Nuclear Estrogen Receptor Concentrations Research Articles

Estrogen receptors in the diagnosis and treatment of hormone-dependent tumors

The paper presents the current data available on the etiology of tumor diseases, among other things, shows the role of hormones, namely: estrogens and their receptors, in the mechanism responsible for the occurrence of these diseases. Each tumor was shown to have its receptor status and to be unresponsive to this or that therapy differently. The efficiency of treatment and its prognosis may be determined if the receptor composition of an involved organ is estimated correctly. The authors summarize the data available in the literature, as well as the results of their own investigations explaining the selective effect of estradiol receptor agonists and antagonists in various tissues. The mRNA varieties that potentially encoding for the synthesis of different subtypes of estrogen receptors (ER) - ER-α and ERβ, which are also coded by various genes located in different chromosomes. Pituitary adenomas as hormone-dependent masses are described in detail. The authors data on the concentration of nuclear estrogen receptors in different types of adenomas are given.

Role of sex hormones in development of pituitary adenoma.

Role of sex hormones in the development of pituitary adenomas was investigated by analyzing the content of nuclear estradiol and testosterone receptors in different tumors of the anterior pituitary: prolactinomas, meningiomas, growth hormone-producing adenomas, astrocytomas, neurinomas, and ependymomas. The concentration of nuclear estrogen and androgen receptors in prolactin-secreting pituitary adenomas was much higher than in growth hormone-producing adenomas and other pituitary tumors.

Effects of Pregnancy Hormones on Maternal Responsiveness, Responsiveness to Estrogen Stimulation of Maternal Behavior, and the Lordosis Response to Estrogen Stimulation

The aim of the study was to determine whether there is an increase in responsiveness to estrogen stimulation of maternal behavior and lordosis responsiveness during pregnancy. Using separate groups of pregnancy-terminated females, we measured the initial maternal responsiveness of hysterectomized–ovariectomized (HO) females and their responsiveness to estrogen stimulation. Maternal behavior latencies were studied in females HO on the 8th, 10th, 13th, 16th, or 19th day of pregnancy (8HO–19HO) and in nonpregnant HO (NPHO) females. Groups were injected sc with estradiol benzoate (EB) in doses ranging from 0 to 200 μg/kg and tested for maternal behavior (retrieving, crouching, and licking pups). In addition, we investigated whether there is an increase during pregnancy (following HO) in lordosis responsiveness to estrogen stimulation. Lordosis behavior was studied in pregnant HO females (days 8, 16, and 22) and NPHO females given 0 to 200 μg/kg EB. There was an increase in maternal responsiveness in oil-treated HO females starting around midpregnancy. From early pregnancy on there was also an increase in maternal responsiveness to 20 μg/kg EB. In late pregnant females (16HO) there was a further increase with 50 μg/kg EB. There was no increase in lordosis responsiveness to EB stimulation during pregnancy; pregnant and nonpregnant HO females had the same EB threshold for stimulating lordosis behavior. The results of both studies were related to increases during the latter half of pregnancy in nuclear estrogen receptor concentrations in the MPOA, an area that mediates estrogen stimulation of maternal behavior, and the absence of such increases during pregnancy in the VMH, an area that mediates estrogen stimulation of lordosis behavior.

Identification and changes in concentrations of prostaglandin H synthase (PGHS) isoforms in rat myometrium at parturition

The isoform(s) of prostaglandin H synthase (PGHS) present in pregnant rat myometrium have been identified and the ontogeny of their expression studied during late gestation and parturition. Concentrations of PGHS have been related to changes in concentration of nuclear and cytosolic estrogen (ER) and progesterone receptors (PR) occurring at this time. Nuclear PR concentrations were maximal on days 16–18 of pregnancy, decreased from days 18 to 22 (delivery) and fell 24 hours postpartum. Nuclear ER concentrations increased significantly from days 20 to 22 of pregnancy and fell postpartum. Whereas the ratio of nuclear ER/PR was firmly in favour of progesterone action on days 16–20 it increased on day 22 corresponding to increased estrogen action. Western immunoblotting with specific antibodies revealed a single 72 kDa PGHS-1 isoform in myometrium at each timepoint. There was no evidence for the inducible PGHS-2 isoform in myometrium. Densitometric analysis showed the concentration of PGHS-1 increased significantly from day 16 to a maximum at the time of delivery on day 22 and decreased immediately afterwards. Expression of the constitutive PGHS-1 isoform is associated with the changing ratio of nuclear ER/PR and may therefore be hormonally regulated.

