Studies on the uterine, cytoplasmic estrogen binding protein. Thermal stability and ligand dissociation rate. An assay of empty and filled sites by exchange

Interaction of estrogen-nitrosourea conjugates with the estrogen receptor in rat uterus

Several estrogen-nitrosourea conjugates have been synthesized with the aim of producing more selective cytotoxic agents. The conjugates were shown to compete with estradiol for binding to cytosolic estrogen receptor in rat uterus; the relative binding affinities for N-(2-chloroethyl)-N'-(3,17 beta-dihydroxyestra-1,3,5(10)-trien-17 alpha-yl)methyl-N-nitrosourea (17 alpha-CNU), N-(2-chloroethyl)-N'-(3-hydroxyestra-1,3,5(10)-trien-17 beta-yl)-N-nitrosourea (17 beta-CNU), and N-(2-chloroethyl)-N'-2,3-di(p-hydroxyphenyl)-pentanyl-N-nitrosoure a (HEX-CNU) were 2, 0.4, and 0.2, respectively, using a binding affinity of 100 for estradiol. In the ligand exchange assay, cytosolic receptors preloaded with 17 alpha-CNU and HEX-CNU were found to lose some of their estradiol (E2) binding sites, suggesting that binding to estrogen receptor (ER) may be irreversible. An increase of nuclear accumulation of ER was observed in the presence of 17 alpha-CNU and HEX-CNU. In the rat system, even at a 10,000-fold excess, these two agents failed to show any antagonism of the uterotrophic effect of E2 in vivo. The low binding affinity and instability of these conjugates may account for their lack of antiestrogen activity. On the other hand, 17 alpha-CNU at 100 or 1000 micrograms/day and HEX-CNU at 1000 micrograms/day demonstrated significant uterotrophic activity. This study did not resolve whether the stimulation of uterine growth was due to the parent estrogen-nitrosourea conjugate or to decomposition and/or metabolic products.

Estradiol regulation of the synthesis of uterine proteins with clusters of proline- and glycine-rich peptide sequences

Estradiol (E2) regulates the synthesis of uterine proteins at both the transcriptional and translational levels. E2 induces an increase in the specific amino acid acceptor activity of uterine tRNA, with the largest increases seen for proline, glycine and methionine. The synthesis of three uterine proteins that are rich in proline and glycine, estrogen receptor, progesterone receptor and glucose-6-phosphate dehydrogenase, is induced by E2. E2-induced increases in these proteins were preceded by an correlated with stimulation of tRNA acceptor activity for proline and glycine and these responses were specifically and simultaneously inhibited by prior azaserine treatment, which inhibits the E2-induced repair and synthesis of the 3'-CCA acceptor terminus of tRNAs. The high frequency and clustering of proline and glycine residues in estrogen receptor, progesterone receptor and glucose-6-phosphate dehydrogenase suggests that the translating ribosomes may slow down during synthesis of these proteins due to limiting levels of these tRNAs in E2-deprived uteri.

26-[125I]iodoponasterone A is a potent ecdysone and a sensitive radioligand for ecdysone receptors

The effects of ecdysone, the steroid molting hormone of arthropods, are of considerable interest both to insect physiologists and to those studying steroid-regulated gene expression. Yet progress in understanding ecdysone receptors has been inhibited by the lack of a suitable highly radioactive hormone analog with high affinity for the receptor. Here we report that the synthetic ecdysteroid 26-iodoponasterone A is one of the most active ecdysones known, inducing half-maximal morphological transformation in Drosophila Kc167 cells when present at 0.5 nM. 26-[125I]Iodoponasterone A can be prepared at a specific activity of 2175 Ci/mmol (1 Ci = 37 GBq) by reaction of the precursor 26-mesylinokosterone with carrier-free Na125I. The radiolabeled material binds to Kc167 cell ecdysone receptors specifically and with affinity (Kd ca. 3.8 X 10(-10) M). Thus, 26-[125I]iodoponasterone A appears to be a superior radioligand for ecdysone receptors on grounds both of affinity and of specific activity. Its ready availability should greatly facilitate studies of these receptors.

A study on the effect of a single dose of tamoxifen on uterine hyperaemia and growth in the rat

1 The effect of a single subcutaneous dose of tamoxifen on the rat uterotrophic response was investigated. 2 The parameters examined were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors. 3 Tamoxifen or its metabolites proved to be capable of eliciting a uterotrophic response of 35-42 days duration. The changes seen in uterine blood flow and weight are discussed in relation to oestrogen receptor distribution.

11 beta-chloromethyl-[3H]estradiol-17 beta: a very high affinity, reversible ligand for the estrogen receptor

It has been suggested that binding of 11 beta-chloromethyl estradiol (11 beta-CME2) to the estrogen receptor is irreversible, since its complex with receptor fails to undergo exchange with estradiol (E2). To investigate this behavior directly, 11 beta-CME2 was prepared in high specific activity, tritium-labeled form: The binding of [3H]11 beta-CME2 to the estrogen receptor from lamb and rat uterus and MCF-7 human breast cancer cells was shown to be fully reversible; the 11 beta-CME2 complex with receptor, as well as that of a structural analog 11 beta-ethyl estradiol, however, do not dissociate or exchange with [3H]E2 over a 22 h period at 25 degrees C. By competitive or direct binding assays, the affinity of 11 beta-CME2 for the estrogen receptor can be estimated to be as much as 10- to 30-fold higher than that of E2. The complexes of estrogen receptor from MCF-7 cells with [3H]11 beta-CME2 and [3H]E2 show identical velocity sedimentation profiles on sucrose gradients, under conditions when the receptor is either a monomer of a dimer. Because of its very high affinity and unusual dissociation kinetics, [3H]11 beta-CME2 should be a very useful ligand for studies of estrogen receptor dynamics and in the assay of estrogen receptor concentrations in tumors and tissues.

