Free diiodotyrosine effects on protein iodination and thyroid hormone synthesis catalyzed by thyroid peroxidase.
(49/457)
Free diiosotyrosine exerts two opposite effects on the reactions catalyzed by thyroid peroxidase, thyroglobulin iodination and thyroid hormone formation. 1. Inhibition of thyroglobulin iodination catalyzed by thyroid peroxidase was observed when free diiodotyrosine concentration was higher than 5 muM. This inhibition was competitive, suggesting that free diiodotyrosine interacts with the substrate site(s) of thyroid peroxidase. Free diiodotyrosine also competively inhibited iodide peroxidation to I2. 2. Free diiodotyrosine, when incubated with thyroid peroxidase in the absence of iodide was recovered unmodified; in the presence of iodide an exchange reaction was observed between the iodine atoms present in the diiodotyrosine molecule and iodide present in the medium. Using 14C-labelled diiodotyrosine, 14C-labelled non-iodinated products were also observed, showing that deiodination occurred as a minor degradation pathway. However, no monoiodo[14C]tyrosine or E114C]tyrosine were observed. Exchange reaction between free diiototyrosine and iodide is therefore direct and does not imply deiodination-iodination intermediary steps. Thyroglobulin inhibits diiodotyrosine-iodide exchange and vice versa, again suggesting competition for both reactions. These results support, by a different experimental approach, the two-site model for peroxidase previously described by us in this journal. 3. Free diiodotyrosine when present at a very low concentration, 0.05 muM, exerts a stimulatory effect on throid hormones synthesis. The relationship between diiodotyrosine concentration and thyroid hormone synthesis give an S-shaped curve, suggesting that free diiodotyrosine acts as a regulatory ligand for thyroid peroxidase. Evidence is also presented that free diiodotyrosine is not incorporated into thyroid hormones. Therefore, thyroid peroxidase catalyzes only intra-molecular coupling between iodotyrosine hormonogenic residues. 4. Finally, although no direct proof exists that these free diiodotyrosine effects upon thyroglobulin iodination and thyroid hormone synthesis are physiologically significant, such a possibility deserves further investigation. (+info)
Painless thyroiditis associated with severe inflammatory reactions in amyloid goiter: a case report.
(50/457)
We report the case of a 64-year-old woman with rheumatoid arthritis (RA) associated with high grade fever, malaise, and painless swelling of thyroid gland. Laboratory findings showed severe systemic inflammatory reactions, including increases in various cytokines such as IL-6. Gallium-67 citrate imaging revealed intense uptake in the painlessly enlarged thyroid gland. Histologically, biopsied specimens of thyroid showed diffuse amyloid infiltrations, which included amyloid A (AA) protein. Biopsies of rectum and stomach revealed similar amyloid depositions, indicating that the amyloid had a secondary origin, potentially due to RA. All clinical symptoms were relieved by intravenous pulsatile administration of methylprednisolone followed by oral prednisone, resulting in prolonged hypothyroid status. To our knowledge, this is the first case report in Japan describing painless thyroiditis with severe inflammatory reactions in amyloid goiter. (+info)
Fine needle aspiration biopsy of thyroid nodules.
(51/457)
BACKGROUND: Fine needle aspiration biopsy (FNA) is a routine diagnostic technique for evaluating thyroid nodules. Many reports in adults consider that FNA is superior to thyroid ultrasonography (USG) and radionuclide scanning (RS). Only five studies have been published on FNA of childhood thyroid nodules. AIMS: To investigate the reliability of FNA in the evaluation and management of thyroid nodules, and compare the results of FNA, USG, and RS with regard to final histopathological diagnosis. METHODS: FNA was performed in 46 children with thyroid nodules after USG and RS examination. We investigated the sensitivity, specificity, accuracy, and positive and negative predictive values of USG, RS, and FNA in their management. RESULTS: Six patients who had malignant or suspicious cells on FNA examination underwent immediate surgery. The other 40 patients received medical treatment according to their hormonal status. Fifteen of these nodules either disappeared or decreased in number and/or size. Surgery was performed in 25 patients who did not respond to therapy. Statistical analysis revealed sensitivity, specificity, accuracy, and positive and negative predictive values respectively as follows: 60%, 59%, 59%, 15%, and 92% for USG; 30%, 42%, 39%, 12%, and 68% for SC; 100%, 95%, 95%, 67%, and 100% for FNAB. CONCLUSION: FNAB is as reliable in children as in adults for definitive diagnosis of thyroid nodules. Using this technique avoids unnecessary thyroid surgery in children. (+info)
Haemodynamic changes following treatment of subclinical and overt hyperthyroidism.
