Effects Of Thyroid Hormone Excess Research Articles

Add-On Effect of Selenium and Vitamin D Combined Supplementation in Early Control of Graves' Disease Hyperthyroidism During Methimazole Treatment.

Prompt and stable control of hyperthyroidism is fundamental to avoid the detrimental effects of thyroid hormone excess, and antithyroid drugs, mainly methimazole (MMI), represent the first-line treatment for Graves’ disease (GD) hyperthyroidism. Decreased serum concentrations of selenium (Se) and calcifediol (25(OH)D, VitD) have been reported in newly diagnosed GD patients in observational studies. Low Se levels might exacerbate oxidative stress by compromising the antioxidant machinery’s response to reactive oxygen species, and low VitD levels might hamper the anti-inflammatory immune response. We performed a randomized controlled clinical trial (EudraCT 2017-00505011) to investigate whether Se and cholecalciferol (VitD) addition to MMI is associated with a prompter control of hyperthyroidism. Forty-two consecutive patients with newly-onset GD and marginal/insufficient Se and VitD levels were randomly assigned to treatment with either MMI monotherapy or MMI combined with Se and VitD. Se treatment was withdrawn after 180 days, while the other treatments were continued. Combination therapy resulted in a significantly greater reduction in serum FT4 concentration at 45 days (-37.9 pg/ml, CI 95%, -43.7 to -32.2 pg/ml) and 180 days (-36.5 pg/ml, CI 95%, -42 to -30.9 pg/ml) compared to MMI monotherapy (respectively: -25.7 pg/ml, CI 95%, -31.6 to -19.7 pg/ml and -22.9 pg/ml, CI 95%, -28 to -17.3 pg/ml, p 0.002). Data at 270 days confirmed this trend (-37.8 pg/ml, CI 95%, -43.6 to -32.1 pg/ml vs -24.4 pg/ml, CI 95%, -30.3 to -18.4 pg/ml). The quality of life (QoL) score was investigated by the validated “Thyroid-related Patient-Reported Outcome” questionnaire (ThyPRO). ThyPRO composite score showed a greater improvement in the intervention group at 45 days (-14.6, CI 95%, -18.8 to -10.4), 180 (-9, CI 95%, -13.9 to -4.2) and 270 days (-14.3, CI 95%, -19.5 to -9.1) compared to MMI group (respectively, -5.2, CI 95%, -9.5 to -1; -5.4, CI 95%, -10.6 to -0.2 and -3.5, CI 95%, -9 to -2.1, p 0-6 months and 6-9 months <0.05). Our results suggest that reaching optimal Se and VitD levels increases the early efficacy of MMI treatment when Se and VitD levels are suboptimal.

TSH secreting pituitary tumor — an experience of 20 years follow-up

Thyrotropinoma is a rare pituitary tumor that causes the development of thyrotoxicosis syndrome as a result of hyperproduction of thyroid stimulating hormone (TSH). In the Russian literature over the past 10 years, one case of thyrotropinoma in a child, four cases of TSH-producing pituitary adenoma in women and only one in a man have been described. The article presents a unique clinical case of a 20-years history of observation of a patient with TSH-oma. The rarity of this disease led to the fact that it took more than 10 years to make a correct diagnosis. The first operation of thyroid gland was performed before the diagnosis of pituitary adenoma and inappropriate TSH secretion syndrome. That right hemithyroidectomy was supposed to cure a toxic adenoma of thyroid gland. The diagnosis of thyrotropin-secreting piruitary tumor was established only after 6 years even after finding a combination of pituitary adenoma and thyrotoxicosis. After that, the patient steadfastly refuses neurosurgical treatment, despite the presence of macroadenoma with intrasellar growth. The therapy with somatostatin analogs led to patient’s intolerance with gastrointestinal side effects and hospitalization for acute pancreatitis. The absence of the therapy due to low compliance led to long-term persistence of thyrotoxicosis. The absence of signs and symptoms of expanding tumor mass (visual field defects, loss of vision, headache, partial or total hypopituitarism) demonstrates the slow growth of this kind of pituitary tumor. The long-term effect of elevated TSH levels led to diffuse goiter with compression of the neck organs, and the need of the surgical treatment of the thyroid. Stable euthyroidism after the operation led to stable normoglycemia in the patient with previously diagnosed diabetes mellitus type 2. This fact should keep an attention of physicians and endocrinologists to screen for the secondary reasons of hyperglycemia in a patient with diabetes mellitus manifestation. Long-term history of thyrotoxicosis led to the deleterious effects of thyroid hormone excess on the heart (atrial fibrillation, cardiomyopathy, cardiac failure). Those effects are still observed even after thyroidectomy and medical euthyroidism achievement. This fact demonstrates the importance of early diagnosis and treatment of TSH-omas.