Discrete early changes in cellular subpopulations of rat uterine and anterior pituitary estrogen receptors in response to acute exposure to exogenous estradiol

Distribution of estrogen receptors among ligand-occupied and unoccupied species in cytosolic and nuclear subcellular compartments has been analyzed as an acute response to administration of 5 micrograms of estradiol in adult female rats. Patterns of anterior pituitary and uterine receptor turnover were monitored at intervals over a 5-h period, using either intact or 2-weeks ovariectomized animals. In terms of total cellular receptor content, initial levels were higher in castrate animals, but rapidly fell to intact levels within an hour following estradiol injection. Cycloheximide given shortly before estradiol had no effect on total pituitary receptor patterns, but appeared to result in an elevation in total uterine receptor content at early intervals. Unoccupied cytosol receptors were rapidly depleted and, with the exception of castrate pituitary samples, showed some replenishment within 5 h, all of which was cycloheximide-sensitive. Initially, occupied cytosol receptors were low in intact rats, but were present at levels approaching those of the unoccupied cytosol receptor forms in the ovariectomized rat tissues. Occupied cytosol receptor levels fluctuated in response to estradiol. Subpopulations of nuclear receptors, especially the unoccupied species, showed significant tissue specificity. In the uterus, unoccupied nuclear forms were initially present in high amounts, and the levels did not change in response to estradiol administration. In the pituitary, the levels of these receptors rose and subsequently fell over the 5-h interval. Cycloheximide conferred a similar biphasic response to estradiol upon the otherwise insensitive unoccupied nuclear forms of the uterus. Occupied nuclear receptors turned over completely during the 5-h study interval, with the kinetics being faster in the castrate than the intact tissues. Cycloheximide affected occupied nuclear forms of the uterus only, dramatically increasing their levels in response to estrogen and causing prolonged retention in the castrate animal model. Collectively, the cycloheximide effects on this system are consistent with early estrogen induction or stimulation of a protein which inhibits accumulation of occupied or unoccupied receptor species within the nucleus. This re-examination of all forms of cellular estrogen receptors as they fluctuate acutely in response to exogenous estrogen has revealed several heretofore undetected responses which must be incorporated into the overall scheme of early estrogen action.

Characterization of the in vitro stability of the rat hepatic receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The in vitro stability of the Ah receptor from rat hepatic cytosol was evaluated by [3H]TCDD binding studies, gel filtration, and sucrose density gradient ultracentrifugation. Thermal inactivation of unoccupied receptor followed first-order kinetics between 5 and 40 degrees C, with an estimated Ea for inactivation of approximately 35 kcal/mol. Protease inhibitors did not reduce and dilution slightly increased the inactivation rate at 20 degrees C. Recovery and 20 degrees C stability decreased with increasing ionic strength. The TCDD-receptor complex was less susceptible to degradation at 20 degrees C, even in the presence of 0.4 M KCl. Specific binding was markedly pH dependent, with maximum recovery at 7.6. Analysis of the pH curve suggested that cysteine sulfhydryl groups may be involved in TCDD binding. Dithiothreitol (1 mM) maximized recovery and 20 degrees C stability, and addition of the thiol largely reactivated binding sites lost from cytosol prepared without it. Removal of low molecular weight components of cytosol by gel filtration resulted in a rapid 20 degrees C inactivation rate that could not be lessened by dithiothreitol. Glycerol (10% v/v) and EDTA (1.5 mM) maximized recovery of specific binding, but both decreased 20 degrees C stability in a concentration-dependent manner. Calcium chloride (4 mM) increased stability at 20 degrees C by approximately 20%, and retarded the characteristic shift in sedimentation coefficient from approximately 9 to approximately 6 S in high-salt sucrose gradients. The fact that sodium molybdate (20 mM) decreased recovery and 20 degrees C stability when dithiothreitol was present but slightly increased stability in its absence suggested an antagonism between the two compounds. Molybdate mitigated the inactivation induced by 0.4 M KCl, an effect which may be related to the observation of dual peaks in molybdate-containing high-salt sucrose gradients. These data indicate that thermal inactivation of the unoccupied rat hepatic Ah receptor primarily may be due to physical rather than enzymatic processes; (ii) sulfhydryl oxidation, removal of low molecular weight cytosolic components, and high ionic strength result in rapid rates of inactivation at 20 degrees C; and (iii) the large degree of protection conferred by TCDD binding implies a very tight ligand-receptor interaction, and as such accords with TCDDs extraordinary potency and persistence in producing its toxic and biochemical effects.

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.

