The selective isolation of the uterine oestradiol-receptor complex by binding to oligo(dT)-cellulose. The mediation of an essential activator in the transformation of cytosol receptor

Activated oestrogen receptor in human breast cancer: clinical and biochemical correlates

The oestrogen receptor (ER) contains a DNA-binding site, the activity of which can be determined by its binding to oligo(dT)-cellulose. In premenopausal women with breast cancer, 53 per cent of ER-positive tumours were capable of binding to oligo(dT)-cellulose (activated ER): the corresponding proportion in postmenopausal patients was 70 per cent (P less than 0.005). Disease recurrence was significantly increased in patients whose tumours contained non-activated rather than activated ER. The presence of activated ER was associated with a significant increase in the median activity of creatine kinase in premenopausal and postmenopausal patients. In postmenopausal patients the incidence of progesterone receptor was higher in tumours that contained activated ER than in tumours that contained ER not capable of binding to oligo(dT)-cellulose (non-activated). The incidence of activated ER was not related to disease stage or nodal involvement at the time of sampling. The data suggest that ER-positive tumours can be divided, according to the activity of the DNA-binding site, into subgroups with differing biological properties.

Testicular cytosol factors inhibit the binding of steroid-receptor complexes to chromatin

Testicular and prostatic androgen-receptor complexes as well as uterine estradiol-receptor complexes, partially purified by ammonium sulfate precipitation (15-37%), were bound to germ cell chromatin. At equivalent concentrations, less testicular androgen-receptor complexes bound to chromatin than did the other two steroid-receptor complexes. Addition of a partially purified testicular androgen-receptor preparation with prostatic androgen-receptor or uterine estradiol-receptor preparation to the binding interaction mixture reduced the binding of either of the latter two steroid-receptor complexes to chromatin. These data suggest the presence of inhibitory factor(s) in the testicular receptor preparations. Testicular cytosols were fractionated by ammonium sulfate precipitation into fractions A (15-37% saturation), B (37-50%) and C (50-75%). All fractions inhibit binding of these steroid-receptor complexes to chromatin. Fractions A and B appear to be heat labile, while fraction C was more stable. Further fractionation of A and C fractions on DEAE cellulose yielded A1 and C1 (filtrates) as well as A2 and C2 (0.3 M NaCl eluents), respectively. Subfractions A1, A2, and C2 contained inhibitory factors for the binding of steroid-receptor complexes to chromatin while C1 showed no effect. These data demonstrated that testicular cytosol contains a variety of inhibitory factors which affect the binding of both androgen-receptor and estradiol-receptor complexes to chromatin.

Effect of ribonuclease on the physico-chemical properties of estrogen receptor

Estrogen receptors (ER) from rat and rabbit uterine cytosol were examined for their sensitivity to ribonuclease (RNase). After RNase treatment, a major part of rabbit uterine ER was converted from the 7S to 3-4S form, and its binding to DNA-cellulose was increased by 40%. Similar treatment on rat uterine ER showed a shift from 7S to 4.5S, and the DNA-cellulose binding was stimulated by 20%. Measurement of endogenous RNase levels showed that lower RNase concentration in rabbit uterine cytosol coincided with larger stimulation of DNA-cellulose binding by exogenous RNase. These results indicate that a major part of 7S ER is susceptible to RNase, and cleavage of bound RNA seems to uncover additional binding sites for DNA. In contrast to the general thinking that 4S to 5S transformation is essential for nuclear binding, we have observed that RNase-treated rat uterine ER did not undergo such a transformation by warming at 25 degrees C, while DNA-cellulose binding of the receptors increased. Thus, temperature activation could occur independent of 4S to 5S transformation.

Activation of oestrogen receptor complexes: evidence for the distinct regulation of ligand and oligonucleotide binding sites

The activation of the rat uterine oestrogen receptor has been measured in vitro by its binding to oligodeoxythymidylate cellulose (oligo(dT] and was found to be sensitive to the time and temperature of prior incubation of cytosol with oestradiol. The presence of 20 mM dithiothreitol promoted receptor activation and was partially inhibited by 10 mM molybdate; molybdate also inhibited the time- and temperature-dependent activation of receptor. The nucleotides GTP, ATP, ADP, CTP and UTP all promoted receptor activation; the effect of GTP was significantly greater than that of ATP. It is unlikely that phosphate donation is involved in receptor activation as the effects of GTP could be reproduced by p[NH]ppG (guanosine 5'-[beta, gamma-imido]triphosphate), while PPi was also effective in activating receptor. The results provide evidence for the distinct regulation of the oligonucleotide- and ligand-binding domains, since manipulations which promoted binding to oligo(dT) did not affect either ligand binding capacity or the rate constant and composition the biphasic dissociation of the ligand receptor complex.