Тиреотропинома — опыт 20-летнего наблюдения

Thyrotropinoma is a rare pituitary tumor that causes the development of thyrotoxicosis syndrome as a result of hyperproduction of thyroid stimulating hormone (TSH). In the Russian literature over the past 10 years, one case of thyrotropinoma in a child, four cases of TSH-producing pituitary adenoma in women and only one in a man have been described. The article presents a unique clinical case of a 20-years history of observation of a patient with TSH-oma. The rarity of this disease led to the fact that it took more than 10 years to make a correct diagnosis. The first operation of thyroid gland was performed before the diagnosis of pituitary adenoma and inappropriate TSH secretion syndrome. That right hemithyroidectomy was supposed to cure a toxic adenoma of thyroid gland. The diagnosis of thyrotropin-secreting piruitary tumor was established only after 6 years even after finding a combination of pituitary adenoma and thyrotoxicosis. After that, the patient steadfastly refuses neurosurgical treatment, despite the presence of macroadenoma with intrasellar growth. The therapy with somatostatin analogs led to patient’s intolerance with gastrointestinal side effects and hospitalization for acute pancreatitis. The absence of the therapy due to low compliance led to long-term persistence of thyrotoxicosis. The absence of signs and symptoms of expanding tumor mass (visual field defects, loss of vision, headache, partial or total hypopituitarism) demonstrates the slow growth of this kind of pituitary tumor. The long-term effect of elevated TSH levels led to diffuse goiter with compression of the neck organs, and the need of the surgical treatment of the thyroid. Stable euthyroidism after the operation led to stable normoglycemia in the patient with previously diagnosed diabetes mellitus type 2. This fact should keep an attention of physicians and endocrinologists to screen for the secondary reasons of hyperglycemia in a patient with diabetes mellitus manifestation. Long-term history of thyrotoxicosis led to the deleterious effects of thyroid hormone excess on the heart (atrial fibrillation, cardiomyopathy, cardiac failure). Those effects are still observed even after thyroidectomy and medical euthyroidism achievement. This fact demonstrates the importance of early diagnosis and treatment of TSH-omas.

SAT-462 Coronary Vasospasm-Induced Myocardial Infarction: An Uncommon Presentation of Thyrotoxicosis

Background: Coronary artery vasospasm-induced myocardial infarction is a rare cardiac complication of untreated thyrotoxicosis. Diagnosis is difficult due to the transient and unpredictable occurrence of coronary spasm [1]. Clinical Case: A 47-year-old Hispanic female smoker presented with a one-week history of severe, intermittent substernal chest pain radiating to the left arm. The pain was associated with palpitations and shortness of breath. She was afebrile with a heart rate of 100, a blood pressure of 119/59, a fine tremor, and brisk reflexes. No lid lag or proptosis was appreciated. The thyroid was enlarged, non-tender, without palpable nodules. ECG showed T- Wave Inversions in leads V1-V2 and ST depressions in V4-V5. Chest pain was relieved by SL nitroglycerin.Lab results showed a peak Troponin of 0.20 (N < 0.06), TSH 0.01 mU/L (N > 0.45mU/L), free T4 5.54 (N < 1.46 ng/dl), total T3 4.50 pg/mL (N < 1.37 ng/mL), free T3 21.0 ng/mL (N < 4.4 pg/ml), TSI 3.61 IU/L (N < 0.55 IU/L), thyrotropin R Ab 7.47 IU/L (N < 1.75 IU/L) and thyroglobulin Ab 1.3 IU/ml (ULN < 0.9 IU/ml). Thyroid US showed a heterogeneous enlarged thyroid gland with increased vascularity.For her NSTEMI she was treated with a heparin drip, aspirin, clopidogrel, atorvastatin, propranolol, and isosorbide mononitrate. Methimazole was started to treat thyrotoxicosis. Cardiac catheterization revealed coronary vasospasm without evidence of valvular or coronary artery disease. Methimazole restored euthyroidism and she has not had recurrence of angina. Discussion: Rarely, hyperthyroidism can present with transient myocardial ischemia secondary to coronary artery vasospasm in patients with normal coronary arteries. The etiopathogenesis is unclear and may relate to a direct metabolic effect of excess thyroid hormone on the myocardium. In a Korean study evaluating chest pain in patients who underwent coronary angiography, the incidence of coronary vasospasm was 5%, occurring most frequently in women under 50 years of age with thyrotoxicosis [2]. Conclusion: Patients who present with angina and are thyrotoxic should be evaluated for vasospasm. Females under 50 years old with Graves’ disease are at highest risk. Treatment includes antithyroid medications along with nitroglycerin, and we can consider calcium channel blockers including diltiazem. Treatment of thyrotoxicosis eliminates recurrence of vasospasm [3].

