Effects of ethidium bromide on the extractability of nuclear receptor-estrogen complex.

In previous reports we challenged the concept that uterine nuclei of rats contain two forms of estrogen receptors, one salt extractable and the other salt resistant. Although it is likely that a certain fraction of the nuclear bound receptor-estrogen complex exists as a ternary high-affinity acceptor-receptor-estrogen complex, current salt extraction procedures do not allow discrimination between receptor-17beta-estradiol complexes associated with high-affinity and low-affinity nuclear binding sites. Recent reports suggested that the DNA-intercalating agent ethidium bromide selectively extracted those sites that appeared to be salt resistant. In view of contradictory reports to this effect, we have attempted to clarify this issue. The data presented indicate that ethidium bromide is not a useful tool for the identification of a specific class ("salt-resistant") of nuclear binding sites for receptor-17beta-estradiol complexes. This conclusion is based on measurement of nuclear bound receptor-17-beta-estradiol following KCl and/or ethidium bromide extraction by using both the direct assay and the nuclear exchange assay.

Effect of chemotherapeutic agents on the formation of estrogen-receptor complex in human breast tumor cytosol.

We have examined the effect of Adriamycin (doxorubicin), cytoxan, methotrexate, and oncovin on [3H]estradiol binding to the cytoplasmic estrogen receptor of rat uterus and human breast tumors. When the estrogen binding assay was performed in the presence of these drugs over concentrations ranging from 1 x 10(-8) to 1 x 10(-4) M, no effect on the formation of specific [3H]estradiol-receptor complexes as determined by the dextran-coated charcoal method was observed.

Post-coital contraceptive activity and estrogen receptor binding affinity of phenolic steroids.

Estradiol, estradiol-16alpha, estriol and a series of positional isomers of estriol were tested for their post-coital contraceptive activity, and their ability to compete with estradiol for the cytosolic estrogen receptor protein of rat uteri. Estrogenicity was determined for each compound in immature rats with single injections and in mature castrated rats by injecting the lowest fully contraceptive dose for four consecutive days. All compounds were active anti-implantational agents, varying in required dosage from 4 mug to 2000 mug (total dosage over 4 days). The rank order or contraceptive activity was found to be: estradiol greater than estriol = epiestriol greater than 11beta - (OH) - estradiol greater than estradiol - 16alpha greater than 7alpha-(OH)-estradiol greater than 6beta-(OH)-estradiol, while the order of estrogenicity at levels of contraceptive activity in the ovariectomized mature rat was: epiestriol = estriol less than 7 alpha - (OH) - estradiol less than estradiol - 16alpha less than 6beta - (OH) - estradiol = 11beta - (OH)- estradiol less than estradiol-17beta. Reasonably good correlation between competition for estrogen receptor and anti-implantational activity was observed. The most active binding competitors were estradiol-16alpha, epiestriol, and estriol which showed an affinity from 50-20% that of estradiol, while the other compounds had 3% or less binding competition for estradiol.

Differences in the physicochemical characteristics of androgen-receptor complexes formed in vivo and in vitro.

This study compares the physicochemical characteristics of the androgen-receptor hormone complexes formed in vitro by incubation of prostatic cytosol with tritiated 5 alpha-dihydrotestosterone (DHT) and methyltrienolone (R1881; 17 beta-hydroxy-17 alpha-methyl-4,9, 11-estra-trien-3-one) with those of hormone-receptor complexes formed in vivo upon hormone injection. [3H]DHT and [3H]R1881 had similar affinities for the androgen receptor in vitro (Kd = 0.3 nM). Dissociation of DHT at 0 C from the receptor complexes formed in vitro or in vivo was much slower than that of R1881. Furthermore, DHT and R1881 dissociated much more slowly from the cytoplasmic receptor labeled in vivo than in vitro. The sedimentation characteristics of the in vitro and in vivo formed hormone-receptor complexes were similar when analyzed on sucrose density gradients containing 400 mM KCl and 10 mM Na2MoO4. Higher concentrations (50 mM) of Na2MoO4, however, prevented the salt-induced disaggregation of the in vitro formed receptor complexes, which sedimented at 7-8S. In contrast, androgen-receptor complexes formed in vivo sedimented as 5.5S complexes, even in the presence of 50 mM molybdate. These differences were paralleled by the elution patterns from Sephacryl S-200. A further difference was found in the sensitivity of the hormone-receptor complex to the organic mercurial reagent mersalyl acid. This reagent, at 0.2 mM, induced ligand exchange of 80-90% of the in vitro formed hormone-receptor complexes, whereas it was nearly ineffective with complexes formed in vivo. Finally, the prostatic androgen receptor content 1 h after injection of radioactive steroid into castrated rats was 12-14 pmol/mg DNA, while incubation of tissue slices at 37 C yielded only 3-4 pmol receptor/mg DNA.