Changes in the density of nuclear estrogen receptors in urogenital tissue during pseudopregnancy in the rabbit

To elucidate the possible role of progesterone in pregnancy-induced urinary incontinence, the concentration of nuclear estrogen receptors (E2R) was measured in the urogenital tissues of non-pregnant (controls) and on days 6, 12 and 18 of pseudopregnancy in the rabbit. Whereas in the uterus E2R levels decreased by at least five-fold by day 6 of pseudopregnancy, changed little through day 12 and increased again at day 18, in the vagina and urethra only a small and insignificant decrease and increase occurred at days 6–12 and day 18, respectively. The receptor affinity, as judged by the computed KD values, did not change significantly in any of the preparation during pseudopregnancy. Similar changes in the E2R density were observed in rabbits treated with progesterone. These data provide further and concrete evidence for the tissue specificity in the downregulation of E2R by progesterone.

Proliferation index as a prognostic marker in breast cancer

The proliferative activity of tumors has been extensively investigated with different approaches, among which the use of the monoclonal antibody Ki-67 represents an easy and reliable means of assessing cell proliferation. In this study, the proliferative activity of 129 primary breast cancers was investigated, and the results were related to prognosis. Tumor samples, obtained from 129 patients who underwent surgery between January 1987 and December 1988, were processed for staining by an immunohistochemical procedure (avidin-biotin complex). The median time of observation was 42 months (range, 31-55 months). Life-table analysis (Mantel-Cox) was used to assess the probability of disease-free survival (DFS) and overall survival (OS). Tumors with high Ki-67 proliferation indices (> 20%) were associated with a higher 4-year probability of relapse of disease (55.3% versus 79.1%; P = 0.003) and death (71% versus 95.6%; P = 0.00005) when compared with tumors with low Ki-67 values. In addition, this proliferative parameter maintained its prognostic significance when the patients were stratified according to lymph node involvement, menopausal status, and nuclear estrogen receptor content. Tumor proliferative activity as evaluated by the monoclonal antibody Ki-67 seems to be an effective indicator of prognosis in breast cancer for DFS and OS.

Estrogen Responsiveness of Vitellogenin Gene Expression in Rainbow Trout (Oncorhynchus mykiss) Kept at Different Temperatures

We have examined the effect of ambient water temperature on the ability of juvenile rainbow trout to respond to estradiol (E2) injection with vitellogenin (Vg) synthesis. Vg appeared in serum within 24 hr of E2 injection in fish kept at 15° and rose to 70 mg/ml over a 10-day treatment period during which four injections of E2 were given. A group of fish kept at 9° responded more slowly to the same multiple injection protocol and showed Vg accumulation of only 8.9 mg/ml on the 10th day. Hepatic Vg mRNA levels accumulated more rapidly and extensively in animals treated and kept at 15° than at 9°; however, differences in serum Vg concentrations could not simply be attributed to differences in Vg mRNA levels. The ratio of serum Vg:Vg mRNA increased steadily over the treatment period, especially in the 15° group, suggesting greater efficiency or capacity for translation and/or processing of the Vg protein at the higher temperature. Examination of hepatic nuclear estrogen receptor (ER) concentrations revealed a three- to five-fold increase in high-affinity E2-binding activity within the first 24 hr after injection in both temperature groups. Nuclear ER levels remained elevated to roughly the same extent in both groups throughout the 10-day period. Differences in nuclear ER concentrations and serum E2 concentrations could not account for the large differences in Vg mRNA and protein levels between the two temperature groups. Furthermore, a single injection of E2 at 15° was able to induce higher levels of Vg mRNA and protein than multiple injections at 9°. We suggest that temperature modulates the responsiveness of the liver to E2 at stages which are independent of E2 or ER concentrations.

