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S Ichii

Publications and source records attributed to S Ichii.

At least 73 records · Page 4Linked to original sources
PubMed1984

Stability of receptor complexes in the rat liver bound to glucocorticoids of different biopotencies.

To examine the behavior in the receptor-acceptor system of glucocorticoids of different biopotencies, the stability of receptor complexes of dexamethasone (Dex), prednisolone (Pred) and corticosterone (Cort) in cytosols, nuclei and nuclear extracts from the rat liver was compared. Receptor complexes bound to these ligands were relatively stable at 0 degrees C, but at 25 degrees C a rapid liberation of ligands was observed. However, differences in the rate of temperature-dependent decay of these receptor complexes were obvious; the Dex receptor complex was the most stable, the receptor complex bound to Cort liberated the ligand most rapidly and the stability of the Pred-receptor complex was the intermediate of these two. The addition of molybdate and dithiothreitol stabilized the receptor complexes in cytosols but these agents accelerated the liberation of ligands from the complexes in nuclei and nuclear extracts. Among the factors examined, only bovine serum albumin decreased the rate of decay in the nuclear-bound receptor complexes. From these observations, it appears likely that different mechanisms may contribute to the dissociation of ligand from receptor complexes in cytosols, nuclei and nuclear extracts.

Animals↗
PubMed1984

Stability of receptor complexes in the rat ventral prostate and seminal vesicle bound to androgens: thermodynamic study.

To examine the behaviour of the receptor-acceptor system of androgen of different biopotencies, we compared the stability of receptor complexes of dihydrotestosterone (DHT), methyltrienolone (R1881) and testosterone (Test) in cytosols, nuclei and nuclear extracts from ventral prostate and seminal vesicle of rats. Liberation of ligand from receptor complexes bound to these ligands followed the first-order kinetics. The rate constant for ligand liberation at 25 degrees C varied with the ligand. The receptor complexes bound to Test were most labile, while the receptor complexes bound to DHT were relatively stable, and intermediate stability was observed in the receptor complexes bound to R1881 under the conditions employed in the present study. Thermodynamic characteristics of the stability of the complexes were also different in these three androgens. The Arrhenius plots of the rate constant for the liberation of ligand from R1881- and DHT-receptor complexes in cytosols and nuclei showed curvilinearities, but the plots for Test-receptor complexes were almost linear. In addition, the stabilizing effect of molybdate on R1881- and DHT-receptor complexes in cytosols was observed in the range of low temperature, while the effect on Test-receptor complexes was significant at the higher temperature. The differences observed in the present study seem to be related to the difference in the biological potency of these androgens.

Animals↗
PubMed1983

Biopotency and nuclear binding of glucocorticoids.

Nuclear binding abilities of 3 glucocorticoids, dexamethasone (Dex), prednisolone (Pred) and corticosterone (Cort), which exhibited different biopotencies were compared in vitro. cytosols labelled with 3H-Dex, 3H-Pred and 3H-Cort from the rat liver prepared by incubation at 0 degrees C for 16 hr were bound to isolated liver nuclei in rates of approximately 25%, 9% and 1% of added radioactivity, respectively. Nuclear binding rates observed were correlated with biopotencies of these steroids. Time course studies of the cytosol binding revealed that the difference in the nuclear binding ability of these ligands was attributable, at least in part, to the metabolic transformation of ligands during the incubation period. A significant portion of 3H-Pred and 3H-Cort was transformed to polar metabolite(s) even under the incubation conditions at 0 degrees C. Kd's of the cytosol binding to 3H-Dex which was metabolically stable were decreased with the length of incubation time, significantly lower Kd being observed in the cytosol incubated for 16 hr than in those incubated for 2 and 6 hr. Kd's and the number of maximum binding sites were erratic when the ligands received biotransformation during the course of incubation. Transformed 3H-Pred and 3H-Cort during the incubation still exhibited features of the protein bound state. Besides biotransformation of ligands, structure related difference in the nuclear binding ability of these glucocorticoids was also observed. These observations suggest that metabolic susceptibility as well as structure related ability of the nuclear binding may contribute to the biopotency of glucocorticoids.

