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F Svec

Publications and source records attributed to F Svec.

At least 127 records · Page 7Linked to original sources
PubMed1988

Corticosterone regulates the level of hepatic glucocorticoid receptors in mice.

The effect of exogenous corticosterone on the level of mouse hepatic glucocorticoid receptor was monitored to ascertain whether agonist-induced glucocorticoid receptor regulation takes place in living animals as it does in isolated cell systems. Adrenalectomized male Swiss-Webster mice were given 1 mg of corticosterone ip and 24 hr later the glucocorticoid receptor binding capacity of a high-speed cytosolic extract of liver was measured. It was shown that at this time point the administered steroid had been totally cleared and thus, the decrease in binding capacity was a reflection of downregulation. Receptor binding capacity was decreased by 25%. Downregulation was not permanent; 48-72 hr after the injection receptor content returned to baseline. Multiple daily injections of corticosterone were no more effective at causing downregulation than a single injection. It is concluded that glucocorticoid agonists downregulate their own receptors in the glucocorticoid target organs of intact animals as they do in cloned cell models.

Adrenalectomy↗
PubMed1987

Hydrogels in endovascular embolization. III. Radiopaque spherical particles, their preparation and properties.

The synthesis and properties of spherical radiopaque hydrogel particles designed for endovascular occlusion are reported. These particles were prepared by the hydroxyl acylation of low crosslinked poly (2-hydroxyethyl methacrylate) beads with a nontoxic radiopaque compound based on triiodobenzoic acid, without affecting their properties which are advantages in medical practice. The effect of the iodine content on the size of dry and swollen particles is discussed. It has been found that an iodine content of about 25-30 wt% is desirable in order to obtain an easily recognizable X-ray image. These particles make the immediate control of embolus application easy and enable periodical inspection of the polymer to check the successful blockage of the vessel. They also open up the method of endovascular occlusion to further improvement.

Contrast Media↗
PubMed1987

The effect of including molybdate in the eluting buffer used for DEAE-cellulose chromatography on the quantitation of glucocorticoid receptor transformation.

This study analyzes the effect of including molybdate in the elution buffers used in DEAE cellulose chromatography on the fraction of glucocorticoid receptor which elutes as the transformed species. Inclusion of molybdate leads to a significant decrease in the fraction of receptor eluting as transformed; samples which appear to be nearly 50% transformed if eluted in the absence of molybdate were found to be less than 10% transformed when analyzed using a buffer which contained 5 mM molybdate. This decrease was not caused by loss of receptor or a reversion of transformation. DEAE cellulose accelerates receptor transformation. It is concluded that DEAE cellulose should not be used to quantitate transformation unless molybdate is included in all buffers.

Animals↗
PubMed1986

Glycidyl methacrylate copolymers as suitable supports for immobilizing antigens and antibodies.

Glycidyl methacrylate copolymers modified with 1,6-diaminohexane were activated with glutaraldehyde. Such activated supports were directly bound to the chosen antisera. Prepared immunosorbents contained ca. 40 mg of bound protein and were able to purify 2-5 mg of antigen (alkaline proteinases Esperase and Maxatase) per 1 g of solid support. Chaotropic agent (2.5 M ammonium thiocyanate in phosphate or Tris buffer) enabled antigen to be released quickly, the properties of the immunosorbent remaining unchanged.

Acrylates↗
PubMed1986

Hydrogels in endovascular embolization. II. Clinical use of spherical particles.

In this study we report the results of clinical experiments, obtained with spherical particles made from poly(2-hydroxyethyl methacrylate) used in the embolization of arteriovenous anastomoses, in the suppression of pulmonary haemorrhage and haemoptysis and in the occlusion of some other arteries. So far we have used these particles in the treatment of 187 patients. It must be stressed that the advantage of spherical particles consists in the simplicity of their introduction into the blood vessel through a catheter, while in the blood vessel itself the particle swells in blood still more, when compared with the particle size in saline. This results in an immediate and permanent haemostatic effect. No revascularization occurs.

