Determination of thyroid hormones in dietary supplements using liquid chromatography-tandem mass spectrometry.

More than 27 million Americans have some kind of thyroid disease. Numerous dietary supplements claiming to support healthy thyroid function and healthy metabolism and balance or promote weight loss are available for purchase in retail stores and on the internet. In the literature, there have been reports of adverse events associated with the consumption of thyroid hormone-containing products. In this study, an LC-MS/MS method was developed and validated for the analysis of thyroxine (T4), 3,3',5-triiodo-l-thyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,5-diiodothyronine (3,5-T2) and 3,3'-diiodothyronine (3,3'-T2) in dietary supplements. Sonication with methanol was used for the extraction of free hormones from nonglandular products. The tissue-bound hormones from glandular thyroid products were extracted using a modified enzymatic digestion, in which the matrix was first extracted by sonication with methanol and then by enzymatic digestion with proteases. Both extraction methods provided acceptable recovery values between 78% and 116%. Fifty-eight products making claims related to thyroid management were purchased over the internet from 2017-2018 and quantitatively analyzed for five hormones using the validated methods. Eleven out of 19 glandular products were found to contain quantifiable amounts of hormones. Maximum daily servings were also calculated for each product based on label information. The maximum amount of T4, T3, and rT3 per daily serving in the glandular products were up to 210, 32, and 7.6 µg/day, respectively. In the case of nonglandular products, which were labeled to contain plant extracts, vitamins, minerals, diiodo compounds, and so forth, the amounts of 3,5-T2 and 3,3'-T2 were up to 740 and 2700 µg/day, respectively.

Copper sulfate and arginine supplements on performance, thyroid hormones and blood biochemistry of broilers fed with canola meal-based diets / Avaliação da suplementação com sulfato de cobre e arginina sobre o desempenho, hormônios tireoidianos e bioquímica sanguínea de frangos alimentados com dietas à base de canola

The present evaluated the effects of copper sulfate solution (CSS) and arginine powder (Arg) supplements on performance, thyroid hormones and blood biochemistry of broiler chickens fed with canola meal (CM)-based diets. The experimental design was completely randomized with a 3 × 3 factorial and 9 treatments, corresponding to 3 levels of CSS (0, 125 and 250 mg/kg) and 3 levels of Arg (0, 0.1 and 0.2%) (n = 45 per treatment). Feeds were offered ad libitum for 21 days, from 22 to 42 days of age. Feed efficiency was significantly affected by the dietary addition of 250 mg/kg CSS and 0.2% Arg, and by the CSS × Arg interaction. CM supplemented with CSS improved the thyroid gland status and increased the plasma levels of triiodothyronine and thyroxine. Birds fed diets supplemented with 0.2% Arg had lower blood glucose level than the other treatments. The addition of 250 mg/kg CSS and 0.2% Arg reduced the stress caused by the rapid growth of broilers, also increasing the overall bird welfare.

O objetivo do presente trabalho foi avaliar os efeitos da suplementação com solução de sulfato de cobre (SSC) e arginina em pó (Arg) sobre o desempenho, hormônios tireoidianos e bioquímica sanguínea de frangos de corte alimentados com dietas à base de canola DC. O desenho experimental foi completamente casualizado com fatorial 3 × 3 e nove tratamentos correspondentes a três níveis de inclusão de SSC (0, 125 e 250 mg/kg) e três níveis de Arg (0, 0,1 e 0,2%) (n = 45 para cada tratamento). As rações foram oferecidas ad libitum por 21 dias, de 22 até 42 dias de idade. A eficiência alimentar foi significativamente afetada pela adição de 250 mg/kg de SSC e 0,2% de Arg, assim como pela interação SSC × Arg. A suplementação da DC com SSC melhorou os parâmetros da glândula tireoide e aumentou os níveis plasmáticos de triiodotironina e tiroxina. As aves alimentadas com dietas suplementadas com 0,2% de Arg apresentaram menor nível de glicose sanguínea do que as dos demais tratamentos. A adição de 250 mg/kg de SSC e 0,2% de Arg reduz o estresse causado pelo rápido crescimento dos frangos, além de melhorar as condições gerais de bem estar das aves.

Biotin Interference in Assays for Thyroid Hormones, Thyrotropin and Thyroglobulin.