An analysis of the decrease in the assayed level of charged bovine estrogen receptor observed at physiological ionic strength

Lower assayed levels of heifer uterine estrogen receptor (ER) occur at physiologic ionic strength when ER is separated from [3H]estradiol by Dextran-coated charcoal treatments, or by gel filtration on Sephadex or polyacrylamide resins. The assayed level of charged ER in buffers containing 150-200 mM ionic strength is approximately one-half that of ER levels assayed in buffers either at 0-50 or 400-450 mM ionic strength. Treatment of ER with trypsin or molybdate eliminates this observed reduction. Evidence is presented that the decrease results from a preferential adsorption of ER to the assay resins at 150-200 mM ionic strength. This adsorption is likely to be mediated by a hydrophobic region of the ER, which is removed by trypsin cleavage.

Activated oestrogen receptors in breast cancer and response to endocrine therapy

The status of oestrogen and progesterone receptors has been measured in 147 primary breast tumours. In addition to the measurement of cytoplasmic oestrogen receptors, the ability of these receptors to bind to oligo(dT)-cellulose has been assessed. This indicates the capability for activation of cytoplasmic receptors to a form able to bind in the nuclear compartment in vivo and thus be part of a functional receptor pathway. All the receptor concentrations measured were increased in the postmenopausal group of patients. All nuclear oestrogen receptors in this group were available for labelling at 4 degrees C, in contrast to the premenopausal group. The apparent functionality of the oestrogen receptor pathway could be equally assessed either by the co-presence of cytosol progesterone receptor with nuclear oestrogen receptor (30 or 4 degrees C) or with activated cytosol oestrogen receptor. The presence of activated cytosol oestrogen receptor was as reliable (80%) as the presence of either nuclear oestrogen receptor at 30 (83%) or 4 degrees C (81%) in predicting the response of breast tumours to endocrine therapy.

Human androgen insensitivity mutation does not alter oligonucleotide recognition by the androgen receptor-DHT complex

We studied the binding of dihydrotestosterone-receptor complexes (DHT-R) from human genital skin fibroblasts to oligodeoxyribonucleotides and DNA. Following incubation of fibroblasts with 2 nM [3H]DHT (45 min, 37 degrees C), DHT-R were prepared as total fibroblast sonicates (sonication of cells in 0.5 M KCl), intact fibroblast cytosol (100000 X g supernatant) or intact fibroblast nuclear extract (sonication of nuclei in 0.5 M KCl). DHT-R were also prepared by incubation of fractionated fibroblast cytosol with 4 nM [3H]DHT (4 h, 0 degrees C). Optimal conditions were established for binding of DHT-R from total fibroblast sonicates to oligo-dT cellulose: 60 min, 0 degrees C, low salt (0.05-0.10 M KCl), linearity with DHT-R concentration, and nucleotide saturation. With total fibroblast sonicates the rank order of DHT-R binding was oligo-dT approximately equal to -dG greater than DNA greater than -dC greater than or equal to -dA approximately equal to -dI. Intact fibroblast cytosol displayed a similar preference of DHT-R binding to oligo-dT and -dG but the binding was quantitatively higher than for total fibroblast sonicates, the binding for fractionated fibroblast cytosolic DHT-R formed at 0 degrees C being quantitatively lower. However, binding of DHT-R from cytosol (0 degrees C) to DNA-cellulose was equal to that for DHT-R from cytosol (37 degrees C). Binding of DHT-R from intact fibroblast nuclear extracts was lower than for total fibroblast sonicates. Preparations from cells of patients with receptor-negative, complete androgen insensitivity lacked both DHT-R formation and specific oligonucleotide binding. Binding of oligonucleotides to DHT-R from cells of patients with receptor-positive, complete androgen insensitivity could not be distinguished from that of normal cells. These results suggest: (a) androgen receptor-steroid complexes recognize and bind to certain preferred deoxyribonucleotides; (b) various factors affect the quantitative binding of DHT-R from different cellular preparations to deoxyribonucleotides; and (c) neither qualitative nor quantitative abnormalities for DHT-R of complete androgen-insensitive patients were detectable from oligonucleotide or DNA binding.

