Thyroid C cell function during fasting and refeeding of young and old rats

Age-related alterations in the structure and function of many organs often become apparent under stimulation of their function. Although the ageing process affects the regulation of mineral homeostasis, the function of thyroid C-cells that secrete calcitonin (CT) under the conditions of fasting and refeeding, a way of dietary manipulation that reveal the existence of age-related changes of follicular thyroid cells, has not been characterized. Therefore, we investigated the number of C-cells and serum CT concentration in young (4 mo) and old (26 mo) male rats fasted for 48 hours, and then refed for 4 or 24 hours. We found significantly higher number of C-cells in thyroids of old vs young rats both under basal conditions, and after fasting/refeeding. Correspondingly, serum calcitonin level was higher in fed or fasted old rats vs young ones. However, in young rats refeeding decreased, whereas in old animals increased serum concentrations of calcitonin. Thus, the control of serum calcium concentration, that was well preserved in old rats, occurs at the expense of increased serum CT level both under basal conditions, and after refeeding. These observations suggest that C-cell function is altered in ageing.     

Thyroid hormone prevention of disorders of cardiac contractile function during stress

The depression of cardiac contractility has been observed in rats during the immobilized stress in state of relative physiological rest and maximal load. In the animals pretreated with thyroid after stress the indexes of intensity and rate of myocardial contraction and relaxation didn't differ from the control, and during the maximal load the myocardium was characterized by the less expressed decrease of the structure functioning intensity and the higher rate of relaxation. The data obtained show that the physiological doses of thyroid hormones prevent the myocardium from contractile disorders during stress.     

Thyroid function in patients during long-term treatment with amiodarone]

Thyroid function was evaluated in 31 patients with disturbances of heart rhythm both before and after 13 months of treatment with amiodarone. An increase in blood serum T4 concentration and transient increase (only during the first three months of treatment) in TSH concentration have been observed in almost all the patients studied. Clinically evident form of hyperthyroidism was found only in one female patient. In two patients the changes in hormone concentrations suggesting hyperthyroidism were not accompanied by clinical manifestations, and in four patients there was no clinical hypothyroidism despite hormone levels suggesting such a state. In addition to the determinations of T3, T4 and TSH also the results of TRH-TSH test played an important role in diagnosing both hypo- and hyperthyroidism.     

A case of Graves' disease with false hyperthyrotropinemia who developed silent thyroiditis.

We encountered a patient who developed silent thyroiditis during the course of Graves' disease. The diagnosis of silent thyroiditis was made on the basis of a low thyroidal 131I uptake, no response to the thyrotropin releasing hormone (TRH) test, and subsequent hypothyroidism despite the presence of high titers of thyrotropin (TSH) receptor antibody (TRAb) and thyroid stimulating antibody (TSAb). The patient, in addition, had a discrepancy between serum TSH and thyroid hormone values. This was due to the presence of interfering substances that react to mouse IgG in the sera since serum TSH levels were decreased in a dose dependent manner by the addition of increasing amounts of mouse IgG to the sera. It should therefore be noted that silent thyroiditis can develop in patients with Graves' disease. Furthermore, clinicians should be aware that two-site immunoassay kits that use mouse monoclonal antibodies are subject to interference by some substances, possibly antibodies which react to mouse IgG.     