Binding of 7 alpha, 17 alpha-dimethyl-19-nortestosterone (mibolerone) to androgen and progesterone receptors in human and animal tissues.

In rat uterus and prostate, 7 alpha, 17 alpha-dimethyl-19-nortestosterone (DMNT) binds to the androgen receptor specifically and with high affinity. However, this steroid does not bind to glucocorticoid receptors, since it does not displace binding of [3H]triamcinolone acetonide in calf thymus cytosol. In calf uterine and human breast tumor cytosols DMNT binds to the androgen and progesterone receptors, since binding of [3H] DMNT is displaced by unlabeled 16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3, 20-dione triamcinolone acetonide, and 5 alpha-dihydrotestosterone (DHT). Conversely, binding of [3H]16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione is effectively competed for by unlabeled DMNT but not by DHT. The observed differences in binding of [3H]DMNT to rat and calf uterine cytosols suggest the species specificity of progesterone receptors. Unlike DHT, DMNT has no appreciable binding to human sex-steroid binding globulin. These findings suggest DMNT as a suitable ligand for measurement and characterization of androgen receptors in rat and human prostate.

Interaction of estradiol and estriol with uterine estrogen receptor in vivo and in excised uteri or cell suspensions at 37 C: noncooperative estradiol binding and absence of estriol inhibition of estradiol-induced receptor activation and transformation.

The partial agonist and antagonist properties of estriol (E3) have been related to the brief nuclear retention of receptor-E3 complexes and to the lower affinity of E3 for the receptor compared to estradiol (E2). More recently, it was proposed that the partial agonist/antagonist activity of E3 may be due to its ability to eliminate positive cooperative binding of [3H]E2 to cytosolic estrogen receptor. In this model, positive cooperativity is related to receptor activation and transformation. We first examined the long term effects of E3 on E2 action in vivo. Mature ovariectomized rats were treated for 16 days with E2, E3, or mixtures of these two substances delivered through Alzet pumps at a constant hourly rate (E2, 0.04 microgram; E3, 0.4 and 0.04 microgram; E2 and E3, 0.04 and 0.4 microgram). The effects of E3 on uterine growth, induction of progesterone receptor synthesis, and activation (nuclear binding) of estrogen receptor suggest that when given continuously, E3 acts as a full agonist and does not inhibit E2 action. Furthermore, incubation of uteri at 37 C with [3H]E2 in the presence of a 1- to 20-fold molar excess of nonradioactive E3 did not alter the subcellular distribution of receptor-[3H]E2 complexes (80% nuclear and 20% cytosolic), demonstrating that E3 does not inhibit E2-induced receptor activation (i.e. the increased nuclear binding of receptor). Similarly, 4S to 5S transformation of [3H]E2-labeled estrogen receptor in intact uteri was not inhibited by E3. Equilibrium binding of [3H]E2 to uterine cell suspensions at physiological temperature (37 C) was noncooperative; nonradioactive E3 did not alter the affinity of the estrogen receptor for [3H]E2; Dixon plot analysis indicates that E3 is a purely competitive inhibitor of [3H]E2 binding. This, in conjunction with the lower affinity of the receptor for E3 than for E2, adequately explains the agonistic-antagonistic properties of E3.(ABSTRACT TRUNCATED AT 250 WORDS)

Conversion of estrogen receptor from a state with low affinity for estradiol into a state of higher affinity does not require 4S to 5S dimerization.