Comparative effects of progesterone, norgestrel, norethisterone and tamoxifen on the abnormal uterus of the anovulatory rat

Progesterone therapy results in partial reversibility of histological abnormalities of the rat uterus exposed to constant oestrogen stimulation and is associated with a decrease in nuclear oestrogen receptor content, which may underlie the tissue response to hormone treatment [White, Moore, Elder & Lim (1982) Biochem. J. 202, 535-41]. The synthetic progestins norgestrel and norethisterone used in this study were as effective as progesterone in decreasing the content of nuclear oestrogen receptor. However, only norgestrel had an ameliorative effect on epithelial hyperplasia and metaplasia. The non-steroidal anti-oestrogen tamoxifen caused a significant decrease in both nuclear and cytosol oestrogen receptor content without any change in luminal epithelial hyperplasia and metaplasia. Each progestin caused an increase, whereas tamoxifen caused a decrease, in the proportion of nuclear oestrogen receptors that were unoccupied. Each compound caused a decrease in the content of cytosol progesterone receptor. The effectiveness of compounds used as oestrogen antagonists is discussed with reference to their mode of action.

Progesterone therapy results in partial reversibility of uterine abnormalities of the adult anovulatory rat

The effects of progesterone therapy (5 mg, administered subcutaneously daily for 6 days) on the abnormal uterus of adult anovulatory Wistar rats have been studied. These rats, rendered anovulatory by neonatal treatment with testosterone propionate or clomiphene citrate, displayed severe hyperplasia and metaplasia of the uterine luminal epithelium and a disproportionately high content of nuclear oestrogen receptor, as a result of constant oestrogen stimulation unrelieved by progesterone [White, Moore, Elder & Lim (1981) Biochem. J. 196, 557-565]. Progesterone therapy resulted in the virtual elimination of the hyperplasia and metaplasia and a corresponding decrease in the content of nuclear oestrogen receptor with the proportion of the unoccupied nuclear receptor being increased to values exhibited by normal cyclic females. There was also a decrease in the content of progestin receptors, a putative index of oestrogenic stimulation. Further, in the testosterone-treated group, progesterone therapy resulted in the restoration of oestrogen receptor translocational responses to oestradiol stimulation. Progesterone treatment of these anovulatory rats thus provides a model system for investigating the biochemical mechanisms underlying progestin antagonism and regulation of oestrogen-stimulated cell proliferation.

The binding of rat uterine cytosol oestrogen receptors to oligodeoxythymidylate--cellulose. Its relationship to a stable form of receptor complex with separate ligand- and oligonucleotide-binding sites

The interaction of rat uterine cytosol oestrogen-receptor complexes with the synthetic acceptor oligo(dT)--cellulose was studied. Differences in the stability of receptor complexes and their ability to bind to oligo(dT)--cellulose on storage at 4 degrees C or when exposed to increased temperatures indicated heterogeneity of steroid- and oligonucleotide-binding sites. Dilution, dialysis and (NH4)2SO4 precipitation increased the interaction of receptor complexes with oligo(dT)--cellulose (a step termed activation). This increase may be the result of the removal of low-molecular-weight cytosol components which inhibit receptor activation, dimerization to the 5 S form, which binds to oligo(dT)--cellulose, or interaction of 5 S receptor with the oligonucleotide. Cytosol oestradiol--receptor complexes exhibited biphasic dissociation kinetics. All these manipulations resulted in an increase in the proportion of the slow-dissociating component equivalent to the increase in receptor binding to oligo(dT)--cellulose. In contrast, addition of 10mM-sodium molybdate to cytosol decreased both oligo(dT)--cellulose binding and the proportion of receptor with slow dissociation kinetics. The inclusion of proteinase inhibitors did not affect interactions of receptor with oligo(dT)--cellulose nor the dissociation kinetics. These results suggest that oligo(dT)--cellulose binding may serve to quantify the proportion of cytosol receptor in an active form capable of nuclear interaction and to help to ascertain whether a receptor system is fully functional. This binding procedure could prove useful in the evaluation of oestrogen responsivity under normal and pathological conditions.

