Total Serum T4 Concentrations Research Articles

Abdominal Ultrasound Examination Findings in 534 Hyperthyroid Cats Referred for Radioiodine Treatment Between 2007-2010.

BackgroundThe prevalence of concurrent disease in hyperthyroid cats is unknown.ObjectivesTo identify the prevalence of concurrent intra‐abdominal disease using abdominal ultrasound examination (AUS) in hyperthyroid cats referred for radioactive iodine treatment (RIT) and to determine whether the requirement for pretreatment AUS is justified.AnimalsFive hundred and thirty‐four client‐owned cats diagnosed with hyperthyroidism and referred for RIT.MethodsRetrospective study. Age, breed, sex, body weight, clinical signs, total serum T4 concentration, blood urea nitrogen (BUN) concentration, serum creatinine concentration, urine specific gravity (USG), AUS results, and biopsy or cytology results, or both (if obtained) were collected from the medical records.ResultsThe prevalence of concurrent disease identified using AUS in hyperthyroid cats referred for RIT was 36.1%; 22.8% of the cats in the study had renal disease and 2.4% had confirmed neoplasia. Significant differences in median USG (P value 0.032) and median BUN (P value 0.028) were found between cats that had abnormal kidneys on AUS compared to those with normal‐appearing kidneys. Only 2.2% of the cats were not treated with RIT as a result of changes identified on AUS and subsequently obtained cytology or biopsy results.Conclusions and Clinical ImportanceThe results indicate that pretreatment AUS in hyperthyroid cats referred for RIT is unnecessary in most patients.

Direct Construction of an Open-Sandwich Enzyme Immunoassay for One-Step Noncompetitive Detection of Thyroid Hormone T4

To establish a sensitive noncompetitive immunoassay for thyroxine (T4), we attempted to isolate anti-T4 antibodies from a phage display library based on a phagemid pDong1 ( Dong et al. Anal. Biochem.2009, 36, 386 ), which was designed to enable open-sandwich enzyme-linked immunosorbent assay (OS-ELISA) after selection on immobilized antigen. After the Fab-displaying phage library made from the splenocytes of T4-KLH immunized mice was subjected to biopanning on T4-BSA, two T4-specific clones were obtained. When they were assayed by indirect competitive ELISA, both clones showed low IC(50) (5-13 ng/mL), indicating their high affinity to T4. When they were used for OS-ELISA that detects antigen-dependency of the interaction between variable domains V(H) and V(L), a clone successfully detected 1 ng/mL of T4 with a working range superior to that of competitive IA. OS-ELISA was also performed with maltose binding protein (MBP)-fused V(H)/V(L) of this clone, which showed a detection limit less than 0.1 ng/mL T4. Moreover, the assay showed cross-reactivity with T3 similar to that of competitive ELISA, and also gave a reasonable total serum T4 concentration (90 ng/mL) from ethanol-extracted sample serum using the recombinant proteins. This is the first direct construction of an OS-ELISA system bypassing hybridoma, which will be applicable to the detection of many other small molecule antigens.

Die canine Hypothyreose – eine diagnostische Herausforderung?

Hypothyroidism is one of the most common endocrinopathies in dogs. Clinical symptoms and hematological and biochemical parameters lead to a first suspicion. To confirm diagnosis can be challenging, however. Determination of total serum T4 concentration is accepted as the primary screening test for the disease, and low serum T4 concentrations are intuitively suggestive of hypothyroidism. However it is well known that low T4 concentrations are frequently encountered in euthyroid dogs with various nonthyroidal diseases and in dogs receiving certain pharmacologic agents. Since assessment of endogenous TSH (canine TSH) using current canine TSH assays shows normal values in a high percentage of hypothyroid dogs (up to 40%), its diagnostic value is only limited. The TSH-stimulation test can still be recognized as the gold standard for the diagnosis of hypothyroidism in dogs. Determination of circulating T4 concentration before and 6 hours after the administration of exogenous TSH (recombinant human TSH, Thyrogen ® ) provides an assessment of the functional reserve capacity of the thyroid gland with minimal change in post-TSH T4 concentration, compared with the basal concentration, expected in dogs with hypothyroidism. Also this test can be influenced by nonthyroidal illness and by medications known to affect thyroid function. This suppressing influence seems to be less pronounced using a higher dose of TSH. Therefore, to improve the discriminatory power of the TSH stimulation test to differentiate between euthyroid-sick and primary hypothyroidism, the higher dose should be used in cases in which testing cannot be delayed. More recently, ultrasonography and scintigraphy have been used for the diagnosis of primary hypothyroidism. Using ultrasonography, a sensitivity of 98% was reported if size and echogenicity of the gland were combined. However, specificity was as low as 77% and care must be taken when measuring the gland because of a relatively high interobserver variability. Preliminary results using scintigraphy to discriminate between hypothyroid and non-thyroidal illness seem promising. However, due to its limited availability and the high expenditure, to date it cannot be used in clinical practice. Therefore, at present, if test results are obscure and a final diagnosis cannot be made, it is recommended to repeat the tests at a later time point.

