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At least 19 recordsLinked to original sources
PubMed1976

Glucocorticoid receptors: evidence for a second, non-glucocorticoid binding site.

Previous studies on cytoplasmic glucocorticoid receptors and enzyme induction led to the classification of steroids as inducers (optimal or sub-optimal), antagonists, or inactive steroids, with respect to their activity as glucocorticoids. The receptor was postulated to exist in allosteric equilibrium between two conformational states, one "active" and the other "inactive". Steroids behaved as inducers (optimal or sub-optimal), antagonists, or inactive steroids depending on their relative affinity for the active and inactive conformational state of the receptor. Another possible model would invoke multiple binding sites on a single receptor with interactions between the binding sites depending upon the particular steroid bound. To test this latter possibility, an experimental technique was developed to measure the rate of dissociation of tritiated dexamethasone ([3H]DM) or tritiated aldosterone ([3H]A) from the glucocorticoid receptor of rat liver or kidney cytosol. The dissociation of the [3H]DM-receptor at 25 C was not due to irreversible denaturation, and minimal recombination of the receptor with [3H]DM occurred. Progesterone and a number of other steroids consistently and significantly increased the dissociation rate of [3H]DM-receptor complexes in both liver and kidney cytosol. An identical effect was seen with hepatic glucocorticoid receptors labelled with [3H]A, like dexamethasone an optimal inducer. All steroids which enhanced glucocorticoid-receptor dissociation were either antagonists or sub-optimal inducers. Thus, it is postulated that glucocorticoid receptors have at least two classes of binding sites, and that occupation of the second site increases the dissociation rate of agonists from glucocorticoid receptors.

Aldosterone↗
PubMed1978

Glucocorticoids in mammary secretions and blood serum during reproduction and lactation and distributions of glucocorticoids, progesterone, and estrogens in fractions of milk.

Concentrations of glucocorticoids were measured in milk and blood serum during the estrous cycle, prepartum, parturition, postpartum, and early and late lactation. Glucocorticoids in milk did not change during the estrous cycle, averaging .35 ng/ml whereas they averaged .50 ng/ml prepartum, 3.08 ng/ml at parturition, and .50 ng/ml 1 wk postpartum. Glucocorticoids in milk declined from .59 ng/ml to .25 ng/ml as lactation advanced from 1 to 10 mo. Concentrations of glucocorticoids in blood serum were approximately 8 to 10 ng/ml during all reproductive states. There was no positive relationship between percentage of milk fat and concentrations of glucocorticoids in milk. Cortisol was the predominant glucocorticoid in serum; in milk corticosterone concentrations exceeded those of cortisol. Glucocorticoids, being more polar, had higher affinity for the nonlipid portion of milk; in contrast, progesterone, estradiol 17beta, and estrone were located predominantly in the lipid fraction of milk.

Animals↗
PubMed1978

Glucocorticoid receptors and glucocorticoid-sensitive secretion of neutral proteinases in a macrophage line.

A continuous line of mouse macrophages (P388D1) has been shown to secrete elastase, collagenase, and plasminogen activator at activities comparable to those of macrophages elicited by an inflammatory stimulus in vivo. At physiologic concentrations anti-inflammatory glucocorticoids selectively and reversibly inhibited secretion of the three proteinases but did not inhibit secretion of lysozyme, a constitutive enzyme produced by the P388D1 cells. The secretion of the neutral proteinases was inhibited 50% by 2 to 10 nM dexamethasone. Proliferation of the macrophages was also glucocorticoid sensitive. The P388D1 macrophages contained about 4000 saturable glucocorticoid-binding sites per cell. Concentrations of hormone saturating the high affinity receptor site (for dexamethasone the dissociation constant for steroid-receptor binding, Kd, was 4 nM) correlated well with concentrations inhibiting secretion of the proteinases. Only glucocorticoids and progesterone competed for binding to the specific receptors. Temperature-sensitive translocation of hormone-receptor complexes from "cytoplasm" to nucleus similar to that found with rat thymocytes was demonstrated. Thus, the interaction between glucocorticoids and the P388D1 cell line provides a model for the regulation of macrophage secretion of neutral proteinases under normal and stress conditions.

