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At least 577 records · Page 32Linked to original sources
PubMed2000

Localization of thyroid hormone receptor beta2 in the ventral medullary neurons that synthesize thyrotropin-releasing hormone.

Altered thyroid statuses are associated with autonomic disorders. Thyrotropin-releasing hormone (TRH) synthesized in medullary raphe pallidus (Rpa), raphe obscurus (Rob) and the parapyramidal regions (PPR) regulates vagal and sympathetic preganglionic motoneurons. Hypothyroidism increased TRH gene expression and c-Fos immunoreactivity (IR) in these nuclei. Whether these increases represent a direct action of thyroid hormone was studied by detecting the presence of thyroid hormone receptor beta2 (TRbeta2) in pro-TRH-synthesizing neurons in the Rpa, Rob and the PPR using immunohistochemistry with specific TRbeta2 antiserum and in situ hybridization with digoxigenin-labeled pro-TRH cRNA probe. TRbeta2 IR was widely distributed throughout the medulla and primarily localized within the cell nuclei. Particularly intense immunostaining was presented in the Rpa, Rob and the PPR neurons. The combination of immunohistochemistry with in situ hybridization revealed that all pro-TRH mRNA-positive neurons in these ventral medullary nuclei were also TRbeta2 IR positive. The numbers of TRbeta2 IR-positive neurons in each nucleus were identical in both euthyroid rats and hypothyroid rats induced by 6-n-propyl-2-thiouracil in drinking water for 4 weeks. The finding that TRbeta2 localized in pro-TRH-synthesizing neurons in the ventral medullary nuclei provides an anatomical substrate for a direct thyroid hormone action on these neurons in the regulation of TRH gene expression, which may contribute to the altered autonomic activity in different thyroid statuses.

Animals↗
PubMed1992

Effects of short-term growth hormone treatment on PTH, calcitriol, thyroid hormones, insulin and glucagon.

We measured changes in serum insulin-like growth factor-1 (IGF-1), calcitriol, parathyroid hormone (PTH), thyroid hormones, insulin, and plasma glucagon in response to seven days of treatment with a pharmacological dosage of recombinant human growth hormone (r-hGH) (0.1 IU/kg sc twice daily) or placebo in 20 normal male volunteers to evaluate whether the effect of r-hGH on biochemical bone markers could be attributed to changes in these hormones. Serum IGF-1 (p < 0.001) and vitamin D-binding protein (p < 0.001) increased steadily during treatment returning to baseline at day 14. Total calcitriol (p < 0.01) and free calcitriol index (p < 0.001) increased transiently at day 4. Furthermore, serum insulin (p < 0.001) and both total (p < 0.001) and free triiodothyronine (p < 0.02) increased during treatment, while serum PTH and plasma glucagon remained unchanged. In conclusion, pharmacological doses of r-hGH increased not only IGF-1 but also free-calcitriol index, insulin, and free T3. The increase in these hormones may be co-responsible for some of the observed effects of r-hGH on bone turnover and calcium homeostasis.

Adult↗
PubMed1988

[Thyroid hormone metabolism in nonthyroidal illnesses. II. A new method for measuring serum thyroid hormone binding inhibitor and its clinical application].