(52/457)
OBJECTIVE: Hyperthyroidism has profound effects on the cardiovascular system, including reduced systemic vascular resistance (SVR) due to relaxation of vascular smooth muscle cells, enhanced heart rate (HR) and cardiac output (CO) due to an increase in cardiac diastolic relaxation, contractility and heart rate. Subclinical hyperthyroidism is characterised by reduced serum TSH levels despite free thyroxine (T4) and tri-iodothyronine (T3) estimates within the reference range, in subjects with no obvious symptoms of hyperthyroidism. We measured haemodynamic changes (using impedance cardiography) in subjects with endogenous subclinical hyperthyroidism in order to elucidate whether these patients had signs of excess thyroid hormone at the tissue level. DESIGN: The patients were otherwise healthy women with a multinodular goitre (n=6; age 47-81 years; serum TSH 0.006-0.090 mU/l and normal free T4 and T3 estimates), studied before and after normalisation of TSH (0.280-1.120 mU/l) by means of radioiodine treatment, and they were compared with 9 overt hyperthyroid patients (2 with multinodular goitre and 7 with Graves' disease) in the untreated state and after euthyroidism had been obtained. RESULTS: Treatment of the subclinical hyperthyroid women resulted in 11% reduction in HR (P<0.02), 19% reduction in CO from (means+/-s.d.) 6.93+/-2.15 l/min to 5.58+/-1.94 l/min (P<0.05), and 30% increase in SVR (P<0.02). Similar but more pronounced changes were seen in the hyperthyroid group: 17% reduction in HR, 25% reduction in CO and 46% increase in SVR (all at least P<0.05). Taking all 15 patients together, thyroid function (as measured by free T3 index (FT3I) or TSH) correlated significantly to the haemodynamic parameters as follows: the higher the thyroid function the lower the mean arterial pressure and SVR, and the higher the CO and central aortic compliance (stroke volume/pulse pressure) (P<0.05). Plasma norepinephrine increased significantly after treatment of the overt hyperthyroid patients, whereas epinephrine did not change, and no changes were seen among subclinical hyperthyroid patients. CONCLUSION: Treatment of endogenous subclinical hyperthyroidism resulted in significant changes in several haemodynamic parameters regarding the heart and the vascular system, compatible with some degree of excess tissue exposure to thyroid hormones in the untreated state. Our data favour more aggressive treatment of these patients, and endogenous subclinical hyperthyroidism might be regarded as a mild form of hyperthyroidism. (+info)
Prevalence and characteristics of postpartum thyroid dysfunction in Tehran.
(53/457)
OBJECTIVE: To determine the prevalence of postpartum thyroiditis (PPT), one of the autoimmune disorders of the thyroid which usually occurs in women in the first year after parturition. PPT presents with periods of transient thyrotoxicosis and hypothyroidism, in many cases resulting in permanent hypothyroidism. DESIGN: The study involved 1040 mothers who had contacted five health centers in Tehran for vaccination of their children. METHODS: Signs and symptoms of hypothyroidism and thyrotoxicosis, and the presence of goiter (using the World Health Organization classification), were sought. Serum T3, T4, TSH, anti-TPO and anti-Tg antibodies were measured at 3, 4.5, 6 and 9 months after parturition. In those with hypothyroidism or thyrotoxicosis and a matched group of normal women, thyroid sonography was performed. RESULTS: The prevalence of thyroiditis was 11.4%. Hypothyroidism and thyrotoxicosis occurred in 68 and 42 mothers respectively. Nine had thyrotoxicosis followed by hypothyroidism. There was one case of Graves' disease. Out of 68 hypothyroid patients, 33 women underwent treatment with levothyroxine (because of the severity of symptoms) for 12 months. Six women showed increased TSH at 6 weeks after discontinuation of thyroxine. Stage II goiter (World Health Organization classification) were observed in 21.8% of patients and in 6.7% of pospartum euthyroid women (P<0.001). Positive anti-TPO was found in 61.5% of patients and in 19% of the control group; positive anti-Tg was found in 58% of patients and in 6% of the control group (P<0.001). Sonographic changes were observed in 96% of the patients and in 7% of the control group (P<0.001). There was no significant correlation between the occurrence of thyroiditis and parity, the age of the mother, a previous history of thyroid disease in the patient or family, breast-feeding, or the gender of the child. CONCLUSION: The results of this study show a high prevalence of PPT in Tehranian women. This may be due to the length and frequency of follow-up and/or the transition from low to adequate iodine intake. The major difference with respect to other studies is the low frequency of the biphasic form of PPT. (+info)
Outcomes and complications of thyroid surgery: retrospective study.