Temporal and receptor correlates of the estrogen response in sheep

Uterine blood flow and uterine cytosol and nuclear estrogen receptors were measured at critical times during estradiol-induced vasodilatation in acute anesthetized and chronic conscious sheep preparations at estradiol bolus injection frequencies from 1 to 24 hours. During acute experiments, the uterine blood flow response was muted and cytosol estrogen receptor replenishment did not occur whereas full replenishment occurred in 12 hours in conscious ewes. In ewes treated with daily estradiol that had a stable daily uterine blood flow response, the uterine blood flow response 24 hours after uterine biopsy was similar to the preoperative one. Analysis of the duration of peak uterine blood flow levels and the rate of uterine blood flow descent from peak levels showed that an interval of 18 hours between estradiol injections was necessary for the uterine blood flow response to approximate that observed after 24 hours. These observations suggest: (1) that uterine vascular receptor replenishment is delayed compared with that of the total uterus; (2) that operative stress compromises cytosol estrogen receptor metabolism and possibly nuclear estrogen receptor function; (3) that the delayed maximum uterine blood flow response to estradiol in ewes previously untreated with estradiol is due to a trophic uterine effect of daily estradiol stimulation.

Non-stoichiometric nuclear-cytoplasmic redistribution of estrogen receptor in adult rat uterus, following estradiol injection

In immature and ovariectomized rats acutely injected with estradiol (E2), accumulation of estradiol receptor complexes (E2R) from the uterine cytosol to the nucleus has been shown to be quantitative by numerous investigators. In the present study, translocation of E2R from the cytosol to the nuclear fraction in adult and ovariectomized estrogen prestimulated rats was analyzed. Twenty micrograms of E2, dissolved in saline containing 10% ethanol and 1 g% bovine serum albumin (B.S.A.) were injected intraperitoneally to the animals and 2 h later E2R in the cytosol and crude nuclear fractions were assayed by exchange techniques. Unlike a 91% recovery of the depleted cytosol E2R in the nuclear fraction of ovariectomized rats, only 39.2 and 27.5% were recovered in the adult and ovariectomized estrogen prestimulated rat uterus respectively. Moreover, depending on the temperature and duration of nuclear suspension incubation, from 18 up to 80% of the recovered nuclear E2R were solubilized in the incubation medium and nuclear post-incubation washes and could be measured by hydroxylapatite treatment (HAP). Saturation assays showed a plateau from 12 nM E2 3H onwards up to 80 nM. The Kd values computed for the receptors in the nucleus and HAP in all the three groups were of the order of 2 X 10(-9) M. In conclusion, after E2 administration to adult or ovariectomized estrogen prestimulated rats, a stoichiometric recovery of the depleted cytosol E2R in the nuclear fraction was not observed, even when leakage of nuclear receptor into the medium in course of exchange was taken into account. Chronic estrogenization appeared to modify the dynamics of uterine receptor.

Conformational and electrostatic properties of unoccupied and liganded estrogen receptors determined by aqueous two-phase partitioning

The technique of aqueous two-phase partitioning (ATPP) has been used to characterize conformational and electrostatic properties of unoccupied and liganded rat uterine estrogen receptors. The adaptation of the hydroxylapatite receptor assay with ATPP systems has permitted estrogen receptor (ER) partition coefficients to be accurately determined, even when the partitioning process results in significant loss of ER binding capacity. The pH and salt dependences of estrogen receptor partition coefficients indicate that the theory governing partitioning behavior can be accurately applied to partitioning data obtained with crude cytosols. This technique has revealed a ligand-induced change in the properties of the unoccupied receptor that precedes the process of heat-induced transformation in vitro. The difference in partitioning behavior between unoccupied and nontransformed estrogen receptor is observed in all combinations of buffers and salts tested and is of equal magnitude as the difference between partition coefficients of nontransformed and transformed ER. The partition coefficients of both unoccupied and nontransformed ER are constant over the ER concentration range in which binding cooperativity has been previously demonstrated. The combined effects of salt and pH on ER partition coefficients indicate a pI of approximately 5.5 for both unoccupied and nontransformed estrogen receptors. However, the partition coefficients at the pI differ. It is concluded that estradiol binding to its unoccupied receptor results in a change in surface properties of the ER monomer that is independent of receptor transformation and makes the receptor less hydrophobic.

Identification of immunoassayable estrogen receptor lacking hormone binding ability in tamoxifen-treated rat uterus

Using two different monoclonal antibodies to human estrogen receptor (ER), the enzymeimmunoassay was performed. The values of ER contents in human breast cancer and untreated rat uteri obtained by this procedure were correlated well with those by [3H] estradiol binding assay. When estradiol was injected to immature rats, the enzymeimmunoassay showed the uterine receptor dynamic pattern similar to those analyzed by exchange assays. In contrast, tamoxifen administration induced the immunoassayable but nonsteroid binding form of ER. This ER-like antigen was the heat-labile molecule with the sedimentation constant of 7 S while ER in untreated rat uterine cytosol sedimented at 9 S. These results suggest the presence of unique molecular state of ER induced by tamoxifen.