Background: Biotin has been reported to interfere with several commonly used laboratory assays resulting in misleading values and possible erroneous diagnosis and treatment. This report describes a prospective study of possible biotin interference in thyroid-related laboratory assays, with a comparison of different commonly used assay platforms. Materials and Methods: Thirteen adult subjects (mean age 45 ± 13 years old) were administered biotin 10 mg/day for eight days. Blood specimens were collected at three time points on day 1 and on day 8 (baseline, two, and five hours after biotin ingestion). Thyrotropin (TSH), free triiodothyronine (fT3), free thyroxine (fT4), total triiodothyronine (TT3), total thyroxine (TT4), thyroxine binding globulin (TBG), and thyroglobulin (Tg) levels were analyzed with four different platforms: Abbott Architect, Roche Cobas 6000, Siemens IMMULITE 2000, and liquid chromatography with tandem mass spectrometry (LC-MS/MS). TSH, fT3, fT4, TT3, and TT4 were measured with Abbott Architect and Roche Cobas 6000. fT3, fT4, TT3, and TT4 were also measured by LC-MS/MS. Tg was measured by Siemens IMMULITE 2000. TBG was assessed with Siemens IMMULITE 2000. Results: Significant changes in TSH, fT4, and TT3 measurements were observed after biotin exposure when the Roche Cobas 6000 platform was used. Biotin intake resulted in a falsely lower Tg level when measurements were performed with Siemens IMMULITE 2000. At the time points examined, maximal biotin interference was observed two hours after biotin exposure both on day 1 and day 8. Conclusions: A daily dose of 10 mg was shown to interfere with specific assays for TSH, fT4, TT3, and Tg. Physicians must be aware of the potential risk of erroneous test results in subjects taking biotin supplements. Altered test results for TSH and Tg can be particularly problematic in patients requiring careful titration of levothyroxine therapy such as those with thyroid cancer.

Effects of methadone, opium tincture and buprenorphine maintenance therapies on thyroid function in patients with OUD.

Various types of medications are used as maintenance therapies for substance use disorder; However, the side effects of these drugs are shown to restrict their use and increase the risk of relapse in patients. As a result, alternative maintenance therapies are tested in the hope for optimum therapy. Since opium tincture is a new and innovative maintenance treatment in Iran, we attempted to compare the therapeutic and side effects of opium tincture with two standard therapies, i.e., methadone and buprenorphine. Hence, thyroid function was tested in three methods of maintenance therapies with methadone, buprenorphine, and opium tincture in a cross-sectional study. In this study, 150 patients with the mean age of 51.63 ± 13.56 years and a history of opioid or opioid-derivatives use disorder, underwent the maintenance treatment with methadone, buprenorphine, and opium tincture at Bojnurd Addiction Treatment Centers in northeastern Iran. These patients were selected using convenience sampling. Then, they were placed into three treatment groups of methadone, buprenorphine, and opium tincture. The thyroid functionality was assessed with measuring TSH, fT4, fT3, T3RU, and Anti TPO, carried out in a reference laboratory. Finally, these data were analyzed by ANOVA using SPSS.16 software. The results showed that there was no significant difference in the average levels of TSH, fT3, fT4, and Anti TPO in these treatment groups; except for T3RU concentration, which was increased significantly in the opium tincture group as compared to the methadone treated group. Also, the frequency of fT4, and T3RU disorders demonstrated a significant change in three groups. The findings of the present study demonstrated that opium tincture in comparison with methadone could increase T3RU levels resulting in euthyroidism possibly through TBG.

The effects of synbiotic supplementation on thyroid function and inflammation in hypothyroid patients: A randomized, double­blind, placebo­controlled trial.

BACKGROUND: There is a positive link between thyroid homeostasis and the composition of gut microbiota. A limited number of studies have suggested the efficacy of probiotic products on levothyroxine metabolism and thyroid hormone activity. Therefore, the purpose of this study was to investigate the effect of synbiotic supplementation on thyroid function, inflammation markers, and blood pressure in subjects with hypothyroidism. METHODS: This study was conducted as a randomized, double-blind, placebo-controlled trial involving 60 patients with hypothyroidism. Participants were randomly recruited into two groups to receive either 500 mg/day of synbiotic (n = 30) or a placebo (n = 30) for 8 weeks. RESULTS: Thyroid-stimulating hormone concentration, levothyroxine dose, and fatigue severity scale score were significantly decreased after the 8-week intervention in the synbiotic group (P < 0.05), while there were no significant differences seen in the placebo group. In addition, FT3 at the end of intervention was significantly higher (P = 0.001) in both groups, although these changes were not significant between the two groups (P = 0.259). Synbiotic supplements led to a significant elevation in serum CRP (P = 0.006), but this increase was not significant between groups (P = 0.699). Moreover, no statistical significance was observed within or between groups in terms of anti-thyroid peroxidase, systolic blood pressure and diastolic blood pressure (P > 0.05). CONCLUSION: Synbiotic supplementation among hypothyroid patients for 8 weeks may have beneficial effects on thyroid function. Further studies with larger sample size and longer duration are needed to confirm the current findings.