It is well known that serum T3 and T4 concentrations are often decreased in patients with nonthyroidal illnesses (NTI). The purpose of this study was to elucidate the possible role of serum thyroid hormone binding inhibitor (THBI) in lowering serum T4 in patients with NTI using the originally developed method for measuring THBI. 125I.T4 and 0.05 micromilligram of pooled normal serum was applied to the Sephadex G.25 column equilibrated in advance by 0.1N NaOH, and 4 micromilligram of 0.075M veronal buffer, pH 8.6 (Buffer) was added. 125I.T4 thus adsorbed on the column was then eluted by adding the charcoal treated thyroxine-free serum (used as thyroxine binding protein (TBP) solution) with THBI which had been extracted from the serum by diethyl ether or standard sodium oleate solution (0.125 approximately 1.0 mumol/column). When the radioactivity of the eluate was counted, the gradual decrease in radioactivity was observed with increase in sodium oleate due to the inhibition of 125I.T4 and TBP binding. Thus, THBI in serum could be expressed as mumol sodium oleate equivalent from the dose response curve for binding inhibition. Coefficients of intrassay and interassay variations in this assay were 6 and 17%, respectively when sera from patients with acute myocardial infarction (AMI) were measured. THBI from 15 normal controls ranged from 0 to 0.27 (mean +/- SD: 0.11 +/- 0.08) mumol sodium oleate equivalent, the normal range being less than 0.27 mumoles. In 12 patients with AMI and 12 with end-stage malignancy (cancer), serum T4 levels were below the normal range in 9 and 8 cases, respectively. In these patients, serum THBI was positive in as many as 10 (83%) and 11 (92%) cases, respectively. Serum T4 and THBI were serially measured after admission in patients with AMI. Serum T4 concentrations showed their lowest values on the first, second or third hospital day and they gradually increased to the normal range by the seventh day. On the other hand, serum THBI showed their highest value on the first hospital day in 8 cases of AMI, and they gradually decreased thereafter. A statistically significant negative correlation was observed between serum T4 and THBI in these patients (r = -0.63, p less than 0.01). Moreover, statistically significant positive correlations were observed between serum THBI and FFA in both AMI and cancer patients (r = 0.89, p less than 0.01; r = 0.88, p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Humans↗
PubMed1999

A comparison of recombinant human thyrotropin and thyroid hormone withdrawal for the detection of thyroid remnant or cancer.

Recombinant human TSH has been developed to facilitate monitoring for thyroid carcinoma recurrence or persistence without the attendant morbidity of hypothyroidism seen after thyroid hormone withdrawal. The objectives of this study were to compare the effect of administered recombinant human TSH with thyroid hormone withdrawal on the results of radioiodine whole body scanning (WBS) and serum thyroglobulin (Tg) levels. Two hundred and twenty-nine adult patients with differentiated thyroid cancer requiring radioiodine WBS were studied. Radioiodine WBS and serum Tg measurements were performed after administration of recombinant human TSH and again after thyroid hormone withdrawal in each patient. Radioiodine whole body scans were concordant between the recombinant TSH-stimulated and thyroid hormone withdrawal phases in 195 of 220 (89%) patients. Of the discordant scans, 8 (4%) had superior scans after recombinant human TSH administration, and 17 (8%) had superior scans after thyroid hormone withdrawal (P = 0.108). Based on a serum Tg level of 2 ng/mL or more, thyroid tissue or cancer was detected during thyroid hormone therapy in 22%, after recombinant human TSH stimulation in 52%, and after thyroid hormone withdrawal in 56% of patients with disease or tissue limited to the thyroid bed and in 80%, 100%, and 100% of patients, respectively, with metastatic disease. A combination of radioiodine WBS and serum Tg after recombinant human TSH stimulation detected thyroid tissue or cancer in 93% of patients with disease or tissue limited to the thyroid bed and 100% of patients with metastatic disease. In conclusion, recombinant human TSH administration is a safe and effective means of stimulating radioiodine uptake and serum Tg levels in patients undergoing evaluation for thyroid cancer persistence and recurrence.

Adult↗
PubMed2001

Thyroid hormone response element-like sequence in anuran matrix metalloproteinase 1 gene is responsive to in vivo thyroid hormone administration.

