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PubMed2003

Hyperthyroidism modifies ecto-nucleotidase activities in synaptosomes from hippocampus and cerebral cortex of rats in different phases of development.

Here we investigate the possible effects of the hyperthyroidism on the hydrolysis of the ATP to adenosine in the synaptosomes of hippocampus, cerebral cortex and blood serum of rats in different developmental phases. Manifestations of hyperthyroidism include anxiety, nervousness, tachycardia, physical hyperactivity and weight loss amongst others. The thyroid hormones modulate a number of physiological functions in central nervous system, including development, function, expression of adenosine A(1) receptors and transport of neuromodulator adenosine. Thus, hyperthyroidism was induced in male Wistar rats (5-, 60-, 150- and 330-day old) by daily injections of L-thyroxine (T4) for 14 days. Nucleotide hydrolysis was decreased by about 14-52% in both hippocampus and cerebral cortex in 5 to 60-day-old rats. These changes were also observed in rat blood serum. In addition, in 11-month-old rats, inhibition of ADP and AMP hydrolysis persisted in the hippocampus, whereas, in cerebral cortex, an increase in AMP hydrolysis was detected. Thus, hyperthyroidism affects the extracellular nucleotides balance and adenosine production, interfering in neurotransmitter release, development and others physiological processes in different systems.

Adenine Nucleotides↗
PubMed1998

Central hyperthyroidism.

Central hyperthyroidism is a rare condition in which thyrotoxicosis results from primary overproduction of TSH by the pituitary gland with subsequent thyroid enlargement and hyperfunction. The two known causes of central hyperthyroidism are TSH-producing pituitary tumors (TSHomas) and the syndrome of PRTH. Both of these entities are characterized by clinical thyrotoxicosis, diffuse goiters, elevated circulating levels of free T4 and T3, and a nonsuppressed serum TSH. It is critical to distinguish central hyperthyroidism from the much more common types of primary hyperthyroidism, all of which have undetectable TSH values. TSHomas and PRTH can usually be differentiated from one another by measuring the serum alpha-subunit and the TSH response to intravenous TRH or exogenous thyroid hormone, and by pituitary imaging studies. TSHomas are usually benign adenomas arising from the monoclonal expansion of neoplastic thyrotropes. Causative oncogenes have not yet been convincingly identified. PRTH is a nonneoplastic disorder caused by inherited mutations in the gene for the thyroid hormone receptor beta; it is a poorly understood variant of GRTH. For unclear reasons, in PRTH, the pituitary gland is resistant to the feedback inhibitory effects of circulating thyroid hormones while peripheral tissues respond normally, causing patients to experience the toxic peripheral effects of thyroid hormone excess. TSHomas are best treated by transphenoidal surgical removal. Radiotherapy is indicated for inoperable or incompletely resected tumors. Octreotide administration is a useful adjunct for preoperatively reducing tumor size and for the medical management of surgical treatment failures. PRTH is ideally treated by chronically suppressing TSH secretion with medications such as D-thyroxine, TRIAC, octreotide, or bromocriptine. If such therapy is ineffective or unavailable, thyroid ablation with radioiodine or surgery may be employed with subsequent close monitoring of both thyroid hormone status and pituitary gland size.

Adenoma↗
PubMedDate not supplied

Treatment of hyperthyroidism in Down syndrome: case report and review of the literature.

Thyroid disorders are common in individuals with Down syndrome (DS). Hyperthyroidism occurs much less frequently than hypothyroidism in this population, but is likely to be underestimated. We report a case of an institutionalized adult male with DS and hyperthyroidism. He was treated with radioactive iodine and, when reviewed 11 weeks later, was found to be markedly hypothyroid. We also review the literature on the three treatment options for hyperthyroidism in DS: surgery, medical treatment, and radiotherapy. We concluded that the place of radioiodine in the treatment of hyperthyroid patients with DS is yet to be defined.

Adult↗
PubMed2003

[Post-radiotherapy hyperthyroidism: a rare complication of cancer treatment in the child].