Over-the-Counter "Adrenal Support" Supplements Contain Thyroid and Steroid-Based Adrenal Hormones.

OBJECTIVE: To assess whether dietary supplements that are herbal and/or animal-derived products, marketed for enhancing metabolism or promoting energy, "adrenal fatigue," or "adrenal support," contain thyroid or steroid hormones. METHODS: Twelve dietary adrenal support supplements were purchased. Pregnenolone, androstenedione, 17-hydroxyprogesterone, cortisol, cortisone, dehydroepiandrosterone sulfate, synthetic glucocorticoids (betamethasone, dexamethasone, fludrocortisone, megestrol acetate, methylprednisolone, prednisolone, prednisone, budesonide, and triamcinolone acetonide) levels were measured twice in samples in a blinded fashion. This study was conducted between February 1, 2016, and November 1, 2016. RESULTS: Among steroids, pregnenolone was the most common hormone in the samples. Budesonide, 17-hydroxyprogesterone, androstenedione, cortisol, and cortisone were the others in order of prevalence. All the supplements revealed a detectable amount of triiodothyronine (T3) (63-394.9 ng/tablet), 42% contained pregnenolone (66.12-205.2 ng/tablet), 25% contained budesonide (119.5-610 ng/tablet), 17% contained androstenedione (1.27-7.25 ng/tablet), 8% contained 17-OH progesterone (30.09 ng/tablet), 8% contained cortisone (79.66 ng/tablet), and 8% contained cortisol (138.5 ng/tablet). Per label recommended doses daily exposure was up to 1322 ng for T3, 1231.2 ng for pregnenolone, 1276.4 ng for budesonide, 29 ng for androstenedione, 60.18 ng for 17-OH progesterone, 277 ng for cortisol, and 159.32 ng for cortisone. CONCLUSION: All the supplements studied contained a small amount of thyroid hormone and most contained at least 1 steroid hormone. This is the first study that measured thyroid and steroid hormones in over-the-counter dietary "adrenal support" supplements in the United States. These results may highlight potential risks of hidden ingredients in unregulated supplements.

Positive correlation of thyroid hormones and serum copper in children with congenital hypothyroidism.

Thyroid hormones are of central relevance for growth and development. However, the underlying molecular mechanisms are still not fully understood. Recent studies in humans and mice have demonstrated that serum levels of selenium (Se) and copper (Cu) are positively affected by thyroid hormones. Given the importance of these trace elements for many biochemical processes, we tested whether this interaction is found in children at risk for hypothyroidism, potentially providing a novel factor contributing to the disturbed development observed in congenital hypothyroidism (CH). We conducted a cross-sectional analysis of 84 children diagnosed with CH displaying a wide range of thyroid hormone concentrations. Serum Se and Cu concentrations were measured by total reflection X-ray fluorescence. Data for thyrotropin (TSH) were available in all, thyroxine (T4) and free thyroxine (fT4) in the majority and triiodothyronine (T3) in 29 of the children. Spearman rank analyzes were performed. Cu and thyroid hormones showed a strong positive correlation (Cu/T4, rho=0.5241, P=0.0003; Cu/T3, rho=0.6003, P=0.0006). Unlike in adults, no associations were found between Se and any of the thyroid hormones. Our data highlight that serum Cu and thyroid hormones are strongly associated already in early postnatal life. Severely hypothyroid children are thus at risk of developing a Cu deficiency if not adequately nourished or supplemented. This finding needs to be verified in larger groups of children in order not to miss an easily-avoidable risk factor for poor development.