The formation at 37 C of a nondissociable receptor-estradiol complex

The receptor-estradiol complex formed in rat uterine cytosol when heated at 37 C converts from a dissociable to a nondissociable form. The conversion is best observed in cytosols pretreated with charcoal at 0 C which renders the subsequently formed receptor-estradiol complexes thermostable at 37 C. In the presence of dithiothreitol the heated complex remains dissociable. Tamoxifen does not form nondissociable complexes with the estradiol receptor. It is proposed that the nondissociable form of the receptor complex is a required phase in the mechanism of estradiol action.

HPLC separation of anti-estrogen and estrogen receptor binding components of mouse plasma

Proestrous mouse plasma and urine were subjected to diethyl ether extraction, enzyme hydrolysis and HPLC separation of estrogen components. Radioimmunoassay of the treated proestrous samples with a broad spectrum anti-estrogen serum failed to detect estradiol-17 beta, estrone or estriol. HPLC chromatograms contained two peaks of immunoreactive and estrogen receptor binding material with polarities between those of estriol and estradiol-17 beta. Similar peaks were detected in HPLC chromatograms of urinary extracts from ovariectomized and ovariectomized-adrenalectomized mice. The least polar of the two peaks produced a mass spectrum identical to that of authentic equol [7-hydroxy-3-(4'-hydroxyphenyl)chroman], a phytoestrogen metabolite. The presence of significant quantities of circulating equol in all strains studied, combined with apparently low plasma levels of endogenous classical estrogens during proestrus, confound attempts to study estrogen secretion in the mouse.

Testosterone-estradiol-binding globulin binds to human prostatic cell membranes

Specific binding sites for human testosterone-estradiol-binding globulin have been found on human prostatic cell membranes. Scatchard analysis reveals both a high and a low affinity binding site for [125I]testosterone-estradiol-binding globulin. The high affinity site is specific for testosterone-estradiol-binding globulin, whereas the low affinity site also binds human corticosteroid-binding globulin and human transferrin.

Replenishment of uterine estrogen receptor in chronically estrogenized rats

Replenishment of uterine estrogen receptor (ER) following a single injection of estradiol-17 beta (E2) was examined in chronically estrogenized rats. Subcutaneous implantation of E2-pellet for 7 days in ovariectomized rats resulted in a significant stimulation of uteri with regard to wet tissue weight, DNA content and progesterone receptor content, with a shift of ER distribution. An intraperitoneal injection of 5 micrograms E2 in the E2-implanted rats induced a significant decrease in soluble ER (from 141.1 +/- 12.6 to 69.2 +/- 8.8 fmol/mg protein) with a concomitant increase in nuclear ER (from 58.2 +/- 8.6 to 129.2 +/- 11.6 fmol/100 micrograms DNA) 1 h after the injection. However, soluble ER was rapidly replenished, which was accompanied by nuclear ER reduction, and both values returned to the pre-injection levels at 4 h after the injection. An administration of 150 micrograms cycloheximide, that effectively blocked protein synthesis in the uterus of the E2-implanted rats, completely inhibited the replenishment of soluble ER induced by 5 micrograms E2. These findings, combined with our previous findings that replenishment of ER following a single E2 administration in the pituitary of chronically estrogenized rats was inhibited by cycloheximide, suggest that replenishment of ER is entirely dependent on protein synthesis in chronically estrogenized rats.

Evaluation of microtitre plates for the routine assay of oestrogen and progesterone receptors in tissue extracts

A time- and material-saving assay of oestrogen and progesterone receptors in tissue extracts using enzyme-linked immunosorbent assay quality microtitre plates and microtitre-compatible equipment is described. The results from simultaneous determinations in microtitre plates and in conventional tubes show the former to yield higher receptor values. Furthermore, the results of a large series of measurements in microtitre plates compare favourably with previously obtained results from assays in tubes.

Progesterone-mediated suppression of estradiol receptors in cynomolgus macaque cervix, endometrium and oviduct during sequential estradiol-progesterone treatment

We used sequential treatment with implants of estradiol (E2) and progesterone (P) to create varied hormonal states in a group of spayed cynomolgus macaques. The reproductive tracts were removed, and nuclear and cytosolic estrogen receptors were analyzed in the cervical mucosa, endometrium, and oviducts. Nuclear receptor quantities were greater in tissues of E2-treated monkeys than in tissues of spayed animals. Sequential P treatment, even in the presence of continuous E2, decreased the amounts of nuclear and cytosolic E2 receptors. In the oviduct and endometrium, the P-mediated suppression of receptors occurred within 1 or 2 days. In the cervix, suppression occurred only if the serum P:E2 ratio was elevated to twice the amount (approximately 100:1) usually found during the luteal phase of the menstrual cycle (approximately 50:1) in this species. Of these three reproductive tract tissues, the cervix had the highest threshold for suppression by P of E2 receptors in the presence of E2.

Cryptic estrogen binding protein complicates analysis of estrogen receptor distribution

The response of rat uterine estrogen receptor sub-species to injection of 5 micrograms estradiol has been investigated in intact and 4-weeks' ovariectomized adult animals. Determinations of occupied and unoccupied receptor subcellular fluctuations reveal significant differences not detectable under standard assays which measure only total nuclear and unoccupied cytosolic receptors. Both animal models manifest a high level of unoccupied nuclear receptors which are inaccessible to estrogen. In contrast to the intact animal, uteri from castrate animals have a high level of occupied receptors in the cytosol, which remains high following estrogen exposure. Receptor processing occurs in the castrate, but not the intact, animal. The results demonstrate that traditional assays are complicated by the presence and simultaneous measurement of non-responsive receptor species which quantitatively differ widely among animal models and will give rise to an erroneous interpretation of the pattern of estrogen-induced turnover of its receptor.

