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At least 55 records · Page 3Linked to original sources
PubMed1988

[Basal and TRH stimulated TSH secretion and determination of total thyroxine (T4). Thyroxine-binding capacity and free thyroxine index (FT4-I) in patients with chronic uremia].

In 11 patients with chronic uremia both the basal and TRH stimulated TSH levels and T4, TBC and FT4-I were determined. The investigations were repeated in 2 cases after renal transplantation. TSH and T4 in serum were determined by RIA, TBC by radio reagent assay. FT4-I was calculated. In 8 patients the basal TSH levels were in the normo- and in 3 in the hypothyreotropic range. In 9 patients the response to TRH was adequate. There were deviations from the physiological range in 7 patients for T4 and in 6 for FT4-I.

Adult↗
PubMed1990

Immunological quantitation of rat and mouse thyroxine-binding globulins. Ontogenesis and sex-dependence of the circulating levels of the thyroxine-binding globulins.

We describe the preparation of monospecific antisera against a thyroxine-binding globulin partially purified from immature rat sera by affinity chromatography on thyroxine-Sepharose. The antisera are used for the rocket immunoelectrophoresis assay of rat thyroxine-binding globulin and also, owing to their partial cross-reactivity with mouse thyroxine-binding globulin, for the quantitation of this serum binding protein in the mouse. The thyroxine-binding globulin is measured in developing rats and in sexually mature male and female rats and mice. The results of the ontogenetic study confirm the postnatal surge of serum thyroxine-binding globulin levels, formerly demonstrated with binding techniques. They allow further to define the correlations, dependent on age, of the immunoquantitated thyroxine-binding globulin and transthyretin levels with the abilities of the sera to bind thyroxine. In sexually mature rats and mice we demonstrate an opposite sex-dependence of thyroxine-binding globulin levels, characterized by increased levels of the protein in the female rats versus increased levels of the protein in the male mice. This is the first report of immunological quantitation of rat and mouse thyroxine-binding globulins.

Aging↗
PubMed1984

Acute effect of exogenous thyroxine dose on serum thyroxine and thyrotrophin levels in treated hypothyroid patients.

Acute effects of exogenous thyroxine on the serum thyroxine (T4), free thyroxine (FT4) and thyrotrophin (TSH) levels were studied in 20 hypothyroid women during the long-term maintenance therapy. All patients were euthyroid by clinical and laboratory parameters (T4). In nine patients TSH secretion was totally suppressed (less than 1 mu/l) by the mean dose of 178 micrograms thyroxine. Eleven patients had TSH values greater than 1 mu/l. Their mean thyroxine dose (132 micrograms) was not significantly lower than that which totally suppressed the TSH secretion. Ingestion of thyroxine resulted in maximal T4 and FT4 levels at 2 h after taking the drug. Simultaneously TSH concentration reached its minimum. The results indicate that it is necessary to know when the patient has taken the thyroxine in relation to determination of T4, FT4 and TSH levels in order to make the right decisions about the substitution dose of thyroxine. Thus it is essential to take blood sample for hormone determination before the patient ingests the daily thyroxine dose. However, among hypothyroid patients substituted by thyroxine there are individuals whose TSH secretion is not suppressed by normal T4 and FT4 levels.

Adult↗
PubMed1986

Effect of long-chain fatty acids on the binding of thyroxine and triiodothyronine to human thyroxine-binding globulin.

The effect of long-chain fatty acids on the binding of thyroxine to highly purified human thyroxine-binding globulin has been studied by equilibrium dialysis performed at pH 7.4 and 37 degrees C. At a fixed molar ratio of 2000:1 of fatty acid to thyroxine-binding globulin, the degree of binding inhibition based on the percent change in nK value relative to the control as determined from Scatchard plots was: palmitic, 0%; stearic, 0%; oleic, 76%; linoleic, 69%; and linolenic, 61%. At a 500:1 molar ratio of oleic acid to thyroxine-binding globulin, equivalent to 0.125 mM free fatty acid in serum, thyroxine binding was inhibited by 18%, increasing to 93% at a 4500:1 molar ratio. At molar ratios of oleic acid to thyroxine-binding globulin of 1000:1, 2000:1 and 4000:1, the degree of inhibition of triiodothyronine binding was 24%, 41% and 76%, respectively. The results indicate that the unsaturated long-chain fatty acids are potent inhibitors of thyroxine binding to thyroxine-binding globulin, whereas the saturated fatty acids have little or no effect on thyroxine binding.

Fatty Acids↗
PubMed1994

Different competition of thyroxine binding to transthyretin and thyroxine-binding globulin by hydroxy-PCBs, PCDDs and PCDFs.