Leptin treatment during lactation increases transfer of iodine through the milk

We have previously shown that protein restriction during lactation is associated with changes in iodine secretion into the milk and that a pup's serum leptin concentration was increased at the end of lactation. So, here we evaluate whether leptin treatment during lactation affects iodine transfer through the milk to the pups. Lactating rats were divided into two groups: the leptin (Lep) group, single injected with recombinant rat leptin (8 μg/100g of body weight, daily for 3 consecutive days), and the control (C) group that received the same volume of saline. We studied iodine transfer to the pups through the milk on Days 4, 12 and 21 of lactation. In those days, the dams were separated from their pups for 4 h. Then, the mothers received an injection of 131I (2.22×10 4 Bq ip) and the pups were allowed to nurse for 2 h. The animals were sacrificed 2 h later. Leptin, total serum T3 and total serum T4 concentrations were higher ( P<.05) in pups of Lep mothers only on Day 4, suggesting a higher transfer of leptin through the milk at this period, probably with a direct stimulatory effect on thyroid hormone secretion. In other periods, however, even without a detectable increase in a pup's serum leptin concentration, maternal leptin administration increased the pup's thyroid iodine uptake (Day 12, 39%; Day 21, 34%), probably caused by a higher transfer of iodine through the milk, since they had a higher gastric content of 131I on Days 12 (31%) and 21 (128%).

Immunologic and endocrine effects of the flame-retardant pentabromodiphenyl ether (DE-71) in C57BL/6J mice

Polybrominated diphenyl ethers are manufactured for use as flame retardants in commercial plastics and textiles in Europe and North America. These studies investigated the acute and subchronic immunotoxicity and endocrine effects of a commercial pentabromodiphenyl ether mixture, DE-71, in female C57BL/6 mice. Mice were orally exposed to acute single doses of DE-71 of 0, 0.8, 4.0, 20, 100, or 500 mg/kg, or to subchronic daily doses totaling 0, 250, 500, or 1000 mg/kg over a 14 day period. Immunotoxicity was assessed by measuring the plaque-forming cell response to sheep erythrocytes (SRBC) and natural killer cell (NKC) activity (basal and poly I:C stimulated) to YAC-1 target cells. Liver cytochrome P450 content and activities (ethoxyresorufin- o-deethylase (EROD) and pentoxyresorufin- o-deethylase (PROD)) as well as corticosterone (CS) and thyroxine (T4) concentrations were also measured. PROD activity was induced 3–5-fold in mice exposed acutely or subchronically to DE-71 at doses >250 mg/kg. EROD activity and total microsomal cytochrome P450 content were significantly induced only in mice treated subchronically with DE-71; maximum induction of EROD was 3.3-fold. Total serum T4 concentrations were significantly lower in mice treated acutely with DE-71 at all doses except the 100 mg/kg dose. Total and free T4 concentrations were dose-dependently decreased in DE-71-treated mice following subchronic exposure. Plasma CS levels were elevated following subchronic exposure to DE-71. The elevation of CS was correlated with order of capture at necropsy, suggesting an interactive effect of DE-71 and stress. In regard to immunotoxicity, significant suppression of the anti-SRBC response was seen only in mice exposed subchronically to 1000 mg DE-71/kg, an exposure that also resulted in decreased thymus weight. NKC activity was not altered by exposure to DE-71.