(54/457)
OBJECTIVE: To study the outcome and complications of thyroid surgery. DESIGN: Retrospective study. SETTING: Regional hospital, Hong Kong. PATIENTS: Three hundred and twelve patients (266 women and 46 men) underwent thyroid surgery between January 1994 and December 1999. MAIN OUTCOME MEASURES: Complications of thyroidectomy for various thyroid diseases according to surgical technique used. RESULTS: Capsular dissection gradually became a more popular surgical technique: 33% and 58% in the first and second halves of the study period respectively (P<0.001). The overall rate of permanent vocal cord palsy was 2%. Near-total thyroidectomy became the preferred surgical treatment for toxic goitre over the study period. The incidence of recurrent hyperthyroidism was reduced from 21% to 7% (P>0.1, not significant). The incidence of hypoparathyroidism was approximately 30% after thyroidectomy for cancer. CONCLUSION: Capsular dissection is increasingly utilised in thyroid surgery. Low complication rates can be achieved after thyroidectomy for benign diseases. Hypoparathyroidism, however, is a relatively common complication after surgery for thyroid cancer. (+info)
The role of local mass media in promoting the consumption of iodized table salt.
(55/457)
Iodine deficiency disorder (IDD) is currently an important public health problem in Turkey. The use of iodized salt is a sample and cheap solution. The purpose of this study was to determine the prevalence of iodized salt use in the Trabzon region and the effect of a local mass-media education program in increasing usage. The overall aim was to use the findings to inform future health management and health education activities, and shape further development of the IDD program. Prior to the intervention, the prevalence of iodized salt consumption was 54.5%. Following the 3-month education program it increased to 62.4%. There was a significant difference in the pre- and post-intervention findings (P = 0.00237). The results show that the use of local mass media is effective in raising the prevalence of iodized salt use. Local mass media could therefore be used as part of a national strategy to prevent iodine deficiency disorders. (+info)
Study of biochemical prevalence indicators for the assessment of iodine deficiency disorders in adults at field conditions in Gujarat (India).
(56/457)
The main objective of this study was to assess the severity of iodine deficiency disorders (IDD) in the adult populations of the Baroda and Dang districts from Gujarat, western India using biochemical prevalence indicators of IDD. The other aim of this study was to establish a biochemical baseline for adequate iodine intake as a result of program evolution in the face of multiple confounding factors, like malnutrition and goitrogens responsible for goiter. A total of 959 adults (16-85 years) were studied from two districts (Baroda and Dang) and data was collected on dietary habits, anthropometric and biochemical parameters such as height, weight, urinary iodine (UI) and blood thyroid stimulating hormone (TSH). Drinking water and cooking salt were analyzed for iodine content. All subjects, irrespective of sex and district, showed median UI = 73 microg/L and mean blood TSH +/- SD = 1.59+/-2.4 mU/L. Seven per cent of the studied population had blood TSH values > 5 mU/L. Females in Baroda and males from Dang district were more affected by iodine deficiency as shown by a lower median UI. Mean TSH was significantly higher in women from both districts as compared to men (P = 0.001). The blood spots TSH values > 5 mU/L were seen in 20% of women from Dang. The normative accepted WHO values for UI and TSH for the severity of IDD as a significant health problem are not available for target population of adults. Urinary iodine normative limits and cut-offs are established for school-aged children. Blood spot TSH upper limit and cut-off values are available for neonate populations. The IDD has not been eliminated so far, as more than 20% of both male and female subjects had UI < 50 microg/L. Males were more malnourished than females in both districts (P < 0.05). Pearl millet from Baroda contained flavonoids like apigenin, vitexin and glycosyl-vitexin. Dang district water lacked in iodine content. Iodine deficiency disorder is a public health problem in Gujarat, with the Baroda district a new pocket of IDD. High amounts of dietary flavonoids in Baroda and Dang, malnutrition and an additional lack of iodine in Dang water account for IDD. (+info)