Thyroid gland function during cross adaptation to heat and cold in man

Plasma thyroxine (T₄), triiodothyronine (T₃) and thyrotropin (TSH) levels were monitored in 10 healthy euthyroid male subjects of the age group 20 to 30 years before and during heat and cold acclimatisation schedule in a sequential manner. The subjects were exposed to 45C DB and 30% relative humidity in a hot chamber for 2 hours daily for 8 consecutive days. Subsequently they were exposed to cold for 4 hours daily at 10C for 21 days. The mean plasma T₄ and T₃ concentration before exposure to heat were 7.87±0.82 ug/dl and 159.8±9.1 ng/dl respectively. A significant decrease in both T₄ (p<0.05) and T₃ (p<0.01) levels to mean values of 6.4±0.76g/dl and 129±7.9 ng/dl was recorded on day 4 of exposure to heat. Further significant decrease (p<0.05) over the preceding T₃ levels was observed on day 8 of heat exposure. Plasma T₄ and T₃ on day 21 of cold exposure was not significantly different from the levels reckoned after last day of heat exposure but was significantly lower than the pre-exposure values. Throughout the thermal stress schedule there was no change in the TSH levels. These observations suggest that a decrease in thyroid hormone levels during exposure to heat might be an adaptive process which continues even during cold acclimatisation.     

Urinary N-acetyl-beta-D-glucosaminidase (NAG) activity in patients with Graves' disease, subacute thyroiditis, and silent thyroiditis: a longitudinal study.

Urinary N-acetyl-beta-D-glucosaminidase (NAG) activity was measured longitudinally in 12 patients with Graves' disease, 5 patients with subacute thyroiditis, and 1 patient with silent thyroiditis, and compared with that of 36 normal controls. The patients with Graves' disease and subacute thyroiditis were treated with anti-thyroid drug (methimazole or propylthiouracil) and prednisolone, respectively. On the other hand, no treatment was given to the patient with silent thyroiditis. Since two patients with Graves' disease clearly showed transient deterioration of the thyroid function during the treatment period, data from these two patients were separately investigated. Urinary levels of NAG in the remaining ten patients with Graves' disease before, 1, 3, 6 and 12 months after the treatment were 15.59 +/- 7.93 (SD), 8.96 +/- 6.82, 4.39 +/- 2.33, 3.46 +/- 2.24, and 3.63 +/- 2.38 U/g.creatinine (g.Cr.), respectively. Those obtained before, 1 and 3 months after the treatment were significantly higher than those of the controls (2.85 +/- 1.12 U/g.Cr.). Free thyroid hormone levels became normal or low 3 months after the treatment. The two Graves' patients mentioned above showed a transient increase in urinary NAG with concomitant changes in free thyroid hormone levels. Urinary NAG levels in the patients with subacute thyroiditis before, 2, 4, and 6 weeks after the treatment were 16.56 +/- 10.97, 6.76 +/- 2.79, 3.14 +/- 0.48 and 3.70 +/- 1.44 U/g.Cr., respectively. Those obtained before and 2 weeks after the treatment were significantly higher than those of the controls. Free thyroid hormones were normal 2 weeks after therapy. Urinary NAG in the patient with silent thyroiditis was 9.60 U/g.Cr. on the first visit and gradually decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thyroid function and obesity in children and adolescents

The aim of this retrospective study was to investigate the frequency of thyroid dysfunction as assessed by TSH, T3 and T4 in a large cohort of 290 obese and 280 healthy children. In addition, thyroid autoantibodies were measured in random subgroups of 123 obese and 80 control children, iodine excretion in 50 and thyroid volume in 23 of the obese children. Elevated TSH levels (>4 U/l) were found in 22 obese children (7.5%), but only in one control (0.3%). The medians of TSH and T3 concentrations were normal, but significantly higher in the obese group than in the controls, while T4 levels did not differ. The prevalence of positive thyroid autoantibodies was increased in the obese children, for the most part in those with elevated TSH. There was no evidence for iodine deficiency as a cause of the average increase of TSH. We conclude that in childhood obesity TSH and T3 levels are significantly increased; in most cases, however, these increases are not accounted for by thyroid autoimmunity or iodine deficiency. As a consequence, TSH elevations with normal thyroid hormone levels in obese children don't need any thyroxine treatment, if thyroid disorders were definitely excluded beforehand.     

