Control of estrogen and androgen receptors in the rat pineal gland by catecholamine transmitter

Sucrose gradient studies of rat pineal cytosol incubated with ³H-estradiol (female pineals) or ³H-5 α -dihydrotestosterone (male pineals) revealed a radioactivity peak in the 8 S region which disappeared after superior cervical ganglionectomy or incubation with excess unlabeled hormone. Ganglionectomy decreased significantly estradiol and testosterone uptake by the pineal gland $\text{in vitro}$ as well as high affinity binding to pineal cytoplasmic and nuclear components. Norepinephrine treatment counteracted all the effects of ganglionectomy but was unable to modify hormone uptake and binding by the pineal gland of sham-operated controls. Pre-treatment with actinomycin D or propranolol but not with phentolamine impaired norepinephrine effects; propranolol blockage however was only partial. Administration of isoproterenol, L-dopa or phentolamine increased hormone uptake by denervated pineals. The effects of isoproterenol were also observed $\text{in vitro}$ and were blocked by propranolol. These results indicate that sex steroid receptors in the pinealocytes are controlled by norepinephrine via beta-adrenergic receptors and that depletion of neural norepinephrine enhanced responsiveness of pineal hormone receptors to exogenous catecholamines.     

Interactions of 17beta-estradiol and L-norepinephrine on the rat uterus.

Norepinephrine increased the in vitro uptake of 3H-estradiol by the uterus of spayed rats. This effect was observed at 15 and 30 min but not at 90 min. Norepinephrine also increased the binding of 3H-estradiol by the nuclear (p less than 0.02) and the cytosol fractions (p less than 0.01) when incubated with uterine homogenates, suggesting that norepinephrine does not require the presence of the intact tissue to exert its effects. The in vivo uptake of 3H-estradiol and the determination of the number of binding sites were performed in the uterus of rats treated with estradiol and estradiol plus norepinephrine. Norepinephrine alone increased the uptake of 3H-estradiol and the number of binding sites. The highest increment in both parameters was observed in the uterus of rats treated with estradiol plus norepinephrine. The estradiol Ka of the rat uterus cytosol treated with estradiol alone or plus norepinephrine was higher than that observed in the group without estradiol, suggesting the presence of different proteins that bind estradiol. These results indicate that norepinephrine increases the entrance of estradiol into the rat uterus both in vitro and in vivo.     

Estradiol-17β receptors in the immature rat ovary

Estradiol binding components in the cytosol and nuclear fractions of the ovary from immature rats (22–28 days old) were characterized by $\text{in vitro}$ methods. Several of the biochemical characteristics of the estradiol binding components in the ovarian tissue were compared with the estradiol receptor from the uterus. The results suggest that the ovarian estradiol binding components are similar to the specific high affinity estradiol receptors in the uterus. In the cytosol of intact rat ovary a significant fraction of the total binding sites was found to be occupied, presumably by the endogenous estrogen. Following hypophysectomy there was a significant increase in the available cytosol binding sites. Evidence for translocation of cytosol receptor-estrogen (RE) complex to the nucleus was obtained for the ovary. The sedimentation properties of the RE complex of the ovary and the uterus are similar. The ovarian cytosol RE complex sediments at 7-8S in glycerol gradients at low ionic strength and at 4S in sucrose gradients at high ionic strength. Following extraction with 0.4 M KCl the ovarain nuclear RE complex sediments at 5S in sucrose gradients which is identical to that of the uterine nuclear receptor.     

Inhibition of rat uterine estradiol receptor by aurintricarboxylic acid

Estradiol-receptor complex from rat uterus has been shown to have an affinity for DNA-cellulose and ATP-Sepharose. This DNA and ATP binding of estradiol receptor was observed to be sensitive to low concentrations (0.01–0.2mM) of aurintricarboxylic acid. The inhibitor was more effective when added to preparations that contained activated estradiol-receptor complex. Steroid binding properties of the receptor remained intact under the above conditions as judged by charcoal adsorption assays and sucrose gradient analysis. In addition, a 40% inhibition in the nuclear translocation of cytosol estradiol receptor was observed when rat uteri were incubated with 10nM [³H] estradiol under an atmosphere of 95% O₂ and 5% CO₂ in the presence of aurintric-carboxylic acid. Our results suggest that aurintricarboxylic acid is an effective inhibitor of rat uterine estradiol receptor and that it may be acting by interfering with site(s) on the estradiol receptor which may be exposed upon activation and are subsequently involved in processes such as ATP binding, nuclear uptake and DNA binding.     