Uso de cinacalcet para el control del hiperparatiroidismo en pacientes con diferentes grados de insuficiencia renal / Use of cinacalcet for the management of hyperparathyroidism in patients with different degrees of renal failure

Antecedentes: Los efectos de cinacalcet en el hiperparatiroidismo secundario (HPTS), persistente o asociado a hipercalcemia han sido descritos en pacientes en diálisis. Objetivos: Analizar la eficacia y seguridad de cinacalcet en HPTS no sometido a diálisis y sus efectos sobre marcadores de recambio óseo. Métodos: Estudio analítico observacional, no aleatorizado, longitudinal, de pacientes con enfermedad renal crónica (ERC) e HPTS (PTH > 80 pg/mL); con normohipercalcemia (≥8,5mg/dL), tratados con cinacalcet. Resultados: La dosis media de cinacalcet fue de 30mg/día en un 66,7%. Estudiamos 15 pacientes (10 mujeres), con edad de 66,0±17,93 años. Etiología desconocida en 20% de los casos. Registramos variables sociodemográficas y parámetros de función renal. Comparamos valores basales, tras 6 y 12 meses. Descendieron los niveles de iPTH (392,4±317,65 vs. 141,8±59,26) y calcio (10,3±0,55 vs. 9,4±1,04). Aumentaron los valores de fósforo (3,7±1,06 vs. 3,9±0,85) y ß-CTX (884,2±797,22 vs. 1.053,6±999,00), sin variaciones significativas del FG, calciuria y demás marcadores óseos. Registrados 2 abandonos (intolerancia digestiva y paratiroidectomía, respectivamente). Conclusiones: Cinacalcet a dosis bajas es eficaz en el manejo del HPTS del paciente con ERC no tratado mediante diálisis, al disminuir la iPTH y la calcemia, sin ocasionar efectos adversos graves ni variación significativa de la función renal (AU)

Background: The effects of cinacalcet in persistent and/or hypercalcaemia-associated secondary hyperparathyroidism (SHPT) have been described in patients on dialysis. Objectives: To evaluate the efficacy and safety of cinacalcet in SHPT not on dialysis and its effects on bone turnover markers. Methods: Non-randomised, longitudinal, observational, analytical study of patients with chronic kidney disease (CKD) and SHPT (PTH> 80 pg/mL) as well as normo- or hypercalcaemia (≥8.5mg/dL), treated with cinacalcet. Results: Mean cinacalcet dose was 30mg/day in 66.7%. We studied 15 patients (10 women), aged 66.0±17.93years. The aetiology was unknown in 20% of cases. Sociodemographic variables and renal function parameters were recorded. We compared values at baseline as well as after 6 and 12 months. Calcium (10.3±0.55 vs. 9.4±1.04) and iPTH (392.4±317.65 vs. 141.8±59.26) levels decreased. Increased levels of phosphorus (3.7±1.06 vs. 3.9±0.85) and ß-CTX (884.2±797.22 vs. 1053.6±999.00) were detected, although there were no significant changes in GFR, urinary calcium or other bone markers. Two patients withdrew from the study (gastrointestinal intolerance and parathyroidectomy, respectively). Conclusions: Cinacalcet at low doses is effective in the management of SHPT in CKD patients who are not on dialysis. Its use reduces iPTH and calcaemia, without causing serious side effects or significant changes in renal function (AU)

Suplementación de yodo en la gestación y lactancia / Iodine supplementation in pregnancy and lactation

El beneficio de la suplementación con yodo durante la gestación en las áreas con deficiencia grave de yodo está bien establecido. En el año 2004 la Organización Mundial de la Salud incluyó a España entre los países con adecuada ingesta de yodo y varios estudios recientes confirman que la ingesta de yodo es suficiente en la población española. Los profesionales españoles, sin embargo, se han encontrado con recomendaciones contradictorias, lo que ha generado confusión e incertidumbre en la práctica a seguir en cuanto a la suplementación de yodo a la mujer gestante o en periodo de lactancia. A los clínicos e investigadores les preocupa que las situaciones de déficit de yodo leve o moderado puedan relacionarse con un peor desarrollo de los niños, pero la suplementación rutinaria de yodo en la gestación no está exenta de riesgo. PrevInfad considera que, al tratarse de una medida profiláctica que afecta a dos individuos -madre e hijo- y que se aplica al conjunto de una población sana, debe primar el principio de precaución y que no existen pruebas de calidad suficiente para determinar el balance entre los beneficios y los riesgos de la suplementación farmacológica de yodo durante la gestación y la lactancia, por lo que sugiere que no se realice esta intervención (AU)