Up-regulation of the uterine estrogen receptor and its messenger ribonucleic acid during the mouse estrous cycle: the role of estradiol.

Uterine estrogen receptor (ER) and ER mRNA were measured in cycling and ovariectomized (OVX) estrogen-treated mice to probe the physiological regulation of the intracellular distribution and biosynthesis of ER. On proestrus, when plasma estradiol (E2) levels are highest, the cell nuclear ER concentration was 2.4-fold greater than on metestrus. This increase was primarily attributable to an increase in total cellular ER (cytosolic plus nuclear ER) and only secondarily to an activation of ER, as measured by its redistribution from the cytosolic (i.e. nuclear-extractable) to the nuclear (nonextractable) fraction. Total cellular ER concentration was 1.8-fold higher on proestrus than on metestrus, whereas the fraction of total ER in the nuclear compartment (i.e. the percentage activated) was only 1.3-fold higher. The concentration of cellular ER mRNA was 3-fold greater on proestrus than on the other days of the estrous cycle, suggesting that the increased concentration of ER on proestrus was a consequence of increased ER gene expression. In OVX mice, physiological and, to a lesser extent, supraphysiological levels of E2 increased cell nuclear ER. As in proestrous mice, the increased ER content contributed more than ER activation to the increased cell nuclear ER concentration. Physiological, but not supraphysiological, concentrations of E2 increased ER mRNA in OVX mice. Together, these results suggest that up-regulation by E2 of ER mRNA and ER accounts for most of the increased nuclear binding of ER on proestrus. E2-dependent activation and consequent DNA binding of ER presumably initiate this process, but quantitatively account for only a small fraction of the increased nuclear binding of ER.

Nuclear estrogen receptor binding in microdissected brain regions of female rats during pregnancy: Implications for maternal and sexual behavior

Previously, we showed that changes in nuclear estrogen receptor (NER) concentrations within large dissections of the preoptic area and hypothalamus of pregnant rats might underlie changes in both maternal and sexual behaviors. To more precisely localize these biochemical changes, NER concentrations were measured in microdissected nuclei within the preoptic area and hypothalamus of pregnant rats on days 8, 16 and 22. Results indicated that NER levels changed significantly throughout pregnancy and that the magnitude and direction of change was site specific. Although a different pattern of change was found in each nucleus, NER levels in most preoptic area nuclei were significantly higher by the 16th day of pregnancy compared to those on day 8, while receptor levels in most hypothalamic nuclei did not increase until day 22 of pregnancy. The higher NER levels found in preoptic area nuclei of female rats as pregnancy advances can be correlated with growing maternal responsiveness during pregnancy, while elevated concentrations of NER in hypothalamic nuclei at the end of pregnancy may indicate preparation for postpartum estrus.

Effect of clomiphene citrate treatment on endometrial estrogen and progesterone receptor induction in women

