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J Brtko

Publications and source records attributed to J Brtko.

At least 73 records · Page 4Linked to original sources
PubMed1992

Effect of protease inhibitors and substrates on 3,5,3'-triiodothyronine binding to rat liver nuclear receptors.

The effect of protease inhibitors N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-carbobenzoxy-L-phenylalanine chloromethyl ketone (ZPCK) at concentrations ranging from 1.5 x 10(-6) mol/l to 1.5 x 10(-4) mol/l on the specific binding of 3,5,3'-triiodothyronine (T3) to rat liver nuclear receptors was evaluated. Both TPCK at 1.5 x 10(-5) mol/l (P < 0.001) and ZPCK at 1.5 x 10(-6) mol/l (P < 0.05) showed the inhibition of T3 binding to nuclear receptors. The evaluation of T3 binding data following separation of unbound TPCK from treated nuclear receptors on a Sephadex G-25 column showed that the inhibition of T3 binding was irreversible, since a substantial decrease of the equilibrium association constant (Ka) was found when compared to the mock samples lacking TPCK. In addition, similar inhibitory effect on T3 specific binding to rat liver nuclear receptors was found at 5.0 x 10(-4) mol/l by protease substrates L-tyrosine benzyl ester (P < 0.001), L-tyrosine ethyl ester (P < 0.02), L-tryptophan methyl ester (P < 0.02) and L-tryptophan ethyl ester (P < 0.05). The data suggest that: 1. both protease inhibitors and substrates tested inhibited T3 specific binding to T3 nuclear receptors; 2. this may support the hypothesis that T3 receptors like other receptors encoded by c-erbA gene possess a site that recognize both serine protease inhibitors and substrates in its hormone binding domain.

Amino Acid Chloromethyl Ketones↗
PubMed1992

Effect of triiodothyronine on rat liver polysome profiles and translational activity of mRNA after partial hepatectomy.

The administration of 3,5,3'-L-triiodothyronine (T3) (200 micrograms/100 g) to rats immediately after partial hepatectomy led to an increase in total polysome content of residual hepatocytes (as measured 18 h postoperatively) which exceeded that observed after partial hepatectomy in the absence of hormone. The percentage of free ribosome pool remained the same after partial hepatectomy irrespectively on the absence or presence of T3. After partial hepatectomy the sedimentation pattern of total polysomal fraction (isolated 18 h postoperatively) shifted towards smaller aggregates as compared with that isolated from sham operated animals. T3 did not affect this pattern. The translational capacity of mRNA isolated from regenerating liver after 18 h was higher than that of mRNA isolated from sham operated animals. T3 increased the translational capacity of mRNA isolated from regenerating liver if administered immediately after surgery. Two dimensional electrophoresis of translated products showed that one of the typical proteins recently characterized with Mr 25,000 pI 6.9 appeared after partial hepatectomy and was significantly increased when T3 was administered immediately after surgery. These results show that thyroid hormone can enhance some of the characteristics features of liver regeneration involved in the synthesis of proteins typical for the process of liver regeneration.

Animals↗
PubMed1991

Partial hepatectomy alters serum hormone levels in rats.

The level of thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), thyroxine (T4), 3,5,3'-L-triiodothyronine (T3), corticosterone, testosterone and insulin in serum were measured at 1, 12, 48 and 120 h after partial hepatectomy (PH) or sham operation in rats. After PH the level of ACTH and corticosterone was significantly elevated while that of TSH, T4 and testosterone was decreased and returned to the values found in sham operated animals within 5 days. The level of T3 was unchanged. These results show an increase in the function of pituitary-adrenal axis and a decrease in that of pituitary-thyroid axis shortly following PH with the tendency to return to normal function within five days.

Adrenocorticotropic Hormone↗
PubMed1990

Nuclear binding of thyroid hormones and activity of malic enzyme and ornithine decarboxylase in rat liver during postnatal development.

