The Joint Effects of Bisphenols and Iodine Exposure on Thyroid during Pregnancy

The aim of this research was to study the combined effects of bisphenols and iodine exposure on the thyroid gland during pregnancy. We included 162 pregnant women from a cohort established in Shanghai. Urinary concentrations of bisphenol A, bisphenol B(BPB), bisphenol C(BPC), bisphenol F, bisphenol S, and bisphenol AF(BPAF) were examined. Bayesian kernel machine regression (BKMR) and quantile g-computation models were used. The geometric means of BPA, BPB, BPC, BPF, BPS, BPAF, and ΣBPs levels in urine were 3.03, 0.24, 2.66, 0.36, 0.26, 0.72, and 7.55 μg/g creatinine, respectively. We observed a positive trend in the cumulative effects of BPs and iodine on serum triiodothyronine (FT3) and free thyroxine (FT4), as well as a U-shaped dose-response relationship between BPs and the probability of occurrence of thyroperoxidase autoantibody positivity in women with low urinary iodine concentration. In addition, a synergistic effect on the probability of occurrence of thyroid autoantibody positivity was observed between BPF and BPB, as well as between BPC and BPAF in this study. There were adverse health effects on the thyroid after co-exposure to BPs and iodine. Even if pregnant women were exposed to lower levels of BPs, women with iodine deficiency remained vulnerable to thyroid autoimmune disease.

Screening for drugs potentially interfering with MCT8-mediated T3 transport in vitro identifies dexamethasone and some commonly used drugs as inhibitors of MCT8 activity

BACKGROUND

Monocarboxylate transporter 8 (MCT8) is the first thyroid hormone transporter that has been linked to a human disease. Besides genetic alterations other factors might impair MCT8 activity.

AIM

This study aimed at investigating whether some common drugs having a structural similarity with TH and/or whose treatment is associated with thyroid function test abnormalities, or which behave as antagonists of TH action can inhibit MCT8-mediated T₃ transport.

METHODS

[¹²⁵I]T₃ uptake and efflux were measured in COS-7 cells transiently transfected with hMCT8 before and after exposure to increasing concentrations of hydrocortisone, dexamethasone, prednisone, prednisolone, amiodarone, desethylamiodarone, dronedarone, buspirone, carbamazepine, valproic acid, and L-carnitine. The mode of inhibition was also determined.

RESULTS

Dexamethasone significantly inhibited T₃ uptake at 10 μM; hydrocortisone reduced T₃ uptake only at high concentrations, i.e. at 500 and 1000 μM; prednisone and prednisolone were devoid of inhibitory potential. Amiodarone caused a reduction of T₃ uptake by MCT8 only at the highest concentrations used (44% at 50 μM and 68% at 100 μM), and this effect was weaker than that produced by desethylamiodarone and dronedarone; buspirone resulted a potent inhibitor, reducing T₃ uptake at 0.1-10 μM. L-Carnitine inhibited T₃ uptake only at 500 mM and 1 M. Kinetic experiments revealed a noncompetitive mode of inhibition for all compounds. All drugs inhibiting T₃ uptake did not affect T₃ release.

CONCLUSION

This study shows a novel effect of some common drugs, which is inhibition of T₃ transport mediated by MCT8. Specifically, dexamethasone, buspirone, desethylamiodarone, and dronedarone behave as potent inhibitors of MCT8.

Bisphenol A and thyroid hormones: Bibliometric analysis of scientific publications

Bisphenol A (BPA) is a well-known endocrine-disrupting chemical which can cause potential health risks and interfere with thyroid hormones through multiple avenues. This study aimed to evaluate the hotspots and emerging trends on BPA and thyroid hormones by using a bibliometric method.Publications related on BPA and thyroid hormones were downloaded from Science Citation Index-Expanded database. Annual outputs, high yield journals, countries, institutions, authors and their cited times were summarized. In addition, keywords co-occurrence, burst references and citation networks were bibliometric analyzed.From 2000 to 2019, 418 articles were published. Both of the Environment International and Environmental Health Perspectives, United States, Chinese Academy of Sciences and Antonia M. Calafat were the most recorded journals, countries, institutions and authors, respectively. The main research area was Toxicology. In addition of the retrieve term "bisphenol-a" and "thyroid-hormone", "in-vitro", "exposure" and "endocrine disruptors", were the hotspot keywords and "triclosan", "oxidative stress" and "united-states" were the most recent trends keywords. "Thyroid hormone action is disrupted by Bisphenol A as an antagonist" published on The Journal of Clinical Endocrinology & Metabolism by Kenji Moriyama in 2002 got both the highest burst score and citation score. Six groups were clustered and the mechanism of BPA's effect on thyroid hormones, and the exposure of BPA and potential risks in children and pregnant women were the two main large fields.The number of publications in the field of BPA and thyroid hormones has increased tremendously since 2000. The research hotspot ranged from mechanism researches in animal models to epidemiological studies. "Thyroid hormone action is disrupted by bisphenol A as an antagonist" of Kenji Moriyama provided important building blocks in the field. The impact of BPA on thyroid hormones, especially pregnant women and children, was the latest research frontiers and might be the future direction of this filed in the following years.

Assessment of biotin interference in thyroid function tests

The aim of the study was to systematically characterize the interference of biotin on thyroid function tests and biotin washout periods.Ten healthy adults were recruited with administration of 5 and 10 mg/d biotin for 7 days. Analyte concentrations of thyroid function tests were measured at baseline prior to starting biotin and from 2 hours to 2 days after withdrawal of 5 and 10 mg/d biotin. The outcomes were compared the baseline with the several points after taking biotin at Roche cobas e602, Beckman UniCel DxI 800, and Abbott Architect 2000 immunoassay platforms, respectively.Ingesting 5 or 10 mg/d of biotin for 7 days could produce positive or negative interference among the thyroid function tests at Roche cobas e602 and Beckman UniCel DxI 800 systems, but no interference on Abbott Architect 2000. Interference duration of 5 mg/d biotin for Roche cobas e602 and Beckman UniCel DxI 800 of thyroid function tests lasted for 8 hours, while 10 mg/d biotin interfered with Roche cobas e602 or Beckman UniCel DxI 800 for 1 day or 2 days.This study provides valuable guidance on biotin washout periods at doses common in over-the-counter supplements necessary to avoid false assay results.Trial registration: ChiCTR1800020472.

Propranolol inhibits myocardial infarction-induced brown adipose tissue D2 activation and maintains a low thyroid hormone state in rats

Considering the recognized role of thyroid hormones on the cardiovascular system during health and disease, we hypothesized that type 2 deiodinase (D2) activity, the main activation pathway of thyroxine (T4)-to-triiodothyronine (T3), could be an important site to modulate thyroid hormone status, which would then constitute a possible target for β-adrenergic blocking agents in a myocardial infarction (MI) model induced by left coronary occlusion in rats. Despite a sustained and dramatic fall in serum T4 concentrations (60-70%), the serum T3 concentration fell only transiently in the first week post-infarction (53%) and returned to control levels at 8 and 12 weeks after surgery compared to the Sham group (P<0.05). Brown adipose tissue (BAT) D2 activity (fmol T4·min-1·mg ptn-1) was significantly increased by approximately 77% in the 8th week and approximately 100% in the 12th week in the MI group compared to that of the Sham group (P<0.05). Beta-blocker treatment (0.5 g/L propranolol given in the drinking water) maintained a low T3 state in MI animals, dampening both BAT D2 activity (44% reduction) and serum T3 (66% reduction in serum T3) compared to that of the non-treated MI group 12 weeks after surgery (P<0.05). Propranolol improved cardiac function (assessed by echocardiogram) in the MI group compared to the non-treated MI group by 40 and 57%, 1 and 12 weeks after treatment, respectively (P<0.05). Our data suggested that the beta-adrenergic pathway may contribute to BAT D2 hyperactivity and T3 normalization after MI in rats. Propranolol treatment maintained low T3 state and improved cardiac function additionally.

Cleavage Region Thyrotropin Receptor Antibodies Influence Thyroid Cell Survival In Vivo

Background: Graves' disease is associated with thyrotropin receptor (TSHR) antibodies of variable bioactivity. Recently, antibodies have been characterized that bind to the cleavage region of the TSHR ectodomain (C-TSHR-Ab), and their ability to induce thyroid cell apoptosis in vitro via excessive cell stress involving multiple organelles was demonstrated. Methods: To investigate the in vivo effects of C-TSHR-Ab, first a murine monoclonal antibody (mAb) directed against residues 337 to 356 of the TSHR cleavage region was developed, and then it was injected into mice. Results: These injections caused reduced serum total triiodothyronine and thyroxine and increased TSH levels compared to control mAb-injected mice. The C-TSHR-mAb induced histological evidence of endoplasmic reticulum stress, mitochondrial stress, and apoptosis in the thyroid glands. C-TSHR-mAb-mediated apoptosis was associated with cellular infiltrates consisting mostly of macrophages, dendritic cells, and neutrophils, while T- and B-lymphocytes were scarce. In addition, in the treated mouse thyroid tissue, hyper-citrullination of histone H3 was also found. This is known to occur via peptidylarginine deiminase 4 and plays an important role in the formation of neutrophil extracellular traps, which are likely to be partly responsible for thyroid infiltration, as seen in many autoimmune diseases. Examination of thyroid tissue from patients with Graves' disease also showed increased stress and some thyrocyte apoptosis compared to normal thyroid tissues. Conclusions: The fact that the C-TSHR-mAb induced accumulation of macrophages, neutrophils, and dendritic cells indicates that innate immunity plays a central role in shaping the adaptive immune response to the TSHR. In addition, this study provides further evidence that the hinge region of the TSHR ectodomain is intimately involved in the immune response in autoimmune thyroid disease.