The polynucleotide binding sites of estradiol receptor complexes

As a model for interaction of steroid receptors with DNA, the binding of estradiol receptor complexes (E2R) to oligodeoxynucleotides, covalently linked to cellulose, was studied in detail. Binding was optimal at concentrations of monovalent cationic salts at, or near, isotonic levels and was selective for intracellular receptors in contrast to extracellular steroid binding proteins. Among the oligomers, the order of affinity was oligo dG greater than oligo dT greater than oligo dC greater than oligo dA greater than oligo dI. The binding to oligo dG was stable to 37 degrees C exposure and the processes of adsorption and desorption, while reactivity with oligo dT, oligo dC and oligo dA was labile. The decrease in binding following purification was restored by histone 2B. Oligo dG binding was the most resistant to inhibition by cibacron blue F3GA (CB) and pyridoxal-5-phosphate. On the basis of these data, a hypothesis is proposed for the interaction of mouse uterine cytosol E2R with prevalent nonspecific and putative specific sequences of DNA.

The relationship of the oestrogen and progestin receptors in the abnormal uterus of the adult anovulatory rat. Effects of neonatal treatment with testosterone propionate or clomiphene citrate

The neonatal administration of testosterone propionate to Wistar rats resulted in anovulatory adults in persistent vaginal oestrus. Clomiphene citrate had a similar effect. In both groups of adults, hyperplasia of the uterine epithelium and occasional metaplasia was observed. The uterine nuclear and cytosol oestrogen and progestin receptors of these anovulatory rats were found to have affinities for their respective ligands similar to those of normal females. The nuclear oestrogen receptor comprised occupied and unoccupied components, as in normal females. The content of the nuclear oestrogen receptor was comparable with that of females in the late dioestrous or pro-oestrous phase. This content was higher in the clomiphene-treated group. Despite the relatively high nuclear oestrogen receptor content the content of progestin receptors, a putative index of the oestrogenic response, was lower in the treated rats than in normal adult females throughout the cycle. Administration of oestradiol to both treatment groups resulted in depletion of cytosol oestrogen receptor content 1 h later, which, however, was not reflected by an increase in the content of nuclear oestrogen receptors. There was no measurable increase in progesterone receptor content in treated rats after daily administration of oestrogen (5 microgram/rat) for 3 days. These changes in sex-hormone-receptor interactions involving an impairment of the normal oestrogenic response may be associated with the abnormal differentiation of the uterus in these sterile, anovulatory animals.

An oestrogen receptor activator protein in rat uterine cytosol

Earlier reports of oestrogen receptor binding to DNA indicated that a protein which does not bind oestrogen might be involved in the conversion of the 4S oestradiol receptor to the 5S form but no direct evidence for the existence of this protein was presented. This receptor transformation or activation step is thought to be a requirement for events in the nucleus. We considered it likely that such a protein might be similar to the cytoplasmic proteins which stimulate eukaryotic RNA polymerases. These are basic proteins which are not adsorbed to DEAE cellulose and have a sedimentation coefficient of approximately 3S. To examine this possibility, we fractionated unlabelled uterine cytosol by DEAE-cellulose chromatography. Unlabelled cytosol was used to avoid the possibility that such a factor might be retained on the column as a component of the receptor--oestradiol complex. Here we present evidence of a protein present in uterine cytosol which forms a complex with the 4S form of the oestrogen receptor to produce a 5S-activated form. This activated form binds to uterine nuclei, DNA-cellulose and native calf thymus DNA. The cytosol protein, which we call receptor activation factor, does not bind oestradiol, has a sedimentation coefficient of approximately 3S and does not bind to DEAE-cellulose.