Reduced affinity for thyroxine in two of three structural thyroxine-binding prealbumin variants associated with familial amyloidotic polyneuropathy.

T4-binding prealbumin (TBPA), a protein synthesized by the liver, circulates as a tetramer and transports 15-20% of T4. We studied 3 variants of the TBPA monomer recently identified in serum and amyloid fibrils of patients affected by familial amyloidotic polyneuropathy (FAP). They represent single amino acid substitutions at positions 30 (type I), 60 (Appalachian), and 84 (type II). Tests of thyroid function and the apparent association constant (Ka) of T4 binding to TBPA were measured in whole serum from 14 carriers of FAP identified clinically, by amino acid sequence analysis, or by DNA restriction fragment analysis. Significant reduction of Ka was found in subjects with FAP types I and II, but not in subjects with the Appalachian type. Mean (+/- SD) values of 0.24 +/- 0.08 X 10(7) M-1 for type I and 0.26 +/- 0.10 X 10(7) M-1 for type II were significantly (P less than 0.0001) lower than those for normal relatives (1.39 +/- 0.30 X 10(7) M-1) or unrelated normal subjects (1.41 +/- 0.18 X 10(7) M-1). The mean Ka value for the five subjects with FAP of the Appalachian type was slightly but not significantly reduced (1.08 +/- 0.11 X 10(7) M-1). There was no overlap of individual Ka values of subjects with types I and II TBPA with those of subjects from all other groups. Abnormalities of thyroid function included slight but significant reductions of the mean total serum T4 concentration in the subjects with type II FAP and the mean serum total T3 concentration in those with type I FAP. Four subjects with FAP (two type II and two of the Appalachian type) had biochemical evidence of hypothyroidism. The three subjects with total serum T3 levels below the limit of normal had amyloid cardiomyopathy. These results indicate that TBPAs from subjects with FAP types I and II have relatively lower affinity for T4. Although none of the substituted amino acids in these variant TBPAs contribute directly to the surface of the putative T4-binding site, the side chains of amino acids 30 and 84, but not 60, interact with internal residues of the beta-structure which forms the presumed binding site, in agreement with our results of Ka measurements. The high incidence of hypothyroidism is due to the probably fortuitous occurrence of Hashimoto's thyroiditis as well as to partial destruction of the thyroid gland by amyloid deposits.

The effect of tamoxifen therapy on thyroid function tests.

Serum tri-iodothyronine (T3), thyroxine (T4) and thyroid-stimulating hormone (TSH) concentrations were measured in 50 postmenopausal patients with breast cancer receiving tamoxifen therapy. Ten patients (20%) showed an elevation of serum total T4 concentrations and two of these patients showed additional elevation of serum total T3 levels. One patient had a persistently raised free T4 concentration and was considered to be thyrotoxic. Serum thyroxine-binding globulin (TBG) was estimated in six patients with elevated total T4 concentrations and was found to be raised in each case. Total serum T4 concentrations rose in seven of ten additional patients after starting tamoxifen therapy. However this change did not reach statistical significance. This trend in serum T4 concentrations was not shown in ten normal volunteers taking tamoxifen for 1 week.

The transport of thyroid hormones.

1. Hormones have to be transported from their sites of synthesis to their target organs. For lipophilic hormones, such as steroids and thyroid hormones, transport is accomplished by binding to specific serum proteins, in the case of thyroxine (T4) and tri-iodothyronine (T3) to thyroxine-binding globulin (TBG) and prealbumin (PA). Normally about 70% of circulating T4 and 75–80% of T3 is bound to TBG, about 20% of T4 and 10% of T3 to PA and 10–15% of each to albumin, which has a low affinity but high capacity for both hormones [1, 2]. Apart from facilitating transport, binding to serum protein prevents excessive loss of hormone into the urine by glomerular filtration or flooding into cells, and may provide a readily available reservoir in times of need. The union between binding proteins and their ligands is reversible, so that a small proportion of hormone is non-protein-bound or ‘free’, in equilibrium with that which is protein-bound. For T4 this free fraction is normally 0.02-0.04% of the total serum T4 concentration, for T3 about 0.3% [3, 4]. 2. The major binding proteins of T4 and T3 will briefly be described and the nature of free T4 and T3 considered.

