Nuclear Estrogen Receptor Levels Research Articles

Differential effects of aging on estrogen receptor dynamics in hypothalamus, pituitary and uterus of the C57BL/6J mouse.

Estrogen receptor (ER) dynamics and content were measured in the hypothalamus (HYPO), pituitary (PIT) and uterus (UT) of aging mice because of their potential importance to age-related changes in sensitivity to estrogen. Young (3-6 months), and old (22-24 months) C57BL/6J mice were injected with a dose of E2 (0.05 micrograms/10 g body wt) sufficient to achieve maximal levels of nuclear ER (ERn) in all tissues, and the rise and fall of ERn and the depletion and replenishment of cytosolic ER (ERc) were measured 0, 1, 2, 4, 8, 12 and 24 h later. Integrated areas under the ERn profiles in old HYPO, PIT and UT were reduced 34, 28 and 19%, respectively. These reductions were due to (1) lower levels of ERn throughout the profiles, (2) delays in attainment of peak ERn in UT and PIT, and (3) accelerated loss of peak ERn in HYPO. ERc levels were also reduced in old mice, and replenishment of ERc was delayed in old HYPO and PIT, but not in UT. Reductions in total ER (ERn + ERc) were sufficient to account for all reductions and altered dynamics of ERn, except for the delayed attainment of peak ERn in UT. These results indicate that levels and dynamics of nuclear ER are altered during aging, and that most of these changes are secondary to alterations in ER content and turnover rather than a reduced ability of ER to bind to nuclear sites.

Estradiol receptor in the lizard liver ( Podarcis s. sicula). Seasonal changes and estradiol and growth hormone dependence

This study shows that in the liver of the oviparous lizard, Podarcis s. sicula, the estrogen receptor (ER) level increases during the reproductive period (spring) when vitellogenesis occurs. This phenomenon interested both unfilled and filled ER present in the cytosolic and nuclear fractions. The increase in unfilled cytosolic and filled nuclear receptor was positively correlated to the plasma level of vitellogenin. The level of liver ER approximated that of mammalian liver ER and, therefore, it is higher than that reported for the liver of several nonmammalian species. At electrofocusing, liver ER distributes in two pH ranges (pH 6.5–7.5 and 8.0–8.8, respectively). The first form predominated in nuclei of reproductive females or of spayed estrogenized females and could represent the activated form of receptor. Ovariectomy was followed by a decrease in liver ER which can be induced in spayed females by estradiol administration. Pituitary growth hormone (GH) seemed to exert a synergic effect on estradiol liver estrogen receptor regulation. In lizards treated both with estradiol and GH, in fact, there was a significant increase in nuclear filled ER rather than an increase in the level of total nuclear ER.

Correlation between nuclear cytomorphometric parameters and estrogen receptor levels in breast cancer.

The authors studied the relationships existing between various cytomorphonuclear parameters recorded on 25 primary breast cancers and their estrogen receptor (ER) content. Cell image analyses of Feulgen-stained imprint smears, allowing determination of morphologic, densitometric, as well as textural parameters, were assessed by using the SAMBA 200 system (TITN, France). The ER levels were measured by the conventional dextran-coated charcoal assay. The authors then divided the 25 cancers into three categories: (1) "ER-negative or poorly positive tumors," i.e., those having less than 50 fmol ER/mg protein; (2) "ER-positive tumors," i.e., those containing between 50 and 150 fmol ER/mg protein; and (3) "ER highly positive tumors," i.e., those having more than 150 fmol ER/mg protein. The authors' results show that ER-negative or poorly positive breast cancers possess cells with bigger nuclei and higher DNA content, related to higher proliferation index than ER-rich tumors. Furthermore, the chromatin pattern of cells from ER-negative or poorly positive breast cancers is significantly more condensed than the thinly textured chromatin of ER highly positive tumors. Cell image analysis of Feulgen-stained imprints is proposed as an additional tool for grading malignancy.