Two high affinity estrogen binding proteins of different specificity in the immature rat uterus cytosol

The presence of two high affinity estrogen binding proteins in the uterine cytosol of the immature rat has been observed.Besides the 8 S cytosol estrogen $\text{receptor}$, there is a 4–5 S fraction binding estradiol and estrone with a large capacity. In fact, the two binding systems have a different affinity for estradiol and estrone, the receptor binding more the former and the 4–5 S fraction more the latter. Exposure of the cytosol to specific anti-α₁-Fetoprotein antibodies suppresses a large part of the 4–5 S binder, if not the totality. Moreover the estrogen binding 4–5 S fraction decreases with increasing age until puberty, while the $\text{receptor}$ increases. These results suggest therefore that the estradiol-estrone binding 4–5 S peak of the uterine cytosol is mainly made up of Estradiol Binding Plasma Protein-α₁-Fetoprotein (EBP-AFP). Also they confirm that “cytosol” should be taken as an operational fraction which may include extracellular components.During the course of these experiments, it has been observed that the increase of the estradiol $\text{receptor}$ is more rapid than the other uterine cytosol proteins until the 8th day, and that there is a second period of growth when it follows the development of the uterus and of the animal, as if it had reached a constant number of binding sites per cell.     

Reduction of LH-RH pituitary and estradiol uterine binding sites by a superactive analog of luteinizing hormone-releasing hormone

The ability of the Luteinizing Hormone-Releasing Hormone (LH-RH) analogs to displace LH-RH from its pituitary receptors was evaluated $\text{in}\text{vitro}$. The two superactive analogs tested showed higher potency than the antagonists and LH-RH itself, D-Trp⁶-LH-RH being the most potent. The LH-RH specific binding activity in the pituitary fluctuated throughout the age of the rats. The highest number of LH-RH binding sites were seen on day 35 of age (276 fmol × 10^?2/pit) and an increment was induced by 0.05 μg D-Trp⁶-LH-RH (400 fmol × 10^?2/pit). However, 1 μg D-Trp⁶-LH-RH reduced the binding of LH-RH at all the times studied. In the control animals the number of estradiol binding sites increased on day 42 of age, and 0.05 μg D-Trp⁶-LH-RH augmented them on day 35 of age. On the contrary, 1 μg D-Trp⁶-LH-RH diminished the estradiol uterine receptors at all the times studied. Similar results were obtained in the ovariectomized-hypophysectomized rats on day 35 of age. Our studies demonstrated a biphasic action of D-Trp⁶-LH-RH on LH-RH pituitary receptors and a direct effect on uterus which could be mediated through the uterine estradiol receptors.     

Effects of naloxone and acetylcholine on medial thalamic and cortical units in naive and morphine dependent rats.

The administration of 0.5 mg of testosterone propionate (TP) for 3 days to castrated male rats caused ³H-leucine incorporation into pineal proteins to increase significantly by 79%. TP effects depended on time of administration; rats receiving TP at 06.00 h exhibited a significant 150% increase in pineal protein synthesis 24 h later whereas rats injected at 14.00 h only showed a 54% increase in ³H-leucine incorporation into proteins. Superior cervical ganglionectomy decreased pineal testosterone uptake $\text{in vitro}$ by 21% and pineal protein synthesis by 27%; in addition it blocked the stimulatory effects of TP on protein synthesis. Ganglionectomy also modified the $\text{in vitro}$ metabolism of testosterone by pineal cells; it increased the amounts of ³H-androstenedione and decreased ³H-5∝-androstanedione extracted from pineal glands incubated with ³H-testosterone. These results indicate that the sympathetic nervous input reaching the pineal via the superior cervical ganglia is important to modulate the early steps of androgen action on the pinealocytes.     

Studies on the possible role of 2-OH-estradiol in the control of sexual behavior in female rats

$\text{In vitro}$ studies have revealed that 2-OH-estradiol can be produced in the brain and that it can compete with estradiol for hypothalamic cytosol binding sites. In the present study ovariectomized female rats received 2-OH-estradiol via sc or iv injections and/or via direct intracerebral implantation either alone or in combination with vehicles, estradiol or testosterone. Behavioral tests after sc progesterone priming indicated that 2-OH-estradiol has relatively weak estrogenic, and no apparent anti-estrogenic or antiaromatization activity in the induction of sexual receptivity.     