Comparison of thyroid hormone disruption potentials by bisphenols A, S, F, and Z in embryo-larval zebrafish

Several structural analogues of bisphenol A (BPA), e.g., bisphenol F (BPF), bisphenol S (BPS), and bisphenol Z (BPZ), have been used as its substitutes in many applications and consequently detected in the environment, and human specimen such as urine and serum. While BPA has been frequently reported for thyroid hormone disruption in both experimental and epidemiological studies, less is known for the BPA analogues. In the present study, thyroid hormone disrupting effects of BPF, BPS and BPZ, were investigated, and compared with those of BPA, using embryo-larval zebrafish (Danio rerio). At 120 hpf, significant increases in T3 and/or T4 were observed in the larval fish following exposure to BPA, BPF, or BPS. Moreover, transcriptional changes of the genes related to thyroid development (hhex and tg), thyroid hormone transport (ttr) and metabolism (ugt1ab) were observed as well. Thyroid hormone (T4) disruption by BPF was observed even at the concentration (2.0 mg/L) lower than the effective concentration determined for BPA (>2.0 mg/L). Delayed hatching was observed by all tested bisphenols. Our results clearly show that these BPA analogues can disrupt thyroid function of the larval fish, and their thyroid hormone disruption potencies could be even greater than that of BPA. The concentrations which disrupt thyroid function of the larval fish were orders of magnitude higher than those occurring in the ambient environment. However, thyroid hormone disruption by longer term exposure and its consequences in the fish population, deserve further investigation.

Sorafenib-Induced Changes in Thyroid Hormone Levels in Patients Treated for Hepatocellular Carcinoma

CONTEXT

The pathogenesis of tyrosine kinase inhibitor-induced thyroid hormone (TH) alterations are still a matter of debate.

OBJECTIVE

The objective of this study was to determine the effects of sorafenib on TH levels in patients with hepatocellular carcinoma (HCC) and to evaluate possible mechanisms.

DESIGN

We performed a prospective cohort study between 2009 and 2016.

SETTING

This study was conducted at a tertiary referral center.

PATIENTS

This study included 57 consecutive patients with HCC who were treated with sorafenib.

MAIN OUTCOME MEASURE

Thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels were measured every 6 weeks, and extensive thyroid function tests (TFTs) were measured before treatment (t0), after 6 weeks (t6), and at the end of therapy. The effect of sorafenib on TH transport by monocarboxylate transporter (MCT)8 or MCT10 was tested in transfected COS1 cells.

RESULTS

Four patients (7%) developed thyroiditis. Among the other patients, 30% had elevation of TSH or FT4 above the normal range. Overall, between t0 and t6, mean TSH increased from 1.28 to 1.57 mU/L (P < 0.001) and mean FT4 from 18.4 to 21.2 pmol/L (P < 0.001). Simultaneously, the serum triiodothyronine (T3)/reverse triiodothyronine ratio and the (T3/thyroxine) ×100 ratio decreased. Sorafenib decreased cellular T3 uptake by MCT8 and to a lesser extent by MCT10.

CONCLUSIONS

These in vivo data suggest that sorafenib affects TFTs on multiple levels. Our in vitro experiments suggest a possible role of sorafenib-induced inhibition of T3 transport into the cell by MCT8 and MCT10.

Thyroxine increases Serca2 and Ryr2 gene expression in heart failure rats with euthyroid sick syndrome

OBJECTIVE

The current study was aimed at analyzing sarcoplasmic reticulum Ca2+ ATPase (Serca2) and ryanodine receptor type 2 (Ryr2) gene expression in rats subjected to surgery that induced HF and were subsequently treated with T4 using physiological doses.

MATERIALS AND METHODS

HF was induced in 18 male Wistar rats by clipping the ascending thoracic aorta to generate aortic stenosis (HFS group), while the control group (9-sham) underwent thoracotomy. After 21 weeks, the HFS group was subdivided into two subgroups. One group (9 Wistar rats) with HF received 1.0 µg of T4/100 g of body weight for five consecutive days (HFS/T4); the other group (9 Wistar rats) received isotonic saline solution (HFS/S). The animals were sacrificed after this treatment and examined for signs of HF. Samples from the left ventricles of these animals were analyzed by RT-qPCR for the expression of Serca2 and Ryr2 genes.

RESULTS

Rats with HF developed euthyroid sick syndrome (ESS) and treatment with T4 restored the T3 values to the Sham level and increased Serca2 and Ryr2 gene expression, thereby demonstrating a possible benefit of T4 treatment for heart function in ESS associated with HF.

CONCLUSION

The T4 treatment can potentially normalize the levels of T3 as well elevated Serca2 and Ryr2 gene expression in the myocardium in heart failure rats with euthyroid sick syndrome.

Increased Thyroid Hormone Activation Accompanies the Formation of Thyroid Hormone-Dependent Negative Feedback in Developing Chicken Hypothalamus

The hypothalamic-pituitary-thyroid axis is governed by hypophysiotropic TRH-synthesizing neurons located in the hypothalamic paraventricular nucleus under control of the negative feedback of thyroid hormones. The mechanisms underlying the ontogeny of this phenomenon are poorly understood. We aimed to determine the onset of thyroid hormone-mediated hypothalamic-negative feedback and studied how local hypothalamic metabolism of thyroid hormones could contribute to this process in developing chicken. In situ hybridization revealed that whereas exogenous T4 did not induce a statistically significant inhibition of TRH expression in the paraventricular nucleus at embryonic day (E)19, T4 treatment was effective at 2 days after hatching (P2). In contrast, TRH expression responded to T3 treatment in both age groups. TSHβ mRNA expression in the pituitary responded to T4 in a similar age-dependent manner. Type 2 deiodinase (D2) was expressed from E13 in tanycytes of the mediobasal hypothalamus, and its activity increased between E15 and P2 both in the mediobasal hypothalamus and in tanycyte-lacking hypothalamic regions. Nkx2.1 was coexpressed with D2 in E13 and P2 tanycytes and transcription of the cdio2 gene responded to Nkx2.1 in U87 glioma cells, indicating its potential role in the developmental regulation of D2 activity. The T3-degrading D3 enzyme was also detected in tanycytes, but its level was not markedly changed before and after the period of negative feedback acquisition. These findings suggest that increasing the D2-mediated T3 generation during E18-P2 could provide the sufficient local T3 concentration required for the onset of T3-dependent negative feedback in the developing chicken hypothalamus.

Mild Thyroid Hormone Insufficiency During Development Compromises Activity-Dependent Neuroplasticity in the Hippocampus of Adult Male Rats

Severe thyroid hormone (TH) deficiency during critical phases of brain development results in irreversible neurological and cognitive impairments. The mechanisms accounting for this are likely multifactorial, and are not fully understood. Here we pursue the possibility that one important element is that TH affects basal and activity-dependent neurotrophin expression in brain regions important for neural processing. Graded exposure to propylthiouracil (PTU) during development produced dose-dependent reductions in mRNA expression of nerve growth factor (Ngf) in whole hippocampus of neonates. These changes in basal expression persisted to adulthood despite the return to euthyroid conditions in blood. In contrast to small PTU-induced reductions in basal expression of several genes, developmental PTU treatment dramatically reduced the activity-dependent expression of neurotrophins and related genes (Bdnft, Bdnfiv, Arc, and Klf9) in adulthood and was accompanied by deficits in hippocampal-based learning. These data demonstrate that mild TH insufficiency during development not only reduces expression of important neurotrophins that persists into adulthood but also severely restricts the activity-dependent induction of these genes. Considering the importance of these neurotrophins for sculpting the structural and functional synaptic architecture in the developing and the mature brain, it is likely that TH-mediated deficits in these plasticity mechanisms contribute to the cognitive deficiencies that accompany developmental TH compromise.

Does selenium supplementation affect thyroid function? Results from a randomized, controlled, double-blinded trial in a Danish population

OBJECTIVE

Selenium is present in the active site of proteins important for thyroid hormone synthesis and metabolism. The objective of this study is to investigate the effect of selenium supplementation in different doses on thyroid function, under conditions of suboptimal dietary selenium intake.