Estrogenicity of coumestrol in the mouse: fluorescence detection of interaction with estrogen receptors

The estrogenicity of coumestrol, a fluorescent phytoestrogen, has been examined in murine uteri. Coumestrol competed with 17 beta-[3H]estradiol for binding to cytoplasmic estrogen receptors, caused cytoplasmic estrogen receptors to associate with chromatin in the nucleus, and induced progesterone receptors. By use of size-exclusion high-performance liquid chromatography (SEHPLC), the interaction of coumestrol with estrogen receptors was examined directly by monitoring the fluorescence associated with macromolecules having properties characteristic of estrogen receptors. These analyses were made possible by the addition of dimethylformamide to the elution buffer, at a concentration (7.5%) which improved recoveries but did not interfere with estrogen receptor binding. It was possible to detect fluorescent coumestrol at approximately 0.5 nM. All determinations were performed with preparations in which estrogen receptor activity was 3-10 nM. Exposure of these preparations to coumestrol (50 nM) resulted in the elution of increased fluorescent activity in the regions where estrogen receptors eluted during SEHPLC. This fluorescent activity was reduced when diethylstilbestrol, 17 beta-estradiol, hexestrol, or tamoxifen was present as a competitor (2 microM) but was unaffected by testosterone or progesterone. Diethylstilbestrol reduced fluorescence below endogenous base lines and thereby displayed a fluorescence quench property which was not observed with other ligands. When hepatic and renal estrogen receptor preparations were used, the injected receptor activity was observed to be the major limiting factor in detecting the interaction of coumestrol with estrogen receptors. These observations are relevant to attempts to visualize estrogen receptors in tumor cells and demonstrate that accepted biochemical criteria for ligand-receptor interaction can be satisfied when fluorescent ligands are examined.

RU 16117, an orally active estriol-like weak estrogen

RU 16117, the 11 alpha-methoxy derivative of ethynyl estradiol, is an orally active weak estrogen potentially effective in the treatment of estrogen-deficiency in postmenopausal women (climacteric symptoms and severe osteoporosis). Biochemical studies have shown that RU 16117, like estriol, possesses the properties characteristic of a partial estrogen agonist/antagonist. RU 16117 binds to the cytosol estrogen receptor (ER) to form a complex which dissociates much faster than the estradiol complex. This explains its lower nuclear uptake. Furthermore, the nuclear RU 16117 complex also dissociates faster than the estradiol complex. Consequently, although low doses of RU 16117 can induce the majority of the effects of estradiol (increased polymerase A and B activities, cytosol ER replenishment, progestin receptor induction, increased uterine weight), these effects are long-lived only if the dose is considerably increased or if the compound is administered repeatedly or continuously. Since RU 16117 transiently occupies available estrogen binding sites, it can prevent the full response of estradiol. Thus, under appropriate kinetic conditions, it acts as an estrogen antagonist on the above parameters and also on DMBA-induced mammary tumors in the rat. At a daily dose of 24 micrograms for a period of 4 weeks RU 16117 led to 65% reduction in the number of already-established tumors. RU 16117 inhibits basal gonadotropin secretion and decreases the LH response to LHRH. Injection of 5 micrograms s.c. to the rat in estrus markedly inhibited the spontaneous peaks of LH, FSH and PRL measured on the afternoon of expected proestrus. Low doses which block ovulation by 100% had no detectable effect on vaginal cornification, thus suggesting a greater sensitivity at the hypothalamo-pituitary level.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypothalamic-hypophyseal-gonadal axis in the streptozotocin-induced diabetic male rat

In the present work it was observed that the diabetic state alters the hypophyseal response to castration, without the expected increase in the LH serum levels, as found in the control rats. On the other hand, the stimulation of the hypophysis with LHRH resulted in a lower response in the case of the diabetic animal. The results presented herein are in good agreement with the finding of a reduction in the number of androgen binding sites and also with a diminished activity of the 5 alpha-reductase in the hypophysis from diabetic animals. The present results indicate an alteration in the hypophyseal gonadotropin production as well as in the overall process of hypophyseal response in experimental diabetes.

Analysis and properties of the cytosolic estrogen receptor from rat thymus

The equilibrium association constant, KA, and the number of receptor binding sites, Bmax, that characterize the estrogen receptor present in rat thymus were determined using five different methods of data analysis on binding data obtained using a dextran-coated-charcoal assay. The methods of data analysis consisted of fitting the binding data directly to the hyperbolic binding function, fitting the data to the Lineweaver-Burk, Scatchard, and Woolf transforms of the hyperbolic function, and the direct linear plot method of Eisenthal--Cornish-Bowden. The Woolf and Eisenthal--Cornish-Bowden methods gave identical results indicating that added estradiol caused a decrease in KA (competitive inhibition) and a marked decrease in Bmax (noncompetitive inhibition). The Scatchard analyses gave only a very qualitative indication of this trend, while the Lineweaver-Burk analyses gave no indication of any such systematic trend. The results from the computationally more difficult fits to the hyperbolic binding equation were in agreement with the Woolf and Eisenthal--Cornish-Bowden results. Thus, the cytosolic thymus estrogen receptor from the rat shows both competitive and noncompetitive inhibition in the presence of endogenous or exogenous estradiol.

