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Karin Sydow, Dieter Emrich, Olaf Gefeller, and Inge Schreivogel

Sydow K, Emrich D, Gefeller O, Schreivogel I. Quantification of the negative feedback mechanism between pituitary and thyroid in subjects with normal thyroid function. Eur J Endocrinol 1996;135:316–21. ISSN 0804–4643

Using sufficiently sensitive and precise assays, we systematically investigated the correlation between thyrotropin, thyroglobulin, index of free thyroxine and index of free triiodothyronine after different doses of thyroxine (25, 50, 100, 150 μg), which were administered daily for 10 days to individuals with normal thyroid function and in a control group. Analysis of the data using relative median values expressing changes to basal values before administration of thyroxine yielded the following results: (i) thyrotropin and thyroglobulin decreased monoexponentially, depending on the doses of thyroxine administered; (ii) the extent of their decrease showed a linear correlation with the dose of thyroxine administered and was greater for thyrotropin than for thyroglobulin; (iii) the relative velocity of their decrease increased monoexponentially with the dose of thyroxine and did not differ between thyrotropin and thyroglobulin. These results provide strong evidence for a clear quantitative reaction of the feedback mechanism and confirm that the secretion of thyroglobulin is a physiological process dependent on thyrotropin. The high intra-individual variations obtained for thyrotropin were probably due to its pulsatile secretion.

D. Emrich, Department of Nuclear Medicine, University of Göttingen, Robert-Koch-Str. 40, D-37075 Göttingen, Germany

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Stan Benjamens, Robin P F Dullaart, Wim J Sluiter, Michiel Rienstra, Isabelle C van Gelder, and Thera P Links

Objective

Amiodarone is used for the maintenance of sinus rhythm in patients with arrhythmias, but thyroid dysfunction (amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH)) is a common adverse effect. As the onset of AIT and AIH may be unpredictable, the value of long-term regular monitoring of amiodarone treated patients for thyroid dysfunction is still uncertain.

Design

We retrospectively documented the frequency at which overt thyroid dysfunction was preceded by subclinical thyroid dysfunction.

Methods

We included 303 patients treated with amiodarone between 1984 and 2007. AIT was defined as a lowered TSH level with an elevated free thyroxine (FT4) and AIH was defined as an elevated TSH level with a decreased or subnormal FT4. Subclinical AIT was defined as a lowered TSH level with a normal FT4 and subclinical AIH as an elevated TSH level with a normal FT4.

Results

200 men and 103 women, aged 62 ± 12.0 years, suffering from atrial (260) or ventricular (43) arrhythmias, were evaluated. During a median follow-up of 2.8 (1.0–25) years, 44 patients developed AIT and 33 AIH. In 42 (55%) patients who developed AIT/AIH, earlier thyroid function tests showed no subclinical AIT or subclinical AIH. In 35 (45%) patients, AIT/AIH was preceded by subclinical AIT or subclinical AIH (16/44 for AIT and 19/33 for AIH).

Conclusions

In a considerable proportion of patients who developed AIT/AIH, earlier thyroid function tests showed no subclinical AIT/AIH. Less than half of the patients with a subclinical event subsequently developed overt AIT/AIH. This study provides data to reconsider the yield of regular testing of thyroid function to predict overt thyroid dysfunction in amiodarone treated patients.

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Antti Aro, Jussi K. Huttunen, Bror-Axel Lamberg, Risto Pelkonen, Eero Ikkala, Arto Kuusisto, Viljo Rissanen, Jorma Salmi, and Sakari Tervonen

Abstract.

Seventy thyrotoxic patients were treated with carbimazole (36 patients) or propranolol (34 patients) prior to and for 6 weeks after a therapeutic dose of 131I. The therapeutic response was evaluated on the basis of the serum free thyroxine index (FT4I) value and the thyrotoxicosis therapy-index (TTI) of Crooks et al. (1960b). Propranolol alleviated many symptoms and signs (palpitations, hyperkinesia, finger tremor, resting pulse rate) as effectively as carbimazole, whereas others (dyspnoea on effort, tiredness, heat intolerance, sweating, nervousness, bodyweight) were not equally affected. Biochemical euthyroidism was achieved significantly slower in the propranolol group (after 100.6 ± 40.5 days vs. 48.5 ± 24.0 days in the carbimazole group) although the dose of 131I was administered after a mean interval of 22 days from the start of treatment in the propranolol group and after 66 days in the carbimazole group. Between 2 and 6 months after 131I the FT4I and TTI followed a similar course in both treatment groups.

As judged from the TTI scores 2 weeks after the 131I-therapy no evident aggravation of hyperthyroidism occurred in either group of patients. However, one patient in each group showed marked exacerbation of symptoms which was due to inadequate dosage of the drugs. It is concluded that propranolol, given prior to radioactive iodine, is equally effective as carbimazole in preventing aggravation of thyrotoxicosis after the administration of 131I. In the propranolol-treated patients the tests of thyroid function are more reliable during the drug therapy, but the slow development of euthyroidism may be of clinical importance in patients presenting with severe symptoms.