Animals↗
PubMed1983

Receptor recycling: liberation of glucocorticoid receptors from liver nuclei in vitro.

Dynamics of the steroid receptors seems to be the consequence of receptor recycling. In the present study, as a clue to elucidate the mechanism of receptor recycling, factors which affect the rate of liberation of nuclear bound 3H-glucocorticoids were examined in vitro. Among the factors examined, NAD, NADPH, cAMP and p-nitrophenyl phosphate accelerated the liberation of radioactivity from nuclei in a temperature-dependent manner when added to the incubation mixture. The presence of a large amount of unlabeled dexamethasone (Dex) did not modify the rate of liberation. From these results, it was concluded that the metabolism of ligand bound to the receptor is not a necessary step in the liberation of receptor from nuclei. These agents did not influence the binding process of 3H-Dex-receptor complex to DNA-cellulose. Therefore the stimulation of receptor release does not seem to be mediated by reducing the binding affinity between nuclei and receptor complexes. The liberated radioactivity was eluted on a Sephadex G-100 column in the void volume and in macromolecule-unbound fractions. In both fractions, the majority of the radioactivity comigrated with authentic glucocorticoids on thin-layer chromatography.

Animals↗
PubMed1983

Binding sites for glucocorticoids in cytosols from the ventral prostate and seminal vesicle of rats.

Binding sites for 3H-dexamethasone (Dex) were demonstrated in cytosols from the ventral prostate and seminal vesicle of rats only if dithiothreitol (DTT) was present in the incubation mixture. The binding observed in the presence of DTT was high affinity (Kd=1-5 nM) and low capacity (Bmax=approx. 0.1 p mole/mg protein) and exhibited a binding specificity for glucocorticoids. The addition of molybdate (Mo) to the incubation mixture enforced the effect of DTT on the binding but the extent of the effect of Mo in cytosols of the ventral prostate differed from that in the seminal vesicle. The binding sites in the cytosols of these tissues were depleted after administration of Dex to animals. The depletion observed was not due to occupation of the binding sites by injected Dex and this was confirmed by the exchange assay. Addition of the cytosol from the seminal vesicle inhibited the 3H-Dex binding in the liver cytosol but the cytosol from the ventral prostate did not show an inhibitory effect. The binding sites in neither of these male accessory sex organs were modified markedly after the animals were castrated. Although the 3H-Dex binding sites observed in the cytoplasm of male accessory sex organs fit the definition proposed for the steroid hormone receptors, it is not clear whether these tissues are under the influence of glucocorticoid or not; the rate of incorporation of 3H-leucine and 3H-orotic acid into the acid-insoluble fraction from the ventral prostate is not influenced by the administration of Dex to animals.

Animals↗
PubMed1982

Dynamics of glucocorticoid receptor and induction of tyrosine aminotransferase in rat liver.

In order to better understand the role of glucocorticoid receptor in the hormonal action of glucocorticoid, depletion and replenishment of the cytoplasmic receptor and kinetics of induction of tyrosine aminotransferase (TAT) in rat liver were examined after administration of dexamethasone (Dex) and prednisolone. The extent of the receptor depletion and the duration of the depletion period were dose-dependent and were well correlated not only with the biological potency of the steroids administered but also with the kinetics of TAT induction. A linear relationship between the amount of depleted receptor and the kinetics of TAT induction was observed. Pretreatment of animals with a large dose of Dex reduced the response of TAT induction by Dex which was administered 24 h later. This seems to be attributable, at least in part, to the incomplete replenishment of the receptor and also to the increased rate of replenishment of the receptor. The reduced affinity of the partially replenished receptor to glucocorticoid might also participate in lowering the response to the second injection. In conclusion, depletion and replenishment of the cytoplasmic glucocorticoid receptor appeared to be directly responsible for the physiological action of glucocorticoid.

Animals↗
PubMed1982

Nuclear binding sites in the liver for dexamethasone and in the ventral prostate for R1881.