Influence of neonatal diethylstilbestrol treatment on androgen and estrogen receptor levels in the mouse anterior prostate, ventral prostate and seminal vesicle

Perinatal exposure to the synthetic estrogen, diethylstilbestrol (DES), affects the structure of both male and female reproductive systems. Changes may also occur in the levels of steroid hormone receptors. Cytosolic and nuclear androgen and estrogen receptor levels (expressed per mg DNA) from the sex accessory glands of male BALB/c mice exposed neonatally to DES were analyzed by exchange assays. Neonatal DES exposure caused significant decreases in: (1) cytosolic androgen and cytosolic and nuclear estrogen receptor levels in the anterior prostate and (2) cytosolic estrogen receptor levels in the ventral prostate. A significant increase was seen in the cytosolic estrogen receptor levels in the seminal vesicle. Significant decreases in cytosolic protein levels occurred in all DES-exposed glands.

Diethylstilbestrol Metabolites and Analogs: Stereochemical probes for the estrogen receptor binding site

Indenestrol A (IA) and indenestrol B (IB) are analogs and metabolites of diethylstilbestrol (DES). These compounds have high binding affinity with the estrogen receptor (ER) but possess weak uterotropic activity. Due to their chemical structures, IA and IB exist as mixtures of enantiomers. We investigated whether the poor biological activity of these compounds was due to differential activity of the enantiomers. We also utilized these compounds as probes to determine the extent of stereochemical sensitivity in the ER ligand binding site. The IA and IB enantiomers were separated to greater than 98% purity using a chiral high pressure liquid chromatography column. Their enantiomeric nature was confirmed by mass spectrometry and NMR. The purified IA enantiomer peak 1 was derivatized with 4-bromobenzoyl chloride. The resulting di(4-bronobenzoate) IA was analyzed by x-ray crystallography and the absolute enantiomeric conformation assigned is C(3)-R. The IA enantiomers designated IA-R and A-S were assayed by competitive binding to cytosolic ER. The competitive binding index was estradiol, 100; DES, 286; IA-Rac (racemic mixture of IA), 143; IA-R, 3; and IA-S, 285; the index showed that ER demonstrates a stereochemical chiral preference. The IB enantiomers did not show a binding preference: IB, 145; IB-1, 100; and IB-2, 143. The differences in the IA enantiomer binding were shown to be due to competitive interactions by Lineweaver-Burk analysis of saturation binding of estradiol to ER in the presence of 1-, 5-, and 10-fold molar excess of competitor. Differences in binding affinity of the enantiomers could be partially explained by differences in the association rate constant (k+1) determined by association rate inhibition studies in which IA-S was 15 times more active than IA-R. Nuclear estrogen receptor levels were measured 1 h after in vivo treatment with doses of 5-20 micrograms/kg. The IA-Rac produced only 60% of the levels is compared with DES. Nuclear ER levels were checked every 30 min up to 2 h with no apparent difference, indicating that the low early levels were not due to a delayed estrogen receptor retention. When the enantiomers were tested individually only a dose of 10 micrograms/kg IA-S translocated ER to a level comparable to DES, while IA-R showed low levels at several doses. These results suggest that the poor biological activity of IA may be related to the differential ER interaction of its enantiomers.(ABSTRACT TRUNCATED AT 400 WORDS)

Nuclear estrogen receptor binding in the preoptic area and hypothalamus of pregnancy-terminated rats: correlation with the onset of maternal behavior.

Terminating the pregnancies of female rats on day 16 (D 16) by hysterectomy and ovariectomy (HO) and administering estradiol benzoate (EB) systemically or centrally into the medial preoptic area (MPOA) stimulates the onset of maternal behavior 48 h later. Since estrogen's effects are mediated through its intracellular receptors, the present studies measured nuclear and cytosol estrogen receptor concentrations in the POA and hypothalamus (HYP) of female rats during the 48 h when estrogen is active in stimulating maternal behavior. A low dose of EB (5 micrograms/kg) was used which was effective in stimulating maternal behavior in D16HO females but not in nonpregnant HO females of two types. In D16 animals there was a significantly higher concentration of nuclear receptors in the POA than in the HYP at time 0 (before HO and EB) but thereafter levels were similar in the two areas: nuclear receptor levels rose between 6 and 24 h after which they declined. In nonpregnant females, nuclear receptor levels at time 0 were low in both brain regions, rose significantly between 0 and 24 h, and significantly declined between 24 and 48 h similar to the D16 females. There were minimal differences in cytosol receptor levels among all groups at any time. Results from additional groups, nonpregnant HO females given 100 micrograms/kg EB and D16H animals (females whose pregnancies were terminated by hysterectomy only and their ovaries left intact), both of which exhibit maternal behavior at 48 h, support the idea that a high level of nuclear estrogen receptors in the POA followed by a sustained high level is necessary for estrogen stimulation of maternal behavior.