The binding of 3,5,3'-L-triiodothyronine (T3) and thyroxine (T4) on liver nuclear receptors and the activity of malic enzyme and ornithine decarboxylase was examined in infantile rats aged in 1, 3, 7, 23, 29 days and in adult rats. No changes in the affinity constants (Ka) of nuclear receptors were observed for T3 or T4. The maximum binding capacity (MBC) estimated with the use of Scatchard plot analysis was unchanged for T3, the highest MBC for 125I-T4 being noted in rats aged 7 days. Malic enzyme activity in rat liver during the first three neonatal weeks was almost undetectable, but markedly increased on the 29th day. Ornithine decarboxylase activity was found to be significantly higher on the first day after birth as compared with that of the remaining age groups. The findings indicate that the thyroid hormone-nuclear receptor complex in rat liver does not seem to be sufficient for the induction of these enzymes in postnatal period of life.

Animals↗
PubMed1990

[Modulation of the binding characteristics of thyroid hormone receptors by the chemical modification of non-histone nuclear proteins].

Modulation of binding characteristics of thyroid hormone receptors induced by chemical modification of nonhistone proteins is described. At nuclear level, the biological response to thyroid hormones is determined by the formation of hormone-receptor complexes which act as the initiation factor of hormone action. The combination of common biochemical separation methods allows only partial purification of the thyroid hormone receptors. The product of the c-erb-A genes carries the sequence representing the thyroid hormone receptor. At present neither the structure nor the exact amino acid sequence of the specific binding site for the thyroid hormone at the receptor molecule is known. The formation of the biologically active thyroid hormone-receptor complex was found to require the preservation of at least one of the 19 nucleophilic imidazole groups of the histidyl residues of the 3,5,3'-triidothyronine receptor.

Animals↗
PubMed1990

Anterior pituitary: triiodothyronine and/or dexamethasone induced changes in protein formation in thyroidectomized and/or adrenalectomized rats.

Protein formation in the anterior pituitary was investigated in vitro in thyroidectomized (TX) and/or adrenalectomited (AX) rats treated with a single dose of 100 micrograms/100 g of 3,5,3'-triiodothyronine (T3) and/or with a single dose of 10 micrograms/100 g of dexamethazone (DEX) 12 h before sacrifice. Male Wistar rats of a specific pathogen free colony 6 weeks after TX and/or AX receiving 1% calcium chloride and/or saline after surgery were used in the experiments. Non-pooled anterior pituitaries (in acellular condition) complemented with all essential amino acids, CPK, creatine phosphate in a HEPES buffer containing potassium acetate, magnesium acetate and dithiothreitol, were incubated with 35S-methionine at 28 degrees C for 10 or 40 min. The reaction was stopped by EDTA followed by RNAase plus DNAase treatment and the samples were analyzed for total 35S-methionine incorporation or by SDS 12.5% polyacrylamide gel slab electrophoresis (PAGE). As compared to intact rats (100%), TX and/or AX caused a significant diminution of the total 35S-methionine incorporation into protein ranging from 33% to 68% that may be easily restored to 107% by T3 plus DEX treatment. PAGE analysis reflects an appreciable relation between T3 administration and 21.5 kDa protein (growth hormone) formation in the anterior pituitary. In addition, the effect 5,5'-diphenylhydantoine (DPH) on 35S-methionine incorporation in relation to T3 nuclear specific binding was investigated. The data suggest that the decreased protein synthesis de novo is due to a significant diminution of T3 specific binding to nuclear receptors in the anterior pituitary.

Adrenal Glands↗
PubMed1990

[Cell lines in experimental endocrinology].

Cell lines derived of endocrine tissues which are most frequently employed in experimental endocrinology are described. The cell lines represent a useful experimental model for the study of the control of synthesis and release of hormones and hormone-like agents as well as for the study of mechanisms of action of these agents in target tissues at the cellular and subcellular level. A number of the cell lines know so far are able to grow in serumfree media. These media are completely defined. This approach is promising for further progress in cellular endocrinology.