Nuclear translocation of estradiol receptors by the in vivo administration of norethisterone: an alternate mechanism for gonadotropin inhibition

In order to investigate the anti-gonadotropic effect of norethisterone (NET) in long-term ovariectomized rats, we studied the interaction of this synthetic progestin with intracellular steroid receptors in the anterior pituitary by a nuclear exchange assay. The results demonstrated that the administration of NET to long-term ovariectomized rats resulted in nuclear translocation of estradiol cytosol receptors in the pituitary and uterus with a rate of accumulation and nuclear retention being similar in both tissues. Accumulation of nuclear estradiol receptors in the pituitary was in agreement with the rate of LH inhibition in NET-treated rats. The results presented in this communication may explain the anti-gonadotropic activity of NET in long-term ovariectomized rats in addition to its well known progestational activity.

Skeletal muscle cytosol [3H]methyltrienolone receptor binding and serum androgens: effects of hypertrophy and hormonal state

Normal, castrated, and hypophysectomized male rats underwent compensatory hypertrophy of plantaris muscles following surgical removal of their synergistic gastrocnemius muscles. The increases in muscle wet weights above control values, determined when the muscles were in stable-state hypertrophy, were as follows: normal 50%, castrated 50%, and hypophysectomized 32%. There were marked differences in concentration of serum androgens between surgical groups, yet no increases in testosterone or 5 alpha-dihydrotestosterone were observed as a result of hypertrophy. The amount of testosterone binding to serum proteins (approx 94%) was reduced only in hypophysectomized animals that underwent muscle growth. Cytosol androgen receptor specific binding (fmol/mg protein), measured using saturating concentrations of [3H]methyltrienolone (R1881) at 4 degrees C for 20 h for exchange with endogenous steroid, was significantly increased in hypertrophied muscles of normal, (1.77 +/- 0.17 vs 1.16 +/- 0.21), castrated (2.27 +/- 0.20 vs 1.46 +/- 0.03) and hypophysectomized (6.23 +/- 0.56 vs 3.64 +/- 0.30) animals. Receptor dissociation constants (Kd) were approx 10(-10) M in all groups and were not altered by the hypertrophy. These findings show that a major adaptation to skeletal muscle enlargement is an augmentation of cytosol [3H]methyltrienolone receptor binding capacity. This effect occurs in a normal or androgen deficient state.

Estrogen receptor translocation and replenishment in rat hypothalamus and pituitary gland after the application of catecholestrogen or nonsteroidal antiestrogen

The time course of nuclear translocation of estrogen receptors and the replenishment of cytosolic receptor concentrations in the pituitary gland and hypothalamus of ovariectomized/adrenalectomized rats after the application of a high dose (0.1 mg/animal) of the catecholestrogens, 2-hydroxyethynylestradiol or 4-hydroxyethynylestradiol, was identical to that seen after the application of the monophenolic estrogen 17 alpha-ethynylestradiol. A distinctly different pattern of receptor distribution between these cell compartments was observed after the application of the nonsteroidal antiestrogen monohydroxytamoxifen (ICI 79,280) resulting in a prolonged depletion of cytosolic receptor concentrations. It therefore seems unlikely that the proposed antiestrogenic properties of 2-hydroxyestrogens are the result of a blocking of cytosolic receptor replenishment but may be explained by a reduced intrinsic nuclear activity of estrogen receptors complexed with 2-hydroxyestrogens.

Gestational carcinoma of the female breast

Few neoplastic diseases can equal the amazing complexity and sheer perversity of carcinoma of the breast. No doubt as many decades of research lie ahead in its study as already have passed. Clinicians have long appreciated the special relationship of the disease to gestation. Diagnosis and treatment of breast cancer during pregnancy represent only a small part of this fascinating relationship. Although indispensable as research tools, animal models pertain to the human disease only in limited, ill-defined ways. The etiology of human breast cancer remains unclear; chemical, viral, hormonal, genetic, and immunologic theories have all been put forward as possibilities. Although gestation clearly alters both the initiation and growth of mammary tumors, its exact role in the various theoretical considerations remains a mystery. The obstetrician-gynecologist holds an important front-line position in the war against breast cancer, as does any provider of primary care to women, and, indeed, as do women themselves. Rather than decrease vigilance during pregnancy, the physician should pursue with extra vigor any breast mass discovered in the gravid patient, when the clinical examination is even less reliable than usual. The finding of a breast mass usually necessitates biopsy. Except for the inclusion of specific pregnancy-related problems, such as galactocele, the diagnostic spectrum of breast masses removed during pregnancy does not differ from that in nonpregnant women. The discovery of a highly suspicious breast mass, or the confirmed biopsy diagnosis of malignancy, in a pregnant patient should indicate the need for referral to a surgical oncologist versed in this unusual problem. The best approach to gestational breast cancer continues to be the team approach, with consultation from specialists in obstetrics, surgical oncology, anesthesiology, nuclear medicine, radiology, radiation oncology, pathology, and medical oncology. The age and general condition of the patient, the extent of the tumor, the stage of gestation, and the informed opinions of the patient and her spouse help to determine the therapeutic strategy. Careful staging not only guides present therapy but also the therapy of future victims through continued investigation. Most surgeons favor operation without delay if cure seems within reach. Mastectomy, with or without cesarean section, can be accomplished without detriment in the hands of a knowledgeable surgeon-anesthesiologist team. By following certain guidelines, the search for metastasis can be conducted safely and appropriately. The clinical situation occasionally may require the initiation of adjuvant radiotherapy or chemotherapy during pregnancy, by experienced consultants. Ongoing studies of tissue hormone receptors and cell kinetics will continue to give insight into the effects of gestational hormones on breast cancer and can aid in the selection of treatment options for the individual patient...