The aging leydig cell: VII. Cytoplasmic estradiol receptors

Plasma estradiol and cytosolic estradiol receptor levels of testes were determined in a group of young (2–3 months) and old (24 months) Sprague-Dawley rats. Estradiol binding sites for the young rats averaged 5.6 ± 0.3 fmol/mg protein ($\text{x}\text{±}\text{SE, n}\text{=12}$), which was comparable to that of the old rats, 5.7 ± 0.3 fmol/mg protein (n=12). Using Scatchard analyses, the association constants at equilibrium of estradiol receptor binding of the old and young rats were the same, 6.1 × 10¹⁰M^?1. Plasma estradiol levels were also similar in both groups-19.6 ± 2.8 pg/ ml (n=14) for the young and 19.2 ± 2.6 pg/ml (n=10) for the old rats. Our results suggest that impaired testosterone biosynthesis in old rats was not due to elevated plasma estradiol levels or to differences in testicular estradiol receptor content.     

Oxytocin receptors in rat oviduct.

Particles from rat oviduct homogenates sedimenting between 1,000 × g for 10 min and 48,000 × g for 30 min bound [³H]oxytocin $\text{in vitro}$. The apparent K_d for oxytocin binding to high affinity sites in particles prepared from estrogen-treated rats was 1.8 × 10^?9 M. About 215 fmoles of oxytocin were bound per mg of particulate protein. Oviducal preparations from untreated rats had about 25% the affinity for oxytocin of preparations from estrogen-treated rats. Oxytocin analogues were bound to oviducal particles in the same rank order as their uterotonic potencies: (desamino)oxytocin > (4-threonine)oxytocin > oxytocin > (8-lysine)vasopressin ? desaminotocinol. No oxytocin binding could be shown with the particulate fractions from rat ovary. The binding of oxytocin to the oviduct and uterus are similar in affinity, number of binding sites, ligand specificity, and the increase in response to estrogen treatment.     

Concepts related to salt resistant estradiol receptors in rat uterine nuclei: nuclear matrix

When ³H-estradiol (0.1 μg) is injected into immature female rats, virtually all of the label that is recovered with uterine nuclei can be solubilized by 0.6 M KCl. Salt resistant uterine nuclear estrogen binding sites do not become labeled within one hour after the injection of ³H-estradiol, but these sites do exist and can be revealed when isolated nuclei are subjected to an $\text{in vitro}$ estradiol exchange assay. These saturable, high affinity salt resistant sites appear to be associated with the uterine nuclear matrix, a residual structure of the nucleus.     

Androgen on the estrogen receptor I — Binding and in vivo nuclear translocation

In the immature rat uterus, high concentrations of androgens competed specifically with estradiol on the estrogen receptor (RE). This competition was stereospecific for C₁₉ steroids bearing a 17β and/or 3 hydroxyl group. Very low affinity ligands, such as testosterone, could not compete with estradiol at equilibrium but decreased the association rate of estradiol on its receptor. High doses (> 0.4mg) of 5 α aihydrotestosterone provoked $\text{in vivo}$ as $\text{in vitro}$ the nuclear translocation of RE. The nuclear receptor thus formed displayed the same 5.2 S sedimentation constant as that induced by estradiol. We conclude that the weak affinity binding of androgens to the estrogen receptor is sufficient to induce its nuclear translocation $\text{in vivo}$ provided androgen concentration is high enough in uterus to occupy the estradiol binding site. Conversely, progesterone which does not bind RE could not provoke its nuclear translocation.     

ATP-dependent enzyme activating hormone binding of estradiol receptor

Mouse uterus estradiol receptor undergoes a inactivation-reactivation process “in vitro”. The specific estrogen binding activity inactivated by nuclei, apparently through a dephosphorylation process (1,2,3), is reactivated by an ATP-dependent process. The enzyme reactivating the receptor has been purified from calf uterus cytosol. It shows high affinity for the inactive receptor (K_m of ～ 0.3 × 10^?9 mol of 17β-estradiol binding sites/l); it is simulated by MgCl₂ and CaCl₂. Present and previous results suggest that in cytoplasm of intact cells a phosphorylation process makes the receptor able to bind hormone and in nuclei dephosphorylation of receptor causes loss of hormone binding activity.     

Rapid modulation by progesterone and tamoxifen of estradiol effects on nuclear histone acetylation in the uterus of the fetal guinea pig

The effect of estradiol, progesterone, tamoxifen, estradiol + progesterone or estradiol + tamoxifen on the [³H]acetylation of histones in the fetal uterus of guinea pig was studied. The fetuses were injected subcutaneously ‘in situ’ with the hormones or $\text{tamoxifen}\text{+ [}{}^3\text{H}\text{]}\text{acetate}$ alone. In 10 min, estradiol stimulated the acetylation of histone 10–12-times with respect to the control animals. Progesterone and tamoxifen blocked this effect. It is suggested that histone acetylation is an early step induced by estrogen action during intrauterine life and that progesterone and tamoxifen suppress this mechanism very effectively.     