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Colum A. Gorman, James W. Anderson, Eunice V. Flock, Charles A. Owen Jr., and Khalil G. Wakim

ABSTRACT

Thyroiditis was induced in Sprague-Dawley rats by repeated immunization with thyroid extract and Freund's adjuvant. Immunized and control animals were killed at intervals up to 6 hours after intravenous administration of 131I as iodide at 5, 8 and 10 weeks after the first injection. Radioiodinated compounds in the thyroid glands were identified chromatographically. Evidence of moderate thyroiditis was present (histologic appearance, gland weight, and protein-bound iodine-butanol-extractable iodine difference) but the rate of incorporation of radioiodide into thyroxine, the percentage of radioactivity in the gland as iodide, and the MIT/DIT ratio were not significantly different in immunized and control animals. The MIT/DIT ratio was found to vary with time after 131I administration in both immunized and control animals. These studies did not uncover a defect in organification of iodide in experimental thyroiditis similar to that described by others in humans with Hashimoto's thyroiditis.

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GJ Kahaly, HP Dienes, J Beyer, and G Hommel

OBJECTIVE: Iodine is essential for normal thyroid function and the majority of individuals tolerate a wide range of dietary levels. However, a subset of individuals, on exposure to iodine, develop thyroid dysfunction. In this double-blind trial, we evaluated the efficacy and tolerability of low-dose iodine compared with those of levo-thyroxine (T4) in patients with endemic goitre. METHODS: Sixty-two patients were assigned randomly to groups to receive iodine (0.5 mg/day) or T4 (0.125 mg/day) for 6 months. Subsequently, both groups were subject to placebo for another 6 months. Thyroid sonography, determination of thyroid-related hormones and antibodies, and urinary excretion of iodine were carried out at baseline and at 1, 6 and 12 months. RESULTS: At 6 months, markedly increased urinary values of iodine were found in patients receiving iodine (36 microg/24 h at baseline, 415 microg/24 h at 6 months) compared with those receiving T4 (47 microg/ 24 h at baseline, 165 microg/24 h at 6 months; P < 0.0001 compared with iodine group). T4 administration engendered a greater (P < 0.01) decrease in thyroid volume (from 32 ml to 17 ml, P < 0.0001) than did intake of iodine (3 3 ml to 21 ml. P < 0.005). High microsomal and thyroglobulin autoantibody titres were present in six of 31 patients (19%) receiving iodine, and iodine-induced hypo- and hyperthyroidism developed in four and two of them, respectively. Fine-needle biopsy revealed marked lymphocyte infiltration in all six. After withdrawal of iodine thyroid dysfunction remitted spontaneously and antibody titres and lymphocyte infiltration decreased markedly. Follow-up of these six patients for an additional 3 years showed normalisation of antibody titres in four of them. CONCLUSION: Although nearly comparable results were obtained with both treatment regimens regarding thyroid size, partly reversible iodine-induced thyroid dysfunction and autoimmunity were observed among patients with endemic goitre.

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J.-G. Ljunggren, G. Sedvall, K. Levin, and B. Fyrö

ABSTRACT

Rats were treated intraperitoneally (ip) with saline, lithium chloride or propylthiouracil (PTU) for two weeks. The uptake of iodine-125 and iodine-131 into the thyroid gland was markedly reduced by PTU and lithium treatment. PB125I was significantly reduced after lithium and PTU, as was the PBI. There was no evidence for an inhibitory effect of lithium on the biosynthesis of thyroxine or thyroglobulin. Thyroxine synthesis was markedly affected by PTU-treatment. The iodination of tyrosine was particularly reduced.

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Mario Rotondi, Luca de Martinis, Francesca Coperchini, Patrizia Pignatti, Barbara Pirali, Stefania Ghilotti, Rodolfo Fonte, Flavia Magri, and Luca Chiovato

Background

Despite high sensitivity of current assays for autoantibodies to thyroperoxidase (TPO) and to thyroglobulin (Tg), some hypothyroid patients still present with negative tests for circulating anti-thyroid Abs. These patients usually referred to as having seronegative autoimmune thyroiditis (seronegative CAT) have not been characterized, and definite proof that their clinical phenotype is similar to that of patients with classic chronic autoimmune thyroiditis (CAT) is lacking.

Objective

To compare the clinical phenotype of seronegative CAT (SN-CAT) and CAT as diagnosed according to a raised serum level of TSH with negative and positive tests for anti-thyroid Abs respectively.

Methods

A case–control retrospective study enrolling 55 patients with SN-CAT and 110 patients with CAT was performed. Serum free triiodothyronine (FT3), free thyroxine (FT4), TSH, Tg Abs, and TPO Abs were measured in all patients.