Mechanism of action of 2,3,7,8-tcdd and 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) as antiestrogens in the female rat

Several studies have reported that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) acts as an antiestrogen in rodents and human breast cancer MCF-7 cells in culture. It has been proposed that these effects may be related to the induction of estradiol-2-hydroxylase activity which effects a decrease in cellular estradiol levels due to increased metabolism. This study reports the comparative antiestrogenic effects of TCDD and 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) on cytosolic and nuclear estrogen and progesterone receptor levels in both the rat uterus and liver. MCDF, like TCDD, acted as an antiestrogen in the female rat, causing a dose-response decrease in uterine and hepatic cytosolic and nuclear estrogen and progesterone receptor levels; both compounds also antagonized the estradiolinduced increase in uterine wet weights. TCDD was 300 to 700 times more potent than MCDF as an antiestrogen, however the TCDD/MCDF potency ratios as inducers of hepatic monooxygenases were > 150,000. Moreover, the antiestrogenic effects of MCDF were observed at doses which caused minimal induction of hepatic monooxygenases. These results suggest that the antiestrogenicity of TCDD and related compounds is not due to increased metabolism of estradiol.

Estrogen Regulation of Prolactin Gene Transcription in Vivo: Paradoxical Effects of 17β-Estradiol Dose*

We investigated in male rats the effects of a range of doses of 17 beta-estradiol on PRL gene transcription, the level of circulating estradiol, and the levels of nuclear and cytosolic forms of the anterior pituitary estrogen receptor. One hour after 17 beta-estradiol injection, transcription of the PRL gene was significantly stimulated by 0.1 micrograms and maximally stimulated by 1.0 microgram/animal. Lesser stimulatory effects were observed 1 h after injection of 10 or 100 micrograms. At this 1 h point, the level of circulating estradiol was linearly increased relative to the 17 beta-estradiol dose. The level of nuclear form estrogen receptor was increased from 8% of the total receptor content in control rats to 12%, 28%, 50%, and 64% of the total receptor content in rats that received 0.1, 1.0, 10.0, and 100 micrograms, respectively. The anterior pituitaries of rats injected with 100 micrograms 17 beta-estradiol contained 30% fewer measurable estrogen receptors than control rats. Thus, dose-dependent losses of transcriptional responsiveness and measurable estrogen receptor were observed 1 h after injection of the larger doses of 17 beta-estradiol. Twenty-four hours after injection of the various doses of 17 beta-estradiol, PRL gene transcription was stimulated 1.3-fold in response to 0.1 microgram and approximately 2-fold in response to 1.0, 10, and 100 micrograms. At the 24 h point the circulating level of this hormone and the levels of nuclear and cytosolic forms of the estrogen receptor had returned to near their control values. This differing dose responsiveness at 1 and 24 h supports our previously reported observation that estrogen regulates PRL gene transcription in vivo through at least two independent mechanisms.

Effect of pubertal development on estrogen receptor levels and stromal morphology in the guinea pig prostate.

Using an immunocytochemical assay (ERICA) with a monoclonal antibody (H222Sp gamma) to the human estrogen receptor, we have demonstrated a stromal localization of the estrogen receptor in the dorsolateral prostate of the guinea pig. Specific staining of estrogen receptor in the guinea pig prostate was confined to the nuclei of periacinar and interacinar stromal cells. In comparison with prepubertal tissues, estrogen receptor staining intensity was markedly reduced in postpubertal prostatic tissues. No immunoreactive estrogen receptor was detected in the acinar epithelial cells irrespective of the developmental stage of the guinea pig prostate. Electron microscopic examination of the guinea pig prostate showed that the stromal component consists predominantly of smooth muscle cells, which, during pubertal development, undergo marked cytological changes and increase in size. These changes in the prostatic stroma were associated with a greater than fivefold reduction in levels of cytosolic and nuclear estrogen receptor determined by either a radioligand binding assay or an enzyme immunoassay (EREIA) and expressed relative to soluble protein. Morphometric analysis of the prostatic stromal cell density (SCD: nuclei/mm2 interacinar stroma), which is inversely proportional to stromal cell size, indicated that the SCD decreased approximately threefold during pubertal development. Furthermore, cytosolic estrogen receptor levels in mechanically separated prostatic stromal fractions were found to vary concordantly with the SCD during pubertal development. To determine whether estrogen influences normal development of the guinea pig prostate, the effect of various hormonal manipulations on stromal development was examined. Castration of prepubertal animals prevented the threefold decrease in SCD that is characteristic of pubertal development. Treatment of prepubertal castrates with estradiol and 5 alpha-dihydrotestosterone (DHT) in combination over a period equivalent to the transpubertal growth phase resulted in a stromal cell density similar to that seen in prostatic sections from intact postpubertal animals. In contrast, treatment of prepubertal castrates with either estradiol or DHT alone resulted in a prostatic stromal cell density intermediate between that observed in intact prepubertal and postpubertal animals. These findings suggest that both estrogen and androgen are required for the normal development of the guinea pig prostatic stroma.