Feline hyperthyroidism: diagnosis and treatment

Hyperthyroidism is a common endocrinopathy in cats older than 8 years, with no sex or breed predisposition. Benign adenomas and adenomatous hyperplasia of the thyroid gland is observed in the majority of cases. Symptoms reflect the effect of thyroid hormone excess in various systems, with weight loss, polyphagia, polyuria-polydipsia, cardiovascular and gastrointestinal abnormalities being common clinical manifestations. On clinical examination, there is frequently prominent thyroid enlargement. Common laboratory abnormal findings include increased activity of alkaline phosphatase and alanino-aminotransferase, hyperphosphataemia, azotaemia and decreased concentration of ionized calcium and creatinine. Definite diagnosis of the disease is based on the demonstration of increased blood concentration of thyroid hormones.Measurement of thyroxine concentration, alone or in conjunction with concentration of free thyroxine, is usually sufficient to reach a diagnosis. When diagnosis is uncertain, thyroid stimulating hormone, scintigraphy and dynamic function tests can be used. The possibility of concurrent diseases (e.g., renal failure, diabetes mellitus) must be investigated, as their presence has implications on diagnosis and treatment. Medical therapy, thyroidectomy, radionine therapy and low iodine diet are also valid options for treatment. Each has advantages and disadvantages that a clinician must take into consideration before instigating treatment. Prognosis for hyperthyroidism is favourable if no severe disease exists concurrently.

Impaired glucose-stimulated insulin secretion and reduced β-cell mass in pancreatic islets of hyperthyroid rats.

What is the central question of this study? Thyroid dysfunction can have a major impact on pancreatic function. The influence of hyperthyroidism on insulin secretion remains controversial, and the precise mechanism of its effect has not yet been elucidated. What is the main finding and its importance? The results of this study demonstrate that hyperthyroidism leads to impaired insulin secretion. It appears that the defect in insulin secretion in the hyperthyroid state probably reflects a summation of different alterations, including decreased sensitivity of ATP-sensitive K(+) and L-type Ca(2+) channels of the β-cells and reduced β-cell mass. To clarify the mechanism underlying the effect of thyroid hormone excess on pancreatic insulin secretion and abnormal glucose tolerance induced by hyperthyroidism, we investigated the effect of hyperthyroidism on the pancreatic β-cell mass and two key components of the insulin secretory pathway, ATP-sensitive K(+) (KATP ) and L-type Ca(2+) channels. In control and levothyroxine-treated hyperthyroid rats, an intraperitoneal glucose tolerance test was performed, and the insulin secretion and content of the isolated islets were assayed. In order to determine the effect of hyperthyroidism on KATP and L-type Ca(2+) channels, isolated islets were exposed to specific pharmacological agents, including glibenclamide (KATP channel blocker), diazoxide (KATP channel opener) and nifedipine (L-type Ca(2+) channel blocker). Histomorphometric changes and histochemistry of the islet in both groups were compared. Our data indicated that plasma glucose and insulin concentrations during the intraperitoneal glucose tolerance test in the hyperthyroid group were, respectively, higher and lower than in the control group. Insulin secretion and content of the hyperthyroid islets were reduced. The response of hyperthyroid islets to glibenclamide, diazoxide and nifedipine and the percentage change in insulin secretion were lower than those of the control islets. Despite the increase in weight and total volume of the pancreas, the volume of the islets and the total number of insulin-positive cells in hyperthyroid rats were reduced. Our data indicated that reduced insulin secretion in the hyperthyroid group might arise from reduced β-cell mass and an abnormality in some parts of the insulin secretory pathway, including KATP and L-type Ca(2+) channel function.