This study was undertaken to establish whether the heat-promoted conversion of receptor-estradiol complex (RE2) from a state with fast into a state with slow E2 dissociation requires 8S/4S to 5S transformation. The calf uterine estrogen receptor labeled with [3H]E2 at 0 C (state with low affinity for E2) was immobilized on hydroxylapatite (HAP) in the absence (8S oligomer) or presence (4S monomer) of 0.4 M KCl and heated at 28 C in the presence of unlabeled diethylstilbestrol. Under these conditions, the dissociation of [3H]E2 was biphasic and occurred at rates similar to those obtained with R[3H]E2 free in cytosol. In contrast to the latter, however, the heat-promoted conversion of HAP-immobilized R[3H]E2 into a state of higher affinity for E2 was not accompanied by receptor dimerization, since the HAP eluate (0.4 M phosphate buffer) contained only the 4S monomer; upon reheating or desalting of this eluate, 4S to 5S dimerization occurred. The heat-promoted formation of 4S RE2 monomers with higher affinity for E2 was not due to monomer-HAP interactions, since even after elution from HAP, the 4S RE2 remained in the state of higher affinity for E2. Addition of pyridoxal 5'-phosphate to slow dissociating, high affinity 5S R[3H]E2 dimers free in cytosol induced rapid [3H]E2 dissociation, although the receptor remained unaltered in the transformed dimerized state. The effect of PLP was readily reversed by the addition of lysine. It is proposed that the 4S receptor monomers exist in two conformational states; upon E2 binding to the low affinity state, conformational changes result in stronger interactions between the steroid and the amino acid residues of the estrogen-binding domain; thus, the rate of E2 dissociation decreases. The formation of this 4S RE2 state with higher affinity for E2 is independent from receptor dimerization. A model is presented in which 4S to 5S transformation may lead to stabilization of 4S monomers in the conformation with higher affinity for E2.

The synthesis of ribosomal RNA and ribosomal protein and their incorporation into ribosomes in the uterus of the oestrogen-stimulated immature rat.

The effect of oestrogen on the synthesis of ribosomal proteins in the uterus of the immature rat has been investigated. Stimulated synthesis peaks, at 6-7-times control levels, 12 h after a single administration of the hormone. The stimulated synthesis and incorporation of newly made proteins into ribosomal particles exhibit very similar kinetics. The incorporation of newly made rRNA into ribosomes mirrors that of ribosomal protein but lags several hours behind the peak of oestrogen-stimulated rRNA synthesis.

Central alpha-adrenoceptors during the development of hypertension in rats on high and low salt intake.

Our purpose was to investigate the binding characteristics of central alpha-adrenoceptors during the early stages of the development of hypertension in rats on high and low salt (NaCl) intake. We measured alpha 1-[( 3H]prazosin) and alpha 2-[( 3H]rauwolscine) binding in membranes of the hypothalamus and medulla oblongata of six groups of young Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and subtotally nephrectomized WKY (SN) rats with mean arterial blood pressure (MAP) ranging from normotensive to hypertensive levels after 1 week of salt restriction or loading. In the hypothalamus the SN-high salt rats and both SHR groups had elevated alpha 1-number but there was no change in alpha 2-number. Moreover, MAP was positively correlated with mean hypothalamic alpha 1-number in the six groups. In the medulla oblongata alpha 1-number was unaffected. However, high salt diet influenced medullary alpha 2-binding in the opposite manner in WKY rats versus SN rats and SHR. In these latter groups the affinity was increased and the number decreased in response to high salt intake. Furthermore, a positive correlation between MAP and mean alpha 1:alpha 2 ratio existed in both the hypothalamus and the medulla of the six groups. The data suggest that hypothalamic alpha 1-binding capacity was increased in SHR due principally to a genetic condition which is mimicked by salt loading in the SN rats. Medullary alpha 2-adrenoceptors of WKY, which remained normotensive despite salt loading, responded differently to high salt intake than those of the SN and SHR, whose blood pressure rose significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Pramipexole, a dopamine D2 autoreceptor agonist, decreases the extracellular concentration of dopamine in vivo.

