The action of estradiol-17 beta (E2) on thymidine kinase (TK) activity was studied in uteri from immature female rats. It was demonstrated that a single injection of E2 highly stimulated the enzyme activity which reached its maximum level 24 h after hormone administration. Physiological amounts of E2 were efficient and changes in TK activity were observed exclusively in uterus and liver. A single injection of Tamoxifen produced the same effect as E2 but repeated administration resulted in the complete inhibition of enzyme activity. Using antibiotics it was demonstrated that E2 induced the synthesis of new enzyme molecules rather than an increase in enzyme activity. This statement was corroborated by the fact that after hormone administration the increase in TK activity was preceded by an increase in RNA-polymerase activity and followed by that in DNA-polymerase alpha activity. Moreover, the separation of TK isoenzymes on DEAE-Sephadex and the use of d-CTP as inhibitor of the adult isozyme suggested that E2 induced the "fetal" form of the enzyme. In addition, it was demonstrated that TK activity in uteri from ovariectomized adult female rats was enhanced by E2 administration, and that the increase was due to the stimulation of the fetal isoenzyme. It was suggested that TK could be used as a marker of the action of estrogens and antiestrogens in target organs.

Binding of estradiol and 5 alpha-androstane-3 beta-17 beta-diol by the male rat enriched gonadotrope cells

Dispersed pituitary cells from 42-day old male rats were separated using centrifugal elutriation. Based on LH and PRL cellular contents, fractionated cells were pooled into two fractions: "Lactotrope++ population" and "gonadotrope++ population". Estradiol and 5 alpha-androstane-3 beta, 17 beta-diol binding was measured in these fractions. Results revealed that: (1) The steroid receptors are not destroyed by cell dispersion and elutriation. (2) The estradiol receptor content is higher in gonadotrope++ cells than in lactotrope++ cells. (3) The number of binding sites for the two steroids changes in the different fractions: whereas it is exactly similar in "lactotrope++ population", it is much higher for estradiol than for 5 alpha-androstane-3 beta, 17 beta-diol in "gonadotrope++ population". These results suggest two different species--or conformations--of receptor binding sites for estradiol in the male rat pituitary; the first one could link both steroids, the second one would be specific for estradiol.

Androgen receptor-mediated inhibition of estrogen-induced uterine peroxidase

Flutamide, an anti-androgen known to act through the androgen receptor, abolished the inhibitory action of testosterone on the induction of peroxidase in immature rat uteri without affecting inhibition produced by progesterone. The time course of the androgen effect on estrogen-induced uterine peroxidase, uterine weight and glucose 6-phosphate dehydrogenase activity was also determined together with the effect of flutamide on these steroid hormone-sensitive parameters. The possible mechanism of action of these compounds is discussed, particularly in the light of estrogen-induced eosinophilia. It is proposed that the observed interaction between testosterone and estradiol is mediated through their own specific receptors and not by illicit occupation of the estrogen receptor by the androgen. 5-Androstene-3 beta, 17 beta-diol (Adiol), an androgen known to exert estrogenic effects through the estrogen receptor, induced uterine peroxidase and was without significant effect on the action of estradiol, in contrast to testosterone.

Binding and effects of 5 alpha-androstane-3 beta,17 beta-diol in the male rat pituitary

5 alpha-androstane-3 beta,17 beta-diol (Adiol) binds to cytosol proteins from male rat pituitary with a relatively high affinity (KD = 15 +/- 6 nM) and a low capacity (n = 92 +/- 8 fmol/mg protein). These saturable proteins which bind Adiol are characterized as estrogen receptor. This conclusion was based on the binding characteristics, the binding stereospecificity and the sedimentation coefficient in sucrose linear gradients. Moreover. Adiol induces, in vivo, the nuclear translocation of estrogen receptor and some effects of estrogen action. It is efficient to induce progesterone receptor and to increase pituitary protein content but inefficient to increase DNA synthesis. Results suggest a mechanism of Adiol action in the male rat pituitary similar to that observed with androgens in other target tissues. Moreover, the study of Adiol and 17 beta-estradiol binding suggests two forms of estrogen receptor in the cytosol from male rat pituitary. The maximal concentration of binding sites was observed at 22-30 days of age for E2 and at 37-42 days of age for Adiol. On the other hand, the nuclear ontogenic pattern suggested a single class of binding sites for E2 and Adiol in the pituitary nuclei.

Substituted derivatives of A-nor-5 alpha-androstane and A-nor-5 alpha-estrane--structure and affinity for hormonal receptors

The interactions of A-nor-5 alpha-androstane and A-nor-5 alpha-estrane derivatives with the estrogen and androgen receptors, have been evaluated by measuring their relative binding affinities (RBAs), under two sets of incubation conditions in order to discriminate between potent agonists from weak agonists with potential antagonist activities. Surprisingly some of these compounds which do not possess a phenolic hydroxyl group interact somewhat markedly with the estrogen receptor. This interaction is characteristic of weak estrogens, with potential anti-estrogenic activity (RBA values decreasing when increasing time and temperature of incubation). Results are in good agreement with data obtained in vivo. Moreover, some of these compounds interact also to some extent with the androgen receptor. Results will be discussed in order to outline some structure-activity relationships in these series.

Early in vitro stimulation of endometrial (Na+-K+)-ATPase by estradiol

Physiological concentrations of estradiol (2-10 nM) can approximately double the activity of the endometrical (Na+-K+)-ATPase in immature mammalians. This stimulation in vitro is optimum as early as 30 minutes after contact of uteri with the hormone and it is not inhibited by incubation with cycloheximide. Analogues of 17 beta estradiol have little effect on the enzyme activity, but another steroid hormone testosterone, is capable of a similar activating effect.