Estrogen and progestin receptors and aromatase activity in rhesus monkey prostate.

We examined nuclear estrogen receptors (ER) and progestin receptors (PR) in the rhesus monkey prostate. Tissues were obtained from six intact males, five untreated castrates, six castrates treated with testosterone (T) for 6 weeks, and four castrates treated with estradiol (E2) for 6 weeks. Samples of the caudal lobe were either assayed biochemically for ER or stained immunocytochemically (ICC) with monoclonal antibodies against the ER or PR. Prostates from untreated castrates had significantly more ER than tissues from intact or T-treated castrates. In E2-treated castrates, ER number increased compared to that in intact and T-treated castrates. With ICC, ER was found only in the nuclei of the fibroblasts and smooth muscle cells of the stroma, not the glandular, ductal, or urethral epithelial cells. Intact and T-treated castrates had a very small number of positive cells, while untreated and E2-treated castrates had a significantly increased number of positive ER cells in the fibromuscular stroma. With ICC, PR was absent in intact or T-treated animals and barely evident in untreated castrates, but was significantly increased in the fibromuscular stroma of E2-treated castrates. The histological preparations indicated there was no stromal hypertrophy in the E2-treated castrates, but the E2 treatment did cause dilation of the glandular acini. Aromatase activity was measured in prostatic microsomes with a radiometric assay. Levels were low (3-30 fmol/h.mg protein) compared to those in brain and placenta, and no differences in activity were seen between castrates and T-treated castrates. Our data demonstrate that androgens can suppress the level of nuclear ER in the rhesus prostate, and that E2 treatment of castrates can induce PR in the same cells as those that contain ER. Thus, under appropriate conditions, estrogens could affect the rhesus prostate through a receptor-mediated pathway.

Comparative antiestrogenic activities of 2,3,7,8-tetrachlorodibenzo- p-dioxin and 6-methyl-1,3,8-trichlorodibenzofuran in the female rat

The ED50s for the dose-response induction of hepatic microsomal aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) by 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in the female Sprague-Dawley rat were 3.3 and 2.7 nmol/kg, respectively. In contrast, the corresponding ED50 values for induction by the nontoxic 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) were 524 and 578 μmol/kg for AHH and EROD, respectively, and TCDD was > 1.5 × 10 5 more potent than MCDF as an agonist for this response. Cotreatment of the female rats with MCDF (20, 50, or 100 μmol/kg) and TCDD (6.4 nmol/kg) showed that MCDF partially antagonized the induction of AHH and EROD by TCDD and this corresponded with results previously reported in the male rat. Like TCDD, MCDF also caused a dose-response decrease in uterine and hepatic cytosolic and nuclear estrogen (ERc and ERn) and progesterone (PRc and PRn) receptor levels. The relative TCDD MCDF potencies for the reduction of uterine ERc, ERn, PRc, and PRn levels were 293, 569, 560, and 459, respectively, and comparable potency ratios (693, 409, 405, and 424, respectively) were observed in the liver. Since MCDF was active as an antiestrogen at dose levels which caused only minimal induction of hepatic monooxygenases, it is unlikely that induction of these enzymes and the subsequent increased metabolism of estradiol play a role in the antiestrogenic effects of MCDF (or TCDD). The reasons for the differences in the relative potency of MCDF for the “traditional” Ah receptor-mediated response (i.e., AHH induction) and the modulation of steroid hormone receptor binding levels are unknown. MCDF, a compound which exhibits relatively high TCDD receptor binding activity and low toxicity, represents a new class of nontoxic halogenated aromatic antiestrogens that can be utilized to further probe the mechanism of this response in model systems.