Absence of correlation between antiestrogenic activity and binding affinity for the estrogen receptor.

We have compared the binding to the estrogen receptor (R) of different androgens and antiestrogens with their antiestrogenic activities on uterine growth. We found that estradiol (E₂)¹ and hydroxytamoxifen, a potent antiestrogen, displayed the same affinity for R. Conversely, androgens which have a much lower affinity for R and a much higher dissociation rate than E₂, behave at high doses as full estrogens, with no significant antiestrogenic activity. We conclude that there is no correlation between the dissociation rate from R and the antiestrogenic activity of R ligands and that one cannot discriminate between estrogen and antiestrogen ligands by simply evaluating their $\text{in vitro}$ binding to the cytosol R.     

Circadian rhythm and uptake of taurine by the rat pineal gland

Taurine is believed to be a modulator of membrane excitability in muscle and a neuroinhibitory transmitter in the central nervous system. The retina and pineal contain relatively large quantities of taurine. Taurine levels in the retina are reported to be responsive to variations in lighting conditions. We report here a carcadian rhythm for taurine in the mature male rat pineal gland. The maximum taurine concentration occurs at the midpoint of the light period, 24 ± 1.9 nmoles/gland, and the minimum at the beginning of the dark period, 13.9 ± 1.6 nmoles/gland. Sympathectomy by bilateral superior cervical ganglionectomy lowered pineal taurine levels. Constant light and blinding had no effect. Taurine was demonstrated to be taken up by the pineal gland $\text{in}$$\text{vitro}$ in organ culture. The uptake was saturable, K_m = 2.0 mM, and sodium dependent. The close structural analogs hypotaurine and β-alanine inhibited taurine uptake but α-alanine did not. We have demonstrated a circadian rhythm for taurine content in the rat pineal gland and the presence of a sodium-dependent transport system for taurine in the pineal $\text{in}$$\text{vitro}$ in organ culture.     

Characterization of a progestin-binding macromolecule in the amphibian oocyte cytosol.

A [³H]-progestin-binding macromolecule has been isolated from $\text{R}\text{.}\text{pipiens}$ oocyte cytosol and characterized using binding assays, gel filtration, DEAE-cellulose chromatography and ultracentrifugal techniques. Macromolecules present in the prophase oocyte cytosol have a high affinity and specificity for the synthetic progestin R5020 and the intact oocyte will concentrate both R5020 and progesterone 20–40 fold from the medium. This may be the first published case of a cytosol steroid binding macromolecule in a cell system in which the steroid appears to act at an extranuclear level.     

Phosphorylation of calf uterus 17 beta-estradiol receptor by endogenous Ca2+-stimulated kinase activating the hormone binding of the receptor

Direct evidence is presented that uterus 17_β-estradiol receptor is phosphorylated $\text{in}\text{,}\text{vitro}$ by an endogenous kinase. Nuclear phosphatase, cytosol Ca²⁺-stimulated kinase (the former inactivating and the latter reactivating the hormone binding of the 17_β-estradiol receptor) and receptor were purified from calf uterus. 17_β-estradiol binding was inactivated by phosphatase, then reactivated by kinase in the presence of [_γ-³²P] ATP, Ca²⁺ and calmodulin, and the receptor was examined by various methods. The results of gel electrophoresis in non denaturating and denaturating conditions, and of centrifugation through sucrose gradients of receptor preincubated with monoclonal antibodies showed that the receptor is phosphorylated.     

Characterization of specific in vivo binding of neuroleptic drugs in rat brain

$\text{In vivo}$ binding of ³H-spiperone is saturable in the striatum, the limbic system and the frontal cortex but not in the cerebellum. A specific binding is different in all the brain regions thus the amount of labelling in the cerebellum may not be considered as a blank value.³H-spiperone binding revealed a specific subcellular distribution only when a very low dose was injected into rats.$\text{Ex vivo}$ experiments allow the assessment of biochemical profiles of neuroleptic drugs according to their relative affinity for dopamine or serotonin receptors.     

Binding of 5S estradiol receptor to poly-deoxynucleotides

Calf uterus cytosol was incubated with (³H)estradiol and fractionated on Sephadex G-200. Two (³H)estradiol-binding protein fractions were obtained with sedimentation coefficients of 5.1 S and 3.5 S, respectively. The 5.1 S fraction bound to poly dT, poly dA:dT and poly dG:dC to a higher extent than to calf thymus DNA. The 3.5 S fraction did not bind to DNA.