A unique mouse strain that develops spontaneous, iodine-accelerated, pathogenic antibodies to the human thyrotrophin receptor.

Abs that stimulate the thyrotropin receptor (TSHR), the cause of Graves' hyperthyroidism, only develop in humans. TSHR Abs can be induced in mice by immunization, but studying pathogenesis and therapeutic intervention requires a model without immunization. Spontaneous, iodine-accelerated, thyroid autoimmunity develops in NOD.H2(h4) mice associated with thyroglobulin and thyroid-peroxidase, but not TSHR, Abs. We hypothesized that transferring the human TSHR A-subunit to NOD.H2(h4) mice would result in loss of tolerance to this protein. BALB/c human TSHR A-subunit mice were bred to NOD.H2(h4) mice, and transgenic offspring were repeatedly backcrossed to NOD.H2(h4) mice. All offspring developed Abs to thyroglobulin and thyroid-peroxidase. However, only TSHR-transgenic NOD.H2(h4) mice (TSHR/NOD.H2(h4)) developed pathogenic TSHR Abs as detected using clinical Graves' disease assays. As in humans, TSHR/NOD.H2(h4) female mice were more prone than male mice to developing pathogenic TSHR Abs. Fortunately, in view of the confounding effect of excess thyroid hormone on immune responses, spontaneously arising pathogenic human TSHR Abs cross-react poorly with the mouse TSHR and do not cause thyrotoxicosis. In summary, the TSHR/NOD.H2(h4) mouse strain develops spontaneous, iodine-accelerated, pathogenic TSHR Abs in female mice, providing a unique model to investigate disease pathogenesis and test novel TSHR Ag-specific immunotherapies aimed at curing Graves' disease in humans.

Embryonic exposure to excess thyroid hormone causes thyrotrope cell death

Central congenital hypothyroidism (CCH) is more prevalent in children born to women with hyperthyroidism during pregnancy, suggesting a role for thyroid hormone (TH) in the development of central thyroid regulation. Using the zebrafish embryo as a model for thyroid axis development, we have characterized the ontogeny of negative feedback regulation of thyrotrope function and examined the effect of excess TH on thyrotrope development. We found that thyroid-stimulating hormone β subunit (tshb) and type 2 deiodinase (dio2) are coexpressed in zebrafish thyrotropes by 48 hours after fertilization and that TH-driven negative feedback regulation of tshb transcription appears in the thyroid axis by 96 hours after fertilization. Negative feedback regulation correlated with increased systemic TH levels from the developing thyroid follicles. We used a transgenic zebrafish that expresses GFP under the control of the tshb promoter to follow thyrotrope fates in vivo. Time-lapse imaging revealed that early exposure to elevated TH leads to thyrotrope cell death. Thyrotrope numbers slowly recovered following the removal of excess TH. These data demonstrate that transient TH exposure profoundly impacts the thyrotrope population during a critical period of pituitary development and may have long-term implications for the functional reserve of thyroid-stimulating hormone (TSH) production and the TSH set point later in life.

Thyroid Hormone Signaling and Homeostasis During Aging

Studies in humans and in animal models show negative correlations between thyroid hormone (TH) levels and longevity. TH signaling is implicated in maintaining and integrating metabolic homeostasis at multiple levels, notably centrally in the hypothalamus but also in peripheral tissues. The question is thus raised of how TH signaling is modulated during aging in different tissues. Classically, TH actions on mitochondria and heat production are obvious candidates to link negative effects of TH to aging. Mitochondrial effects of excess TH include reactive oxygen species and DNA damage, 2 factors often considered as aging accelerators. Inversely, caloric restriction, which can retard aging from nematodes to primates, causes a rapid reduction of circulating TH, reducing metabolism in birds and mammals. However, many other factors could link TH to aging, and it is these potentially subtler and less explored areas that are highlighted here. For example, effects of TH on membrane composition, inflammatory responses, stem cell renewal and synchronization of physiological responses to light could each contribute to TH regulation of maintenance of homeostasis during aging. We propose the hypothesis that constraints on TH signaling at certain life stages, notably during maturity, are advantageous for optimal aging.