UNLABELLED: Abnormalities of thyroid function, specially hypothyroidism, are common complications of head and neck irradiation for childhood cancer. Hyperthyroidism is rare and can be misdiagnosed. We report two observations of this condition. OBSERVATIONS: The first patient received conventional craniospinal irradiation for a localized medulloblastoma. Three years later, he presented with profuse sweating, irritability and paroxysmal tachycardia. Biologic evaluation revealed a peripheral hyperthyroidism. The patient was treated with antithyroidian hormonal treatment. The second patient received an irradiation for an undifferentiated nasopharyngeal carcinoma. Three years later, she developed a progressive thyrotoxicosis which was attributed to hyperthyroidism after six months of evolution. Hormonal treatment improved the clinical state after several weeks. CONCLUSION: Hyperthyroidism is a rare complication of head and neck irradiation. This condition justifies a periodic and prolonged evaluation of thyroid function.

Adolescent↗
PubMed2003

A fluctuation in adrenocepter- and muscarinic receptor-mediated blood pressure responses in acute hyperthyroid rats.

Hyperthyroidism was induced by daily subcutaneous injections of L-thyroxine (T(4), 0.5 mg/kg/day) for 3 days, 1 week, or 2 weeks to study whether there is a fluctuation in adrenoceptor- and muscarinic receptor-mediated blood pressure responses at a hyperthyroid stage. T(4) treatment for 3 days or 1 week significantly suppressed the pressor response induced by norepinephrine (NE). The depressor responses induced by isoprenaline or acetylcholine (ACh) were increased by T(4) treatment for only 3 days. The pressor response induced by N(G)-nitro-L-arginine (L-NA) was increased by T(4) treatment for only 3 days. Results suggest that adrenoceptor- and muscarinic receptor-mediated blood pressure responses fluctuate in hyperthyroidism caused by T(4) in rats, that the basal nitric oxide (NO) production and/or release are increased in hyperthyroid rats at an early stage of the disease.

Acute Disease↗
PubMed2003

Prevalence of thyroid cancer in hyperthyroidism treated by surgery.

The reported prevalence of thyroid cancer with concurrent hyperthyroidism varies from 0.21% to 9.0%. This variability may be due to multiple factors, such as indications for surgery and histopathologic accuracy. However, this condition is not rare and its prevalence has increased in recent surveys, perhaps as a result of more detailed examinations. The aim of this retrospective study was to determine the prevalence of thyroid cancer in hyperthyroid patients at surgery. Forty-five patients, 34 women and 11 men, underwent surgery for hyperthyroidism in our department between 1989 and 2000. Ages ranged from 14 to 67 years. There were 42 cases of Graves' disease, one of functional multinodular goiter, and two of single toxic nodules. Forty-three patients underwent total thyroidectomy and two underwent total lobectomy. Six cases (13.3%) of thyroid cancer were found, two men and four women with ages ranging from 19 to 48 years. Final histologic examination revealed three papillary carcinomas, one follicular carcinoma, one follicular carcinoma combined with clear-cell carcinoma, and one clear-cell carcinoma. Thus, in our department, the prevalence of thyroid cancer in hyperthyroidism treated using surgery was 13.3%. Our study showed that even a single toxic nodule may occur with concurrent thyroid cancer. Careful evaluation of such patients is needed to exclude the presence of associated malignancy and to determine the most appropriate therapeutic plan.

Adolescent↗
PubMed2000

Serotonin and gastrin cells in rat gastrointestinal tract after thyroparathyroidectomy and induced hyperthyroidism.

Thyroidectomy appears to reduce the serotonin content in the rat brain, whereas hyperthyroidism has the opposite effect. As it is not known whether the serotonin-producing cells of the gastrointestinal tract are influenced by these conditions, the effects of thyroparathyroidectomy and induced hyperthyroidism were studied experimentally, particularly as regards the serotonin- and gastrin-immunoreactive cells of the gastrointestinal tract. Immunocytochemical and quantification techniques were used to localize and determine the numbers of serotonin and gastrin cells. In thyroparathyroidectomized rats the intestine was significantly shorter and the mucosa thinner than in sham-operated and untreated controls, whereas the converse was found in the hyperthyroid rats. Following thyroparathyroidectomy, there were fewer gastrin-immunoreactive cells in antrum and the serotonin-immunoreactive cells were significantly less dense throughout the gastrointestinal tract. In hyperthyroid rats, gastrin-immunoreactive cells were more numerous, as were the serotonin-immunoreactive cells in the small intestine, whereas these cells were fewer in antrum and caecum. In conclusion, the thyroid gland exerts a significant influence on the gastrointestinal tract and on the serotonin-and gastrin-immunoreactive cells. The observed alterations may reflect a direct effect of the thyroid hormones, although indirect factors must also be considered.