A direct adverse effect of clomiphene citrate on the endometrium has been presumed, and interference with estrogen receptor-mediated endometrial estrogen receptor and progesterone receptor induction has been implicated as the mechanism responsible for an increased incidence of luteal phase deficiency in association with clomiphene citrate treatment. To clarify the net influence of clomiphene administration on endometrial steroid receptor induction, we studied five normal ovulatory women, in both a spontaneous and clomiphene-induced (150 mg/day, cycle days 5 to 9) ovulatory cycle. From cycle day 11 blood samples were obtained daily and urinary luteinizing hormone determinations were performed twice daily. Endometrial biopsy was performed on the day of the urinary luteinizing hormone surge and again 13 days after the surge. Serum levels of follicle-stimulating hormone and luteinizing hormone were determined by immunoradiometric assay, estradiol and progesterone by radioimmunoassay, and clomiphene citrate isomer concentrations in treatment cycles by reversed-phase high-performance liquid chromatography and fluorescence detection. Total, cytosolic, and salt-extracted nuclear endometrial estrogen receptor and progesterone receptor concentrations were determined by enzyme-linked immunoassay. Serum estradiol was threefold to fivefold higher (p less than 0.05) in clomiphene-induced than in spontaneous cycles 8 and 10 days before the luteinizing hormone surge, and progesterone was increased (p less than 0.05) from the day of the surge to end of the cycle. Serum enclomiphene rose to plateau between 12 and 6 days before the luteinizing hormone surge (4.1 +/- 0.8 ng/ml, mean +/- SE, n = 19) and fell thereafter to less than 1.0 ng/ml. Zuclomiphene levels increased rapidly between 14 and 8 days before the surge (53.9 +/- 2.8 ng/ml, mean +/- SE, n = 5) and then decreased gradually but remained elevated throughout the luteal phase (29.0 +/- 1.2 ng/ml, mean +/- SE, n = 33). Late luteal endometrial histology was abnormal in one of four available treatment cycle specimens, but the endocrine characteristics and number and subcellular distribution of estrogen receptor and progesterone receptor in the abnormal cycle were not different from those of normal, in-phase cycles.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of thromboxane receptor antagonists on oestrogen-induced uterotrophic responses in the spontaneously hypertensive rat

1. The possible role of thromboxane in the uterotrophic response to oestrogen, in the spontaneously hypertensive rat was investigated by use of the thromboxane receptor antagonists EP092, AH23848 and BM 13.505. 2. The parameters studied were uterine blood flow (measured by the microsphere technique), uterine wet and dry weights and the concentrations of cytosolic and nuclear oestrogen receptors. 3. The antagonists attenuated oestradiol-induced uterine blood flow and significantly reduced both wet and dry uterine weight. These changes were accompanied by decreases in nuclear oestrogen receptor levels. 4. The results suggest a supportive role for thromboxane in oestradiol-induced uterine growth.

Modification of the rat uterine response to oestrogen and tamoxifen by thromboxane antagonists.

1. The thromboxane receptor antagonists EP092, AH23848 and BM 13.505 were used to investigate the role of thromboxane in the uterotrophic response to oestradiol and tamoxifen. 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. Only EP092 potentiated the hyperaemic response to oestrogen but all three thromboxane antagonists inhibited oestradiol-stimulated uterine growth. This inhibition was accompanied by a decrease in nuclear oestrogen receptor concentration. 4. The uterotrophic response to tamoxifen was unaffected by the thromboxane antagonists. 5. The mechanism by which the thromboxane antagonists may be exerting their growth inhibitory effect is discussed, although, whether this effect can be attributed to blockade of thromboxane receptors or to some other mechanism is not clear from this study.

Detection of Ki-67 Proliferation Rate in Breast Cancer: Correlation with Clinical and Pathologic Features

In situ determination of proliferative activity was performed on 203 breast cancers by use of Ki-67 monoclonal antibody and immunohistochemical methods. Tumor proliferation rate was analyzed and correlated to tumor size and nodal status. The relationship between Ki-67 proliferative activity and nuclear estrogen receptor content was also investigated on adjacent tissue sections. Ki-67 values ranged from 1 to 75%, with a median value of 10%. Premenopausal patients had greater Ki-67 values (median value, 14.1%) than postmenopausal ones (median value, 9.8%). The authors observed no correlation with lymph nodal involvement, whereas a statistically significant relationship with tumor size was found (P less than 0.01). An inverse correlation (Spearman's coefficient = -0.56; P less than 0.001) was seen between Ki-67 values and nuclear estrogen receptor content. These results, similar to those reported for other kinetic measurements, suggest that in situ detection of Ki-67 proliferation rate is a useful method for obtaining cell cycle information. Follow-up studies will be needed to assess an eventual prognostic relevance.