Specific binding of 3H-estradiol to the cytosol of rat pancreas and uterus: bound sites in pancreatic extracts do not translocate 3H-estradiol to nuclei suggesting a basic difference in mode of action

In parallel sets of experiments, cytosol fractions from rat pancreas and uterus were incubated with 2 nM 3H-estradiol in the presence or absence of nuclei from pancreas and liver. After incubation for 1 hr at room temperature, the nuclei were removed by centrifugation and specific binding determined in the cytosol fractions as well as in the separated nuclei. The protein that binds 3H-estradiol in uterine extracts translocated the hormone to nuclei of pancreas and liver while the one in pancreas was devoid of this activity. It is presumed, therefore, that modification of transcription is not a primary action of the steroid-bound complex in pancreas.

Unoccupied nuclear oestrogen receptors in the female rat hypothalamus. Increases on oestrogen administration

A major proportion of the hypothalamic nuclear oestrogen receptors were available for complexing with radioactive oestradiol in vitro at 4 degrees C and were apparently unoccupied . At 6 h after oestradiol administration the content of unoccupied nuclear receptors had increased 2.5-fold and represented 71% of the total nuclear receptor content. These results suggest that unoccupied receptors may be active elements in the 'long-term' receptor population of the hypothalamus. Androgenized females had lower contents of these receptors.

Factors affecting the binding of chick oviduct progesterone receptor to deoxyribonucleic acid: evidence that deoxyribonucleic acid alone is not the nuclear acceptor site

Studies on the interaction of the chick oviduct progesterone-receptor complex (P-R) with various nuclear components revealed a variable, nonsaturable binding of P-R to pure deoxyribonucleic acid (DNA). In contrast, a receptor-dependent, saturable, high level of binding of P-R was observed with a nonhistone protein-DNA complex called nucleoacidic protein (NAP). Three categories of factors were identified which affected the binding of P-R to the DNA. These were (1) the conditions of the binding assay, (2) the properties of the receptor, and (3) the state of the DNA. The conditions in the binding assay which affect DNA binding are the choice of the blanks, the salt concentration, and the pH of the assay. The receptor preparations display their own characteristic levels of binding to native DNA. The basis of this DNA binding capacity by each preparation is unknown. Lastly, the purity and the integrity of the DNA itself determine the level of binding of the P-R. Protein impurities, moderate degradation of the DNA by enzymatic or physical fragmentation, and ultraviolet (UV) light treatment greatly enhance the receptor binding to the DNA. The extent of binding to DNA depends on the degree of damage. Interestingly, totally denatured (single-stranded) DNA displays little or no binding of the P-R. Seasonal differences which are observed for the binding of P-R to chromatin in vivo and in vitro and to NAP in vitro do not occur with DNA whether it is undamaged or damaged. It is concluded from these studies that under controlled conditions and by using DNA preparations as native as possible, minimal binding of P-R to pure DNA occurs. The numerous reports in the literature describing marked binding of the steroid-receptor complex to DNA may well be due to conditions described in this paper. Further, it is concluded that native or partially degraded DNA alone does not appear to represent the native nuclear acceptor sites for the chick oviduct P-R. In contrast, the DNA-nonhistone protein (acceptor protein) complexes do show characteristics of the native-like acceptor sites.

Nucleo-cytoplasmic relationships of oestrogen receptors in rat liver during the oestrous cycle and in response to administered natural and synthetic oestrogen

Oestrogen receptors were measured in the cytosolic and purified nuclear fractions of rat liver. Both cytosolic and nuclear receptors bind oestrogen with high affinity (Kd = 1.47 and 2.28 nM respectively) and specificity similar to that of receptors in order oestrogen-target tissues such as the uterus. During the 4-day oestrous cycle the receptor content and distribution between cytosol and nucleus did not vary; in particular, the content of nuclear receptor did not appear to fluctuate in concert with known cyclic changes in the concentration of plasma oestrogen. Injection of 50 micrograms of oestradiol-17 beta or 10 micrograms of ethynyloestradiol resulted in a 4--6-fold increase in the nuclear receptor content, with a concomitant decrease in the unoccupied-receptor content of cytosol 1 h after injection. The nuclear receptors present after injection bind oestrogens with similar affinity (Kd = 2.78 nM) and specificity to receptors present in uninjected animals. The administration of lower doses of either oestrogen was less effective in producing increases in nuclear receptor content. Hence there is apparently substantial translocation of receptor to the nucleus in response to hyperphysiological doses of oestrogen, but not to the physiological changes in plasma oestrogen concentrations during the oestrous cycle. The response to exogenous oestrogens is discussed in relation to the clinical use of synthetic oestrogens and progestogens.