Cell Line↗
PubMed1976

Reductions in glucocorticoid inhibition of glucose oxidation and presumptive glucocorticoid receptor content in rat adipocytes during aging.

Exposure of adipocytes to glucocorticoid hormones in vitro causes inhibition of glucose transport and metabolsim. Maximal inhibition of glucose oxidations is reduced from 42-50 to 22-25 to 5-8% in young, mature, and senescent rat adipocytes, respectively. Percent values also reflect absolute reductions since basal levels of glucose oxidation per cell are constant at all ages. Adipocytes of CD strain rats continue to increase in size throughout their lifespan, while cell size remains constant during the latter 80% of the Wistar adipocyte lifespan. Thus, cellular age, as well as possibly size, seems to be associated with these changes since they occur in adipocytes of both strains. Concentrations as well as absolute numbers of presumptive glucocorticoid receptors per cell are progressively reduced during maturation and aging of adipocytes in both rat strains. Glucocorticoid effects are known to require about 2 h and can be blocked by various antimetabolites during this period, reminiscent of classical steroid receptor-mediated responses. Thus, gradual loss of glucocorticoid receptors from adipocytes during maturation and aging may be related to progressively decreased glucocorticoid responsiveness.

Adipose Tissue↗
PubMed1976

Binding of cytosol receptor-glucocorticoid complexes by isolated nuclei of glucocorticoid-responsive and nonresponsive cultured cells.

Nuclear binding of the AtT-20 cytosol receptor-glucocorticoid complex was studied in a cell-free system using nuclei from steroid-responsive (AtT-20) and nonresponsive (EPO-G1) cell lines, both of which synthesize ACTH. The AtT-20 cell line was derived from a mouse pituitary adenocarcinoma, while the EPO cell line was established from a human malignant melanoma. The nonresponsive EPO cells lacked a cytosol receptor for glucocorticoids, and, when whole cells were incubated with labeled glucocorticoid, they were unable to concentrate the steroid in their nuclei. A cell-free system using AtT-20 cytosol preincubated with labeled glucocorticoid was used to study binding by isolated nuclei. Binding to isolated nuclei from both cell lines was indistinguishable, in terms of temperature sensitivity, binding capacity, and saturability. Sucrose density gradient analyses of KCl extracts of nuclei labeled under these cell-free conditions showed 3.2-3.6 S peaks. In contrast, a 4.0 S peak was observed consistently when unreacted cytosol was analyzed on high-salt gradients, suggesting that interaction with nuclei from both cell lines caused the receptor to alter its sedimentation characteristics. These findings suggest either that all cells contain nuclear acceptor sites and that target cell responsiveness is conferred solely by the presence or absence of the cytosol receptor, or that binding sites detected in isolated nuclei may be different from those observed in intact cells and may, in fact, obscure them.

Animals↗
PubMed1975

Glucocorticoid receptors in lung. Comparison between nonactivated and activated forms of the cytoplasmic glucocorticoid binding protein and their relationship to the nuclear binding protein of fetal rabbit lung.