Animals↗
PubMed1984

Effects of propranolol and of verapamil on heart rate and blood pressure in hyperthyroidism.

Cardiac manifestations of hyperthyroidism have been attributed to enhanced sympathoadrenal activity, but thyroid hormones also have a direct positive chronotropic effect on sinoatrial cells, in which there are slow calcium channels. We evaluated the effects of verapamil on heart rate, PR and QT intervals, and blood pressure in eight patients with hyperthyroidism and compared them to those effects of propranolol. Three doses of propranolol (0.05, 0.1, and 0.2 mg/kg) and verapamil (0.1, 0.2, and 0.4 mg/kg) were injected intravenously after a 72-hr withdrawal period in a double-blind, crossover fashion. Propranolol increased the RR interval from 581 +/- 51 to 734 +/- 65 msec, whereas verapamil did not have any negative chronotropic effect despite prolonging the PR interval. Systolic blood pressure decreased from 134 +/- 5 to 119 +/- 8 mm Hg after verapamil and was not affected by propranolol. Diastolic blood pressure was depressed equally by both drugs. We conclude that verapamil is not a good alternative drug to propranolol in hyperthyroidism. Our data cannot confirm the possibility of an interaction between thyroid hormones and slow calcium channels in patients with hyperthyroidism.

Adult↗
PubMed1981

Fatty-acid desaturation and microsomal lipid fatty-acid composition in experimental hyperthyroidism.

We have studied the influence of experimental hyperthyroidism in the rat on the synthesis of unsaturated fatty acids and on liver microsomal lipid fatty-acid composition. Tri-iodothyronine treatment (25 micrograms/100 g body weight) daily for 3 weeks caused no significant changes in delta 9 (stearate) desaturation but a 24% decrease in delta 6 (linoleate) desaturation. Much larger doses of tri-iodothyronine increased delta 9 desaturation. Liver microsomal fatty-acid composition in hyperthyroidism is altered with significantly increased proportions of stearate and arachidonate and decreased proportions of palmitate, palmitoleate, linoleate (C18:2) and eicosa-8,11,14-trienoate (C20:3). These changes, other than the decreases proportion of C20:3 fatty acid, which may be due to the diminished delta 6 desaturase activity, cannot be attributed to changes in fatty-acid desaturation. Most of these changes were also found to be due not simply to the decreased weight gain or the increased food intake of the hyperthyroid animals. Only the decreased C18:2 fatty-acid proportions could be mimicked by restricting food intake of control animals and none of the changes were prevented by restricting food intake of hyperthyroid animals. Thus most of the changes in microsomal lipid fatty-acid composition are likely to be due to a thyroid hormone effect on peripheral lipid mobilization or lipid degradation.

Animals↗
PubMed1981

Effect of experimental hyperthyroidism on skeletal-muscle proteolysis.

It is not clear whether the muscle wasting commonly observed in hyperthyroidism is due to alteration in the rate of protein synthesis or degradation. The effect of experimental hyperthyroidism on skeletal-muscle proteolysis in the rat was studied by measuring alanine and tyrosine release from isolated skeletal muscles in vitro and 3-methyl-histidine excretion in vivo. Alanine release from the isolated epitrochlaris-muscle preparation was increased as soon as 24h after a 25 microgram dose of L-tri-iodothyronine in vivo. Conversely, alanine release from muscles of hypothyroid rats was decreased, but restored by L-tri-iodothyronine supplementation before death. Furthermore, 3-methylhistidine excretion was increased in hyperthyroid rats throughout an 18-day treatment period. The increased amino acid release from isolated muscles and the increased 3-methylhistidine excretion in vivo strongly suggests that hyperthyroidism increases skeletal-muscle proteolysis. Furthermore, the thyroid-hormone concentration may be an important factor in regulating muscle proteolysis.