Animals↗
PubMed1989

Isotachophoretic determination of short-chain fatty acids in drinking water after solid-phase extraction with a carbonaceous sorbent.

A macroporous carbon sorbent, packed into disposable columns (Separcol-Carb), was investigated for the off-line preconcentration of short-chain fatty acids from drinking water in conjunction with their determination by capillary isotachophoresis (ITP). Of the acids investigated (C1-C9), butyric acid and higher homologues could be enriched into a high degree from samples of drinking water. Their detection limits from the ITP conductivity detector were in the low parts per 10(9) range when an amount equivalent to 8 ml of the sample was taken for analysis. The lowest homologues (C1-C3) were not adsorbed sufficiently to achieve their reasonable enrichment by the sorbent under the working conditions employed (acidification of the sample to pH 2.0). Acetone and diethyl ether were employed for the elution of the adsorbed analytes. The latter was more convenient in the analysis of practical samples as it co-eluted a considerably smaller number of the adsorbed anionic constituents. Octadecyl-bonded silica, evaluated in parallel, was found to be of only very limited utility for the same purpose.

Electrophoresis↗
PubMed1989

Effect of different thyroid state on ornithine decarboxylase activity and receptors of T3 in rat liver.

The effects of thyreoidectomy, of the administration of 3,5,3'-triiodothyronine (T3), of thyroxine (T4) together with the inhibitor of iodothyronine 5'-deiodinase activity 6-propyl-2-thiouracil (PTU) and of PTU alone on rat liver ornithine decarboxylase (ODC) activity was studied. 28 days after thyroidectomy there was a decrease in ODC activity, whereas T3 treatment of normal rats increased enzyme activity. PTU decreased ODC activity in intact rats and inhibited ODC activity in animals treated with T4. Neither thyroidectomy T3, T4 given in vivo nor the polyamines spermine and spermidine added in vitro influenced the binding of 125I-T3 to its receptor in liver nuclei. Only addition of PTU increased Ka significantly (P less than 0.01). It is concluded that ODC activity in the liver is directly correlated with the thyroid state but not to parameters of thyroid hormone receptor in liver nuclei.

Animals↗
PubMed1989

Stabilization, accurate determination, and purification of rat liver nuclear thyroid hormone receptor.

Rat liver nuclear thyroid hormone receptor lost 3.5.3'-tri-iodo-L-thyronine (T3)-binding activity with a half-life of 14 days, 4h, 139 min, 62 min, 16 min or 6 min at 0, 36, 38, 40, 43 or 45 degrees C respectively, when present in crude nuclear extracts. Glycerol increased the half-life of the receptor during heat inactivation. Protection was reversible by removing the glycerol. The receptor was unstable at a pH below 6.0 or above 10.0. We also found a loss of the receptor activity during the separation of bound and free hormone using the resin test. Of several conditions tested for the separation of bound and free hormone, the addition of heated nuclear extract gave the most accurate estimation of bound hormone when using the resin test. Using these characteristics of the receptor, we purified the receptor to 1220 pmol T3-binding capacity/mg protein with a final yield of 14.6 micrograms/4 kg rat liver.

Animals↗
PubMed1989

Study of the role of tryptophanyl and arginyl residues in the specific binding of 3,5,3'-triiodothyronine to rat liver nuclear receptors.