Gene (Rmmp1) of matrix metalloproteinase 1 (MMP1) of the bullfrog, Rana catesbeiana, has been shown previously to contain a thyroid hormone response element (TRE)-like sequence in its 5'-upstream region. The present study aimed to determine whether this TRE-like sequence is functional in vivo as a true TRE, and to characterize the sequences of the 5'-upstream region with respect to the regulation of the activity of the TRE when the TRE-like sequence was proved to be a true TRE. With this aim, various sequences of TRE-like sequence-containing 5'-upstream region were constructed and fused to the enhanced green fluorescent protein gene as a reporter gene. The fusion constructs were bombarded to the skin of bullfrog tadpoles and the activity of the TRE was quantitatively determined by measuring increased intensities of fluorescence when the animals were exposed to thyroid hormone. The present study clearly demonstrated that the sequence of Rmmp1 is a biologically active TRE in vivo. In addition, a unique 36 bp long sequence directly flanked to the 3'-end of the TRE was identified which worked co-operatively with TRE to regulate the transcriptional promoter activity. It should be emphasized that the presence of TRE in the Rmmp1 gene is unique, because its presence has not been reported in the known promoter region of vertebrate MMPs.

Animals↗
PubMed1998

[Pathogenesis of disorder due to thyroid hormone receptor mutation].

Thyroid hormone action is mediated through its nuclear receptor (thyroid hormone receptor; TR). A mutation in the TR causes resistance to thyroid hormone (RTH) with autosomal dominant inheritance. Using T3 binding assay, gel shift assay and transfection study, the pathogenesis of this disorder was elucidated at a molecular level. Mutant TRs lose their T3 binding activity, and inhibit wild type TR action in a dominant negative manner. For this dominant negative inhibition, the preservation of DNA binding and dimerization activities are required. It is indicated that the mutant TR complex competes with wild type TR complex for the DNA binding site to exert dominant negative inhibition. Thus, the functional analyses of mutant TRs are useful to elucidate the molecular basis of this disorder.

Humans↗
PubMed2003

Molecular basis of resistance to thyroid hormone.

Resistance to thyroid hormone (RTH) is a syndrome in which patients have raised serum thyroid hormone (TH) levels and raised or inappropriately normal thyrotropin (TSH) levels. In general, patients exhibit TH resistance in the pituitary and peripheral tissues. Novel techniques and genetically engineered mouse model systems have increased our understanding of thyroid hormone receptor (TR) action, and shed new light on the underlying molecular mechanisms for RTH. In particular, we are learning how mutant TRs from RTH patients can block wild-type TR function, with consequent effects in various tissues and cells. This dominant-negative activity has important implications for other hormone-resistant conditions and in hormone-sensitive tumors. This article examines the molecular basis of RTH.

Animals↗
PubMed1994

Reduction of thyroid hormone levels and alteration of thyroid function by four representative UDP-glucuronosyltransferase inducers in rats.

Male Sprague-Dawley rats (250-275 g) were fed diets containing four representative UDP-glucuronosyltransferase (UDP-GT) inducers, phenobarbital (PB), 3-methylcholanthrene (3MC), and pregnenolone-16 alpha-carbonitrile (PCN), as well as a polychlorinated biphenyl (PCB) mixture for 21 days to determine their effect on thyroid hormone levels and thyroid gland function. On Days 3, 7, 14, and 20, blood was collected and serum levels of free and total thyroxine (T4), free and total triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were determined by radioimmunoassay. On Day 21, following treatment with Na131I, the thyroid glands were removed and weighed, and the amount of 131I incorporated was determined. The livers were removed and microsomes were isolated for determination of T4 UDP-GT activity. UDP-GT activity toward T4 was increased by PB, 3MC, PCN, and PCB approximately 190, 290, 260, and 550%, respectively, per kilogram of body weight. PB, 3MC, and PCN reduced serum total and free T4 30-40%, whereas PCB produced a 80-90% reduction. Total T3 levels were slightly reduced by treatment with PB, PCN, and PCB, but none of the treatments decreased free T3 levels. Serum T4 levels (total and free) were found to correlate with UDP-GT activity toward T4. The reductions in thyroid hormone levels led to an increase in TSH levels by PB, 3MC, PCN, and PCB (approximately 50, 50, 210, and 40%, respectively) on Day 20. The elevation of TSH led to an increase in thyroid gland weight by PCN (60%) and PCB (30%) and an increase in thyroidal 131I uptake by PB (60%), PCN (160%), and PCB (100%). Thus, while reasonable correlations between T4 glucuronidation and reduction of serum T4 can be made, only qualified correlations between reduction of T4 and increase in TSH and increase in TSH and stimulation of the thyroid can be made. In conclusion, three classes of microsomal enzyme inducers, represented by PB, 3MC, PCN, as well as PCB, increase UDP-GT activity toward T4 and decrease T4 levels. It appears that induction of UDP-GT plays a role in the effect of these chemicals on the thyroid gland.

