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At least 199 records · Page 11Linked to original sources
PubMed1994

Thyroid hormone autoantibodies and their implications for free thyroid hormone measurement.

Thyroid hormone autoantibodies (THAA) disrupt the equilibrium between thyroid hormones and their binding proteins. This may lead to spurious estimations of free thyroxine (FT4) and triiodothyronine (FT3) by radioimmunoassay (RIA). In the present study we highlight the importance of THAA by examining the frequency of THAA in consecutive sera sent to a routine district hospital laboratory. Over a period of six months, sera were collected from 200 consecutive hypothyroid, 200 hyperthyroid and seven patients whose clinical and biochemical thyroid status were contradictory. A further 200 patients with non-thyroid autoimmune conditions, 20 patients with insulin autoantibodies and 100 healthy blood transfusion donors were studied. In all sera, both effects of antigen removal on THAA detection and where THAA were found, the effect of their removal on FT4, were examined. The frequencies of THAA amongst hypothyroid, hyperthyroid and non-thyroid autoimmune conditions were 7%, 1.5% and 7.5% respectively, whilst no THAA were found in insulin autoantibody positive patients and 100 blood transfusion donors. However, THAA frequency was highest in those patients whose biochemical thyroid status was widely inappropriate to clinical state (5/7 = 64%). Sera stripped of thyroid hormones prior to THAA detection had significantly higher antibody activity than unstripped sera (p = 0.0027 and p = 0.0123 for T3 and T4 binding respectively). Free thyroxine levels measured by the Amerlex-M RIA kit after antibody removal fell in all 21 THAA positive sera tested. The correlation coefficient between antibody activity in serum with percentage fall in FT4 was 0.79 (Spearman's Rank Correlation Test).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1996

Thyroid hormone metabolism and thyroid diseases in chronic renal failure.

Patients with ESRD have multiple alterations of thyroid hormone metabolism in the absence of concurrent thyroid disease. These may include elevated basal TSH values, which may transiently increase to greater than 10 mU/liter, blunted TSH response to TRH, diminished or absent TSH diurnal rhythm, altered TSH glycosylation, and impaired TSH and TRH clearance rates. In addition, serum total and free T3 and T4 values may be reduced, free rT3 levels are elevated while total values are normal, serum binding protein concentrations may be altered, and disease-specific inhibitors reduce serum T4 binding. Changes in T4 and T3 transfer, distribution, and metabolism resemble those of other nonthyroidal illnesses, while changes in rT3 metabolism are disease specific. Dialysis therapy minimally affects thyroid hormone metabolism, while zinc and erythropoietin administration may partially reverse thyroid hormone abnormalities. Thyroid hormone metabolism normalizes with renal transplantation; however, glucocorticoid therapy may induce additional changes. ESRD patients may have an increased frequency of goiter, thyroid nodules, thyroid carcinoma, and hypothyroidism. Goiter and hypothyroidism may be induced by iodide excess, due to reduced renal iodide excretion, and may be reversed with iodide restriction in some patients. The increased frequency of thyroid nodules and malignancies in ESRD may relate to secondary hyperparathyroidism. After renal transplantation, the higher frequency of thyroid malignancies may relate to the immunosuppressed state. Clinical symptoms and signs and biochemical features of hypothyroidism and hyperthyroidism may be altered by concurrent ESRD. ESRD patients with hyperthyroidism or follicular neoplasms require reduced dosages of Na 131-I depending upon type, frequency, and duration of dialysis therapy.

Combined Modality Therapy↗
PubMed1991

Variations in serum levels of insulin-like growth factor-1, growth hormone and thyroid hormones during lactation in dairy cows.

1. Serum levels of insulin-like growth factor-1 (IGF-1) in dairy cows declined after parturition, remained low during the period of early lactation with peak milk production and rose gradually until the end of lactation thereafter. 2. Growth hormone (GH) levels in sera of cows changed in parallel with milk yields. 3. Serum thyroxine and triiodothyronine levels during lactation remained fairly constant.

Animals↗
PubMed1991

Purification of hepatic N-hydroxyarylamine sulfotransferases and their regulation by growth hormone and thyroid hormone in rats.