DESIGN

The Danish PREvention of Cancer by Intervention with SElenium pilot study (DK-PRECISE) is a randomized, double-blinded, placebo-controlled trial. A total of 491 males and females aged 60-74 years were randomized to 100 μg (n=124), 200 μg (n=122), or 300 μg (n=119) selenium-enriched yeast or matching yeast-based placebo tablets (n=126). A total of 361 participants, equally distributed across treatment groups, completed the 5-year intervention period.

METHODS

Plasma samples were analyzed for selenium and serum samples for TSH, free triiodothyronine (FT3), and free thyroxine (FT4) at baseline, and after 6 months, and 5 years of supplementation.

RESULTS

Plasma selenium concentrations increased significantly and dose-dependently in treatment groups receiving selenium (P<0.001). Serum TSH and FT4 concentrations decreased significantly and dose-dependently by 0.066 mIU/l (P=0.010) and 0.11 pmol/l (P=0.015), respectively, per 100 μg/day increase, with insignificant differences between 6 months and 5 years. No significant effects were found for FT3 and FT3:FT4 ratio.

CONCLUSIONS

In euthyroid subjects, selenium supplementation minutely and dose-dependently affects thyroid function, when compared with placebo, by decreasing serum TSH and FT4 concentrations. Based on these findings, selenium supplementation is not warranted under conditions of marginal selenium deficiency. However, a role for selenium supplementation in the treatment of autoimmune thyroid diseases is still unresolved.

[Effect of selenium on serum TGAb, TMAb, FT3, FT4 and TSH of rats with excessive intake of iodine]

OBJECTIVE

To investigate the effect of selenium on the TGAb, TMAb, FT3, FT4 and TSH level of rats with excessive intake of iodine.

METHODS

Wistar rats were divided into three groups by random:normal control, high iodine group and high iodine plus selenium group. Rats in the high iodine plus selenium group were lavaged with sodium selenite for 10 weeks. The levels of serum TGAb, TMAb, FT3, FT4 and TSH were tested at different time of the experiment.

RESULTS

There were no significant change on levels of FT3, FT4 and TSH (P > 0.05). The levels of TGAb and TMAb in the high iodine group were increased slowly (P < 0.05), but no significant change was observed in the high iodine plus selenium group.

CONCLUSION

Excessive intake of iodine might induce goiter, and selenium might have antagonistic effect on it.

The effect of repeated amphetamine and cocaine administration on adrenal, gonadal and thyroid hormone levels in the rat plasma

Effects of acute and repeated administration of cocaine and amphetamine on adrenal, gonadal and thyroid plasma hormone levels were studied in male rats. Acute and repeated cocaine (15 mg/kg i.p. one dose, or once an hour for 3 hr for 8 days) enhanced the corticosterone level at 45 min after administration. Amphetamine (5 mg/kg i.p. one dose, or twice daily for 14 days) elevated the level of corticosterone after 2 hr. Acute amphetamine increased the progesterone, testosterone and androstenedione plasma levels, whereas acute cocaine had no effect on those parameters. Repeated psycho-stimulants decreased the level of androgens. Neither acute nor repeated administration of psychostimulants had any significant effect on the level of the thyroid hormone T3. The T4 plasma level decreased following repeated amphetamine only. The above results indicate that repeated psychostimulants enhance the activity of the hypothalamo-pituitary-adrenal (HPA) axis and lead to a decrease in the hypothalamo-pituitary-gonadal (HPG) axis activity. On the other hand, the hypothalamo-pituitary-thyroid (HPT) axis seems to be more resistant to the psychostimulant action.

Effect of difluoromethylornithine on thyroid function in rats

BACKGROUND

A variety of stimuli cause a rapid increase in polyamine synthesis by increasing an enzyme ornithine decarboxylase required for the biosynthetic pathway of protein synthesis. Difluoromethyl ornithine is a selective inhibitor of this enzyme and hence arrests cell replication strikingly. Its effects on thyroid gland are studied with respect to change in animal's weight and levels of Triiodothyronine, Thyroxine and Thyroid stimulating hormone. The study was conducted to evaluate the inhibitory effects of Di-fluoromethyl ornithine (DFMO) administration on polyamine metabolism of thyroid gland in rats.

METHODS

The study was conducted on rats weighing 248 to 320 grams, divided into control and DFMO treated group. A dose of 50 mg/rat was administered subcutaneously to the treated group for 5 consecutive days and placebo (normal saline) injections to control group. On sixth day, blood was collected by cardiac puncture and serum was separated. Serum T3, T4 and TSH were analyzed with the help of radioimmunoassay in both groups.

RESULTS

In treated group there was a fall in T3, T4 concentration with significant rise in TSH concentration as compared to control group.

CONCLUSION

DFMO (Difluoro methyl ornithine) decreases cellular proliferation of thyroid gland as is assessed by decrease in thyroid hormone levels. The hypothalamo pituitary thyroid axis however remains intact as is shown by a feedback rise in TSH concentration. DFMO can thus be employed for anti-neoplastic clinical trials on account of interference with activity of ODC (Ornithine Decarboxylase) fundamental for polyamine biosynthesis.

Polychlorinated biphenyls and thyroid hormones in adults: a systematic review appraisal of epidemiological studies

Reported evidence regarding relationships between polychlorinated biphenyls (PCBs) and thyroid homeostasis in adults has been considered contradictory. The objective of this systematic review is to determine a possible association between PCB exposure and the circulating thyroid hormones and thyrotropin (TSH) levels in adults, by analyzing the quality of published studies. A systematic review of epidemiological papers was conducted using PubMed. An evaluation of the quality of 22 studies was performed, and the papers were classified into two tiers: Tier I for studies with higher quality scores (eight) and Tier II for studies with lower quality scores (14). It appears that PCBs can interfere with thyroid hormone homeostasis; however epidemiological evidence is not entirely clear. For triiodothyronine (T3) and thyroxine (T4), Tier I studies showed either an inverse (four cases for T3; five cases for T4) or no significant association (two cases for T3; five cases for T4) with PCBs. In the case of free thyroxine and TSH, the Tier I papers observed no clear association with PCB levels. Rigorous study design, assessment of potential confounding factors, and fuller reporting of methods and results in future studies will facilitate understanding of whether PCB exposure is associated with changes in thyroid function.

Thyroid hormone homeostasis in brain: possible involvement of adrenergic phenomenon in adult rat

BACKGROUND

Imbalance in thyroid hormone concentrations has been linked with profound neurobehavioral alterations in the adult. Peripheral hypothyroidism is associated with a phenomenon of central thyroid hormone homeostasis in adult rat. This central homeostasis mechanism could be maintained by adrenergic interplay due to close physiological association between sympathetic nervous system activity and thyroid hormones. The central homeostasis is characterized by increased cerebrocortical synaptosomal T(3) content, deiodinase type II (DII) activity, and cAMP content.

METHODS

We injected specific alpha- and beta-adrenergic receptor (AR) agonists and antagonists along with an anti-thyroid drug to find out any AR-mediated action on central homeostasis.

RESULTS

The alpha(2)-AR agonist did not alter the onset of central homeostasis, but prolonged its duration. Similar prolongation was observed with alpha(2)-AR antagonist and beta-AR agonist, but these compounds amplified the normal anti-thyroid drug-induced rise in cerebrocortical T(3) content on the day of onset of central homeostasis. Injections of the beta-AR antagonist did not cause any perturbations. All these observations have been supported by parallel changes in cerebrocortical DII activity, cAMP and [Ca(2+)](i) content.

CONCLUSION

There emerges a close correlation between cerebral T(3) content, DII activity, cAMP and [Ca(2+)](i) content that are regulated by the AR system. Thus, thyroid hormone homeostasis in the adult mammalian brain is maintained primarily by the beta-adrenergic pathway along with an unexpected pharmacological involvement of the alpha-ARs.

Standardization of the perchlorate discharge assay for thyroid toxicity testing in rats

The perchlorate discharge assay (PDA) is potentially of high diagnostic value to distinguish between direct and indirect thyroid toxicity mechanisms, provided that standard treatment times are established and positive controls yield reproducible results. Therefore the PDA was evaluated after 2 and/or 4 weeks of treatment with positive control compounds in rats. Phenobarbital, Aroclor 1254 and beta-naphthoflavone (indirect toxic mechanism) enhanced thyroidal radioiodide accumulation, and the administration of potassium perchlorate had no effect on thyroid: blood (125)I ratio. Phenobarbital caused follicular cell hypertrophy and hyperplasia in the thyroid and centrilobular hypertrophy in the liver, without effects on serum triiodotyronine (T(3)), thyroxine (T(4)) levels. Thyroid-stimulating hormone (TSH) levels were moderately increased. Propylthiouracil (direct toxic mechanism) caused severe thyroid follicular cell hypertrophy and hyperplasia, reduced serum T(3) and T(4) levels and increased serum TSH levels, and reduced thyroidal radioiodide accumulation; perchlorate administration significantly reduced thyroid: blood (125)I ratio, demonstrating an iodide organification block. Potassium iodide (direct toxic mechanism) virtually blocked thyroidal radioiodide accumulation, without significant effects on serum T(3), T(4), and TSH levels and a microscopic correlate for higher thyroid weights. Thus, positive controls yielded reproducible results and we conclude that both the 2- and 4-week PDA is suitable to distinguish between direct and indirect thyroid toxicity mechanisms.