Pramipexole (SND 919) is a dopamine D2 autoreceptor agonist which is structurally related to talipexole (B-HT 920), a potential antipsychotic agent. The aim of this study was to investigate the effects of pramipexole on the extracellular concentration of dopamine in vivo. Dopamine and its metabolites, 3,4-dihydrophenylacetic acid and homovanillic acid, were measured in the anterior striatum of freely moving rats by microdialysis and high-performance liquid chromatography with electrochemical detection. Pramipexole (30 and 100 micrograms/kg) caused long-lasting decreases in the extracellular concentrations of dopamine and its metabolites. Talipexole (30 micrograms/kg) produced similar effects. Sulpiride (5 mg/kg), a selective dopamine D2 antagonist, caused a transient increase in the concentration of dopamine and long-lasting increases in the concentrations of its metabolites; it also reversed the effects of pramipexole. SCH-23390 (100 micrograms/kg), a selective dopamine D1 receptor antagonist, caused a transient increase in the concentration of dopamine but did not affect the concentrations of the metabolites. SCH-23390 failed to reverse the effects of pramipexole. These results indicate that pramipexole reduces the extracellular concentrations of dopamine and its metabolites in vivo through a reversible interaction with the dopamine D2 receptor.

WAL 2014--a muscarinic agonist with preferential neuron-stimulating properties.

The ability of WAL 2014 to elicit muscarinic responses was investigated in various in vitro and in vivo models. In CHO cells transfected with human m1- or m3- receptor genes, WAL 2014 was clearly more effective in stimulating the M1-mediated PI response. In isolated tissue preparations, WAL 2014 exhibited full agonist properties in the rabbit vas deferens (putative M1 receptor) and behaved like a partial agonist at M2 receptors in the atrium and M3 receptors in the ileum of guinea-pigs. In the pithed rat, in which the increase in blood pressure is mediated through a stimulation of M1 receptors in sympathetic ganglia, WAL 2014 produced a full dose response curve, whereas the reference compounds RS 86 and arecoline exhibited a bell-shaped behaviour. This is in accord with the view that WAL 2014 selectively activates M1 receptors in sympathetic ganglia, whereas conventional agonists in the same dose range stimulate both ganglionic M1 and vascular M3 receptors. The preferential neuron-stimulating properties were confirmed by EEG recording in the rabbit, in which muscarinic activation occurred at doses similar to those for ganglionic stimulation in the pithed rat. On the other hand, higher doses of WAL 2014 were needed to elicit muscarinic effects in peripheral effector organs, i.e. bradycardia, urinary bladder contraction and increase in airway resistance. It is concluded that WAL 2014 due to its preferential neuronal activity is a promising candidate for a cholinergic substitution therapy in Alzheimer's disease.

An improved procedure for the preparation of rat uterine cell suspensions.

In the present paper we report on an improved procedure for the preparation of free uterine cells which avoids the use of trypsin and employs very low concentration of collagenase. The cells released mechanically from the digested tissue are constantly removed from the enzyme containing medium, thus minimizing exposure to collagenase. 60%-70% of the cells which make up the intact uterus are obtained as free cells and 95% of these cells are viable for at least 15 hours at 37 degrees. Metabolic integrity was assessed by measuring the cell's ability to oxidize glucose and synthesize proteins over extended periods of time. The membrane leucine carrier protein and the membrane Na+/K+ ATPase were found to be fully functional. Electron microscopic analysis of the cells confirmed their structural integrity. Data are presented illustrating that with this system the estrogen binding protein is stable at physiological temperatures. The cells contain approximately 30,000 specific estrogen binding sites, with an apparent KA of 5--6 x 10(9) M-1. At 37 degrees 80% of the hormone receptor complexes were in the nuclear fraction, 20% in the cytoplasm. The similarity of the estrogen receptor binding parameters with those measured in the intact tissue after in vivo hormone adminsistration, together with the cells' structural and metabolic integrity make this procedure for the preparation of uterine cell suspensions in high yields particularly suitable for studies in which minimal cell injury is an essential prerequisite.

Interaction of cyproterone acetate with rat prostatic androgen receptors.