From liver cytosols of male Sprague-Dawley rats, two N-hydroxyarylamine sulfotransferases (HASTs) which sulfate N-hydroxy-2-acetylaminofluorene and a phenolsulfotransferase (PST-I) have been purified about 290-, 690-, and 210-fold, respectively, by the use of DEAE-anion exchange, Blue-Sepharose CL-6B, DEAE-HPLC, and ATP-agarose affinity chromatography. All three enzymes showed almost the same molecular weight of 33 kDa on SDS-polyacrylamide gel electrophoresis. In Western blots using antibody raised against HAST I, the two HASTs, but not PST-I, were detected. The content of total HAST in male rats was estimated as 4-5 micrograms/mg cytosolic protein, about 4 times higher than that in female rats. Direct comparison of the DEAE-HPLC elution profiles of cytosol showed that HAST I and HAST II were male-dominant and male-specific, respectively, in their expression in the livers. Hypophysectomy decreased the level of HAST by 60% in male rats, but had no obvious effect in female rats. Intermittent injection of growth hormone to mimic the male secretory pattern raised the content in hypophysectomized rats of both sexes close to that in intact male rats, while the continuous infusion of growth hormone to mimic the female secretory pattern showed limited effects. In addition, the administration of triiodothyronine stimulated HAST in hypophysectomized rats of both sexes, and the extent of stimulation was nearly the same as observed in the male-type growth hormone treatment. PST-I, in contrast to HAST, showed no clear sex-related difference in hepatic content, and was not apparently affected by growth hormone or triiodothyronine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

A de novo mutation in an already mutant nucleotide of the thyroid hormone receptor beta gene perpetuates resistance to thyroid hormone.

Resistance to thyroid hormone (RTH) is a syndrome of reduced sensitivity to thyroid hormone, most commonly caused by mutations in the thyroid hormone receptor (TR) beta gene. Mutations are mostly located in the ligand-binding domain of the TRbeta, decreasing T(3) binding to the mutant TRbeta molecule, which in turn interferes with the function of the wild-type (WT) TR. A total of 122 different TRbeta gene mutations have been identified so far, with 46 occurring in more than one family. We now report a family with two novel TRbeta mutations occurring in the same nucleotide. The proposita had two children from each of her two marriages. One daughter and one son from each marriage had severe RTH with free T(4) and T(3) levels 3- to 4-fold the mean normal values and unsuppressed TSH, mental retardation, and deafness. The proposita had a missense mutation (GTG to GGG) in codon 458 of the TRbeta gene, resulting in the replacement of the normal valine with glycine (V458G). Although this mutation was transmitted to her affected son, the mutated codon in her affected daughter was GAG, encoding glutamic acid (V458E). Haplotype analysis showed that this de novo mutation occurred on the already mutant allele of the proposita. Cotransfection of each of these mutant TRbetas with the wild-type TRbeta showed a potent dominant negative effect. Large amounts of T(3) were required to dissociate homodimers of the mutant TRbeta bound to DNA. In addition, and in contrast to other mutant TRbetas with severe T(3)-binding defects, homodimer release failed to recruit the steroid receptor coactivator. No defects in heterodimerization with retinoid X receptor-alpha or association with a nuclear receptor corepressor, were identified. These in vitro data are in agreement with the in vivo phenotype of severe RTH. Unique and previously unreported in human inherited diseases is the occurrence of a de novo mutation at an already mutant nucleotide. Because the occurrence by chance is extremely unlikely, it is postulated that the presence of three guanines in the sequence created by the mutant nucleotide of the proposita results in a mutagenic site prone to de novo mutation.

Adult↗
PubMed2003

Thyroid hormone action in the absence of thyroid hormone receptor DNA-binding in vivo.

Thyroid hormone action is mediated by thyroid hormone receptors (TRs), which are members of the nuclear hormone receptor superfamily. DNA-binding is presumed to be essential for all nuclear actions of thyroid hormone. To test this hypothesis in vivo, the DNA-binding domain of TR-beta was mutated within its P-box (GS mutant) using gene targeting techniques. This mutation in vitro completely abolishes TR-beta DNA-binding, while preserving ligand (T3) and cofactor interactions with the receptor. Homozygous mutant (TR-betaGS/GS) mice displayed abnormal T3 regulation of the hypothalamic-pituitary-thyroid axis and retina identical to abnormalities previously observed in TR-beta KO (TR-beta-/-) mice. However, TR-betaGS/GS mutant mice maintained normal hearing at certain frequencies and did not display significant outer hair cell loss, in contrast to TR-beta-/- mice. DNA-binding, therefore, is essential for many functions of the TR, including retinal development and negative feedback regulation by thyroid hormone of the hypothalamic-pituitary-thyroid axis. Inner ear development, although not completely normal, can occur in the absence of TR DNA-binding, suggesting that an alternative and perhaps novel thyroid hormone-signaling pathway may mediate these effects.

Alleles↗
PubMed1988

Characterization of a third human thyroid hormone receptor coexpressed with other thyroid hormone receptors in several tissues.