Influence of female sex hormones on thyroid parameters determined in a thyroid screening

This is a cross-sectional study with a non-randomly selected population to ascertain the influence of female sex hormones on thyroid function. TSH, TT4, FT4, TT3 and FT3 were determined in 251 women using either oral hormonal contraceptives or hormone replacement treatment, 255 women not taking either, and a control group of 900 men. Women with normal thyroid morphology using oral hormonal contraceptives in the pre-menopausal group had a significantly higher TT4 and TT3, and lower FT3, respectively, than both non-users and men. FT4 and TSH remained unchanged. In the peri-/post-menopausal group, thyroid function of women using hormone replacement treatment was not significantly different from non-users, but either women still had a significantly lower FT3 than men. We conclude that oral hormonal contraceptives and hormone replacement treatment increase TT4 and TT3 and do not influence FT4 and TSH. They decrease FT3 which is in contrast to what would be expected theoretically and what has been observed in earlier studies.

Effect of conjugated equine estrogens and tamoxifen administration on thyroid gland histomorphology of the rat

OBJECTIVE

The aim of this study was to evaluate the action of the conjugated equine estrogens and tamoxifen on the morphology of thyroid gland in ovariectomized (OVx) rats.

METHODS

Conjugated equine estrogens (CEE), clinically used as estrogen therapy, is a complex formulation containing multiple estrogens that decrease menopausal symptoms. Thirty ovariectomized rats were randomly divided into 3 treatment groups: GI, vehicle (propylene glycol); GII, CEE 200 microg/kg per day; and GIII, tamoxifen 1 mg/kg per day. Another group of 10 rats with intact ovaries (GIV) was included, treated with the vehicle, and sacrificed during estrous. All animals were treated by gavage for 50 days, after which they were sacrificed. Blood samples were collected, and the thyroid was removed for morphological analysis and PCNA evaluation through immunohistochemical study.

RESULTS

The thyroid follicular cell height was increased in animals treated with CEE (14.90 +/- 0.20 microm), with TAM (14.90 +/- 0.10 microm), and in rats with intact ovaries (15.10 +/- 0.50 microm) in comparison to that of the vehicle group (9.90 +/- 0.20 microm) (P < 0.001). The follicular area was larger in the CEE (2,225 +/- 51 microm2) and TAM (2,127 +/- 67 microm2) groups compared to that of the vehicle group (5,016 +/- 53 microm2). The levels of T4 and T3 in rats treated with CEE, with Tamoxifen and in rats with intact ovaries, were higher than those those in the vehicle group (P < 0.001). The PCNA index in the vehicle group was lower than in other groups.

CONCLUSION

Our data suggest that estrogen and tamoxifen administration has a proliferative effect on the thyroid.

Thiourea-induced thyroid hormone depletion impairs testicular recrudescence in the air-breathing catfish, Clarias gariepinus

We used thiourea-induced thyroid hormone depletion as a strategy to understand the influence of thyroid hormones on testicular recrudescence of the air-breathing catfish, Clarias gariepinus. Treatment with 0.03% thiourea via immersion for 21 days induced hypothyroidism (thyroid hormone depletion) as evidenced by significantly reduced serum T(3) levels. Thiourea-treated males had narrowed seminiferous lobules with fewer spermatozoa in testis, very little or no secretory fluid, reduced protein and sialic acid levels in seminal vesicles when compared to controls. The histological changes were accompanied by reduction in serum and tissue levels of testosterone (T) and 11-ketotestosterone (11-KT), a potent male specific androgen in fish. Qualitative changes in the localization of catfish gonadotropin-releasing hormone (cfGnRH) and luteinizing hormone (LH, heterologous system) revealed a reduction in the distribution of immunoreactive neuronal cells and fibers in thyroid depleted fish. Interestingly, thiourea-withdrawal group showed physiological and histological signs of recovery after 21 days such as reappearance of spermatozoa and partial restoration of 11-KT and T levels. These data demonstrate that thyroid hormones play a significant role in testicular function of catfish. The mechanism of action includes modulating sex steroids either directly or through the hypothalamo (GnRH)-hypophyseal (LH) axis.

The dioxin-like PCB 77 but not the ortho-substituted PCB 153 interferes with chicken embryo thyroid hormone homeostasis and delays hatching

The effects of the dioxin-like polychlorinated biphenyl (PCB) 77 and the ortho-substituted PCB 153 on thyroid hormone availability were investigated during the last week of embryonic development in chicken. High doses of these PCBs (1microg PCB 77 and 20microg PCB 153) were injected into chicken eggs at day 4 of incubation. Blood and tissue samples were collected from day 14 of incubation until 1 day after hatching. We did not observe influences of PCB 153 on thyroid hormone (TH) levels. Treatment with PCB 77, on the other hand, decreased plasma total T(4) concentrations but increased hepatic T(4) levels at day 14 of incubation. Later in development, at stages near the process of hatching, severe decreases of T(4) and T(3) levels were observed in the PCB 77 group, both in plasma and tissues. PCB 77 severely reduced the TH peak that normally coincides with the stage of internal pipping. This reduction was accompanied by a considerable delay in the moment of hatching. We conclude that the dioxin-like PCB 77, but not the ortho-substituted PCB 153, can decrease TH availability towards the end of embryonic development and hence disturb the process of hatching.

Guggulu (Commiphora mukul) potentially ameliorates hypothyroidism in female mice

The efficacy of guggulu, the gum resin of Commiphora mukul in regulating hypothyroidism was evaluated in female mice. In addition to estimating serum levels of thyroxine and triiodothyronine, hepatic 5' monodeiodinase, hepatic glucose-6-phospatase and lipid-peroxidation (LPO), the activities of the anti-oxidative enzymes, superoxide dismutase (SOD) and catalase (CAT), were investigated. While 6-n-propyl-2-thiouracil (PTU, 10.00 mg/kg/d for 30 days) induced hypothyroidism in mice, as evidenced by a decrease in thyroid hormone concentration and in hepatic 5'D-I activity, simultaneous administration of guggulu (200 mg/kg/d for 30 days) reversed this effect, indicating its potential to stimulate thyroid function. Although in PTU treated animals a marginal increase in hepatic LPO was observed, when simultaneously treated with guggulu, it was decreased. A parallel increase in the activity of endogenous antioxidants, SOD and CAT, in the latter group indicated the safe and antiperoxidative nature of the drug. These findings suggest the possible use of guggulu in the amelioration of hypothyroidism.

Effect of grazing pasture with a low selenium content on the concentrations of triiodothyronine and thyroxine in serum, and GSH-Px activity in erythrocytes in cows in Chile

AIM

To determine the effect of grazing pasture that had a low selenium (Se) concentration on serum concentrations of triiodothyronine (T3) and thyroxine (T4), and erythrocyte glutathione peroxidase (GSH-Px) activity in dairy cows.

METHODS

Forty pregnant Friesian cows were grazed on pasture that contained 0.03-0.04 ppm Se on a dry matter (DM) basis. Two months before parturition, 20 cows were randomly selected and treated with 1 mg Se/kg bodyweight subcutaneously, as barium selenate (Group Se-S). The other group (Se-D) was not supplemented. Blood samples were taken before supplementation (-60 days) and 30, 60, 90, 180 and 270 days after parturition, for determination of concentrations of T3 and T4 in serum, and GSH-Px activity in erythrocytes.

RESULTS

Erythrocyte GSH-Px activity in the Se-D group was <60 U/g haemoglobin (Hb) throughout the experiment. Supplementation increased (p<0.05) activities to >130 U/g Hb throughout lactation. Mean serum concentrations of T4 in Se-D and Se-S cows increased from 23.7 (SEM 0.7) and 23.4 (SEM 0.8) nmol/L, respectively, in the prepartum period to 69.6 (SEM 0.1) and 67.6 (SEM 0.2) nmol/L, respectively, at 180 days of lactation (p<0.01), and no effect of Se supplementation was evident. Serum concentrations of T3 in Se-D cows decreased (p<0.05) from 1.6 (SEM 0.1) nmol/L prepartum to 1.0 (SEM 0.2) nmol/L at the beginning of lactation, and remained lower (p<0.05) than those in the Se-S cows which did not decrease after calving and ranged from 1.9 (SEM 0.1) to 2.4 (SEM 0.2) nmol/L throughout lactation.