The benefits of Iodine supplementation in Iodine-deficient areas are well established. The World Health Organization included Spain among the countries with an adequate Iodine intake in 2004 and some recent research papers confirm that Iodine intake is adequate in the Spanish population. Nevertheless, Spanish health professionals have been faced with contradictory recommendations, producing confusion and uncertainty in clinical practice referring to Iodine supplementation in pregnancy and breastfeeding mothers. Clinicians and researchers are concerned that mild or moderate Iodine deficiency could be related to underdevelopment in children, but routine Iodine supplementation in pregnancy is not risk free. The working group PrevInfad (Prevention in Childhood and Adolescence) considers that being a preventive intervention that applies to the total healthy population, the precaution principle must be prioritized, and that there is no evidence on the balance risk-benefit in the pharmacological Iodine supplementation during pregnancy and breastfeeding. For these reasons they suggest not making this intervention

Thyroid hormones in milk and blood of lactating donkeys as affected by stage of lactation and dietary supplementation with trace elements.

The traditional utilization of donkeys (Equus asinus) as dairy animals has recently attracted substantial scientific interest with regard to human nutrition. Donkey milk is well tolerated by infants with cows' milk allergy, useful in the treatment of human immune-related diseases, in the prevention of atherosclerosis, and in-vitro studies showed an anti-proliferative effect. Active 3-3'-5-triiodothyronine (T3) in colostrum and milk could play different physiological roles, systemic and paracrine, for both the mother and the suckling offspring. The aim was to evaluate whether thyroid hormones (TH) concentrations in milk and blood of lactating donkeys change with the advancing lactation and whether they can be affected by dietary supplementation with several trace elements, some of them directly involved with TH synthesis (I), metabolism (Se) and action (Zn). Sixteen lactating jennies were divided into two groups (CTL and TE). Mixed feed for TE was added with Zn, Fe, Cu, Mn, I, Se and Co. Every 2 weeks milk and blood samples were collected at 11·00. Total concentrations of T3 in milk (T3M) and T3 and T4 in plasma (T3P and T4P) were assayed using ELISA kits, validated for the donkey species. T3M was not correlated with TH concentrations in blood, did not change with the stage of lactation, and was significantly higher in TE (4·09 ± 0·07 ng/ml, mean ± SE) than in CTL group (3·89 ± 0·08 ng/ml). T4P (81·8 ± 5·2 ng/ml) and T3P (15·2 ± 1 ng/ml) significantly changed with time, but were not significantly affected by dietary treatment. T3P/T4P ratio was significantly lower in TE group. This study indicates that in donkey milk the concentration of T3, a human-like bioactive compound, can be affected by trace elements intake.

Determination of thyroid hormones and their metabolites in tissue using SPE UPLC-tandem MS.

A solid-phase liquid chromatography tandem mass spectrometry (SPE LC-MS/MS) method was developed to determine thyroid hormones and their metabolites in tissue samples. The separation was achieved using reversed-phase ultra-performance liquid chromatography (UPLC); the mass spectrometric detection was achieved by positive electrospray ionization and multiple reaction monitoring. Prior to the UPLC separation a sample cleanup with a cation exchange was performed. ¹³C6 labeled internal standards were used for the thyroid hormones and their metabolites. The method was linear over a range from 0.23 to 90 nmol/L for thyroxine and from 0.23 to 9 nmol/L for the metabolites. The lower limit of quantification ranged from 0.98 to 1.73 pg on column. Intra- and total assay variation were <10 and <15%, respectively. This method enables us to link thyroid hormone tissue concentrations to local iodothyronine deiodinase expressions, which will enhance our understanding of the regulation of thyroid hormone metabolism on the tissue level.

The role of iron deficiency in persistent goiter.