Administration, Oral↗
PubMed1990

Isolation of a cDNA encoding human Rev-ErbA alpha: transcription from the noncoding DNA strand of a thyroid hormone receptor gene results in a related protein that does not bind thyroid hormone.

A cDNA encoding Rev-ErbA alpha, a member of the thyroid/steroid hormone receptor superfamily, has been isolated from a human fetal skeletal muscle library. This cDNA contains 269 consecutive base pairs identical to a region of a human c-erbA alpha-2 cDNA, but the respective long open reading frames utilize this nucleotide sequence in opposite orientations. Thus, human Rev-ErbA alpha (hRev) is derived from opposite-strand transcription of the c-erbA alpha genomic locus. mRNA encoding hRev was detected in human skeletal muscle by Northern analysis. Comparison of hRev and Rev-ErbA (rRev) reveals 99% identity in the putative DNA-binding and "ligand-binding" (carboxy-terminal) domains. hRev does not bind thyroid hormone (T3), as has also been found for its rat homolog. Interestingly, the human and rat Rev-ErbA alpha cDNAs are dissimilar at their 5' ends, corresponding to the first exon that we have identified in the rat gene. The conservation of the bidirectionally transcribed regions of c-erbA alpha-2 and Rev-ErbA alpha in human and rat suggests that this unusual genomic arrangement has an important function, perhaps related to the regulation of gene expression.

Base Sequence↗
PubMed2002

A thyroid hormone response unit formed between the promoter and first intron of the carnitine palmitoyltransferase-Ialpha gene mediates the liver-specific induction by thyroid hormone.

Carnitine palmitoyltransferase-I (CPT-I) catalyzes the rate-controlling step of fatty acid oxidation. CPT-I converts long-chain fatty acyl-CoAs to acylcarnitines for translocation across the mitochondrial membrane. The mRNA levels and enzyme activity of the liver isoform, CPT-Ialpha, are greatly increased in the liver of hyperthyroid animals. Thyroid hormone (T3) stimulates CPT-Ialpha transcription far more robustly in the liver than in non-hepatic tissues. We have shown that the thyroid hormone receptor (TR) binds to a thyroid hormone response element (TRE) located in the CPT-Ialpha promoter. In addition, elements in the first intron participate in the T3 induction of CPT-Ialpha gene expression, but the CPT-Ialpha intron alone cannot confer a T3 response. We found that deletion of sequences in the first intron between +653 and +744 decreased the T3 induction of CPT-Ialpha. Upstream stimulatory factor (USF) and CCAAT enhancer binding proteins (C/EBPs) bind to elements within this region, and these factors are required for the T3 response. The binding of TR and C/EBP to the CPT-Ialpha gene in vivo was shown by the chromatin immunoprecipitation assay. We determined that TR can physically interact with USF-1, USF-2, and C/EBPalpha. Transgenic mice were created that carry CPT-Ialpha-luciferase transgenes with or without the first intron of the CPT-Ialpha gene. In these mouse lines, the first intron is required for T3 induction as well as high levels of hepatic expression. Our data indicate that the T3 stimulates CPT-Ialpha gene expression in the liver through a T3 response unit consisting of the TRE in the promoter and additional factors, C/EBP and USF, bound in the first intron.