In the absence of salt the cytoplasmic glucocorticoid receptor of fetal rabbit lung sediments at 7 S while the nuclear receptor sediments at 4 S. However, if nuclear extracts are mixed with receptor-depleted cytosol preparations in dilute buffer solutions without added salt, the nuclear 4 S receptor sediments as a 7 S species similar to that observed for the cytoplasmic form under the same conditions suggesting an interaction of the nuclear receptor with other cytosol proteins rather than with itself. In addition, both cytoplasmic and nuclear receptors sediment at 4 S in 0.4 M KCl and a major fraction of the nuclear receptor has an agarose elution profile identical to that of the cytoplasmic receptor. Thus a major fraction of the nuclear receptors is indistinguishable from the cytoplasmic receptors by the methods used. Since the cytoplasmic receptor sediments at 4 S in 0.15 M KCl, it is suggested that in vivo the glucocorticoid receptor may exist as a 4 S species and that the 7 S form described previously may result from an interaction of the 4 S component with other cytosol proteins in hypotonic media. About 25% of the receptor present in nuclear extracts has an agarose elution profile different from that of the cytoplasmic receptor in 0.4 M KCl. This suggests that either the nuclear receptor associates with itself or other nuclear proteins or that more than one form of nuclear receptor exists. Earlier observations suggested that in the absence of hormone the glucocorticoid receptor is localized exclusively in the cytoplasm of lung cells and that the nuclear receptor is formed by a transfer of the cytoplasmic steroid-receptor complex into the nucleus. A prerequisite for this transfer seems to be a modification of the receptor to an active form which can bind to nuclei. This receptor transfomration, referred to in this paper as activation of the receptor, can occur in the absence of nuclei and is highly dependent on temperature and ionic strength. Cytoplasmic receptors activated either by heating or by exposure to high ionic strength are indistinguishable from nonactivated receptors by sucrose density gradient analysis or by agarose gel filtration in solutions containing 0.4 M KCl. Simiarly, no significant difference in the absence of salt is observed after activation by heating. These results suggest that activation of the cytoplasmic glucocorticoid receptor involves conformational changes which favor its transfer and/or binding to nuclear sites rather than conversion of a 4 S species to a faster-sedimenting form by dimerization or by addition of another protein unit as has been proposed for the activation of the estrogen receptor of the rat uterus.

Animals↗
PubMed1978

Interaction of glucocorticoids with macrophages. Identification of glucocorticoid receptors in monocytes and macrophages.

Glucocorticoid binding was measured in resident and thioglycollate-elicited mouse peritoneal macrophages, rabbit alveolar macrophages, and human monocytes. Two assays of binding were used--an assay with intact cells in suspension or monolayers, and an assay of cytosol and nuclear forms of glucocorticoid receptors. The mononuclear phagocytes contained approximately equal to 4--10 X 10(3) high affinity receptor sites per cell, with dissociation constants of approximately equal to 2--8 nM dexamethasone. The binding to the saturable sites was specific for steroids with glucocorticoid or antiglucocorticoid activity. Cortisol, corticosterone, and progesterone competed with dexamethasone for binding, whereas estradiol, dihydrotestosterone, and 11-epicortisol competed very little. Binding of dexamethasone to cytosol and nuclear forms of the receptor complex and temperature-sensitive translocation of cytosol forms to nuclear forms were shown. At 37 degrees C the predominant form of the hormone-receptor complex was nuclear. These results demonstrate that corticosteroids interact with macrophages at physiological concentrations.

Animals↗
PubMed1975

Serum-free growth of HTC cells containing glucocorticoid- and insulin-inducible tyrosine aminotransferase and cytoplasmic glucocorticoid receptors.

HTC cells have been made to grow in chemically defined medium without any macromolecular supplements whatsoever. Initial estimates of their relative amino acid requirements have been made. The cells grown in the defined medium retain many of the differentiated features which have been the focus of investigation in their serum-grown counterparts. Thus, the cells in defined medium contain cytoplasmic glucocorticoid receptors and have tyrosine aminotransferase which can be induced by glucocorticoids, serum or insulin. These cells also produce, in small amounts, an as yet undefined rat serum protein.

Cell Survival↗
PubMed1979

[Calcium and the permissive effect of glucocorticoids: the role of glucocorticoids in an adrenaline-induced increase in the rate of calcium absorption by the ventricular tissue of the rat heart].