Clinical spectrum and therapeutic approach to hepatocellular injury in patients with hyperthyroidism

Liver dysfunction in patients with hyperthyroidism includes abnormalities associated with the effects of thyroid hormone excess, those secondary to drug-induced liver injury, and changes resulting from concomitant liver disease. Our goal was to describe clinical, biochemical, and histopathological patterns in patients suffering from hyperthyroidism and concomitant liver dysfunction and to propose an algorithm of procedures to facilitate diagnosis and management of such cases. This study describes seven patients with liver biochemistry abnormalities detected after diagnosis of hyperthyroidism and one with undiagnosed decompensated hyperthyroidism and acute hepatitis. Two patients showed autoantibody reactivity which, together with liver histology, suggested the diagnosis of classic autoimmune hepatitis. Three patients experienced hepatotoxicity induced by propylthiouracil, the manifestations of which ranged from a benign course after drug withdrawal in one, a longstanding course in another suggesting drug-induced autoimmune hepatitis, and a more severe clinical condition with acute liver failure in a third patient, requiring liver transplantation. The three remaining patients showed no precipitating factors other than thyroid hyperactivity itself. They could be interpreted as having a thyroid storm with different clinical presentations. In conclusion, this series of patients illustrates the most frequent patterns of hepatocellular damage associated with hyperthyroidism and provides an algorithm for their diagnosis and treatment.

Thrombin-activatable fibrinolysis inhibitor in hypothyroidism and hyperthyroxinaemia

Endocrine disorders affect both the coagulation and fibrinolytic systems, and have been associated with the development of cardiovascular diseases. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a link between coagulation and the fibrinolytic system. The aim of this study was to determine the effect of thyroid hormone excess and deficiency on TAFI levels and function. The effect of hyperthyroxinemia on TAFI was studied in healthy volunteers who were randomised to receive levothyroxine or no medication for 14 days in a crossover design. The effect of hypothyroidism on TAFI was studied in a multicentre observational cohort study. Blood was drawn before treatment of patients with newly diagnosed hypothyroidism and when euthyroidism was achieved. Plasma clot-lysis times, activated TAFI (TAFIa)-dependent prolongation of clot-lysis and TAFI levels were measured. Thyroid hormone excess resulted in a hypofibrinolytic condition and in an enhanced TAFIa-dependent prolongation of clot lysis. A trend towards decreased plasma TAFI levels was observed in healthy volunteers who used levothyroxine. Hypothyroidism resulted in hyperfibrinolysis and a reduced TAFIa-dependent prolongation of clot lysis. In conclusion, alterations of TAFIa-dependent prolongation of clot lysis in patients with thyroid disorders may cause an impaired haemostatic balance. The disturbed haemostatic balance in patients with hyperthyroidism might make them prone to thrombosis, while the risk for bleeding may increase in patients with hypothyroidism.

Alterations in coagulation and fibrinolysis after levothyroxine exposure in healthy volunteers: a controlled randomized crossover study

Several hemostatic abnormalities have been reported in hyperthyroidism, but the overall effect of thyroid hormone excess on coagulation and fibrinolysis is unclear. Our aim was to assess whether the use of supraphysiological doses of levothyroxine leads to coagulation activation and inhibition of fibrinolysis. Healthy volunteers were randomized to receive levothyroxine or no medication for 14 days with a washout period of at least 28 days in a crossover design. To study the effects of different degrees of thyroid hormone excess, 16 participants received levothyroxine in a dose of 0.3 mg per day, and 12 received levothyroxine 0.45 or 0.6 mg per day depending on body weight. Several variables of coagulation and fibrinolysis were measured. Levels of von Willebrand factor activity (VWF:RiCo) and antigen (VWF:Ag), factor (F) VIII, plasminogen activator inhibitor-1 (PAI-1) and clot-lysis time were slightly higher after levothyroxine 0.3 mg per day than after the control situation, but only levels of VWF showed a significant increase from baseline. After levothyroxine 0.45 or 0.6 mg per day, levels of fibrinogen increased by 17%, VWF activity by 24%, VWF antigen by 26%, FVIII by 19%, FIX by 14%, FX by 7%, PAI-1 by 116% and clot-lysis time by 14%, and activated partial thromboplastin time decreased by 3%; all were significant changes compared with the control situation. We did not observe clear evidence of coagulation activation. Our data suggest that thyroid hormone excess increases coagulation factor levels and inhibits fibrinolysis in a dose-dependent fashion. This implies an increased risk of venous thrombosis during hyperthyroidism.