Chronic estrogen treatment causes an alteration in uterine estrogen receptor dynamics of rats

Estrogen receptor content and dynamics in the uteri obtained from chronically estrogenized rats were analyzed. 12 day treatment with a subcutaneous implantation of a diethylstilbestrol pellet resulted in maximal stimulation of uteri with regard to wet tissue weight, DNA content, as well as progesterone receptor content without significant alteration of the estrogen receptor level. Estrogen receptor dynamics in just ovariectomized or ovariectomized and diethylstilbestrol-stimulated rats elicited by a single injection of estradiol were next examined using the exchange methods. The cytosol receptor content rapidly declined, with a small and temporary accumulation of the nuclear receptor in the uterus from rats continuously exposed to diethylstilbestrol during the preceding 12 days. A relatively rapid cytosol receptor replenishment was also observed in rats pretreated with diethylstilbestrol. This was accompanied by a rapid decrease in the nuclear receptor level to 70% of the preinjection value at 5 h after estradiol administration. These data are in contrast to findings on uteri of ovariectomized and nonestrogen-treated rats, in which a single injection of estradiol resulted in a prolonged nuclear receptor retention and a delayed cytosol receptor replenishment. Adrenalectomy did not result in a significant change of receptor dynamic patterns, suggesting that adrenal steroids do not play a role in the alteration of receptor dynamics elicited by continuous stimulation with diethylstilbestrol. These observations suggest that a continuous exposure of rat uteri to the estrogen causes an altered regulation of estrogen receptor dynamics by the homologous steroid compared to those in chronically estrogen-deprived rats.

Stabilization of estradiol-receptor complexes by elimination of cytosolic factors

Treating mature rat uterine cytosol with dextran coated charcoal (DCC) for 2 hrs at 0-4C in the absence of ligand causes the subsequently formed receptor-estradiol complex to be stable at 37C. Receptor binding is increased by the DCC treatment for uteri excised at metestrus or diestrus but remains nearly unchanged for uteri obtained at proestrus or estrus. Results suggest that the DCC removes or inactivates factor(s) present in the cytosol which render the receptor complex thermolabile.

Resolution of two fractions of androgen receptor from mouse kidney

Putative androgen receptors from mouse kidney were separated and re-chromatographed on DNA-cellulose columns. With either [3H]-dihydrotestosterone or [3H]-testosterone as ligands, two major fractions of androgen receptors were obtained in both elutions from DNA-cellulose columns; these eluted, respectively, at 140-150 mM NaCl (lower-salt) and 180-190 mM NaCl (higher-salt). Therefore, the two major peaks detectable with extracts of mouse kidney result from differences that are intrinsic to the receptor complexes rather than heterogeneity of the DNA-cellulose matrix. These findings are discussed in relation to two forms of androgen receptors that exist in a different proportion in extracts of brain and in relation to other steroid receptors.

Steroid receptors in rat uteri: postmortem retention of specific binding functions in crude tissue preparations

Steroid receptor measurement by steroid binding analysis is a clinically useful procedure. The determination of steroid binding by specific receptors is thought to reflect the biological status of the test specimen and thereby aid prediction of patient response to endocrine therapy. The need for rapid excision of a specimen and transfer to a cold environment is believed necessary to allow reliable receptor evaluation. The optimal method of processing specimens for receptor assays, however, remains to be determined. This article reports our results on the hormone specific binding functions of rat uterine estrogen and progesterone receptors in relation to their time postmortem in situ. Steroid binding by inactive (cytoplasmic) and activated (nuclear) receptors and the processes of receptor transformation, translocation and nuclear association have been studied. Contrary to generally held notions, our results indicate that the binding functions were not altered up to 1.5 hours postmortem in situ relative to their behavior in incubation media at 2 degrees C. Thus, this apparent stability of the steroid receptors, in situ, allows greater freedom in the procurement of tissues for receptor analyses in clinical and basic research studies.