Nuclear binding sites which exhibit affinity similar to previously reported "Type II" sites (Clark et al., 1978) for estradiol in rat uterus were found in the liver and ventral prostate of rats and showed a binding specificity for glucocorticoid and androgen, respectively. However, both binding sites were qualitatively different from those of the rat uterus; a reducing agent, dithiothreitol, did not block the binding of steroids in the liver and ventral prostate. Extraction of the bound ligands discriminated the binding of the liver from that of the ventral prostate, Triton X-100 solubilized a majority of the bound Dex in liver nuclei, while the effect of KCl treatment was more remarkable on the bound R1881 in nuclei of the ventral prostate. Castration caused a drastic decrease in the binding of ventral prostate, only trace binding was observed at 48 h after hormone deprivation and replacement therapy restored the binding rapidly, at 3 h after testosterone injection almost 70% of the binding was detected. Although adrenalectomy did not result in a profound change in the binding sites of liver, the injection of Dex increased the number of binding sites significantly. The physiological significance of these binding sites is not clear at the present time.

Animals↗
PubMed1981

Depletion and replenishment of glucocorticoid receptor in cytosols of rat tissues after administration of various glucocorticoids.

Administration of steroid hormones evokes a rapid fall in the amount of cytoplasmic receptors in target tissues. This has been considered to be a consequence of the receptor translocation to nuclei, but the physiological significance of depletion of the cytoplasmic receptors after hormone administration has not been fully elucidated. In the present study, depletion and replenishment of the cytoplasmic glucocorticoid receptor in rat tissues were examined after the administration of glucocorticoids of different biological potencies. Dose dependent depletion was observed in all tissues examined and doses required for complete depletion of the receptor were correlated with biological potencies of steroid administered. The receptor in the heart and the skeletal muscle was relatively sensitive to hormone injection while more than 4 times the amount of steroids was required to induce a similar effect in the thymus and the spleen. The duration of the period of depletion of the receptor in cytosols was also dose dependent and correlated to the biological potency of steroid administered. Replenishment took place earlier in the thymus and the spleen than in the heart and the skeletal muscle. Significantly lower binding affinity was observed in the replenished receptors. The administration of cycloheximide in a dose which inhibits more than 95% of 3H-leucine incorporation did not influence either the depletion or the replenishment of the receptor induced by hormone injection. In conclusion, depletion and replenishment of the cytoplasmic glucocorticoid receptor appeared to be closely correlated to the physiological action of hormones.

Animals↗
PubMed1980

Interaction of 3H-dexamethasone-receptor complex with nuclei: inhibition by Ethidium Bromide.

Several binding characteristics of the Dexamethasone (DEX)-receptor complex(RC) to nuclei from rat tissues were examined in the presence of Ethidium Bromide(EB). In the cell-free experiments, EB partially prevented the binding of the liver DEX-RC to nuclei and two kinds of nuclear binding of the DEX-RC, one was sensitive and the other was resistant to EB, were observed. In addition, the EB-resistant nuclear binding that showed a high-affinity and low-capacity nature was observed only in the bindings of the 3H-DEX-RC to nuclei derived from the liver of fetal and adult rats and the thymus of adult rats. The bindings of 3H-5 alpha-Dihydrotestosterone(DHT)-RC and 3H-17 beta-Estradiol(E2)-RC to liver nuclei exhibited low-affinity and non-saturation even in the presence of EB. Furthermore, it was revealed, that the EB-resistant sites of the nuclear binding were for the "DNA-unbound" form of 3H-DEX-RC, while the RC of "DNA-bound" form was bound to the EB-sensitive sites.

Animals↗
PubMed1980

Changes in the cytoplasmic androgen receptor of rat ventral prostate after administration of androgens, antiandrogens and anabolic steroids.