We have investigated the binding of cyproterone acetate (CA) to cytosolic androgen receptors (RC) and translocation of the RCCA complex into the nucleus. In a cell-free system (3H)CA binds to cytosolic androgen receptors with high affinity (KD = 11.6 nM) and limited capacity (180-200 femtomoles/mg protein). (3H)CA, however, dissociates very rapidly from the cytosolic and nuclear androgen receptors (Rn) at 0 degree C. Incubation of RC (3H)CA at 20 degrees C increased its ability to bind to nuclei. Translocation of RC (3H)CA to nuclei of intact cells was demonstrated after incubation of prostatic tissue with (3H)CA in tissue culture medium at 37 degrees C. In vivo administration of CA to castrated rats promoted RCCA translocation but did not induce androgen receptor replenishment. These data demonstrate that CA binds to and translocates androgen receptors to nuclei without concomitant receptor replenishment.

Changes in the sedimentation properties of cytosolic androgen receptors associated with activation in vitro and in vivo.

In cell-free systems androgen receptor (AR) labeled with (3H)DHT at 0 degrees C in the presence of 50mM molybdate remains unactivated (less than 3% binding to nuclei) and untransformed (7-8S on sucrose density gradients containing 0.4M KCl and 50mM molybdate). In the absence of molybdate, however, these complexes undergo activation and transformation even at 0 degrees C, albeit, very slowly. Incubation of unactivated, untransformed AR complexes at 18 degrees C, or at 0 degrees C in the presence of 0.4M KCl, greatly accelerated both activation and transformation. Activation and transformation are also associated with formation of high affinity (3H)DHT-receptor complexes as indicated by decreased rates of (3H)DHT dissociation from the receptor. Cytosolic AR complexes labeled with (3H)DHT in tissue slices at 37 degrees C, or in vivo, undergo rapid activation, transformation and nuclear translocation. The data suggest that activation and transformation of cytosolic AR in cell-free systems is associated with changes in the physicochemical properties of AR similar to those occurring upon hormone binding in intact cells and in vivo.

Studies on the mechanism of estradiol uptake by rat uterine cells and on estradiol binding to uterine plasma membranes.

A method for the preparation of viable uterine cell suspensions is described. Using this system the kinetics of estradiol uptake were studied in order to asses whether the steroid enters uterine cells by passive diffusion (1) or protein mediated diffusion (2). The data presented show that a) the rates of estradiol entry are nonsaturable; b) temperature dependence of uptake kinetics gives a linear Arrhenius plot; c) E2-6-CMO-BSA does not inhibit 3H-E2 uptake; d) uterine plasma membranes do not contain specific estrogen binding sites. Thus, estrogen uptake occures by passive diffusion.

The effects of oestradiol-17 beta on the synthesis and modification of ribosomal proteins in the uterus of the immature rat.

The effects of oestrogen on the incorporation of newly-made ribosomal proteins into the ribosomes of the immature rat uterus has been investigated. Different newly-made proteins were shown to enter ribosomes at different rates and there was some evidence that the hormone exerted differential effects. Oestradiol also stimulated the phosphorylation of ribosomal protein S6 but the effect could be explained by hormone-induced changes in the precursor pools.

Application and validation of an ion-exchange high-performance liquid chromatographic method for measuring adenine nucleotides, creatine and creatine phosphate in mouse brain.

We have modified and applied an ion-exchange high-performance liquid chromatographic method for measuring adenine nucleotides (adenosine monophosphate, adenosine diphosphate and adenosine triphosphate) as well as creatine and creatine phosphate in brain tissue. There was a linear relationship between the area of each peak and the amount of standard injected onto the column in the concentration range 0.5-25 nmol per 50 microliters. The concentrations of creatine phosphate and creatine were not stable in a standard mixture for 20 h at 4 degrees C unless the pH of the standard mixture was adjusted to neutral. We therefore strongly recommended the neutralization of all standard mixtures and samples before storage. The measurements of adenine nucleotides, creatine and phosphate in control mouse brain determined by this method agreed well with an enzymic method of nucleotide measurement. Furthermore, both methods detected similar decreases in the concentrations of adenosine triphosphate and creatine phosphate, together with concomitant increases in the concentrations of adenosine diphosphate, adenosine monophosphate and creatine when mice were placed under anoxic conditions (either 30 s or 2 min); these changes were greater after 2 min of anoxia than after 30 s of anoxia.