CONCLUSIONS

Serum T3 concentrations decreased during early lactation in unsupplemented cows grazing pastures low in Se (0.03-0.04 ppm) and both serum T3 and erythrocyte GSHPx activities were consistently lower throughout lactation compared with Se-supplemented cows. Se supplementation had no effect on serum T4 concentrations.

L’iode 131 comme traitement des goitres bénins

INTRODUCTION

In order to evaluate the efficacy of 131 Iodine on goitre volume and on thyroid function, we studied a cohort of patients exhibiting a multinodular and toxic or non toxic goitre.

METHODS

This retrospective study was conducted at the Marc Linquette clinic in Lille, in collaboration with the department of nuclear medicine. Thirty-eight patients treated with 131 Iodine were included from 1995 to 2001. Clinical examination and serum analyses including TSH, free T4 and T3, anti-thyroid peroxidase and anti-thyroglobulin antibodies and TSH-receptor antibodies measurements were conducted on inclusion and then at 3, 6, 12 and 72 months. The activity of 131 Iodine corresponded to a standard dose or was calculated according to Marinelli's method. We excluded patients who had not undergone assessment at the above-mentioned time schedules.

RESULTS

The treatment was indicated in 30 patients presenting with a non compressive but toxic goitre, in 5 patients with a toxic compressive goitre and in 3 patients with a compressive but non-toxic goitre. Surgery had been excluded for all these patients because of their age, their cardiac status or because they had refused surgery after failure with prior partial thyroidectomy or medical treatment. Among the toxic goitres, TSH levels were low and T3 and T4 increased in 17 patients. In the 18 others, hyperthyroidism was manifested by an isolated decrease of TSH. The thyroid volume before treatment, assessed in 20 patients, was of 18 to 135 cm3 (mean: 53 cm3). Treatment consisted in administration of radioactivity of 3 to 30 mCi in 30 patients and standard activity of 20 to 25 mCi in 8. Functional efficacy with reduction in hyperthyroidism was noted after 3 months, and corrected in nearly all patients after 1 year, and morphological efficacy, with a mean decrease of 33.5% in the size of the goitres. No supplementary surgery was required, notably for the initially compressed goitres. Immediate and long term tolerance was satisfactory.

CONCLUSION

Metabolic 131Iodine radiotherapy is effective for the functional and morphological treatment of goitres with good tolerance and few side effects. 131 Iodine is a reasonable alternative in cases with absolute or relative contraindication for surgery.

The hairless promoter is differentially regulated by thyroid hormone in keratinocytes and neuroblastoma cells

The hair cycle is an extraordinarily complex process relying on spatially and temporally coordinated integration of intercellular signaling, cell division and death, cell migration, and gene expression. The hairless gene (hr) is expressed with hair-cycle-dependent kinetics, and pathogenic mutations in hr are responsible for the hairless and rhino phenotypes in mice and atrichia with papular lesions in humans. In addition to its expression in the skin and hair follicle, hr is also highly expressed in the brain, yet the factors governing its differential cell-type-specific expression have not yet been defined. A thyroid hormone responsive element was previously identified in the rat hr promoter which confers thyroid hormone (T3) responsiveness to heterologous promoter constructs; however, prior studies have not focused on the hr promoter itself. The hairless promoter was cloned, and it is shown that the hr promoter is transactivated by T3 in neuroblastoma cells but not in keratinocytes. Therefore, while T3 has a significant role in the regulation of neuronal expression of hairless, its upregulation in keratinocytes is T3 independent. Furthermore, hr is subject to cell-type-specific negative autoregulation, inhibiting the activity of its own promoter in keratinocytes but not neuroblastoma cells. These findings illustrate a molecular distinction between the regulation of hr expression in defined cell populations.

Prenatal programming of adult thyroid function by alcohol and thyroid hormones

Increasing evidence associates environmental challenges early in life with permanent alterations of physiological functions in adulthood. These changes in fetal environment can trigger physiological adaptations by the fetus, called fetal programming, which may be beneficial before birth but permanently influence the physiology of the organism. In this study, we investigated the potential connection between alcohol-induced decreased maternal thyroid function and the hypothalamic-pituitary-thyroid (HPT) function of adult rat offspring. Plasma 3,5,3'-triiodothyronine (T(3)), thyroxine (T(4)), and thyroid-stimulating hormone (TSH) levels were decreased in alcohol-consuming (E) dams on gestational day 21 compared with ad libitum- (C) and pair-fed (PF) controls. No significant differences were found in HPT function in young offspring (3 wk of age) between diet groups. However, adult fetal alcohol-exposed (FAE) offspring had significantly decreased levels of T(3) along with elevated TSH compared with control offspring. T(4) administration to the mother did not normalize the hypothyroid state of the adult FAE offspring. Interestingly, administration of T(4) to control pregnant dams decreased plasma T(3) of the adult female offspring only, whereas T(4) together with maternal alcohol consumption or pair-feeding led to decreased TSH and T(4) in the adult female offspring. Our results suggest that ethanol consumption and T(4) administration alter maternal HPT function, leading to prenatally programmed permanent alterations in the thyroid function of the adult offspring.

Enhanced rat Hershberger assay appears reliable for detection of not only (anti-)androgenic chemicals but also thyroid hormone modulators

Development of an internationally recognized standard for the Hershberger assay as a screening tool to detect potential (anti-)androgenic chemicals is in progress. In the present preliminary study, we evaluated the reliability of the enhanced Hershberger assay to detect thyroid hormone modulating activity, while concentrating attention on possible confounding influence on evaluation of (anti-)androgenic activity. Castrated or testosterone propionate (TP; 0.2 or 0.25 mg/kg/day)-injected castrated male Crj:CD(SD) IGS rats (seven weeks of age) were dosed for 10 days by oral gavage with vehicle (corn oil) or the following chemicals: propylthiouracil (PTU; 2.5 mg/kg/day), a potent inhibitor of thyroid hormone synthesis, phenobarbital (PB; 125 mg/kg/day) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE; 100 mg/kg/day), two hepatic enzyme inducers that enhance the clearance of thyroid hormones. PTU markedly increased thyroid weights, and decreased serum T3 and T4, and increased serum TSH, also causing marked microscopic alteration of the thyroid gland. In comparison, PB and p,p'-DDE only significantly affect serum T4 and revealed some histopathological findings. The alterations appeared to be more robust in the presence of TP. Furthermore, data for p,p'-DDE demonstrated its anti-androgenic effects, whereas PTU and PB had little or no effects on the weights of androgen-related accessory glands/tissues: the ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, glans penis, Cowper's glands, and levator ani plus bulbocavernosus (LABC) muscles. Weight of the LABC muscles was decreased by PB treatment in TP-treated castrated rats. These findings in the present study suggests that the enhanced Hershberger assay, with evaluation of thyroid histopathology and weights, and hormone levels, appears to be reliable for screening for not only (anti-)androgenic chemicals but also thyroid hormone modulators. In order to evaluate whether the sensitivity and specificity of such a thyroid assay is great enough for routine screening purposes, future experiments including dose-response studies using lower dose levels have to be performed.

Detection of endocrine-modulating effects of the antithyroid acting drug 6-propyl-2-thiouracil in rats, based on the “Enhanced OECD Test Guideline 407”

The antithyroid acting drug propylthiouracil (PTU) was administered to male and female Wistar rats at 0, 0.1, 1, or 10mg/kg body weight for 4 weeks according to the draft protocol of the "Enhanced OECD Test Guideline 407" (enhanced TG 407) in order to investigate its suitability to detect endocrine-mediated effects. The study was conducted with two identical subsets of five animals per sex and dose each to provide data on sensitivity. The modified protocol includes the investigation of additional organ weights, pathology, and histopathology, of thyroid hormones, of spermatozoa, and of estrus cycle. At time of sacrifice, all females were in the diestrus stage as prescribed. Adverse effects were observed in the thyroid gland (hypertrophy/ hyperplasia) and the pituitary gland (hyperplasia of basophilic cells, hypoplasia of acidophilic cells) together with dose-related decreased serum triiodothyronine (T3) and thyroxine (T4) levels and increased thyroid stimulating hormone (TSH) levels. Other effects of PTU included decrease of organ weights, anaemia, impaired blood coagulation, and reduced activity of enzymes. Hence, some of the additional examined endpoints of the enhanced TG 407, e.g., examination of pituitary gland and thyroid hormones, were suitable to detect endocrine-modulating effects of propylthiouracil. Treatment of five animals provides sufficient sensitivity to detect the described adverse effects of propylthiouracil. The enhanced TG is currently under investigation in several laboratories, evaluation of all the results will allow determining its practicability as well as the most suitable additional endpoints.