The effect of the administration of androgens (testosterone and dihydrotestosterone(, antiandrogens (progesterone and cyproterone acetate) and anabolic steroids (Bolandiol, Nandrolone, Furazabol and Methenolone) on depletion and replenishment of the androgen receptor in the cytosol of ventral prostate from castrated rats was examined using 3H-R1881 as the ligand. Administration of androgens lead to a rapid fall in the level of the receptor and the receptor in the cytosol was replenished in the period following treatment. Length of the period of receptor depletion was dependent on the dose of androgen administered. Administration of antiandrogens did not cause any depletion of the receptor and concomitant administration of testosterone induced a pattern similar to that of the depletion observed following administration of testosterone alone. Effect of pretreatment of animals with ethidium bromide, an intercalating dye which has been shown to prevent the in vitro nuclear binding of steroid hormone-receptor complexes, on the depletion of receptor induced by testosterone administration was also insignificant. Anabolic steroids depleted the receptor but the degree of depletion was relatively low. The rate of inhibition of in vitro 3H-R1881 binding by these anabolic steroids was not correlated to the rate of in vivo depletion of the receptor. The significance of these observations is discussed.

Anabolic Agents↗
PubMed1979

Studies on the nuclear binding of steroid hormone-receptor complex; characteristics of binding of nuclei from fetal rat liver to 3H-dexamethasone-liver cytoplasmic receptor complex.

Binding of 3H-dexamethasone (Dex)-rat liver cytoplasmic receptor complex to nuclei from fetal rat livers in vitro exhibited a high-affinity and saturable nature (Kd=1.5 X 10- M, maximal binding sites=470 fmole/mg DNA), and the binding was inhibited competitively by prior injection of Dex in vivo. While binding of 3H-Dex-receptor complex to nuclei from adult rat liver was in low affinity and unsaturable, and injection of Dex prior to the sacrifice of animals did not influence the nuclear binding to 3H-Dex-receptor complex in vitro. Differential salt-extraction with KCl solution of the nuclear bound 3H-Dex receptor complex revealed the presence of salt-extractable and residual forms of bound receptors. The amount of the fraction extracted with 0.3 M KCl reached its maximum at 10 min after the start of incubation, while the 1.0 M KCl-extractable and residual fractions reached their maximum plateaus after 30 min of the incubation. Scatchard analysis revealed that the binding of the receptor complex to the 0.3M and 1.0M KCl fractions was saturable, while the residual fraction did not show any tendency of saturation under the experimental conditions employed in the present study. The results obtained in this work were compared to those which have been reported by other investigators.

Animals↗
PubMed1979

Studies on the nuclear binding of steroid hormone-receptor complex; binding of liver and thymus dexamethasone-receptor complex and prostate dihydrotestosterone-receptor complex to nuclei from various tissues.

To examine the binding specificity of steroid hormone-cytoplasmic receptor complexes to nuclei, binding of 3H-dexamethasone (Dex)-liver, 3H-Dex-thymus and 3H-dihydrotestosterone (DHT)-prostate receptor complexes to nuclei from liver, prostate, thymus, spleen and kidney was studied. It was observed that a significant amount of steroid-receptor complexes was bound to any nuclei used in the present study and the extent of the binding of receptor complexes to nuclei from homologous tissues was not always greater than that to nuclei from heterogenous tissues. However, a significant portion of the 3H-Dex-liver and 3H-DHT-prostate receptor complexes was not absorbed by nuclei from kidney, spleem, and thymus, and the unabsorbed complexes were efficiently bound to liver and prostate nuclei. The results obtained indicate that two types of receptor complex with regard to nuclear binding were present in cytosols of liver and prostate; one binds to nuclei from kidney, spleen, thymus, liver and prostate and the other does not bind to nuclei from kidney, spleen and thymus but does bind to nuclei of liver and prostate. The latter type of receptor complex was not observed in the cytosol from the thymus.

Animals↗
PubMed1978

Nuclei and DNA-binding form of the steroid receptor complex in the liver and the ventral prostate of rats.

Repeated treatments of the liver cytosol prelabeled with 3H-dexamethasone with DNA-cellulose followed by treatments with purified liver nuclei enabled us to assess the amount of two forms of dexamethasone-receptor complex, one binds only to nuclei and the other binds to DNA and nuclei. The comparable amount of these two forms of the receptor complex was detected in the dexamethasone-labeled liver cytosol, while only one form which binds only to nuclei was found in the liver cytosol labeled with antiglucocorticoid, cortexolone. The significant amount of receptor complex which binds to DNA and nuclei was not present in the cytosol from the ventral prostate preincubated with 3H-dihydrotestosterone.

Animals↗