Embolization, Therapeutic↗
PubMed1986

Hydrogels in endovascular embolization. I. Spherical particles of poly(2-hydroxyethyl methacrylate) and their medico-biological properties.

Spherical macroporous particles based on poly(2-hydroxyethyl methacrylate) with defined porosity, swelling and morphology have been developed, and are suitable for endovascular occlusion of various organs. Unlike cylindrical particles, spherical particles are specifically suited for transcatheteral introduction. The method chosen for the preparation of such particles was suspension radical polymerization, where the monomers were dissolved in a mixture of higher-boiling alcohols, and the solution dispersed in water. Physicochemical and medico-biological properties of spherical particles were examined. The residual amounts of monomers and other low-molecular compounds were checked; haematological analyses showed that the value 10(-5) g/g of the polymer was not toxic and contributed to an irreversible aggregation of thrombocytes. The occlusion effect in the vascular lumen was stable. The histomorphological results fully demonstrated the perfect biocompatibility of artificial spherical emboli. The latter met the requirements of application to clinical practice.

Animals↗
PubMed1986

Molybdate affects glucocorticoid receptor chromatography on DEAE cellulose.

How molybdate affects the chromatographic behavior of the glucocorticoid receptor on DEAE cellulose was investigated. Over the range 0-20 mM, molybdate caused a progressive change in the elution positions of both the transformed and untransformed receptor. At 20 mM molybdate, the transformed receptor eluted from the column before application of the KCl gradient. These changes were not due to an increase in conductivity of the buffer caused by molybdate; the conductivity at the peaks of elution were changed. Control studies with bovine serum albumen showed a similar effect by molybdate. Molybdate thus changes the chromatographic elution profiles of proteins. Failure to appreciate this fact can lead to errors in assessing the proportion of transformed and untransformed receptors in an extract.

Chromatography, DEAE-Cellulose↗
PubMed1985

Relationship between intact cell ATP levels and glucocorticoid receptor-binding capacity in the AtT-20 cell.

This study tested the relationship between intact cell ATP levels and glucocorticoid receptor-binding capacity in the AtT-20 mouse pituitary tumor cell. Four treatments were used to alter intact cell ATP levels: incubation with NaF, incubation with 2,4-dinitrophenol, alterations in culture age, and incubation with dexamethasone. Each of these treatments clearly altered glucocorticoid receptor-binding capacity. Their effects on ATP levels, however, were not the same: NaF decreased ATP levels, dinitrophenol decreased ATP levels only transiently, and the last two treatments (increasing culture age and incubation with dexamethasone) produced an inverse relationship between ATP levels and receptor-binding capacity. It is concluded that, at least in the intact AtT-20 cell, receptor-binding capacity is not always directly related to ATP levels.

2,4-Dinitrophenol↗
PubMed1985

Glucocorticoid receptor regulation.

Glucocorticoids, like other classes of steroid hormones, must bind to cellular receptors in order to exert their effects. Because of this central role in mediating hormone action, it is important to elucidate those factors that control receptor content. The purpose of this minireview is to summarize the recent work that explores the mechanisms through which cells modulate their glucocorticoid receptor binding capacity.

Adenosine Triphosphate↗
PubMed1985

Interactions of glucocorticoids with the AtT-20 cell: effect on protein accumulation.

In order to investigate the mechanism through which glucocorticoids downregulate the number of their own receptors in the AtT-20 cell, the effect of glucocorticoids on cell protein metabolism was studied. Glucocorticoids were found to inhibit cellular protein accumulation when included in long-term cultures. The concentrations of agonists that cause a mid-maximal effect are similar to those needed to half-saturate the glucocorticoid receptor, suggesting that the growth-inhibiting effect is receptor-mediated. Two-dimensional electrophoresis of cytosolic extracts of treated and control cells suggested that the effect reflected a general suppression of overall protein accumulation rather than a selective effect on certain classes. Comparison of the protein to DNA ratio of control and dexamethasone-treated cells showed that the latter have higher ratios suggesting that cell composition may be altered by agonists. However, time-course studies of this effect indicated that this is basically an expression of a glucocorticoid effect on cell growth rather than a selective effect on protein metabolism. It is concluded that glucocorticoids inhibit overall AtT-20 cell growth and that this, in turn, manifests itself as a decrease in the rate of protein accumulation. It is suggested that this change in protein metabolism may be a minor component in the mechanism through which glucocorticoids decrease AtT-20 cell ACTH secretion and glucocorticoid receptor number.