The combined effects of Trigonella and Allium extracts in the regulation of hyperthyroidism in rats

The combined effects of Trigonella foenum-graecum and Allium sativum extracts were evaluated for their ameliorative potential in the L-thyroxine-induced hyperthyroidic rat model to contribute to an understanding of interaction between the two extracts. The investigation was carried out using two different doses. A comparison was made with the response of individual plant extracts at the previously studied effective dose in adult Wistar rats rendered hyperthyroidic by daily injections of L-thyroxine (300 microg/kg body wt., s.c.). Propylthiouracil (PTU), an antithyroid drug, was used as a reference compound. Alterations in serum triiodothyronine (T3), thyroxine (T4), glucose, hepatic glucose-6-phosphatase (G-6-Pase) and oxygen consumption were studied as end parameters. Superoxide dismutase (SOD), catalase (CAT) activities, lipid peroxidation (LPO) and reduced glutathione (GSH) were examined to reveal any toxic effects of the drugs. The combined effects of Trigonella and Allium at 200 and 500 mg/kg body wt. respectively, were equipotent as compared to the individual extracts in lowering the serum concentrations of T3 and T4 in hyperthyroidic rats. Our findings reveal that some plant extracts in combination may not always prove to be synergistic. It is therefore suggested that Trigonella foenum-graecum and Allium sativum extracts may be used individually and not together in the regulation of hyperthyroidism.

Effect of Non-Steroidal Aromatase Inhibitor on Blood Plasma Ovarian Steroid and Thyroid Hormones in Laying Hen (Gallus domesticus)

HyLine Brown laying hens at 30 weeks of age were treated twice daily with Fadrozole, a non-steroidal aromatase inhibitor (AI; 1 mg/kg body weight; i.m.) for six consecutive days; control hens received saline. Blood was collected every day 0.5 h after oviposition, i.e. just before AI treatment. Ovarian steroids: progesterone (P4), testosterone (T) and estradiol (E2), and iodothyronines: thyroxine (T4), triiodothyronine (T3) and reverse-triiodothyronine (rT3) were measured in blood plasma by radioimmunoassay methods. In AI-treated hens a gradual delay in oviposition time was observed. AI significantly decreased P4 and E2 levels, maximally by 43% on day 4 and by 74% on day 5, respectively, and elevated T level, maximally by 248% on day 4. Simultaneously, the increases in T4 and T3 levels with no changes in rT3 levels were observed. The maximal effect of AI on T4 and T3 levels was found on day 4 (60% increase) and day 5 (312% increase), respectively. Moreover, statistically significant, negative coefficient of correlation between E2 and T3 (r = -0.51), and positive coefficient of correlation between T and T3 (r = 0.42) in AI-treated hens were found. The results obtained indicate that in mature laying hens there is a strong relationship between ovarian steroids and thyroid hormones, and suppression of E2 synthesis not only disrupts ovarian function but also affects the activity of the thyroid gland and peripheral metabolism of thyroid hormones.

Piperine lowers the serum concentrations of thyroid hormones, glucose and hepatic 5'D activity in adult male mice

Piperine, the main alkaloid of Piper nigrum fruits, was evaluated for its thyroid hormone and glucose regulatory efficacy in adult male Swiss albino mice. Its daily oral administration (2.50 mg/kg) for 15 days lowered the serum levels of both the thyroid hormones, thyroxin (T (4)) and triiodothyronine (T (3)) as well as glucose concentrations with a concomitant decrease in hepatic 5'D enzyme and glucose-6-phospatase (G-6-Pase) activity. However, no significant alterations were observed in animals treated with 0.25 mg/kg of piperine in any of the activities studied except an inhibition in serum T (3) concentration. The decrease in T (4), T (3) concentrations and in G-6-Pase were comparable to that of a standard antithyroid drug, Proylthiouracil (PTU). The hepatic lipid-peroxidation (LPO) and the activity of endogenous antioxidants, superoxide dismutase (SOD), and catalase (CAT) were not significantly altered in either of the doses. It appears that the action of P. nigrum on thyroid functions is mediated through its active alkaloid, piperine. We also suggest that a higher dose of piperine may inhibit thyroid function and serum glucose concentration in euthyroid individuals.

Response of dogs to short-term infusions of carbohydrate- or lipid-based parenteral nutrition

Parenteral nutrition (PN) is used to support intensive care patients. The risk for adverse metabolic effects depends on the composition of infused solutions and the duration of application. The present study in dogs compares metabolic and endocrine effects of two infusion solutions, with either triglycerides or glucose being the major energy sources, administered in a comparatively short infusion period (10 h/day). PN was administered for 9 days to two groups of five adult dogs to meet energy maintenance requirements. In group PN-LIP 61% of the total energy was derived from lipids and 22% from carbohydrates, compared with 21 and 62% in group PN-GLUC. Among routine haematology and clinical chemistry the plasma levels of glucose, triglycerides, insulin, insulin-like growth factor-I (IGF-I), glucagon, 3,5,3'-triiodothyronine and thyroxin were measured in non-infused dogs and at 2, 4, 6, and 8 h after the start of infusion at days 2 and 8 of the study. Infusions protocols did not cause gross metabolic aberrations. During the actual infusions glucose, triglyceride and insulin concentrations were elevated, each depending on the infusion solution. Concentrations of IGF-I, glucagon, 3,5,3'-triiodothyronine, thyroxin and cortisol did not change significantly. In conclusion short infusion periods of 10 h per day were tolerated by healthy dogs without adverse signs, which could improve practicability of PN also in clinical cases.

Postnatal exposure of 2,2',3,3',4,6'-hexachlorobiphenyl and 2,2',3,4',5',6-hexachlorobiphenyl on sperm function and hormone levels in adult rats

Polychlorinated biphenyls (PCBs) are known to affect reproductive system in animals and in accidentally or occupationally exposed humans. Information is lacking on effects of non-dioxin like chlorinated biphenyls (CB) congeners on male reproduction. The aim of this study is to determine whether treatment of postnatal non-dioxin like CB congeners affects sperm function and hormone levels in rats. Male Sprague-Dawley rats received either 2,2',3,3',4,6'-hexachlorobiphenyls (CB 132) or 2,2',3,4',5',6-hexachlorobiphenyls (CB 149) by ip injection of 9.6 or 96 mg/kg at day 21. At 16 weeks, the animals were sacrificed; sperm quality and hormone levels were measured. Body weight, testis and cauda epididymis weights, sperm counts, ROS generation, acrosome reaction rate, serum thyroxine (T(4)), free T(4) and testosterone (TT) concentrations were unaffected. However, treatment of CB 132 and CB 149 caused decreases in sperm motility, curvilinear velocity (VCL), average path velocity (VAP), straight-line velocity (VSL), amplitude of lateral head displacement (ALH) and beat cross frequency (BCF). Serum triiodothyronine (T(3)) level was significantly decreased in CB 132 9.6 mg/kg dose group compared with the controls. On the other hand, a significant decrease was found in free T(3) concentration both in 96 mg/kg of CB 132 and CB 149 groups. In summary, this study showed that CB 132 and CB 149 affects serum levels of triiodothyronine as well as sperm motility, velocity and capability of penetrating oocytes. The mechanism of action and potential effects on human warrant further investigation.

Effect of alloxan and insulin immunoneutralization on circulating thyroid hormone levels in larval landlocked sea lampreys, petromyzon marinus

The effects of alloxan, an insulin (INS)-secreting cell toxin, and INS immunoneutralization on circulating levels of thyroid hormones (thyroxine, T(4); triiodothyronine, T(3)) were examined in larval landlocked sea lampreys, Petromyzon marinus. Animals were injected intraperitoneally with either (Experiment 1) saline (0.6%) or alloxan (20 or 200 microg/g body weight), or with (Experiment 2) normal rabbit serum or anti-lamprey INS. Alloxan (200 microg/g) decreased plasma T(3), but not T(4), in larvae by about 45-80%. Three, six, or nine hr after acute immunoneutralization of lamprey INS with anti-lamprey INS, plasma T(3) levels decreased by 13-30%, relative to controls. These data indicate that INS deficiency can regulate the thyroid system of larval lampreys. There is some suggestion that INS may mediate the metamorphic processes by modulating thyroid hormone concentrations.

Effects of propylthiouracil and bromocryptine on serum concentrations of thyrotrophin and thyroid hormones in normal female horses

REASONS FOR PERFORMING STUDY

There exists a need for better diagnostic tests to characterise thyroid disease in horses. Currently available diagnostic tests fail to differentiate between thyroid gland disorders and thyroid abnormalities resulting from pituitary or hypothalamic problems.

OBJECTIVES

To evaluate the effects of treatment with propylthiouracil (PTU) and bromocryptine (BROM) on serum concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3) and equine thyroid-stimulating hormone (e-TSH, thyrotrophin) in mature horses.

METHODS

Healthy mature horses were treated using either PTU or BROM for 28 days. The effect of treatment on the thyroid axis was assessed by measuring T3, T4, rT3 and e-TSH before and at +14 and +28 days. The effect of PTU and BROM on the response of T3, T4, rT3 and e-TSH to thyrotrophin-release hormone (TRH) administration was also assessed before and at +14 and +28 days of treatment.