It was demonstrated in rat experiments that the ability of the myocardial ventricles to increase 45Ca absorption after the injection of adrenaline was disturbed on the 3rd--5th day following adrenalectomy. The decrease in sensitivity to adrenaline occurred in two phases and was delayed essentially after a fall in the concentration of glucocorticoids in circulation. Chronic in vivo injection of hydrocortisone (2.5 mg per rat) into these animals for 3--5 days restored the effect of catecholamine to a great extent. The restorative effect was weaker when the rats were given a single intravenous hydrocortisone infusion 6 hours before being killed. Increase of the single intravenous dose of the hormone to 5 and 7.5 mg per rat reduced its effect. The authors assume that the described permissive effect of glucocorticoids is determined not by their direct interaction with the cytoplasmic membrane but by hormone induced intracellular synthesis of proteins capable of participating in the regulation of permeability to ions.

Absorption↗
PubMed1978

The effect of glucocorticoids on the maturation of premature lung membranes. Preventing the respiratory distress syndrome by glucocorticoids.

The effect of glucocorticoid on the maturation of premature lung membranes was studied in 121 premature infants by administering variable dosages of Decadron to the 114 mothers prior to delivery. The results were compared with findings in a group of 390 infants born in the same hospital during this study. Administration of all three test doses, 8, 16, and 24 mg., significantly decreased the incidence of RDS in all gestational age and birth weight categories. For infants less than 32 weeks, the incidence was decreased from 75 to 46.2%; those 32 to 36 weeks, from 58 to 20.2%; and in those older than 36 weeks, from 24.4 to 0 per cent. The incidence in infants less than 1,000 grams was reduced from 100 to 71.5%; 1,000 to 1,500 grams, from 67.4 to 21.6%; 1,500 to 2,000 grams, from 52.3 to 22.6%; and in heavier than 2,000 grams, from 38.1 to 13.4%. The results also showed that glucocorticoid does not significantly reduce RDS if administered less than 24 hours prior to delivery. The incidence is reduced more than 50% if administered more than 24 hours prior to delivery.

Birth Weight↗
PubMed1975

Glucocorticoid receptors in lung. Mechanism of specific glucocorticoid uptake by fetal rabbit lung nuclei.

After exposure of fetal rabbit lungs to glucocorticoid in vivo or in vitro, the hormone binds to specific receptors localized in the cytoplasm and in the nuclei. The present studies are compatible with a mechanism by which the nuclear receptor originates from the cytoplasm and arises from a hormone-, temperature-, and ionic strength-dependent transfer of the cytoplasmic receptor into the nucleus. This conclusion is reached from the following observations. Specific binding of glucocorticoid to nuclei from lungs not previously exposed to the hormone is not observed unless the cytosol is also present. In the presence of cytosol, nuclear uptake of the hormone is very slow at 0 degrees but is highly enhanced with increasing temperature. Concomitantly with the increased nuclear uptake there is an equiivalent loss of glucocortoid-receptor complex from the cytosol, indicating that the complex is transferred to the nuclei by a temperature-dependent process. Although the nuclei do not bind the cytoplasmic complex at 0 degrees, they do so provided that the cytosol is briefly heated in the presence of hormone prior to mixing with the nuclei. Thus the cytoplasmic complex must first be activated before it can bind to nuclei..

Animals↗
PubMed1976

Glucocorticoid receptors in corticosensitive and corticoresistant thymocyte subpopulations. I. characterization of glucocorticoid receptors and isolation of a corticoresistant subpopulation.

1. Separation of mouse thymocytes by centrifugation on a discontinuous bovine serum albumin gradient leads to the isolation of four subpopulations of cells. 2. The study of I13H]uridine incorporation in vitro by these subpopulation in the presence of steroid shows that one of them is corticoresistant. 3. However, the binding capacity of these subpopulations measured by incubation with [3H]dexamethasone is very similar. 4. It is therefore concluded that in mouse thymus, in contrast with lymphoma cells, corticoresistance may not be explained by a defect of cytoplasmic glucocorticoid receptors.

Animals↗