Results

Patients with SN-CAT displayed significantly lower mean levels of TSH (6.6±3.4 vs 10.2±9.8 μU/ml; P=0.009), higher mean FT4 levels (1.1±0.2 vs 0.9±0.2 ng/dl; P=0.0002), and similar FT3 levels when compared with CAT patients. Mean thyroid volume was significantly greater in patients with CAT when compared with SN-CAT patients (11.2±6.5 vs 8.1±3.7 ml; P=0.001). Logistic regression demonstrated that FT4 (0.123 (0.019–0.775); (P=0.026)) and thyroid volume (1.243 (1.108–1.394); (P=0.0002)) were significantly and independently related to the diagnosis (CAT/SN-CAT). Patients with SN-CAT had a similar prevalence of thyroid nodules and female gender but a lower prevalence of overt hypothyroidism (5.4 vs 20.9%; P=0.012) as opposed to patients with CAT.

Conclusions

These results suggest an autoimmune etiology of SN-CAT, which, however, seems to have a milder clinical course when compared with CAT.

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J. Myhill, T. H. Oddie, I. B. Hales, and D. A. Fisher

ABSTRACT

  1. Using a whole-body counting technique with 131I-labelled thyroxine, measurements were made in euthyroid volunteers of fractional thyroxine degradation rate, total thyroxine turnover and thyroidal secretion of thyroxine. Thyroidal accumulation of 127I was also calculated from the chemical assay of 24-hour urine.

  2. The measurements were made in 18 subjects during the administration of 0, 100 and 200 μg of thyroxine per day in successive seven-week periods, and in 10 subjects during the administration of 0, 252 and 1009 μg of iodide daily in successive thirteen-week periods.

  3. When thyroxine was administered, the fall in thyroidal secretion rate was found to be parallel to the fall in radioiodine clearance rate. However, during administration of iodide thyroidal radioiodine clearance fell without appreciable alteration in total turnover of thyroxine. In addition thyroid iodine turnover increased progressively with increasing iodine intake and reached a mean value of 221 μg daily on a mean intake of 1250 μg I daily.

  4. The data indicate that the total body turnover of thyroxine is the quantity which is maintained in thyroid homeostasis.

  5. These data also indicate that the most significant effects on thyroid function of a chronic moderate increase in iodine intake are a) an inhibition of iodide concentrating activity, and b) an augmentation of nonthyronine iodide secretion. Neither effect is mediated by TSH.

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Rajata Rajatanavin, La-or Chailurkit, Kanokporn Tirarungsikul, Wirawat Chalayondeja, Uraiwan Jittivanich, and Winit Puapradit

Abstract

To determine the prevalence of thyroid dysfunction in Thai postpartum women, we evaluated thyroid function and thyroid autoantibodies in 812 consecutive unselected women at 1.5 months post partum. At 3.5 months post partum 570 women without previous thyroid abnormality returned for a second set of thyroid function test. The prevalence of thyroid dysfunction was 1.1%, which was less than that reported from other countries. Various types of postpartum thyroid dysfunction, namely, transient thyrotoxicosis followed by transient hypothyroidism, transient thyrotoxicosis or hypothyroidism occurring alone or permanent hypothyroidism were encountered. Eight out of 9 patients with thyroid dysfunction had thyroid autoantibodies. Fine needle aspiration biopsy of the thyroid was done in 4 patients and all showed lymphocytic thyroiditis. Even though Bangkok is an iodine surfeit area, iodine intake is relatively lower than in other areas where the prevalence of postpartum thyroid dysfunction is much higher. The discrepancy in geographic prevalence of postpartum thyroid dysfunction may result from the interaction of immunogenetic heterogeneity of different ethnic background, environmental iodine intake, and other unidentified environmental factors.

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E. Vigouroux

ABSTRACT

The thyroid function in development was investigated in post-natal rats. The thyroid iodine content rapidly increased from birth (137 ± 26 ng iodine/mg thyroid) up to day 10 (338 ± 42 ng iodine/mg thyroid) then increased more slowly up to day 30 (425 ± 34 ng iodine/mg thyroid). The maximal plasma concentration of thyroxine was observed on day 16 (56.9 ± 3.5 ng T4/ml) and of iodide on day 10 (110.2 ± 12.6 ng I−/ml). The turnover rate constant of extrathyroidal thyroxine was higher at birth (8.0 ± 2.3 %/h) than at any older age studied (average 6 %/h). Thyroxine secretion by the thyroid was more intense before weaning (37 ng hormonal iodine/h/100 g body weight on days 10 and 20) than after weaning (22 ± 6 ng hormonal iodine/h/100 g body weight in 30 days old rats). The peripheral deiodination rate of thyroxine represented about 90 % thyroxine secretion rate in newborn and 10 days old rats and only 40% in adult females. In pre-weaning rats, after a single injection of both [131I]L-T4 and [125I]Na, extrathyroidal radioactivity disappeared more slowly than in 30 days old rats and adult animals. This suggests that iodide concentrations of extrathyroidal tissues are higher before than after weaning.