Characterization of the cytosolic estrogen receptor in rat skeletal muscle

A charcoal assay and the synthetic estrogen [6,7-3H]R 2858 (17 alpha-ethynyl-11 beta-methoxyestradiol-17 beta) were used to show that rat skeletal muscle cytosol contains an estrogen receptor, which was characterized with regard to association and dissociation rate-constants at several temperatures. The degradation kinetics was also studied, and was more rapid in the absence than in the presence of ligand. Association, dissociation and degradation were all temperature-dependent. The apparent equilibrium dissociation constant (Kd), however, was not temperature-dependent, and was about 0.1-1.0 nM, whether calculated from the rate constants or determined by Scatchard analysis. Estradiol-17 beta and R 2858 were compared as ligands for Scatchard analysis; the maximum number of binding sites being about the same (120 and 110 fmol/g tissue, respectively, but the Kd was lower for estradiol-17 beta (0.16 nM) than for R 2858 (0.73 nM). Ligand specificity studies (using [3H]R 2858 as well as [3H]estradiol-17 beta) showed that R 2858 binds to an estrogen receptor in rat skeletal muscle. The estrogen receptor interacted both with heparin and with DNA covalently coupled to agarose, and was eluted from either column by NaCl. Chromatography of crude cytosol on heparin-agarose or DNA-agarose lead to an at least 10-fold or 25-fold purification of the estrogen receptor, respectively. DNA-agarose chromatography or ammonium sulfate precipitation did not separate the estrogen receptor from the androgen or glucocorticoid receptors in rat muscle.

Methodology for the synthesis and specific activity determination of 16 alpha-[77Br]-bromoestradiol-17 beta and 16 alpha-[77Br]-11 beta-methoxyestradiol-17 beta, two estrogen receptor-binding radiopharmaceuticals

16 alpha-[77 Br]-Bromoestradiol-17 beta (3a) has been synthesized from estrone enol diacetate (1) by bromination with Na77Br and hydrogen peroxide-acetic acid, followed by reduction with lithium aluminum hydride to give a mixture of 16 alpha-[77 Br]-bromoestradiol-17 beta (3a) and 16 alpha-[77Br]-bromoestradiol-17 alpha (3b) from which the desired epimer (3a) can be obtained in 50% overall radiochemical yield (from Na77Br) by HPLC. Analogous procedures can be used in the preparation of 16 alpha-[77Br]-bromo-11 beta-methoxyestradiol-17 beta. (4a) The effective specific activities of these radiopharmaceuticals, determined by binding to the uterine estrogen receptor, are 900-1500 Ci/mmol. Both have affinity and good binding selectivity for the estrogen receptor and are useful as imaging agents for mammary tumors.

The dissociation rate of estrogen receptor-ligand complexes is increased by high concentrations of steroids and antiestrogens

The first-order dissociation rate constant, k-, of estradiol from uterine estrogen receptor, measured kin the presence of micromolar concentrations of diethylstilbestrol, increased linearly over a large concentration range (0-300 microM) of diethylstilbestrol. The experimental K- measured appears to be the sum of a basal dissociation rate constant corresponding to the spontaneous dissociation in the absence of diethylstilbestrol, and a diethylstilbestrol-induced dissociation rate constant, which is proportional to both the diethylstilbestrol concentration and the inverse of the cytosol concentration. Diethylstilbestrol induced the dissociation of estradiol in all species studied (lamb, calf and rat) and of estrone and 2 antiestrogens in lamb uterus. Various steroids and triphenylethylene antiestrogens also efficiently induced the dissociation of estradiol from the estrogen receptor. However, the potency of these inducers, which varied greatly, was not correlated with the binding affinity for the estrogen receptor. Structural characteristics and the hydrophobicity of the inducers, however, did appear to be important parameters. The relative efficiency of inducers varied depending on the ligand that was bound to the receptor. This induced dissociation allows the complete dissociation of estrogen receptor-[3H]-ligand complexes in a short time (less than 24 h) at low temperatures without alteration of the level of [3H] ligand bound non-specifically and can therefore be used to measure the [3H] ligand bound to the receptor by exchange at 0-4 degree C. From the specificity and the high doses of inducers required to make possible the observation of a significant effect, we conclude that the induced dissociation probably does not have a biological role.

Rapid analysis of estrogen and progesterone receptors using gel-exclusion high-performance liquid chromatography

Estrogen and progesterone receptors prepared from mouse, rat, and human uteri, as well as from human breast cancers, have been characterized by gel-exclusion high-performance liquid chromatography. The qualitative relationships previously established by sedimentation analysis between the cytoplasmic [aggregated (approximately 8S), deaggregated (approximately 4S), and trypsinized (approximately 3.6S)] and nuclear (approximately 5S) forms of the rat uterine estrogen receptor were maintained by this technique. Differences in the partition of estrogen and progesterone receptors from the same species as well as interspecies differences in these receptors were reproducibly observed. Multiple forms of human estrogen and progesterone receptors could clearly be resolved in a single analysis and were distinct from serum steroid binding tissue contaminants. Separation analyses, performed at flow rates up to 2 mL min-1, were capable of resolving all receptor forms in 10--12 min with the column returning to base line in 25 min. With this exclusion gel column (TSK-G3000SW) as a background upon which to reference different receptor forms, eight distinct partitions or elution positions have been enumerated. This approach has considerable promise for the rapid characterization of different forms of steroid-receptor proteins. Moreover, it should provide a critical advantage in minimizing the opportunities for receptor modification during separation analysis and in maximizing the opportunity to study short-lived interactions between receptors and physiologic or pharmacologic ligands.