Response of the mouse uterus to nafoxidine stimulation: agonism and antagonism.

Nafoxidine (NAF) acts as an estrogen agonist or antagonist depending on the animal model used. In the CD-1 mouse uterus, a three-day uterine bioassay of NAF produced a bell-shaped dose response curve with a maximal uterine wet weight increase at 200 micrograms/kg; this dose produced only a fractional increase in uterine dry weight. Combination treatment with NAF and estradiol antagonized estradiol stimulation of both wet and dry weight parameters. The time course of uterine wet weight stimulation following a single injection of NAF had an early pattern (0-10 h) similar to that of estradiol. However, at later times after stimulation, the patterns changed dramatically: the low NAF dose (200 micrograms/kg) returned to control levels by 24 h; estradiol and the high dose NAF (1.7 mg/kg) showed sustained stimulation, which peaked at 36 h with NAF compared to 24 h for estradiol. Nuclear estrogen receptor (ER) levels were measured after a single injection of 1.7 mg/kg NAF and showed a bimodal pattern similar to that seen with estradiol, with increases at 1 h and 8 h, although the overall ER levels were elevated above those seen with estradiol. Cytosolic ER levels with NAF decreased by 1 h and remained low up to 48 h. NAF treatment did stimulate uterine DNA and RNA synthesis, with a delayed time course compared to estradiol. DNA synthesis following a single 1.7 mg/kg dose of NAF was 2.5 times higher than that produced by 20 micrograms/kg estradiol. NAF treatment resulted in hypertrophy and hyperplasia in the luminal epithelium but not in the glandular epithelium. Long-term exposure to estradiol for 5 wk resulted in development of uterine cystic glandular hyperplasia and increased secretory activity; long-term exposure to NAF produced a more significant tissue hyperplasia but no secretions. These studies show that NAF stimulates some of the receptor-mediated responses attributed to an estrogen agonist in the mouse uterus; but, when co-administered with estradiol, NAF antagonizes some aspects of estrogen action.

Characterization of turtle liver nuclear estrogen receptors, seasonal changes, and pituitary dependence of cytosolic and nuclear forms

AbstractA nuclear hepatic estrogen receptor was characterized in the female turtle Chrysemys picta for the first time. The characteristics of this receptor were similar to those previously described in the cytosol, using DNA‐cellulose column chromatography (Riley et al., '87). The development of a different method for measurement of turtle cytosolic estrogen receptors allowed comparison of cytosolic and nuclear estrogen receptor regulation. Cytosolic and nuclear estrogen receptors exhibited high affinity (Kd, nuclear, 2.3 × 10−9M), limited capacity (10 – 170 fmol/g liver), steroid specificity for natural and synthetic estrogen, and target tissue specificity. Sucrose gradient analyses of crude cytosol revealed specific peaks of radioactivity at 4S and 9S, however a single 4S peak was present in nuclear extracts and ammonium sulfate precipitated cytosol. The levels of liver nuclear estrogen receptor changed significantly during the annual reproductive cycle, while cytosolic receptors were maintained at a constant level. Vitellogenic animals had higher levels of nuclear estrogen receptor and a greater percentage of total receptor in the nuclear fraction. In nonreproductive animals with low nuclear and high cytosolic estrogen receptor, short term (20 h) or chronic (1 week) estrogen exposure resulted in an increase in nuclear receptor to levels similar to naturally vitellogenic animals; however, depletion of cytosolic receptor was observed. Hypophysectomy of reproductively inactive animals resulted in loss of nuclear estrogen receptors in both control and estrogen‐injected turtles and restoration was achieved by ovine growth hormone (oGH) replacement. Cytosolic estrogen receptor levels and depletion after estrogen treatment were unaffected by hypophysectomy, however an increase above control occurred in hypophysectomized turtles treated with oGH. These data suggest that both estrogen and a pituitary factor similar to oGH are necessary for the achievement of high levels of nuclear estrogen receptor associated with vitellogenesis.