BACKGROUND: Iodine deficiency has been identified as a significant public health problem in Iran. The main strategy for controlling iodine deficiency was nationwide salt iodination. Over 10 years after starting this program, goiter is still endemic in school children. Iron deficiency may have interfered with the iodine intervention program. The objective of the present study was to evaluate the relationships between iron status, thyroid hormone profile, and the prevalence of goiter 11 years after implementation of the salt iodination program. METHODS: In this study which was conducted in Marvdasht, Shiraz, 1188 students aged eight to 13 years were enrolled. Goiter was graded according to the classification by the World Health Organization (WHO). Serum concentrations of thyroid hormones and thyroid stimulating hormone were determined using commercial kits. The urinary iodine level was measured using the digestion method. RESULTS: Goiter was endemic (39.6%); the majority of participants had grade 1 thyromegally. Despite the endemic status of goiter in southern Iran, the urine content of iodine reflected a normal iodine intake. The prevalence of iron deficiency was 16.4%. The iron-deficient patients had a significantly higher thyroid stimulating hormone level and lower free T4 concentrations than those with a normal serum ferritin level (P<0.001). CONCLUSION: Iron supplementation may improve thyroid metabolism in children but we still have to investigate the role of other goitrogens in this area.

Selenium status and cardiovascular risk profile in healthy adult Saudi males.

The purpose of this research was to investigate the relationship between selenium levels, thyroid function and other coronary risk factors in 140 Saudi subjects without overt coronary heart disease stratified by age. Demographic data and serum fasting lipid profile, glucose, thyroid function tests, selenium status and dietary intake was assessed. The relationships between selenium status, thyroid function and cardiovascular risk factors were assessed by univariate and multivariate analysis. The results showed that thyroid hormone levels did not differ with age. Erythrocyte glutathione peroxidase (GPx) levels were significantly higher in the youngest vs. oldest tertile (p<0.0001). Selenium and iodine intake did not differ significantly with age tertile, but the average intake for the population sample was below the estimated average requirements for both elements. Serum lipoprotein (a) concentrations correlated with selenium (r = 0.417, p<0.0001) and TSH (r = 0.172, p<0.05). After adjustment for confounding variables; serum fT(4) and erythrocytes GPx remained significant determinants of serum TSH levels, whilst serum selenium and TSH were determinants of serum fT(4) levels. Serum Lp(a), a coronary risk factor, was strongly related to measures of selenium status. A significant relationship between measures of selenium status and thyroid function was found. Serum Lp(a) a known risk factor for cardiovascular disease was also related to selenium status in our population.

The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infant.

BACKGROUND: Thyroid hormone is crucial for brain development during foetal and neonatal life. In very preterm infants, transient low levels of plasma T4 and T3 are commonly found, a phenomenon referred to as transient hypothyroxinaemia of prematurity. We investigated whether breast milk is a substantial resource of thyroid hormone for very preterm neonates and can alleviate transient hypothyroxinaemia. Both the influence of breast feeding on plasma thyroid hormone levels and the thyroid hormone concentration in preterm human milk were studied. METHODS: Two groups were formed from the placebo group of a randomized thyroxine supplementation trial in infants born at < 30 weeks' gestational age on the basis of the mean breast milk intake during the third, fourth and fifth weeks of life. One group received more than 50% breast milk (mean breast milk intake 84%, n = 32) and the other group less than 25% breast milk (mean breast milk intake 3.3%, n = 25). Plasma thyroid hormone concentrations were compared between the two groups. Breast milk was collected from mothers of infants participating in the same trial and the thyroxine concentration in breast milk was measured with RIA after extraction. RESULTS: No significant differences were found between both groups in plasma concentrations of T4, free T4, T3, TSH, rT3 and thyroxine-binding globulin (TBG), which were measured once a week. Thyroxine concentration in breast milk ranged between 0.17 microg/l and 1.83 microg/l (mean 0.83, SD 0.3 microg/l) resulting in a maximum T4 supply of 0.3 microg/kg via ingested breast milk. In formula milk, the T4 concentration was equally low. Protease treatment did not influence the measured T4 concentrations. CONCLUSIONS: No differences in plasma thyroid hormone between breast milk-fed and formula-fed infants were found. The amount of T4 present in human milk and formula milk is too low to alter the hypothyroxinaemic state of preterm infants.

Effects of feeding high dosages of vitamin E to laying hens on thyroid hormone concentrations of hatching chicks.