Serum free thyroxine and triiodothyronine concentrations in subacute thyroiditis.

Serum absolute free T4 (AFT4) and T3 (AFT3) concentrations were studied in 10 patients with subacute thyroiditis whose total serum T4 levels were elevated, and values were compared with those obtained in 10 patients with untreated Graves' disease, whose total serum T4 concentrations were elevated to the same level as in the former group. The mean (+/- SD) basal metabolic rate in patients with subacute thyroiditis was 16 +/- 14.8%, significantly (P less than 0.001) lower than that in patients with Graves' disease (48.7 +/- 15.7%). Serum T4-binding globulin concentrations measured by RIA were normal and did not differ from those in Graves' disease patients. The percentage of free T4 and AFT4 were both elevated in subacute thyroiditis to a degree comparable to that seen in Graves' disease. The serum total T3, serum free T3 fraction and AFT3 were also elevated, but both total T3 and AFT3 were significantly (P less than 0.05 and P less than 0.05, respectively) lower than in Graves' disease patients. Therefore, the ratios of T3 to T4 and AFT3 to AFT4 were significantly (P less than 0.01 and P less than 0.01, respectively) lower than in Graves' disease patients. These results indicate that the significantly lower basal metabolic rate and milder manifestations of thyrotoxic symptoms in subacute thyroiditis than in Graves' disease might be explained by the low ratios of T3 to T4 and AFT3 to AFT4 as well as the short duration of chemical hyperthyroidism.

4 Investigation and treatment of hypothyroidism

INVESTIGATION The investigation of patients with suspected hypothyroidism falls naturally into two stages. Preliminary investigation is required to determine the level of thyroid function and confirm, or refute, a clinical diagnosis of thyroid failure, and the use of other diagnostic procedures is required to identify the cause of hypothyroidism in some patients. Tests to Determine the Level of Thyroid Function The laboratory techniques available for assessing the level of thyroid function fall into three groups and the use of each allows different aspects of impaired thyroid function to be defined. The three groups of techniques are: tests of thyroid function; tests of peripheral tissue function; and tests of hypothalamic--pituitary function. The techniques have been reviewed in detail elsewhere (Evered, 1974, 1976). Tests of thyroid function Direct or indirect techniques for measuring circulating thyroid hormone concentrations have been widely available for many years. Serum thyroxine (T4) concentration may be measured by a competitive protein binding assay (Murphy, 1965) or by radioimmunoassay (Mitsuma et al, 1972). These procedures measure total serum T4 concentration, and thus alterations in thyroxine-binding globulin (TBG) capacity (e.g. pregnancy, oral contraceptive therapy, liver disease, etc.) may lead to total hormone concentrations which are at variance with the clinical assessment of the patient. The serum T4 concentration can, however, be corrected for changes in TBG by carrying out a thyroid hormone binding test (e.g. T3 resin uptake, T3 Sephadex uptake), which will estimate residual TBG capacity and may be used to calculate a free thyroxine index (FTI) (Clark and Horn, 1965). The older technique of estimating the protein-bound iodine (PBI) concentration also

The concentration and binding of thyroxine in the serum of patients with the testicular feminization syndrome: observations on the effects of ethinyl estradiol and norethandrolone.

In 6 castrated patients with the complete testicular feminization syndrome, values for total and free thyroxine (T4) concentration in serum, as well as the T4-binding capacities of thyroxine binding globulin (TBG) and thyroxine binding prealbumin (TBPA), were within normal limits. As expected, patients with TFS responded to 0.02 mg ethinyl estradiol daily with increases in both the T4-binding capacity of TBG and the concentration of serum T4 and a decrease in the proportion of free T4. The magnitude of the responses was similar to that obtained in 3 normal patients given the same dose of ethinyl estradiol. In a normal patient receiving ethinyl estradiol, norethandrolone (40 mg daily) produced the expected decrease in TBG and total T4 concentration and increase in the percentage of free T4. In contrast, in 4 patients with TFS receiving ethinyl estradiol, norethandrolone did not influence TBG, total serum T4 concentration, or the proportion of free T4. A similar lack of effect of norethandrolone on TBG was ...