Alanine↗
PubMed2003

Hyperthyroidism increases the uncoupled ATPase activity and heat production by the sarcoplasmic reticulum Ca2+-ATPase.

The sarcoplasmic reticulum Ca2+-ATPase is able to modulate the distribution of energy released during ATP hydrolysis, so that a portion of energy is used for Ca2+ transport (coupled ATPase activity) and a portion is converted into heat (uncoupled ATPase activity). In this report it is shown that T4 administration to rabbits promotes an increase in the rates of both the uncoupled ATPase activity and heat production in sarcoplasmic reticulum vesicles, and that the degree of activation varies depending on the muscle type used. In white muscles hyperthyroidism promotes a 0.8-fold increase of the uncoupled ATPase activity and in red muscle a 4-fold increase. The yield of vesicles from hyperthyroid muscles is 3-4-fold larger than that obtained from normal muscles; thus the rate of heat production by the Ca2+-ATPase expressed in terms of g of muscle in hyperthyroidism is increased by a factor of 3.6 in white muscles and 12.0 in red muscles. The data presented suggest that the Ca2+-ATPase uncoupled activity may represent one of the heat sources that contributes to the enhanced thermogenesis noted in hyperthyroidism.

Adenosine Triphosphatases↗
PubMed1988

Autonomic control of heart rate during dynamic exercise in human hyperthyroidism.

1. The relative contribution of the sympathetic and parasympathetic components of the autonomic nervous system to the regulation of the chronotropic response to dynamic exercise was evaluated indirectly in nine patients with thyrotoxicosis and in seven normal volunteers. All subjects were women, with equivalent ages in both groups. Six of the nine patients with hyperthyroidism were reevaluated after clinical compensation of the disease with propylthiouracil. 2. Heart rate responses were evaluated during discontinuous dynamic effort maintained for 4 min on a bicycle ergometer at levels of 5, 15, 25 and 50 W, and also of 75 W in normal individuals. The study was also performed under conditions of sympathetic pharmacological blockade with propranolol (0.2 mg/kg body weight). 3. Even though the magnitude of the total increase in heart rate evoked by each level of dynamic exercise was equivalent in normal and hyperthyroid patients, the tachycardiac response occurring at the beginning of the exercise, which depends on a predominantly vagal mechanism, was substantially different from that observed after 30 s of effort, when sympathetic contribution becomes more important. The hyperthyroid patients showed considerably lower increases in heart rate than the normal individuals during the initial 30 s of effort, with the opposite occurring from this moment onward. 4. In the hyperthyroid patients, beta-adrenergic blockage depressed tachycardia after 30 s of effort at the 15 and 50 W levels, whereas in normal individuals this effect was only manifested at 50 and 75 W. 5. The patients who obtained clinical compensation showed a pattern of chronotropic response which tended to be close to that shown by normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Nervous System↗
PubMed1998

Normalization of serum thyrotrophin by means of radioiodine treatment in subclinical hyperthyroidism: effect on bone loss in postmenopausal women.

BACKGROUND: Patients with subclinical hyperthyroidism (reduced serum TSH and normal free T4 and T3 concentrations) have slightly increased bone turnover and might have reduced bone mass, especially among postmenopausal women (due to concomitantly reduced oestrogen production), as also seen during suppressive L-T4 treatment. OBJECTIVE: We have evaluated whether normalization of serum TSH using radioiodine treatment (RAI) in postmenopausal women with a nodular goitre and subclinical hyperthyroidism, protects against bone loss? DESIGN: Prospective, non-randomized study, outpatients 2 years follow-up. PATIENTS: Postmenopausal women with a nodular goitre, biochemically subclinical hyperthyroidism (TSH < 0.2 mU/I, and signs of a growing goitre or compression symptoms. Sixteen were treated with RAI (median dose 555 MBq) (+RAI), whereas 12 were followed without treatment (-RAI). MEASUREMENTS: Serum TSH (third generation technology), free T4 and T3 indices, and bone mass (BMD) as measured by Dual Photon Absorptiometry (4 in each group) (only spine) or Dual X-ray Absorptiometry (DEXA) (both spine and hip), were measured yearly for up to 2 years. RESULTS: The two groups did not differ regarding age, thyroid hormone parameters, and absolute levels of BMD at spine and hip. RAI resulted in normalization of TSH in all 16 women, and FT4I as well as FT3I decreased to 78% after one year (P < 0.01). These parameters did not change in the untreated group, thus serum TSH remained reduced. BMD at the spine tended to increase (n.s.) after RAI to (median) 101.9% after one year, and 101.5% after 2 years. In contrast the -RAI group experienced a continued fall in BMD to 97.3% after one year, and 95.5% after 2 years, both reduced as compared to the +RAI group (P < 0.02). BMD of the hip also increased after RAI, to 102.3% after one year, and 101.7% after 2 years. In contrast BMD in the -RAI group decreased to 94.8% after one year, and 98.0% after 2 years, both lower than in the +RAI group (P < 0.01). CONCLUSIONS: Subclinical hyperthyroidism due to a nodular goitre in postmenopausal women resulted in a continued loss of bone mass of about 2% per year. Radioiodine treatment resulting in normalization of serum TSH prevented this continued bone loss for at least 2 years. Our study supports earlier intervention in such patients.