RESULTS

Treatment with PTU led to a significant reduction in serum concentrations of T3, T4 and rT3 on Day 28 and increase of e-TSH on Day 28 (P < 0.05). Treatment with BROM did not cause any measurable effect on serum concentrations of T3, T4, rT3 or e-TSH. The percentage increment by which serum concentration of T4, T3 and e-TSH increased following stimulation with TRH was decreased by treatment with PTU for 28 days (P < 0.05) but were not affected by treatment with BROM for 28 days.

CONCLUSIONS

These results suggest that 1) treatment with PTU may be used in horses as a model of primary hypothyroidism; 2) the use of BROM as a model of secondary hypothyroidism in horses is not supported; and 3) e-TSH assay deserves further investigation for the clinical diagnosis of thyroid axis dysfunction in horses.

POTENTIAL RELEVANCE

Propylthiouracil effectively causes primary hypothyroidism. There is substantial variability between horses with respect to their sensitivity to this substance when administered orally. Further studies pertaining to the characterisation of equine thyroid disorders are warranted and the use of both PTU for the experimental induction of primary hypothyroidism and e-TSH for the diagnostic characterisation of thyroid disorders in horses should be considered.

Hormonal, morphological, and physiological responses of yellow perch (Perca flavescens) to chronic environmental metal exposures

The effects of a chronic environmental exposure to metals on the hormonal, physiological, and reproductive status were assessed in yellow perch (Perca flavescens) sampled in six lakes situated along a contamination gradient of Cd, Zn, Cu, Pb, and Ni in the mining region of Rouyn-Noranda, Québec. Fish were captured in the summer and fall, and sampled before or after a confinement of one hour. Metal concentrations in the kidneys and the interrenal tissues (homologous to mammalian adrenals) were measured to compare tissue-specific metal accumulation. An exposure-related decrease of condition factor, gonadosomatic index (GSI), branchial Na+/K(+)-ATPase activity, plasma thyroxine (T4), triiodothyronine (T3), and 17 beta-estradiol and an impaired capacity to enhance cortisol levels after confinement were observed. Fish from the metal-contaminated lakes possessed gonads at less mature stages and exhibited structural alterations of their gills, interrenal cells, and thyroid follicle epithelium. A comparison of the morphological, biochemical, and physiological endpoints measured in the present study revealed that plasma concentrations of hormones and parameters of gill function were the most affected by metal contamination. The results of this study indicate that lifelong exposures to sublethal concentrations of metals alter the physiological functions of fish and delay reproduction.

[Influence of topically applied iodides on urinary iodine excretion and thyroid function]

PURPOSE

The present study was undertaken, to evaluate whether ophthalmic drug, containing iodine applied to conjunctival sac might result in a significant increase of urine iodine excretion and thus might be indirectly associated with the risk of iodine-induced hyperthyroidism. The aim of the study was to examine the occurrence of biochemically relevant changes in urine iodine excretion and in thyroid function after topical administration of ophthalmic drug containing iodine.

MATERIAL AND METHODS

In the study twenty-two patients without a history of thyroid disease were examined. The Vitreolent (Ciba Vision) was applied topically to conjunctival sac four times a day for one month. The urinary iodine excretion, using "Rapid Urinary Iodine Test" (Merck KgaA) and parameters of thyroid function (TSH, FT3, FT4) were measured before starting and after therapy.

RESULTS

The data showed, that was a significant increase in urinary iodine excretion at the end of therapy; as far as thyroid function was concerned, neither changes in level of TSH nor thyroid hormones were observed.

Effects of sertraline treatment on plasma cortisol, prolactin and thyroid hormones in female depressed patients

The aim of the study was to evaluate the effects of 4 and 24 weeks of sertraline treatment (average dose 42.5 mg/day) on plasma hormone levels in 15 female patients with major depression. Baseline levels of triiodothyronine (T(3)) were lower, while cortisol, prolactin (PRL), thyroid-stimulating hormone (TSH), and thyroxin (T(4)) levels did not differ from the values in 16 female controls. There was a positive correlation between the scores on the Montgomery-Asperg Depression Rating Scale and baseline cortisol levels. Treatment with sertraline for 4 weeks increased plasma cortisol levels, while 24 weeks of sertraline treatment increased plasma T(3) levels in depressed patients. Neither 4, nor 24 weeks of sertraline treatment affected PRL, T(4) and TSH levels in depressed patients. The data show different and time-dependent effects of sertraline treatment on plasma cortisol, PRL and thyroid hormones in female depressed patients.

Symptomatic hyperthyroidism in a patient taking the dietary supplement tiratricol

An 87-year-old woman was referred for evaluation of nervousness, tremor, insomnia, and fatigue of 2 months' duration. Initial laboratory evaluation revealed a suppressed thyrotropin level and an elevated triiodothyronine level. A review of her medications revealed that she had started taking several dietary supplements at the recommendation of her chiropractor before the onset of symptoms. One of these was tiratricol (3,5,3'-triiodothyroacetic acid or Triac), a substance sold as a dietary supplement despite classification as a drug by the Food and Drug Administration. Tiratricol has weak thyromimetic effects, can inhibit pituitary thyrotropin secretion, and in higher doses can significantly stimulate metabolism. Such was the case with this patient who presented with signs, symptoms, and biochemical evidence of hyperthyroidism that promptly resolved after discontinuation of tiratricol therapy. To our knowledge, this is the first reported case of documented thyrotoxicosis secondary to tiratricol use. Because tiratricol is still available for sale on several Internet sites, this case emphasizes the importance of inquiring about the use of dietary supplements in all patients. The availability of such products on the Internet increases the already complex task of monitoring patients' use of dietary supplements.

Effect of freeze dried extract of Olea europaea on the pituitary-thyroid axis in rats

The effect of an aqueous extract of olive (Olea europaea) leaf on the thyroid activity was studied. The results suggest a stimulatory action of the extract on the thyroid, unrelated to the pituitary.

Thyroid-stimulating hormone in adult euthyroid and hypothyroid horses

The purpose of this study was to validate a thyroid-stimulating hormone (TSH) assay in a model of equine hypothyroidism. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in 12 healthy adult mares and geldings, aged 4 to greater than 20 years. before and during administration of the antithyroid drug propylthiouracil (PTU) for 6 weeks. Serum concentrations of equine TSH, total and free thyroxine (T4), and total and free triiodothyronine (T3) were measured. Before PTU administration, mean +/- standard deviation baseline concentrations of TSH were 0.40 +/- 0.29 ng/mL. TSH increased in response to TRH, reaching a peak concentration of 0.78 +/- 0.28 ng/mL at 45 minutes. Total and free T4 increased from 12.9 +/- 5.6 nmol/L and 12.2 +/- 3.5 pmol/L to 36.8 +/- 11.4 nmol/L and 23.1 +/- 5.9 pmol/L, respectively, peaking at 4-6 hours. Total and free T3 increased from 0.99 +/- 0.51 nmol/L and 2.07 +/- 1.14 pmol/L to 2.23 +/- 0.60 nmol/l and 5.78 +/- 1.94 pmol/L, respectively, peaking at 2-4 hours. Weekly measurements of baseline TSH and thyroid hormones during PTU administration showed that total and free T, concentrations fell abruptly and remained low throughout PTU administration. Total and free T4 concentrations did not decrease dramatically until weeks 5 and 4 of PTU administration, respectively. A steady increase in TSH concentration occurred throughout PTU administration, with TSH becoming markedly increased by weeks 5 and 6 (1.46 +/- 0.94 ng/mL at 6 weeks). During weeks 5 and 6 of PTU administration, TSH response to TRH was exaggerated, and thyroid hormone response was blunted. Results of this study show that measurement of equine TSH in conjunction with thyroid hormone measurement differentiated normal and hypothyroid horses in this model of equine hypothyroidism.

The hypothalamo-pituitary-thyroid (HPT) axis: a target of nonpersistent ortho-substituted PCB congeners

Coplanar polychlorinated biphenyls (PCBs) cause adverse effects in developing and adult animals. Less is known about the effects of nonplanar ortho-substituted PCBs. We investigated the effects of 2 nonplanar PCB congeners, 95 (2,3,6-2',5'-penta CB) or 101 (2,4,5-2',5'-penta CB), and estradiol on selected endocrine parameters. In Study 1, weanling female Sprague-Dawley (S-D) rats were given a single dose of PCB 95 ip at 4, 8, 16, and 32 mg/kg/day for 2 consecutive days and killed 24 h after the last dose. PCB 95 exposure caused a dose-dependent (p < 0.001) decrease in serum thyroxine (T4) levels. Serum thyroid stimulating hormone (TSH) concentrations did not change, but prolactin (PRL) levels increased in a nonlinear (with dose) manner. No significant changes were seen in thyroid gland morphology and pituitary lactotroph number. In Study 2, progression or regression of effects was assessed by lengthening the time and a second congener was tested. Weanling female S-D rats received a single dose of PCB 95 or PCB 101 ip at 16 and 32 mg/kg/day for 2 days and were killed 48 h after the last dose. PCB 95 and PCB 101 both decreased serum T4 (p < 0.001) and hypothalamic dopamine (DA; p < 0.05) levels. No changes were seen in serum triiodothyronine (T3), TSH, and PRL concentrations. Morphological analysis of the thyroid gland showed a decrease (p < 0.05) in colloid area in rats treated with PCB 95 or 101. However, the epithelial cell height increased only in PCB 95 treated rats. Thyroid epithelial cell proliferation increased (p < 0.05) following exposure to estradiol and PCB 95. The results suggest that the HPT axis appears to be a target of ortho-substituted PCBs. PCB 95 was more effective than PCB 101 in causing these changes.