Animals↗
PubMedDate not supplied

Recent advances in understanding thyroid hormone receptor coregulators.

Thyroid hormones (L-triiodothyronine, T3; L-tetraiodothyronine, T4) regulate normal cellular growth and development, and general metabolism as well. Their various actions are mediated by the thyroid hormone receptor, a ligand-dependent transcriptional factor belonging to the nuclear hormone receptor superfamily. The recent discovery of coregulators (coactivators, corepressors, and cointegrators) has greatly enhanced our understanding of thyroid hormone receptor functions. Hence we review and discuss, in brief, the potential role of thyroid hormone receptor coregulators involved in diverse cellular activities.

Animals↗
PubMed1993

Thyroid hormone resistance syndromes.

The thyroid hormone resistance syndromes are disorders in which the body's tissues are resistant to the effects of thyroid hormone. Generalized resistance to thyroid hormone (GRTH) is characterized by resistance in the pituitary gland and in most or all of the peripheral tissues. Affected individuals have elevated serum thyroid hormone levels and inappropriately normal or elevated thyroid-stimulating hormone (TSH) but are usually clinically euthyroid and require no treatment. Selective pituitary resistance to thyroid hormone (PRTH) is characterized by resistance in the pituitary gland but not in peripheral tissues. Patients have elevated serum thyroid hormone levels and normal or elevated TSH levels and are clinically thyrotoxic. Therapy is usually necessary, but current choices are not completely satisfactory. Selective peripheral resistance to thyroid hormone (PerRTH) is characterized by resistance in peripheral tissues but not in the pituitary. The only patient thus far described had normal serum thyroid hormone and TSH levels but was clinically hypothyroid and improved with thyroid hormone administration. All of these disorders are probably more common than is generally recognized and are often misdiagnosed and inappropriately treated. GRTH, in most cases studied, results from a mutation in the thyroid hormone receptor beta gene causing an amino acid substitution in or a partial or complete deletion of the thyroid hormone-binding domain of the receptor. The causes of PRTH and PerRTH remain to be determined.

Diagnosis, Differential↗
PubMed1983

Hypothalamic portal blood immunoreactive TRH in the rat: lack of effect of hypothyroidism and thyroid hormone treatment.

Possible thyroid hormone regulation of hypothalamic thyrotropin-releasing hormone (TRH) secretion was studied by measurement of hypophyseal portal blood TRH concentrations in normal, hypothyroid and thyroid hormone treated rats. TRH was measured by radioimmunoassay of methanol extracts of blood. Extraction recovery was good. Endogenous TRH immunoreactivity (IR-TRH) was destroyed by incubation with normal human serum and it co-migrated with synthetic TRH in a thin layer electrophoresis and chromatography system. Mean portal blood IR-TRH concentrations ranged from 1041 to 2834 pg/ml in the various groups of rats studied. No consistent differences were found in portal blood IR-TRH concentrations in normal, hypothyroid or thyroid hormone treated rats. Peripheral blood IR-TRH concentrations were similar in normal rats and rats subjected to forebrain and hypothalamic removal. These results indicate that TRH secretion into the hypothalamic-pituitary portal system is not regulated by thyroid hormone and that forebrain and hypothalamic secretion do not contribute importantly to peripheral blood TRH.

Animals↗
PubMed2005

Coregulator interactions with the thyroid hormone receptor.

The thyroid hormone receptor (TR) directly regulates the transcription of thyroid hormone-responsive genes in response to changing levels of thyroid hormone. Mechanistically TR utilizes a complex set of binding interactions, with hormone, response elements, and coregulatory proteins, to provide specific local control of patterns of transcriptional response that are partially responsible for inducing the tissue-selective responses to the circulating hormone. One of the apparently dominant phenomena in the regulation of thyroid hormone responses is the protein interactions between TR and its coregulators. This review summarizes the current state of knowledge with respect to the identity of these coregulators, their interaction with TR, and the consequences of those interactions.

Amino Acid Sequence↗