Aged↗
PubMed1998

Leptin and the pituitary-thyroid axis: a comparative study in lean, obese, hypothyroid and hyperthyroid subjects.

OBJECTIVE: To study interactions between leptin and the pituitary-thyroid axis, both in euthyroid and dysthyroid states. SUBJECTS AND MEASUREMENTS: We investigated the relationships of plasma leptin to levels of free thyroid hormones and TSH in 18 patients with newly diagnosed hyperthyroidism, 22 with newly diagnosed primary hypothyroidism, and 32 lean (body mass index [BMI] < 30) and 37 obese (BMI > 30 kg/m2) euthyroid subjects. Hypothyroid patients were restudied during thyroxine replacement treatment. RESULTS: Median [interquartile range] plasma leptin concentrations were highest in obese euthyroid subjects (31.5 [19.0-48.0] and in untreated hypothyroid patients (19.2 [11.5-31.5]), and lowest levels in untreated hyperthyroid patients (8.9 [5.5-11.1]) and lean euthyroid control subjects (6.6 [3.9-14.4] micrograms/l (Kruskall-Wallis one-way analysis of variance; P < 0.0001). In euthyroid subjects, plasma leptin levels were higher in obese than in lean subjects (P < 0.00001). In obese subjects plasma levels of TSH correlated with percentage body fat (r = 0.67; P < 0.001) and plasma leptin (r = 0.61; P < 0.001). In untreated hyperthyroid subjects plasma leptin was unrelated to free T3, and in untreated hypothyroidism plasma leptin was unrelated to either free T3 or TSH concentrations (all P = NS). In untreated hyperthyroid, but not hypothyroid, patients plasma leptin concentrations correlated with BMI (r = 0.57; P = 0.02). Treatment of hypothyroidism with thyroxine resulted in a significant reduction in plasma leptin concentrations from 20.8 (11.8 to 31.6) to 12.9 (4.6-21.2) micrograms/l (P = 0.005), but BMI did not change significantly in the hypothyroid subjects being studied prospectively. CONCLUSIONS: (i) In euthyroid subjects, plasma leptin and TSH levels correlate, and both are positively correlated with adiposity. (ii) Plasma leptin was significantly elevated in hypothyroid subjects, to levels similar to those seen in obese euthyroid subjects. (iii) Treatment of hypothyroidism resulted in a reduction in the raised plasma leptin levels. The data are consistent with the hypothesis that leptin and the pituitary-thyroid axis interact in the euthyroid state, and that hypothyroidism reversibly increases leptin concentrations.

Adult↗
PubMed1996

Clinical outcome of radioiodine treatment of hyperthyroidism: a follow-up study.