Influences of photoperiod on sexual behaviour, neuroendocrine steroid receptors and adenohypophysial hormone secretion and gene expression in female golden hamsters

Exposure to short daylengths arrests the oestrous cycle, provokes daily gonadotrophin surges and reduces the ability of exogenous oestradiol to trigger behavioural receptivity in golden hamsters. In order to examine neuroendocrine effects of photoperiod which might underlie these responses, ovariectomized hamsters were maintained under long or short photoperiods for 54 days before treatment with cholesterol or various doses of oestradiol-17 beta. Short days reduced the ability of low doses of oestrogen to prime hamsters for the induction of oestrus by progesterone. Upon repetition of oestrogen priming 2 weeks later, photoperiod was without significant influence on the concentrations of nuclear oestrogen receptors or cytosolic progestin receptors in a block of tissue containing the hypothalamus and preoptic area. Oestradiol treatment provoked significant increases in serum concentrations of LH and prolactin in the afternoon, but photoperiod did not alter the positive-feedback efficacy of this gonadal steroid hormone. Adenohypophysial LH-beta subunit and prolactin mRNAs were suppressed by short days in ovariectomized hamsters not treated with oestradiol. Oestradiol decreased expression of the LH-beta subunit gene in both stimulatory and inhibitory photoperiods, but increased prolactin mRNA abundance in both long and short days. Photoperiod therefore exerts pronounced steroid-independent effects on phasic LH and prolactin secretion, but regulation of adenohypophysial abundance of LH-beta subunit and prolactin mRNAs by oestradiol is not markedly influenced by daylength. Photoperiodic regulation of the priming effects of oestradiol on behavioural receptivity may result from modulation of events occurring subsequent to steroid-receptor interactions, or involve changes in receptor populations not detectable by the present methods.

Cytosol and nuclear estrogen receptor binding in the preoptic area and hypothalamus of female rats during pregnancy and ovariectomized, nulliparous rats after steroid priming: Correlation with maternal behavior

In a previous study, high nuclear estrogen receptor concentrations in the preoptic area (POA) were found on Day 16 of pregnancy to prime females to respond to a subsequent low dose of estradiol benzoate (EB) after hysterectomyovariectomy by exhibiting maternal behavior in 48 hr. Receptor concentrations in the POA were found to be higher than those in the hypothalamus (HYP). The present study investigated when nuclear estrogen receptors increase during pregnancy in POA and when the difference in receptor concentrations between POA and HYP occurs. An attempt was made to reproduce these pregnancy changes with a 16-day treatment of estrogen and progesterone in Ovariectomized (OVX), nulliparous rats. In Experiment 1, we measured cytosol and nuclear estrogen receptor concentrations in the POA and HYP of female rats during pregnancy. Nuclear receptor concentrations in the POA increased beginning on Day 10, increased again on Day 16, and continued at this high level for the remainder of pregnancy. Nuclear estrogen receptor concentrations in the HYP remained at a lower level throughout most of pregnancy until Day 22 when they increased significantly. In Experiment 2, we tested the maternal behavior and measured estrogen receptor concentrations in OVX, steroid-primed, nulliparous rats after hysterectomy (H) and EB treatment. While 90% of estradiol (E) + progesterone (P)-primed females displayed short-latency maternal behavior 48 hr after H and EB treatment, 46% of E + vehicle (V)-treated controls were maternal. At 0 hr (prior to H and EB treatment), there was a significantly larger nuclear receptor accumulation in the POA but significantly attenuated receptor binding in the HYP. P treatment significantly affected cytosol and nuclear estrogen receptor dynamics. Differences in nuclear estrogen receptor concentrations were shown to be based on the number of available binding sites and not to changes in receptor affinity for estradiol.