The role of tryptophane and arginine residues of rat liver receptors for the specific binding of 3,5,3'-triiodothyronine (T3) was studied by chemically modifying the receptor molecule. Soluble T3 receptor fraction was prepared from purified rat liver nuclei and the kinetics of the modification of a tryptophane indol ring of nuclear receptor by N-bromsuccinimide (NBS) in the presence of excess -SH protecting agent was examined. Moreover the kinetics of the formation of N5-(4-oxo-1,3-diazospiro[4,4]non-2-ylidene)-I-ornithine or N7,N8-(1,2-dihydroxycyclohexyl-1,2-ylene)-L-arginine from arginine residue(s) of nuclear receptor by 1,2-cyclohexanedione was investigated. The efficiency of the reactions were followed spectrophotometrically and the modified nuclear receptor fraction separated from chemical modifiers on a Sephadex G-25 column was assayed at pH 8.0 for T3 specific binding. The T3 specific binding was tested by Scatchard plot analysis. No changes in nuclear receptor Ka or MBC were observed after 1,2-cyclohexanedione treatment. Tryptophanyl residue(s) of the receptor molecule may play an effective role in the maintaining the nuclear receptor in a conformation optimal for T3 binding.

Animals↗
PubMed1989

[Molecular basis for the action of thyroid hormones].

The mode of action of thyorid hormones at molecular level is described. The hormone reaches the target cell presumably by active transport and then it binds specifically to the plasma membrane, cytosol and mitochondria. Yet from the standpoint of its action, the most important binding is that to the cell nucleus. The nucleus receptor was partially isolated and its physico-chemical properties were determined. The hormone-receptor complex induces gene expression involving generation of specific ribonucleic acids and subsequent production of specific proteins (enzymes). The latent time interval for protein production is of varying length. Triiodothyronine induces in the liver the production of a specific protein which plays a role in the synthesis, metabolism, and storage of lipids.

Animals↗
PubMed1988

Study of the role of histidyl, tyrosyl, alpha- or epsilon-amino residues in the specific binding of 3,5,3'-triiodothyronine to rat liver nuclear receptors.

The role of histidyl, tyrosyl, alpha-or epsilon-amino residues of rat liver nuclear receptors for the specific binding of T3 was studied by chemically modifying the receptor molecule. The kinetics of the formation of N-carbethoxyhistidyl derivative from histidyl groups of nuclear receptors by diethylpyrocarbonate was examined. The modified nuclear receptor fraction was separated from diethylpyrocarbonate by gel filtration and the T3 binding parameters (Ka and MBC) at pH 8.0 were tested by Scatchard plot analysis. At 0.1 mmol/l diethypyrocarbonate, the value of Ka was significantly (P less than 0.01) decreased without any change in maximal binding capacity (MBC). The modification of alpha- or epsilon-amino groups of nuclear receptors by excess of trinitrobenzenesulfonic acid, 6.3 mmol/l at pH 8.5, resulted in a 4-fold increase in MBC of T3 specific binding without any change in Ka. In addition, acetylation of tyrosyl residues of nuclear receptors at pH 7.5 with an excess of 24 mmol/l N-acetylimidazole was performed. No changes in nuclear receptor Ka or MBC were observed after N-acetylimidazole treatment. Histidine and/or amino groups of the receptor molecule seem to hold a key position in the generation of the biologically active T3-nuclear receptor complex in the rat liver.

Amino Acids↗
PubMed1988

Effects of forskolin and triiodothyronine on cyclic AMP production in rat thymocytes.

The effects of forskolin, 3,5,3'-L-triiodothyronine, and isobutyl methylxanthine on the accumulation of cyclic AMP were studied in rat thymocytes in vitro. Forskolin was found to stimulate markedly the production of intracellular cAMP which was partially released from the cells into the medium. Isobutyl methylxanthine, an inhibitor of cAMP phosphodiesterase, markedly potentiated the effect of forskolin on intracellular cAMP concentration, while triiodothyronine was ineffective. However, triiodothyronine acted synergically with forskolin and/or isobutyl methylxanthine. It was confirmed that low forskolin concentrations modulate the effects of the hormone.

Animals↗
PubMed1988

Binding parameters of rat liver nuclear receptors for T3 after partial hepatectomy or bilateral adrenalectomy and serum T4 and T3 levels.