Adrenocorticotropic Hormone↗
PubMed1985

Biopotency of corticosterone and dexamethasone in causing glucocorticoid receptor downregulation.

The biopotencies of dexamethasone and corticosterone in causing glucocorticoid receptor downregulation in the AtT-20 cell were assessed and compared to their affinity for the isolated, cytosolic glucocorticoid receptor. Dexamethasone depleted receptor by 50% at a concentration of 4.6 nM. Its Kd for the receptor was 9.1 nM. The comparable values for corticosterone were 520 and 18.8 nM respectively. These results suggest that receptor depletion is a receptor mediated process; at some point the steroid must be bound to receptor in order to cause depletion. Further, the discrepancies between the two values for corticosterone support the hypothesis that it is the transformed receptor that is depleted.

Animals↗
PubMed1985

The effect of molybdate on glucocorticoid receptor transformation and translocation in intact, viable AtT-20 mouse pituitary tumor cells.

The effect of 20 mM molybdate on the transformation and translocation of glucocorticoid receptors in intact AtT-20 mouse pituitary tumor cells was investigated. To test whether transformation of the receptor was inhibited during in vivo incubations with both molybdate and glucocorticoid, the DEAE cellulose elution profile of extracted receptor was determined. It was found that receptors from both high speed cytosols and nuclear extracts were transformed. To test whether translocation was affected by molybdate, the fraction of glucocorticoid-receptor complexes found in the nucleus was determined. At 37 degrees C, in the absence of molybdate, 55-60% of the glucocorticoid receptor complexes were in the nuclear compartment. Molybdate did not effect the magnitude of nuclear translocation. Control studies suggested that the agent entered the cells, however. Cold exposure (0 degrees C) reduced nuclear translocation to 20-25%. It is concluded that in vivo, either molybdate is not able to interact with the receptor or transformation in vivo is not mediated by the same molybdate-sensitive mechanisms currently being studied using broken cell-preparations.

Animals↗
PubMed1985

Glucocorticoid receptor number in ob/ob mice and streptozotocin-treated rats.

As one step in characterizing the effectiveness of glucocorticoid hormones in states of abnormal carbohydrate metabolism, the number and affinity of glucocorticoid receptors in cytosolic extracts of liver and kidney from ob/ob mice and pancreata from streptozotocin-treated rats were determined and compared to values derived from normals. Scatchard analysis revealed that each tissue contained the same number of glucocorticoid receptors as its control when expressed in terms of receptor number per mg of cytosolic protein. Similarly, the affinity of these receptors for dexamethasone was unchanged. It is concluded that these two forms of diabetes are not associated with abnormalities of glucocorticoid receptor number.

Animals↗
PubMed1984

Characterization of the AtT-20 cell's 'repleting' glucocorticoid receptor.

Glucocorticoids deplete the AtT-20 mouse pituitary tumor cell of its glucocorticoid receptors. Once placed into steroid-free medium, however, these 'receptor-deplete' cells gradually regain their ability to bind glucocorticoids displaceably. The goal of this paper is to determine whether replete binding-species is indeed a glucocorticoid receptor, and whether any precursor or modified forms are seen during repletion. Once depleted, cells take nearly 3-4 days to replete their full complement of cytosolic glucocorticoid-binding species. Scatchard analysis revealed only one binding site, of which the affinity for dexamethasone was identical to that of the native receptor. The steroid-binding specificity of the 'replete' binding species was exactly the same as that of the original receptor. The molecular size and surface charge density of the glucocorticoid-binding species obtained throughout the process of repletion were identical to those of the original receptor. Finally, studies in which replete cells were exposed to glucocorticoid agonists showed that the cell was able to decrease its production of ACTH, indicating that the regenerated binding species was able to function as a biologically active glucocorticoid receptor. We conclude that the replete species is a glucocorticoid receptor identical to the original, and that probably no precursor or modified forms of the repleting receptor exist.