Long-term experimental feeding of 20,000 ppm alpha-tocopheryl acetate to laying hens caused a significant (P < 0.05) decrease in hatching rates as compared to the control group, which was fed a diet containing 19 ppm alpha-tocopherol. When the thyroid hormones in the developing chicks were checked on incubation days 16, 19, 21, and 22, the following results were ascertained: During the latter part of incubation, increases in plasma concentrations of thyroxine and triiodothyronine were observed. No significant differences in hormone concentrations (P > 0.05) between the control and the treatment group were observed during incubation days 16, 19, and 22. However, on the day of hatching (day 21 of incubation) significantly lower (P < 0.05) triiodothyronine concentrations in chick embryos of piped eggs were found in the treatment group. Moreover, thyroxine concentrations in non-piped eggs and in hatched chicks were found to be significantly higher as compared to the control group. Given these results, one concludes that extremely high dosages of vitamin E may affect thyroid hormone concentrations of hatching chicks, and therefore, the chicks might be inhibited in pipping the egg shell. Hypothetically, the hepatic enzyme 5'-monodeiodinase is involved in the mechanism of inhibition.

In utero methylmercury exposure differentially affects the activities of selenoenzymes in the fetal mouse brain.

Pregnant ICR mice were subcutaneously injected with 0,5, or 3x3 mg Hg/kg of methylmercury (MeHg) on days 12,13, and 14(G12-14) of gestation and were sacrificed on G17. Activity of selenoenzymes, including glutathione peroxidase (GPx) and 5'- or 5-iodothyronine deiodinases (5'-DI, 5-DI), was determined in fetal brain and placenta. MeHg did not affect the concentration of Se in these tissues, while it significantly inhibited the activity of GPx in the fetal brain and placenta, but not in the maternal brain. Although the levels of thyroid hormones in the maternal and fetal plasma were not affected by MeHg, 5-DI decreased and 5'-DI increased in the fetal brain, as if they had responded to hypothyroidism. Because the level of T4 in the fetal plasma was not affected by MeHg, these changes in enzymatic activities may result in a harmful excess of T3 in the fetal brain. In addition, 5-DI activity was increased in the placenta of MeHg-treated mice. These effects of prenatal MeHg exposure on fetal and placental DIs differed from those of dietary-induced Se deficiency, where the activities of DIs were decreased or not affected. Further evaluation of the effect of MeHg on selenoenzymes, especially 5-DIs, is warranted.

Selenium deficiency alters thyroid hormone metabolism in guinea pigs.

In guinea pigs, activity of glutathione peroxidase in most organs is markedly lower than in organs of other rodents despite comparable dietary intakes and tissue levels of selenium. To determine if metabolism of selenium with respect to other selenoproteins also differs in guinea pigs, we measured the effects of selenium intake on thyroid hormone metabolism. Weanling male Hartley Albino guinea pigs were fed a selenium-deficient Torula yeast-based diet, or the same diet supplemented with 0.5 mg selenium/kg diet as sodium selenate for 72 d. Growth was impaired in guinea pigs fed the unsupplemented diet. Activity of glutathione peroxidase was higher in tissues and plasma of supplemented guinea pigs than in selenium-deficient animals. However, it was still far lower than reported values for other rodent species. In selenium deficiency, activity of type 1 5'-iodothyronine deiodinase was 60% less in liver and 45% less in kidney. Concentration of thyroxine was 68% lower in kidney of selenium-deficient animals, and levels of 3,3',5-triiodothyronine in kidney and plasma were 44 and 31% lower, respectively. Thus, with the exception of thyroxine concentrations, thyroid hormone metabolism responds to selenium deficiency in guinea pigs as it does in rats, although the magnitude of that response is not as great.

Effects of thyroid hormone deiodination on regulation of thyroid axis in undernourished rats.

The possible influence of hypothalamic and pituitary 5'-deiodinase II (5'-D-II) activity and 3,5,3'-triiodothyronine (T3) content on the modulation of thyroid-stimulating hormone (TSH) synthesis was studied. 1) Alterations in 5'-D-II activity and hypothalamic and pituitary T3 content produced by undernutrition were observed in fetal (21 days) and neonatal rats vs. controls. 2) After thyroidectomy, plasma TSH increased in both populations, undernourished and control, but pituitary TSH increased only in the former and not in the latter. The results obtained by giving small doses of thyroxine (T4; 0.5 micrograms/100 g body wt) to intact and thyroidectomized rats suggest a lower inhibitory effect by T4 on the pituitary in undernourished than in control rats. Although hypothalamic and pituitary 5'-D-II activity increased in both groups after thyroidectomy, the percentage increase was lower in undernourished vs. control rats, resulting in lower overall T3 content in tissues from undernourished animals. These studies on thyroid axis regulation show the in vivo regulation of TSH synthesis by hypothalamic and pituitary 5'-D-II activity and T3 content.