Comparative activities of 2,3,7,8-tetrachlorodibenzo- p-dioxin and progesterone as antiestrogens in the female rat uterus

The comparative antiestrogenic effects of progesterone and 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) on cytosolic and nuclear estrogen (ER c and ER n, respectively) and progesterone (PR c and PR n, respectively) receptor levels were determined in female Long Evans rats. Estradiol treatment typically increases ER and PR levels in target cells or tissues and these proteins have been proposed as markers of estrogen action. 2,3,7,8-TCDD causes a dose-dependent decrease in uterine ER c, ER n, PR c, and PR n levels which persist up to 7 days. Progesterone treatment caused significant decreases in uterine ER c, ER n, and PR n levels; however, after 7 days, the effects of the hormone on receptor levels were diminished. The effects of 2,3,7,8-TCDD and progesterone on hepatic ER and PR levels were comparable to those observed in the uterus. Treatment of the rats with estradiol (5 μg/kg), estradiol (5 μg/kg) plus progesterone (1 mg/animal), or 2,3,7,8-TCDD (80 μg/kg) showed that both progesterone and 2,3,7,8-TCDD significantly antagonized the estradiol-mediated increases in uterine (and hepatic) ER c, ER n, PR c, and PR n levels and for 2,3,7,8-TCDD the decreased receptor levels persisted for up to 7 days. In vitro studies with freshly isolated uterine strips demonstrated that both 2,3,7,8-TCDD and progesterone antagonized the estradiol-mediated increases in ER and PR levels. Previous studies suggest that the antiestrogenic activity of progesterone is due, in part, to the induction of proteins which are involved in decreasing ER n levels in target cells. Moreover in the uterine strip assay procedure, it was previously shown and reproduced in this study that the decrease in uterine ER n by progesterone was inhibited by both protein and RNA synthesis inhibitors over a 4-hr incubation period. In contrast, the 2,3,7,8-TCDD-mediated decrease in uterine ER n was inhibited only by actinomycin D and not by cycloheximide or puromycin. These in vitro studies thus confirm that both progesterone and 2,3,7,8-TCDD exhibit comparable antiestrogenic effects invivo and in vitro; however, the results suggest that these effects are expressed through different mechanisms.

Progesterone abbreviates the nuclear retention of estrogen receptor in the rat oviduct and counteracts estrogen action on egg transport.

Progesterone has synergistic or antagonistic effects on several estrogenic actions. The effects of progesterone on estrogen-induced accelerated ovum transport and on the dynamics of estrogen receptors in the rat oviduct were examined. The involvement of the progesterone receptors in these phenomena was assessed. On Day 1 of pregnancy, rats were treated with estradiol, estradiol plus progesterone, or either one plus the progesterone receptor-blocking agent RU486. Control animals received the oil vehicle alone. The number of eggs remaining in the oviduct was assessed 24 h after treatment. Cytoplasmic and nuclear estrogen receptor levels in the oviduct, as well as plasma concentrations of estradiol and progesterone, were measured at various intervals--up to 11 h and 24 h after treatment, respectively. Accelerated oviductal egg transport induced by estrogen was blocked by the concomitant administration of progesterone. This effect of progesterone was not associated with changes in estrogen circulating levels and was preceded by a reduction in the total amount of estrogen receptors and by a shortened retention of estrogen receptors in the nucleus. The effects of progesterone on egg transport and on the levels of estrogen receptors were reversed by blocking the progesterone receptor with RU486, suggesting that both effects were receptor-mediated. These findings demonstrate that progesterone antagonizes the effect of estrogen on oviductal egg transport in the rat, and suggest that this antagonism is mediated by a reduction both in the amount of estrogen receptors and in their retention time in the nucleus.

Retention of masculine sexual behavior following castration in male B6D2F1 mice

The reduction of masculine sexual behavior following castration varies widely among genotypes. In contrast to the loss of sexual behavior by castrasted males of other strains, males of the B6D2F1 genotype retain the ejaculatory reflex for many weeks after castration. The present study examined this retention phenomenon. Masculine sexual behaviors were measured before and after castration or sham operation in male C57BL/6J, DBA/2J, and B6D2F1 mice. Castrated C57BL/6J and DBA/2J males showed a rapid decline in copulatory behavior. In contrast, 30% of the B6D2F1 males continued to ejaculate 25 weeks after castration. Regardless of whether or not sexual behaviors were retained, levels of plasma testosterone and hypothalamic nuclear estrogen receptors were reduced by castration. These results suggest that the intra- and inter-strain differences in the retention of sexual behavior following castration are not due to differences in levels of steroid hormones. Further, some B6D2F1 males retain the ability to copulate in the absence of gonadal hormone levels required for the maintenance of sexual behavior in other genotypes.