Adrenocorticotropic Hormone↗
PubMed1984

The physico-chemical properties of the AtT-20 cell's glucocorticoid receptor during depletion.

Glucocorticoid agonists decrease the number of glucocorticoid receptors in the cloned AtT-20 mouse pituitary tumor cell. To investigate whether the structure of the receptor is altered during this process, we monitored the physico-chemical properties of the nuclear and cytosolic receptors undergoing depletion. Agarose chromatography, DEAE-cellulose chromatography and sucrose gradient ultracentrifugation were employed. Cells were sampled after 2, 24, 48 and 96 h incubation with 10 nM tritiated triamcinolone acetonide. Agarose chromatography yielded, in each case, a single receptor-containing peak that had a Stokes radius of 5.8 nm. Nuclear and cytosolic glucocorticoid receptors from each preparation eluted from DEAE-cellulose as a single, symmetric peak at a KCl concentration of 0.075 M. Sucrose gradient ultracentrifugation of all samples also yielded only a single peak. For each technique the amount of receptor recovered was inversely related to the length of intact cell incubation. Thus, depletion of the glucocorticoid receptor is not accompanied by observable changes in its size, surface charge or hydrodynamic properties. These results suggest that the first step of agonist-induced glucocorticoid receptor depletion in the AtT-20 cell involves the loss or alteration of the receptor's steroid-binding site.

Animals↗
PubMed1984

Comparison of glucocorticoid receptor depletion and the suppression of ACTH secretion in the AtT-20 cell.

Glucocorticoids exert two effects on the cloned AtT-20 mouse pituitary tumor cell: they inhibit its production of ACTH and decrease its content of glucocorticoid receptors. In this paper the time courses of these two processes are compared to ascertain whether there is a link between them. The initial part of the time course of glucocorticoid receptor depletion was measured during an incubating of intact cells with 10 nM tritiated glucocorticoid. This showed that receptor depletion commenced at 4-6 h, but the half time of depletion was 30 h. Cell fractionation studies demonstrated that the decrease in receptor number occurred proportionately in both the nuclear and cytosolic fractions. The time course of dexamethasone suppression of ACTH secretion was measured under similar conditions. These studies showed that suppression was complete within 24 h. Comparison of these results led to the conclusion that although dexamethasone's effect on both receptor depletion and ACTH secretion is rapid, its effect on ACTH secretion is complete clearly before its effect on receptor depletion. Long term (3 week) dexamethasone incubations showed that even after dexamethasone had depleted the cell's receptor content to only a fraction of its initial value, its inhibitory effect on ACTH was undiminished. These results suggest that agonist action is not dampened with time. Taken together, these studies suggest that depletion is not a step in the mechanism of steroid-hormone action in the AtT-20 cell nor is it involved in diminishing the magnitude of agonist action. Instead, more likely, depletion is the process which removes redundant, spare glucocorticoid hormone receptor complexes.

Adrenocorticotropic Hormone↗
PubMed1984

The binding of deoxycorticosterone by the AtT-20 cell.

The AtT-20 cell contains a steroid hormone binding site besides the glucocorticoid receptor. It binds 11-deoxycorticosterone (DOC) but not glucocorticoids, estrogens, mineralocorticoids, or progestins. Scatchard analyses could not quantitate the number of these sites, but suggested that there are many and that they have a low affinity for DOC. This new site is in the particulate fraction of the cell and at least part of the binding is associated with nuclei. The AtT-20 cell metabolizes DOC; up to 50% of the intracellular steroid is converted into a metabolite. Overall, although this new site could be involved in mediating antiglucocorticoid hormone action, its "low" binding affinity and location in the particulate fraction suggests that more likely it represents part of a hormone-metabolizing system.

Animals↗