In an earlier study several hydroxylated polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) competitively displaced [125I]thyroxine (T4) from transthyretin with different potencies. Transthyretin is the major T4 transport protein in plasma of rodents. In man, however, thyroxine-binding globulin transports most of the T4 in blood. In this study, hydroxylated PCBs, PCDDs and PCDFs were tested in an in vitro competitive binding assay, using purified human thyroxine-binding globulin and [125I]T4 as the displaceable radioligand. None of the tested hydroxylated PCBs, PCDDs and PCDFs inhibited [125I]T4 binding to thyroxine-binding globulin. In addition, some T4 derived compounds, e.g., tyrosine, mono-iodotyrosine, di-iodotyrosine and tri-iodophenol were tested on both transthyretin and thyroxine-binding globulin to investigate possible differences in structural characteristics determining T4 binding to thyroxine-binding globulin and transthyretin. The T4 derived compounds also did not inhibit [125I]T4 binding to thyroxine-binding globulin as tested in the in vitro assay. However, tri-iodophenol and to a lesser extent di-iodotyrosine inhibited [125I]T4-transthyretin binding. These results indicate a marked difference in T4 binding to thyroxine-binding globulin or transthyretin. The hydroxylated PCBs, PCDDs and PCDFs can inhibit T4 binding to transthyretin, but not to thyroxine-binding globulin, and thus may cause different effects in rodents and man.

Benzofurans↗
PubMed1971

Human thyroxine-binding globulin and thyroxine-binding pre-albumin: dissociation rates.

1. A simple method is described for estimating the rate of thyroxine dissociation from binding sites in plasma.2. At tracer concentrations in human plasma thyroxine dissociates at two distinct exponential rates. These are due to the two thyroxine-binding proteins present in human plasma.3. The t((1/2)) for thyroxine dissociation from thyroxine-binding globulin is 8.1 +/- 0.7 (S.E.) min at room temperature and 38.6 +/- 2.1 sec at 37 degrees C.4. The t((1/2)) for thyroxine dissociation from thyroxine-binding pre-albumin is 53 +/- 5.0 sec at room temperature and 7.9 +/- 0.3 sec at 37 degrees C.5. Dissociation of thyroxine from both proteins is a single exponential process, suggesting that each protein has only one type of specific binding site.6. These results indicate that the minute pool of free thyroxine in plasma is turning over about 100 times each second, with about two thirds of this flux being due to release and binding of the hormone by pre-albumin.

Binding Sites↗
PubMed1982

Total over free thyroxine ratio: prediction of thyroxine binding globulin.

Both total thyroxine and free thyroxine concentrations are measured in the Immophase free thyroxine assay. These total and free thyroxine results allow a prediction of the accessory concentrations of thyroxine-binding globulin (TBG). Since abnormal concentrations of TBG often cause problems in the evaluation of thyroid function, we evaluated the possibility of predicting these abnormal values from total and free thyroxine results. Two ways of predicting abnormal concentrations of TBG were evaluated on statistical grounds. The first method, a simple total thyroxine/free thyroxine ratio, proved to be better than the second method, which corrected for the influence of the other thyroxine binding proteins (result: a calculated concentration of TBG). The total thyroxine/free thyroxine ratio predicts abnormally low TBG values, below a ratio fo 4,000 (certainty 45%) and abnormally high TBG values, above a ratio of 6,400 (certainty 89%).

Female↗
PubMedDate not supplied

Inhibition of rat hepatic thyroxine 5'-monodeiodinase by propylthiouracil: relation to site of interaction of thyroxine and glutathione.

When rat liver cytosol, dialyzed free of glutathione, was chromatographed on Sephadex G-100 after incubation with 35S-propylthiouracil, 2 peaks of bound radioactivity were observed, 1 of which contained nearly all the thyroxine 5'-monodeiodinase activity in rat liver cytosol. Binding of propylthiouracil to this peak was inhibited by glutathione but not by thyroxine. Approximately 25% of 35S-propylthiouracil initially bound to the thyroxine 5'-monodeiodinating activity peak remained bound after dialysis, precipitation with trichloroacetic acid, and multipe extractions with ethanol, methanol, and chloroform, suggesting that binding was at least in part covalent. Dialysis studies showed that the presumed covalent binding of 35S-propylthiouracil to the thyroxine 5'-monodeiodinase peak could be inhibited by glutathione, dithioerythritol, and unlabelled propylthiouracil but not by oxidized glutathione or thyroxine. Conversely, thyroxine binding was unaffected by thiol compounds. We studied the kinetics of thyroxine 5'-monodeiodination by radioimmunoassay techniques using rat liver homogenates as source of enzyme and observed the dependence of enzymic reaction upon glutathione (Km = 2.4 mM). Propylthiouracil inhibited the reaction and this inhibition could be overcome with increasing glutathione concentrations. We conclude that the thiol-dependent thyroxine 5'-monodeiodinase is inhibited by propylthiouracil through its covalent binding, probably as mixed disulfide, to s site on the enzyme at which glutathione interacts either as a cosubstrate or reducing agent. This binding site is separate from the site at which thyroxine binds.

Animals↗