Characterization of cystic endometrial hyperplasia (CEH) in swine leukocyte antigen (SLA) miniature swine: Serum hormone and endometrial estrogen receptor concentrations

Swine leukocyte antigen (SLA) female miniature swine often exhibit a pathological condition classified as cystic endometrial hyperplasia (CEH). Based on direct examination of the uteri by mid-ventral laparotomy five and four pigs were assigned to CEH and non-CEH groups, respectively. The serum concentrations of estrone (E 1), estradiol (E 2), progesterone (P), testosterone (T) and luteinizing hormone (LH) were determined during a synchronized estrous cycle for both groups of animals. There were no significant differences ( P > 0.05) in the serum concentrations of E 1, E 2 and T during the estrous cycles of CEH and non-CEH groups. Peak (mean ± s.e.m.) level of LH of the CEH group was found to be significantly lower ( P < 0.05) than that of the non-CEH group (4.7 ±0.9 and 7.9 ±1.5 μg/l, respectively). Mean serum P concentration (32.1 ±6.4 nmol/l) in CEH pigs was, however, significantly lower ( P < 0.01) than that of non-CEH pigs (67.1 ± 8.9 nmol/l). Additionally, luteolysis occurred 2 days earlier in CEH pigs, compared to normal animals. The concentrations of cytosolic estrogen receptors in the endometria of CEH and non-CEH animals were not significantly different ( P > 0.05) during the luteal phase. The concentration of unoccupied nuclear estrogen receptors in the endometrium of CEH pigs was, however, significantly lower ( P < 0.05) than that of non-CEH animals (32.5 ±4.5 vs. 105.8 ±11.8 fmol/mg protein, respectively). The dissociation constants of cytosolic and nuclear estrogen receptors in the endometria of CEH and non-CEH groups were similar. These studies indicate that CEH in SLA miniature swine was associated with lower serum progesterone concentration and reduced concentration of unoccupied endometrial nuclear estrogen receptors.

Effects of day length on sheep neuroendocrine estrogen and progestin receptors

Gonadal steroid hormone receptors were studied in anterior pituitary, preoptic area, and hypothalamus of ovariectomized ewes. We established that systemic administration of estradiol benzoate elevates levels of nuclear estrogen receptor concentrations and results in the appearance of cytosolic progestin receptor the binding characteristics of which are comparable with that reported in rats and guinea pigs [0.1 nM Kd, binding site density (Bmax) of 111, 22, and 2 fmol/mg protein in pituitary, medial basal hypothalamus, and preoptic area, respectively]. Brain tissues also contained a second, low-affinity progestin binding site. To examine possible effects of photoperiod on neuroendocrine steroid receptors, two groups of sheep were exposed to artificial photoperiods. Ewes experienced alternating periods of long (LD 16:8) or short (LD 8:16) days for 290 days to induce breeding season or anestrous states. Animals were then ovariectomized and given steroid treatments designed to mimic a luteal phase followed by either follicular phase levels of estradiol or withdrawal of all exogenous hormones before determination of neuroendocrine steroid receptor concentrations. Despite the ability of long photoperiods to arrest ovarian cyclicity, magnify negative feedback actions of estradiol upon luteinizing hormone, and reduce the ability of estrogen to trigger behavioral estrus, photoperiod did not influence nuclear estrogen receptor concentrations or the induction of cytosolic progestin receptors in the pituitary, hypothalamus, or preoptic area.

Glucocorticoids Inhibit Estradiol-Mediated Uterine Growth: Possible Role of the Uterine Estradlol Receptor

Stress-related activation of the hypothalamic-pituitary-adrenal axis (HPA) is associated with suppression of the reproductive axis. This effect has been explained by findings indicating that corticotropin-releasing hormone suppresses hypothalamic gonadotropin-releasing hormone (GnRH) secretion via an opioid peptide-mediated mechanism, and that glucocorticoids suppress both GnRH and gonadotropin secretion and inhibit testosterone and estradiol production by the testis and ovary, respectively. To evaluate whether glucocorticoids suppress the effects of estradiol on its target tissues, we examined the ability of dexamethasone to inhibit estradiol-stimulated uterine and thymic growth in ovariectomized rats. Estradiol alone, given daily for 5 days, caused dose-dependent uterine and thymic growth. Dexamethasone alone, given daily for 5 days, caused a dose-dependent decrease in body weight gain and in thymic growth. When estradiol and dexamethasone were administered simultaneously, however, body weight gain and thymic growth were also inhibited (p less than 0.05). Dexamethasone decreased estradiol-induced uterine cytosolic and nuclear estrogen receptor concentrations (E2 R0, p less than 0.05; E2nR0, respectively), but had no effect on estradiol-induced progesterone receptor concentrations (P4R0, p greater than 0.05). Levels of uterine glucocorticoid receptors were not affected by estrogen and/or dexamethasone treatment. These findings suggest that stress levels of glucocorticoids, administered over a 5-day interval, block the estradiol-stimulated growth of female sex hormone target tissues. This effect may be partially mediated by a glucocorticoid-induced decrease of the estradiol receptor concentration. Thus, another mechanism by which the HPA may influence reproductive function during stress is by a direct effect of glucocorticoids on the target tissues of sex steroids.