A cDNA that encodes a third type of human thyroid hormone receptor (hTR alpha 1) has been isolated from a skeletal muscle library. The cDNA encodes a 410 amino acid protein, Mr = 46,820. When expressed and translated in vitro, hTR alpha 1 binds T3 with an association constant (ka) of 1.8 x 10(9) M-1. Comparison of the DNA sequence of hTR alpha 1 and a previously identified alpha type thyroid hormone receptor (hTR alpha 2) suggests that they could be transcribed from the same gene, and that alternative RNA splicing results in the synthesis of either hTR alpha 1 or hTR alpha 2. Two mRNA (3.2 kilobases and 6 kilobases) of hTR alpha 1 have been detected in several tissues. At least three types of thyroid hormone receptors (hTR alpha 1, alpha 2, beta), which possess similar affinities for hormone ligands, can be expressed in the same tissue.

Amino Acid Sequence↗
PubMed2000

[Effect of aceclofenac on thyroid hormone binding and thyroid function].

Influences of non-steroidal anti-inflammatory drugs (NSAID) on concentrations of thyroid hormones are known for a long time. These effects could be explained with interference between NSAIDs and thyroid hormone binding. We investigated the effects of a single dose of aceclofenac on thyroid function and thyroid hormone binding in 18 healthy volunteers. Serum levels of free thyroid hormones (FT3, FT4) and thyrotropin (TSH) were measured with commercial available kids and thyroid hormone binding was estimated with a specially modified horizontal argarose-gel-electrophoresis prior to and 2 hours after receiving a single dose of aceclofenac. We found a significant decrease in T3 binding on TBG and a significant increase of albumin-bound T3. All other investigated thyroid hormone binding parameters, FT3 and FT4, showed no significant changes. We conclude that aceclofenac leads to a significant redistribution of T3 protein binding. These effects seem to be explained by T3 displacement from TBG induced by aceclofenac.

Adult↗
PubMed1979

Thyrotropin-releasing hormone and thyroid hormones in amniotic fluid.

Immunoassayable TRH (iTRH) was measured in 50 amniotic fluid specimens with a mean concentration of 207 +/- 26 (SE) pg/ml. This iTRH demonstrates parallelism with the standard curve for synthetic TRH. With increasing gestational age there is an increase in iTRH levels in amniotic fluid with a decrease in 3,3',5'-triiodothyronine levels (rT3), while thyroxine levels (T4) remain unaltered. Preliminary data suggest that iTRH levels in amniotic fluid that are less than 150 pg/ml after 32 weeks of gestation may correlate well with low Apgar scores at birth. There was no correlation of rT3 or T4 amniotic fluid levels with the Apgar scores.

Amniotic Fluid↗
PubMed1992

Role of selected endogenous peptides in growth hormone-releasing hexapeptide activity: analysis of growth hormone-releasing hormone, thyroid hormone-releasing hormone, and gonadotropin-releasing hormone.

The purpose of this study was to evaluate the contribution of endogenous GH-releasing hormone (GHRH) to exogenous GH-releasing hexapeptide (GHRP-6) activity, and to determine whether TRH or GnRH are endogenous analogs of GHRP-6. The activity of GHRP-6, a synthetic GH secretagogue, was significantly attenuated in rats administered GHRH antiserum or alpha-methyl-rho-tyrosine to reduce endogenous GHRH concentrations, and also in rats administered 5-50 micrograms/kg of [N-Ac-Tyr1,D-Arg2]-GRF 1-29 amide to block pituitary GHRH receptors. However, GHRP-6 activity was potentiated in rats administered 150 micrograms/kg [N-Ac-Tyr1,D-Arg2]-GRF 1-29 amide, presumably due to partial agonist activity of the GHRH receptor antagonist at the higher dose. These data show that endogenous GHRH contributes to full expression of exogenous GHRP-6 activity in vivo. Like TRH, a subthreshold dose of GHRP-6 was significantly more effective in hypothyroid rats than in euthyroid rats. However, suprathreshold doses of GHRP-6 were less effective in hypothyroid rats. Unlike TRH, GHRP-6 had no effect on GH and prolactin release from GH3 cells, and TRH and GnRH were poor competitors for 3H-GHRP-6 binding sites on pituitary membranes. A GnRH receptor antagonist did not block GHRP-6 activity in vivo, and GnRH administered alone or in combination with GHRP-6, did not stimulate GH release. The results of this study suggest that synergy between GHRH and GHRP-6 seen in pharmacological studies is physiologically relevant, and that TRH and GnRH are not endogenous analogs of GHRP-6.

Animals↗