Specificity of oligodeoxynucleotide binding of mouse uterine cytosol estradiol receptors

The relative capacities of oligodeoxynucleotides, covalently linked to cellulose, to bind estradiol receptor complexes (E2R) of mouse uterine cytosol have been shown to follow the order oligo(dG) > oligo(dT) greater than or equal to oligo(dC) > oligo(dA). The E2R . oligo(dT)-cellulose-binding reaction is more sensitive to Cibacron blue F3GA than is E2R . oligo(dG)-cellulose or oligo(dC)-cellulose binding. Preformed E2R . oligo(dT)- or oligo(dC)-cellulose complexes are dissociated more readily by lower concentrations of KCl or Cibacron blue F3GA than is the E2R . oligo(dG)-cellulose complex. Preincubation of E2R at 37 degrees C results in a rapid loss of binding ability towards oligo(dT)- and oligo(dC)-cellulose, while up to 90% of the binding ability to oligo(dG)-cellulose is retained. On the basis of the differential sensitivities of E2R to temperature and the inhibition by Cibacron blue F3GA of the binding reaction, it is suggested that the polynucleotide-binding domain consists of two types of subsites, one of which has a higher affinity for oligo(dG) residues and the other of which recognizes oligo(dT), oligo(dC), and, to a lesser extent, oligo(dA).

Developmental changes in the content of oestrogen receptors in the hypothalamus of the female rat

Hypothalamic cytosol and nuclear oestrogen receptors are present at birth. A 2-fold increase in cytoplasmic receptor content occurs by the second week, whereas the first significant and equivalent increase in nuclear receptor occurs in the fourth week. The latter reflects reported increases in oestradiol availability thought to lead to complete feminine sexual differentiation. The presence of nuclear receptors in the newborn suggests a requirement for oestrogenic stimulation in early development.

Stimulation of oligonucleotide binding of estradiol receptor complexes by accessory proteins

During purification of E2R using oligo(dT)-cellulose chromatography, a receptor accessory factor (RAF) was identified in the cytosol of mouse kidney. This factor stimulates the binding of purified E2R to oligo(dT)-, oligo(dC)-, and oligo(dA)-cellulose as well as to DNA cellulose. It is a heat-stable, trypsin-resistant protein with an apparent molecular weight of between 10 and 30,000 daltons. Although structurally unrelated, similar stimulation of oligonucleotide binding was seen with calf thymus histones and, to a lesser extent, egg white lysozyme. Individual histones, especially H2a, H2B, and H3, also facilitate rebinding of purified E2R to oligo(dT)-cellulose, while H1 is less effective. Furthermore, histones stabilize the holoreceptor during sedimentation at 4 degrees and 12 degrees C. The N- and C-terminal half molecules of H2b were generated by cyanogen bromide-mediated cleavage and the N-terminal half was found to duplicate the effects of the parent molecule, both in binding and holoreceptor stabilization. These data suggest that the in vivo binding of E2R to DNA can be modulated by accessory proteins of cytosol and nuclear origin.

Uterine oestrogen-receptor binding to oligo(dT)-cellulose. An inhibitor from hypothalamic cytosol

The binding of rat uterine cytosol oestrogen receptor in vitro to oligo(dT)-cellulose is mediated by an activating factor in the cytosol [Thrower, Hall, Lim & Davison (1976) Biochem. J. 160, 271-280]. A potent inhibitor of this binding is present in hypothalamic cytosol. This inhibitor may have a role in vivo in regulating receptor translocation in the hypothalamus.