Differential effects of estradiol and 16 alpha-hydroxyestrone on pituitary and preoptic estrogen receptor regulation.

16 alpha-Hydroxyestrone (16OHE1), an endogenous metabolite of estradiol (E2), binds to the estrogen receptor (ER) with low affinity, but is estrogenic in various bioassay systems. 16OHE1 binds covalently to the ER in vitro, exhibits prolonged estrogenic bioactivity in vivo, and has been implicated in several estrogen-dependent diseases. This study examined the effects of 13 days of continuous infusion of E2 or 16OHE1 on lordotic behavior, pituitary growth, and ER regulation in the cytosolic and nuclear fractions of the pituitary and preoptic area of both sexes. Finally, simultaneous pituitary nuclear exchange assays and enzyme immunoassays were performed to search for covalent 16OHE1-ER complexes in vivo. E2 induced lordosis and pituitary growth in both sexes, while 16OHE1 was only slightly less effective. While E2 treatment increased nuclear ER concentrations 2-fold vs. control values, it decreased both cytosolic and total (cytosolic plus nuclear) ER concentrations in pituitary and preoptic area by approximately 3-fold vs. control values in both sexes by exchange assay. In contrast, 16OHE1 did not decrease total pituitary ER concentrations and only minimally decreased total preoptic ER concentrations. Simultaneous exchange assay and immunoassay of pituitary nuclear extracts demonstrated proportionate increases in ER levels in female vs. male and in E2-treated vs. 16OHE1-treated rats. The ratios of (ER enzyme immunoassay divided by ER-exchange) for each rat were similar regardless of metabolite administration. The correlation of individual measurements implied that ER localized to the nuclear fraction by either E2 or 16OHE1 retained both exchangeability and immunoassayability to similar extents, but did not support the presence of 16OHE1-ER covalent complexes. The results of this study suggest that 16OHE1 has significant estrogenic bioactivity, as manifest by its effects on lordosis and pituitary growth, but, in contrast to E2, does not decrease pituitary ER concentrations and only minimally decreases preoptic ER concentrations. This property may be important in the proposed pathogenetic action of 16OHE1 in estrogen-dependent disease.

Effects of the β-isomer of hexachlorocyclohexane on estrogen-sensitive human mammary tumor cells

The effects of the β-isomer of hexachlorocyclohexane (β-HCH) on the induction of the cytosolic progesterone receptor (PgRc), on the redistribution of the estrogen receptor (ER), and its affinity for ER were investigated in the estrogen-sensitive human mammary tumor cell line MCF-7. The effects of β-HCH were compared to those of estradiol-17β (E 2) and 2,4,6-trichlorophenol (TCP), a major urinary metabolite of β-HCH in rats. β-HCH in concentrations higher than 1 μ m caused induction of PgRc whereas TCP was essentially without effect up to a cytotoxic concentration of 100 μ m. Furthermore, β-HCH (10 μ m) caused redistribution of ER, i.e., decrease of cytosolic ER concentration and increase of nuclear ER concentration, in a way similar to E 2. In contrast to this, β-HCH up to a molar excess of 6 × 10 4 (concentration 30 μ m) caused no significant displacement of [ 3H]E 2 from ER indicating that β-HCH has no substantial affinity for ER. It is concluded that β-HCH has estrogenic properties which are at variance with the failure to demonstrate binding of β-HCH to ER.