Interferon-induced thyroiditis during treatment of chronic hepatitis C

Thyroid function disorders affect between 5% and 15% of patients treated with IFNα and RBV for chronic hepatitis C. Women and patients with thyroid peroxidase antibodies (TPOAb) found before the treatment are at risk of developing the disorders (46.1% vs. 5.4%). The spectrum of IFNα-induced thyroiditis (IIT) includes two groups. Disorders with an autoimmune background are: presence of thyroid autoantibodies without clinical disease, Hashimoto's disease and Graves' disease. The second group comprises diseases caused by the direct toxic effect of IFNα on the thyroid gland, i.e. destructive thyroiditis and non-autoimmune hypothyroidism. Thyroid diseases are not an absolute contraindication for IFNα and RBV therapy. In patients diagnosed with thyroid dysfunction, before the antiviral therapy it is necessary to achieve euthyreosis. Thyroid function disorders may occur at any moment of the therapy. The earliest have been observed in the 4th week of treatment, and the latest 12 months after its termination. During the therapy, in order to diagnose IIT early, it is recommended to determine TSH level every 2-3 months depending on the presence of TPOAb before the treatment. The diagnosis and treatment of thyroid function disorders should be conducted in co-operation with an endocrinologist.     

Inner speech during silent reading reflects the reader's regional accent

While reading silently, we often have the subjective experience of inner speech. However, there is currently little evidence regarding whether this inner voice resembles our own voice while we are speaking out loud. To investigate this issue, we compared reading behaviour of Northern and Southern English participants who have differing pronunciations for words like 'glass', in which the vowel duration is short in a Northern accent and long in a Southern accent. Participants' eye movements were monitored while they silently read limericks in which the end words of the first two lines (e.g., glass/class) would be pronounced differently by Northern and Southern participants. The final word of the limerick (e.g., mass/sparse) then either did or did not rhyme, depending on the reader's accent. Results showed disruption to eye movement behaviour when the final word did not rhyme, determined by the reader's accent, suggesting that inner speech resembles our own voice.     

Thyroid function and metabolic syndrome in the population-based LifeLines cohort study

Background

The metabolic syndrome (MetS) is a combination of unfavourable health factors which includes abdominal obesity, dyslipidaemia, elevated blood pressure and impaired fasting glucose. Earlier studies have reported a relationship between thyroid function and some MetS components or suggested that serum free thyroxine (FT4) or free triiodothyronine (FT3) levels within the normal range were independently associated with insulin resistance. We assessed how thyroid function relates to MetS prevalence in a large population-based study.

Methods

Data of 26,719 people of western European descent, aged 18–80 years from the Dutch LifeLines Cohort study, all with normal thyroid stimulating hormone (TSH), FT4 and FT3 levels (electrochemiluminescent immunoassay, Roche Modular E170 Analyzer), were available. MetS was defined with the revised National Cholesterol Education Programs Adults Treatment Panel III (NCEP ATP III) criteria. We calculated prevalence of all MetS components according to TSH, FT4 and FT3 quartiles.

Results

At similar TSH levels and age (mean 45 yrs), men had significantly higher levels of FT4, FT3, blood pressure (BP), heart rate, total and LDL-cholesterol, triglycerides (TG), and creatinine, but lower HDL-cholesterol compared to women (all p < 0.001). In total, 11.8% of women and 20.7% of men had MetS. In men, lower FT4 levels were associated with higher prevalence of MetS and all MetS components. In women, lower FT4 quartile was only associated with a higher prevalence of elevated TG, waist circumference, and MetS. However, when corrected for confounding factors like age, BMI, current smoking and alcohol consumption, a significant relationship was found between FT3 and three MetS components in men, and all five components in women. Moreover, the highest quartiles of FT3 and the FT3FT4 ratio predicted a 49% and 67% higher prevalence of MetS in men, and a 62 and 80% higher prevalence in women.

Conclusions

When corrected for possible confounding factors, higher plasma levels of FT3 are associated with several components of the MetS. Only in men, lower FT4 is related to MetS. In the highest FT3 and FT3FT4 quartiles, there is a 50–80% increased risk of having MetS compared to the lowest quartile. Further studies are needed to assess the possible causality of this relationship.