OBJECTIVES: To study the clinical outcome of treatment of hyperthyroid patients with radioiodine. DESIGN: Records of patients treated for hyperthyroidism with radioiodine from 1989 to 1992 were examined in 1994, and a questionnaire was sent to patients < or = 70 years with Graves' disease (GD) and toxic nodular goitre (TNG) to obtain information regarding thyroxine substitution, smoking habits and present state of health. SETTING: Outpatients in a thyroid unit; follow-up by primary care. SUBJECTS: Seven hundred and fifty-four patients with hyperthyroidism treated with radioiodine, 327 receiving the questionnaire, 72% response rate. INTERVENTION: Radioiodine treatment using a delivered absorbed dose method, aiming at an absorbed dose to the thyroid of 100-120 Gy. MAIN OUTCOME MEASURES: Statistical analysis of clinical records and results from questionnaire. RESULTS: Only 10% of the patients needed more than one treatment. At the time of follow-up, thyroxine supplementation was given to 178 (93%) of the GD and to 21 (47%) of the TNG patients. Smoking was more common in GD patients than in the general population (44% vs. 26%; P < 0.001). Smoking GD patients experienced eye discomfort more often than smoking TNG patients (53% vs. 7%; P < 0.001). Weight gain after therapy was a problem in 79% of the hyperthyroid individuals. CONCLUSIONS: Few patients needed retreatment and most of the GD patients had thyroxine after 1-5 years after therapy. Smoking patients, especially those with GD, had more eye symptoms. At follow-up, the euthyroid patients still consider themselves having a poorer health than individuals in the general population.

Adult↗
PubMed2006

Diagnostic tests for hyperthyroidism in cats.

The diagnosis of hyperthyroidism, one of the most common disorders affecting elderly cats, is usually straightforward and considered routine by most practitioners. Nowadays, however, most cats suffering from hyperthyroidism tend to be diagnosed earlier and at a milder stage of the disease than those cats diagnosed 10 to 25 years ago. There are, in fact, a growing number of cats with clinical signs of hyperthyroidism and palpably large thyroid glands whose baseline serum total thyroid hormone concentrations are within the normal or borderline range, making diagnosis problematic. This paper reviews the available tests used to confirm a diagnosis of hyperthyroidism in cats and discusses their overall usefulness.

Animals↗
PubMed2002

Relationship between semi-quantitative thyroid palpation and total thyroxine concentration in cats with and without hyperthyroidism.

In 155 cats, both with and without clinical signs of hyperthyroidism, total thyroxine (TT4) concentrations were compared to a sensitive, semi-quantitative thyroid palpation technique. On the basis of TT4 concentrations, 23 of the 155 cats were classified as hyperthyroid. The size of individual thyroid glands was scored between '0' (non-palpable) and a maximum of '6'. One or more enlarged thyroid glands (score >0) were palpated in 22 of the 23 hyperthyroid cats and in 78 of the 132 euthyroid cats. However, none of the 132 euthyroid cats had a thyroid lobe score of greater than '3' whereas 18 of the 23 hyperthyroid cats had a thyroid lobe score of '4' or greater, and in two of the five that had scores below '4' there was evidence of intrathoracic functional thyroid tissue on scintigraphy.

Animals↗
PubMed1999

Serum fructosamine concentrations in hyperthyroid cats.

Serum fructosamine concentrations were measured in 35 healthy cats and in 30 hyperthyroid cats before and 30 days after curative radioiodine ((131)I) treatment. Hyperthyroid cats were divided into those with 30 day post-treatment total thyroxine (T4) concentrations within (EuT4) or below (HypoT4) the reference range. The median (semi-interquartile range, SIR) fructosamine concentration was significantly lower in hyperthyroid compared with healthy cats (295. 0 (18.5) micromol l(-1)) both before (254.0 (27.6) micromol l(-1)) and after (268.5 (28.0) micromol l(-1)) treatment (P < 0.001 in each case). (131)I therapy was associated with increases in serum fructosamine (mean increase 20.4 micromol l(-1), P = 0.039) and total protein (6.3 g l(-1), P < 0.002) in the HypoT4 group and in globulin concentration in both EuT4 (5.9 g l(-), P < 0.002) and HypoT4 (5.2 g l(-1), P = 0.023) groups. There were no direct relationships between the observed elevations in fructosamine concentration and those in total protein or globulin concentrations suggesting that the effect may be due to reduced rates of protein turnover. Reduced values may need to be considered when interpreting serum fructosamine concentrations for monitoring the degree of glycaemic control in diabetic cats with concurrent hyperthyroidism.

Animals↗