Abnormal serum free thyroid hormone levels due to heparin administration

Fractionated or unfractionated heparin may produce artefactual elevation in measured concentrations of free thyroid hormones. Although the specific cause is unknown, it may be a consequence of displacement of thyroid hormones from their binding sites by free fatty acids liberated in vitro. We describe four cases of heparin-induced abnormalities in free thyroid hormone measurements where some diagnostic confusion was generated. Increasing physician awareness of this poorly appreciated entity may avert diagnostic confusion and unnecessary investigation.

Influence of hypothyroid state on 45Ca(2+) influx and sensitivity of rat uterus to nifedipine and diltiazem

The influence of methimazole-induced hypothyroidism on spontaneous rhythmic contractions and Ca2+ channel function of rat uterus was examined. Hypothyroidism significantly reduced the amplitude and frequency of spontaneous rhythmic contractions. Nifedipine (10(-12)-10(-6) M) and diltiazem (10(-9)-10(-4) M) caused concentration-related inhibition of the myogenic responses of the oestrogenised rat uterus obtained from both eu- and hypothyroid rats. However, nifedipine was less potent (IC(50); 5.4 x 10(-9) M; n=6) in hypothyroid rat uterus as compared to euthyroid controls (IC(50): 8.13 x 10(-12) M; n=9) to inhibit the rhythmic contractions. Similarly, diltiazem was less potent (IC(50): 4.57 x 10(-6) M; n=9) to inhibit the uterine spontaneous contractions in hypothyroid than in euthyroid rat uterus (IC(50): 6.4 x 10(-8) M; n=6). A similar decrease in the sensitivity to nifedipine and diltiazem for reversal of K+ (100 mM)-induced tonic contraction was observed in uterus obtained from hypothyroid rats compared to the controls. Both nifedipine and diltiazem were less potent for causing concentration-related inhibition of K+-stimulated 45Ca2+ influx in uterine strips taken from the hypothyroid rats. Thus, the IC(50) values of nifedipine (1.83 x 10(-8) M; n=12) and diltiazem (1.8 x 10(-6) M; n=9) were significantly greater in tissues obtained from hypothyroid rats compared to the controls (IC(50) of nifedipine, 1.15 x 10(-11) M; n=12, diltiazem, 8.1 x 10(-8) M; n=8). Nifedipine-sensitive influx of 45Ca2+ - stimulated either by K+ (100 mM) or Bay k8644 (1,4-dihydro-2,6-dimethyl-5-nitro-4-[2'-(trifluromethyl)phenyl]-3-pyridine carboxylic acid methyl ester) (10(-8) M) was significantly less in uterine strips from hypothyroid rats compared to the controls. The results of the present study suggest that the inhibition of uterine rhythmic contractions may be attributable to a reduction in rat myometrial Ca2+ channel function in the hypothyroid state.

Effects of short-term in vivo exposure to polybrominated diphenyl ethers on thyroid hormones and hepatic enzyme activities in weanling rats

Polybrominated diphenyl ethers (PBDEs), used as flame retardants, are ubiquitous environmental contaminants. PBDEs act as endocrine disruptors via alterations in thyroid hormone homeostasis. We examined thyroid hormone concentrations and hepatic enzyme activity in weanling rats exposed to three commercial PBDE mixtures: DE-71, DE-79, and DE-83R. Female Long-Evans rats, 28 days old, were orally administered various doses of DE-71, DE-79, or DE-83R for 4 days. Serum and liver samples were collected 24 h after the last dose and analyzed for serum total thyroxine (T(4)), triiodothyronine (T(3)), thyroid-stimulating hormone (TSH), hepatic microsomal ethoxy- and pentoxy-resorufin-O-deethylase (EROD and PROD), and uridinediphosphate-glucuronosyltransferase (UDPGT) activities. The PBDE-treated groups did not exhibit significant changes in body weight; however, increased liver weights, as well as 10- to 20-fold induction in EROD and 30- to 40-fold induction in PROD were found in the DE-71-- and DE-79--treated animals. DE-71 and DE-79 caused dose-dependent depletion of T(4), accompanied by up to 3- to 4-fold induction in UDPGT activities. Serum total T(4) was decreased a maximum of 80% for DE-71 and 70% for DE-79 in the highest dose, with benchmark doses (BMDs) of approximately 12.74 mg/kg/day for DE-71 and 9.25 mg/kg/day for DE-79. Dose-related effects in serum T(3) levels were less apparent, with maximal reductions of 25-30% at the highest dose for both DE-71 and DE-79. The two mixtures showed no effect on serum TSH levels. Benchmark dose analysis revealed that the two mixtures were comparable in altering thyroid hormone levels and hepatic enzyme activity. DE-83R was not effective in altering any of the measured parameters. The present study suggests that short-term exposure to some commercial PBDE mixtures interferes with the thyroid hormone system via upregulation of UDPGTS:

Pituitary-thyroid feedback hypersensitivity as a novel cause of hypothyroidism in children

Recognition and treatment of childhood hypothyroidism is essential to prevent serious developmental abnormalities, and neonatal screening based on detection of raised thyrotropin concentrations is routine. We investigated an adolescent who had developmental retardation because of an undiagnosed and novel cause of childhood hypothyroidism associated with normal circulating thyrotropin concentrations. Dynamic testing showed a hypersensitive pituitary-thyroid feedback axis with no evidence of other pituitary or hypothalamic disease, and sequence analysis of four candidate causative genes was negative. A high index of suspicion is required to diagnose and treat this disorder to prevent the consequences of long-term hypothyroidism on development.

Chronic oral administration of CG-3703, a thyrotropin releasing hormone analog, increases wake and decreases cataplexy in canine narcolepsy

The effects on cataplexy and daytime sleep of acute and chronic oral administration of CG-3703, a potent TRH analog were assessed in canine narcolepsy. CG-3703 was found to be orally active and to reduce cataplexy (0.25 to 16 mg/kg) and sleep (8 and 16 mg/kg) in a dose-dependent manner. Two-week oral administration of CG-3703 (16 mg/kg) significantly reduced cataplexy and daytime sleep. The anticataplectic effects of CG-3703 were not associated with changes in general behavior, heart rate, blood pressure, rectal temperature, blood chemistry and thyroid function. Although drug tolerance for the effects on cataplexy and sleep were observed during the second week of chronic drug administration, therapeutic efficacy on cataplexy was improved with individual dose adjustment (final dose range: 16 to 28 mg/kg, p.o.). These results suggest that TRH analogs could be a promising new form of treatment for human narcolepsy.

Changes in vascular reactivity induced by acute hyperthyroidism in isolated rat aortae

Hyperthyroidism was induced by subcutaneous injections of L-thyroxine (T(4)) (500 mg/kg/day) for 3 days in order to study whether adrenergic and muscarinic receptor-mediated vascular responses alter at an early stage of the disease. T(4) treatment was sufficient to induce a significant degree of thyroid weight loss, tachycardia, cardiac hypertrophy, and an elevation in serum T(4) levels. The tension of aortic ring preparations isolated from rats was measured isometrically to investigate the influence of acute hyperthyroidism. The contractions induced by norepinephrine (NE) were significantly suppressed in aortic rings from rats treated with T(4) compared with control rats. N(G)-nitro-L-arginine (L-NOARG), an inhibitor of nitric oxide synthase (NOS), significantly enhanced NE-induced contraction in aortic rings from both control and T(4)-treated rats, and the enhancement was greater in rats treated with T(4) than control rats. The relaxations induced by either acetylcholine (ACh) or sodium nitroprusside (SNP) were also significantly enhanced by T(4) treatment. L-NOARG abolished the relaxation induced by ACh in aortic rings from both control and T(4)-treated rats. L-NOARG shifted SNP-induced relaxation curves of aortic rings from those of control rats to the left, but not with rats treated with T(4). T(4) treatment showed no influence on the amount of endothelial NOS (eNOS) protein. These results suggest that vascular responses alter at an early stage of hyperthyroidism and that it may be due to a modification in the NO system which is independent from the amount of eNOS protein.