Developmental regulation of the estrogen receptor and the estrogen responsiveness of five yolk protein genes in the avian liver.

The magnitude of the expression of five yolk protein genes in the avian liver in response to exogenous estradiol is shown to be developmentally regulated. Though each of these yolk protein genes gains the capacity to respond to estradiol during embryonic development, we demonstrate that maximal responses for the different genes are achieved at distinct ages between 1 and 6 weeks after hatching. This observation prompted us to look for possible correlations between yolk protein gene expression and changes in the expression of estrogen receptors that might also occur after hatching. We discovered that indeed the maximal level of nuclear estrogen receptors (assayed following the administration of estradiol) increases progressively over this same period of development from approximately 1000 receptors per cell at 1 week after hatching to approximately 3500 receptors per cell at 6 weeks after hatching. The latter number represents the fully mature state, as comparable levels of receptors are present in the livers of egg-laying hens. Thus, though increases in the expression of estrogen receptors during embryonic liver development have previously been reported, our results indicate that the changes that occur after hatching are quantitatively far more significant to the developmental program for this transcription factor.

Small apomorphine-induced increase in the concentration of cytosol estrogen receptors in female rat hypothalamus and pituitary

A series of experiments was performed to investigate the previously-reported modulation of estradiol binding in female rat brain and pituitary gland by drugs that influence the dopaminergic system. Injection of the dopamine agonist, apomorphine, at minimum doses of 1–2 mg/kg body weight caused slight increases (in most cases, less than 10%) in the concentration ofcytosol estrogen receptors in the mediobasal hypothalamus and anterior pituitary gland without influencing the concentration in the preoptic area. However, after subsequent injection of a saturating dose of estradiol, the level of nuclear estrogen receptors accumulating did not differ significantly between apomorphine-treated animals and vehicle-injected controls. These results extend, in part, previous reports that have shown an apomorphine-induced increase in the concentration of [ 3H]estradiol in brain and pituitary cell nuclei after an injection of [ 3H]estradiol. However, we failed to observe differences in the concentration of cytosol estrogen receptors as large as would be expected by previous work, and we failed to observe differences in the concentration of nuclear estrogen receptors after estradiol injection.

Hepatic estrogen receptor in human liver disease

Human liver contains estrogen receptors which render it sensitive to estrogen. Specific hormone binding to cytosol and nuclei from normal liver containing such receptors is of high affinity, low capacity, saturable, and specific for steroidal and nonsteroidal estrogens. Although estrogens alter metabolism and may produce disease, little data is available concerning estrogen receptor levels found in diseased liver. Herein we report estrogen receptor levels in human female liver containing diseases associated with oral contraceptives. Binding studies demonstrated cytosolic and nuclear estrogen receptors in human hepatic adenoma and focal nodular hyperplasia. Nuclear estrogen receptor levels in neoplastic tissue were greater than those in normal tissue. In addition, one hepatic adenoma resected from a patient taking tamoxifen contained no cytosolic estrogen receptor, and nuclear estrogen receptor levels were significantly lower than those found in normal tissue. These differences in binding capacity suggest a potential for greater hormone responsiveness in neoplastic liver tissue.

The antiarrhythmic effect of ryanodine in guinea pigs with glycoside poisoning

The content of estradiol and testosterone cytosolic and nuclear receptors has been studied in the pituitary body of adult male rats gonadectomized on day 1-3 after birth (long-term castrates) or in adulthood (short-term castrates). Intact male rats and long- and short-term castrates had the same level of cytosolic and nuclear estrogen receptors. The number of cytoplasmic and nuclear testosterone-binding sites was identical in the pituitary body of adult intact mice and long-term castrates. Contrastingly, the concentrations of androgen cytosolic and nuclear receptors were significantly lower in neonatally castrated males compared to intact adult animals. The results obtained indicate that nuclear testosterone receptors in the pituitary body mediate negative feedback effect of androgen on the release of luteinizing hormone and that the formation of thin mechanism occurs within the first days of life.