Activated steroid-receptor complex. Comparison of assays using DNA-cellulose or homologous nuclei

When soluble steroid-receptor complexes are exposed to DNA-cellulose only activated complexes bind. The specificity of the binding was shown by its dependence on the presence of hormone during activation. However, prolonged incubation of non-activated steroid-receptor complexes with DNA-cellulose led to a progressive activation of these complexes. When the same hepatic cytosol containing heat-activated [3H]triamcinolone acetonide-receptor complexes was titrated by high concentrations of nuclei or DNA-cellulose the former bound 75% of the complexes, the later only 40%. This decreased binding was due on the one hand to a lower initial interaction between DNA-cellulose and activated complexes than between nuclei and these complexes and on the other hand to increased losses during washes when DNA-cellulose was used. For these reasons nuclei and not DNA-cellulose should be used when accurate measurements of the concentration of activated complexes are required. When only comparative data are needed DNA-cellulose may, however, be employed.

The oestrogen receptor in the rat uterus in relation to intra-uterine devices and the oestrous cycle

We investigated the binding characteristics, content and intracellular distribution of nuclear and cytosolic oestrogen receptors in the uteri of rats bearing a unilateral intrauterine device, fitted 14--18 days earlier, at four phases of a 5-day oestrous cycle. The patterns of changes in wet weight and content of cytosolic and nuclear receptor that normally occur during the oestrous cycle were not altered by the presence of the device. At all stages of the cycle the intra-uterine-device-containing horn had a greater wet weight and a correspondingly higher content of cytosolic receptor than its contralateral control horn, the cellular concentration of cytosolic receptor being apparently maintained. However, the intra-uterine-device-containing horn had significantly lower cellular concentrations (i.e. per mg of DNA) of nuclear receptor, particularly at late dioestrus and pro-oestrus. Thus the treated horn showed a decreased translocation of receptor in response to increases in circulating oestrogens. Both horns contained equivalent amounts of an activating factor implicated in translocation and measured in vitro by binding of cytosol receptor to oligo(dT)-cellulose. The presence of an intra-uterine device neither altered the dissociation constants (Kd) of the nuclear and cytosolic oestrogen-receptor complexes nor the stability of the nuclear receptor complex in vitro. The decreased translocation cannot thus be directly attributed to changes in the physical properties of the receptor. This decrease may be responsible for the anti-fertility effect of the intra-uterine device (which affects only the treated horn of the bicornuate rat uterus), since implantation of the blastocyst requires correct concentrations of nuclear oestrogen receptor.

Intracellular relationships of the oestrogen receptor in the rat uterus and hypothalamus during the oestrous cycle

Simultaneous measurements were made of the specific oestrogen receptor in the nuclear and cytosol fractions prepared from the uterus and hypothalamus of 50--81-day-old female rats undergoing a 4-day oestrous cycle. In the uterus, the content of nuclear receptor fluctuated in concert with known cyclic changes in the secretion of oestrogen, being maximal at pro-oestrus. Over the period of 50--81 days, the nuclear content at all phases increased with age, again corresponding to known age-related increases in ovarian secretion of oestrogen. This age-related increase in nuclear content, averaged from the values of the different phases in each age group, was related to equivalent increases in uterine wet weight, an increase of 1 pmol of receptor being accompanied by an increase of 80--90 mg. The concentration of cytosol receptor was maintained constant, with respect to wet weight, throughout the cycle and with age, irrespective of changes in nuclear content. In the uterus of normal mature females, translocation of receptor into the nucleus did not lead to depletion of cytosol receptor, suggesting a process of continuous replenishment/synthesis. In the hypothalamus, the nuclear content of oestrogen receptor was also maximal at pro-oestrus. In contrast with the uterus, the content of hypothalamic cytosol receptor was minimal at this phase and reflects depletion of the cytosol receptor, possibly as a result of translocation. The extent of translocation was low compared with that in the uterus and did not alter with age during the age-period studied. This low nuclear binding of the receptor in vivo is discussed in relation to the presence of a cytosol factor, present in limiting amounts, which in vitro mediates the binding of cytosol receptor to oligo(dT)-cellulose. The difference in the physiological response of the uterus and of the hypothalamus to oestrogens may be related to the extent of nuclear binding of receptor.

The biochemistry of brain development and mental retardation

Mental retardation may be associated with a number of environmental factors such as undernutrition, lead poisoning or exposure to neuroactive drugs during a critical period of brain development. Possible biochemical mechanisms operating in these various conditions and in animal models are reviewed in relation to the vulnerable period hypothesis. Small brains are common in the mentally retarded, and this may be related to a developmental abnormality particularly at the level of the synapse.