Nuclear receptor affinity (Ka) and maximal binding capacity (MBC) for 3,5,3'-triiodothyronine (T3) in rat liver was estimated at 1, 12, 24, 48 and 120 hours after partial hepatectomy and 1, 24, 30, 40 and 120 hours after bilateral adrenalectomy and related to serum T4, T3 levels. Soluble T3 receptor fraction was prepared from purified rat liver nuclei and the values of Ka and MBC were calculated by Scatchard plot analysis from the saturation curves. As compared to sham operated rats a significant diminution in MBC for T3 (P less than 0.05) in the remaining about one third of liver tissue at 12, 24 and 48 hours after partial hepatectomy was observed. The thyroxine (T4) level in serum was diminished (with P ranging from less than 0.001 to less than 0.01) at 12, 24 and 48 hours after partial hepatectomy, while no changes in T3 serum level were found at all indicated time intervals. In contrast, no changes in Ka or MBC for T3 in rat liver nuclear receptor as well as in serum T4 and T3 levels were demonstrated 1, 24, 30, 40 and 120 hours after adrenalectomy. The data reflect an appreciable relation between nuclear receptor occupancy for T3 and serum T4 level after partial hepatectomy, serum T3 level and Ka for T3 of nuclear receptor remaining unchanged.

Adrenalectomy↗
PubMed1987

Effect of thyroxine in vivo on malic enzyme activity in liver cytosol of propylthiouracil and alpha-amanitin treated rats.

The activity of rat liver malic enzyme (L-malate: NADP oxidoreductase/decarboxylating, MDH, E.C. 1.1.1.40) after T4 or T4 + alpha-amanitin treatment was investigated in relation to nuclear specific binding of T4. Specific binding of 125I-T4 to hepatic nuclear sites in rats at 21 days after thyreoparathyreoidectomy (Tx) was significantly increased (P less than 0.01) and was restored within 24 hours after a single dose of T4. Equilibrium association constants Ka estimated in all experimental groups were not attenuated. The activity of MDH increased 48 and 120 hours after a single dose of T4. In contrast, it decreased after Tx and was restored after T4 injection. The initial block of the stimulatory effect of T4 on MDH activity induced by alpha-amanitin observable during the first 48 h was overcome after 120 h when the increase of MDH activity was not only increased to normal values but reached values of T4 treated rats. It seems that the signal for the increase of the activity of MDH induced by thyroid hormones could occur as a secondary phenomenon stimulated by an as yet undefined intracellular process.

Amanitins↗
PubMed1987

Physiochemical factors influencing the stability of solubilized liver nuclear receptor-3,5,3'-triiodothyronine complex in vitro.

Nuclear acidic protein fraction containing saturable receptors for thyroid hormones was prepared from purified rat liver nuclei by extraction with 0.3 mol l-1 KCl. The inhibitory effect of an increasing ionic strength on the 3,5,3'-triiodothyronine (T3) binding to receptors at pH 8.0 for 2 h and tested up to 2.0 mol l-1 KCl was confirmed. The nuclear receptor-T3 complex was found resistant to the effect of a higher ionic strength up to 1 mol l-1 KCl when subsequently incubated at pH 8.0 for 1 h. In addition, a rapid dissociation of the receptor-T3 complex at alkaline pH in the order of 10.5 greater than 10.0 greater than 9.0 greater than 8.0 was re-examined. The effect of ATP ranging from 0.05 mmol l-1 to 1.0 mmol l-1 on the stability of the receptor-T3 complex at pH 8.0 was also studied. The experiments were conducted in the presence of 25 mmol l-1 Na2HPO4 in order to suppress the effect of the phosphate groups of ATP molecule by inorganic phosphate. The data confirmed that the concentration of ATP starting from 0.05 mmol l-1 may cause the dissociation of nuclear receptor-T3 complex in vitro.

Adenosine Triphosphate↗