Thyroid hormone receptor β mediates thyroid hormone effects on bone remodeling and bone mass

Excess thyroid hormone (TH) in adults causes osteoporosis and increases fracture risk. However, the mechanisms by which TH affects bone turnover are not elucidated. In particular, the roles of thyroid hormone receptor (TR) isotypes in the mediation of TH effects on osteoblast-mediated bone formation and osteoclast-mediated bone resorption are not established. In this study we have induced experimental hypothyroidism or hyperthyroidism in adult wild-type, TRα- or TRβ-deficient mice and analyzed the effects of TH status on the structure and remodeling parameters of trabecular bone. In wild-type mice, excess TH decreased bone volume and mineralization. High TH concentrations were associated with a high bone-resorption activity, assessed by increased osteoclast surfaces and elevated concentrations of serum bone-resorption markers. Serum markers of bone formation also were higher in TH-treated mice. TRα deficiency did not prevent TH action on bone volume, bone mineralization, bone formation, or bone resorption. In contrast, TRβ deficiency blocked all the early effects of excess TH observed in wild-type mice. However, prolonged exposure to low or high TH concentrations of TRβ-deficient mice induced mild modifications of bone structure and remodeling parameters. Together our data suggest that TRβ receptors mediate the acute effects produced by transient changes of TH concentrations on bone remodeling, whereas TRα receptors mediate long-term effects of chronic alterations of TH metabolism. These data shed new light on the respective roles of TRs in the control of bone metabolism by TH.

Excess Thyroid Hormone Inhibits Embryonic Neural Stem/Progenitor Cells Proliferation and Maintenance through STAT3 Signalling Pathway

Hyperthyroidism is prevalent during pregnancy, but little is known about the effects of excess thyroid hormone on the development of embryonic neural stem/progenitor cells (NSCs), and the mechanisms underlying these effects. Previous studies indicate that STAT3 plays a crucial role in determining NSC fate during neurodevelopment. In this study, we investigated the effects of a supraphysiological dose of 3,5,3'-L-triiodothyronine (T3) on the proliferation and maintenance of NSCs derived from embryonic day 13.5 mouse neocortex, and the involvement of STAT3 in this process. Our results suggest that excess T3 treatment inhibits NSC proliferation and maintenance. T3 decreased tyrosine phosphorylation of JAK1, JAK2 and STAT3, and subsequently inhibited STAT3-DNA binding activity. Furthermore, proliferation and maintenance of NSCs were decreased by inhibitors of JAKs and STAT3, indicating that the STAT3 signalling pathway is involved in the process of NSC proliferation and maintenance. Taken together, these results suggest that the STAT3 signalling pathway is involved in the process of T3-induced inhibition of embryonic NSC proliferation and maintenance. These findings provide data for understanding the effects of hyperthyroidism during pregnancy on fetal brain development, and the mechanisms underlying these effects.

High free thyroxine levels are associated with QTc prolongation in males

The literature on the effect of excess thyroid hormone on ventricular repolarization is controversial. To study whether free thyroxine (T(4)) and TSH are associated with QTc prolongation we conducted population-based cohort study. This study was conducted as part of the Rotterdam Study and included 365 men and 574 women aged 55 years and older with an electrocardiogram, who were randomly sampled for the assessment of thyroid status (free T(4)/TSH) at baseline, after exclusion of participants with hypothyroidism, use of antithyroid drugs, thyroid hormones or digoxin, left ventricular hypertrophy, and left and right bundle branch block. Endpoints were the length of the QTc interval and risk of borderline QTc prolongation. The associations were examined by means of linear and logistic regression analysis, adjusted for age and gender, diabetes mellitus, myocardial infarction, hypertension, and heart failure. Overall, there was no significant association between TSH and QTc interval (0.8 ms (95% confidence interval (CI) -3.5, 5.2) in the first quintile compared with the fifth quintile). Subjects in the fifth quintile of free T(4) did not have an increased QTc interval (3.2 ms (95% CI -1.1, 7.6)); stratification on gender showed an increment of 10.9 ms (95% CI 3.4, 18.3) in the fifth quintile in men and 1.1 ms (95% CI -4.2, 6.3) in the fifth quintile of free T(4) in women. When compared with subjects in the first quintile, male subjects in the fifth quintile of free T(4) had a significantly increased risk of a borderline QTc interval and QTc prolongation (odds ratio 2.40 (95% CI 1.20, 4.80)). High levels of free T(4) are associated with substantial QTc prolongation in men of up to 10 ms. The fact that free T(4) is also associated with a significantly increased risk of borderline and prolonged QTc values with its risk of sudden cardiac death, endorses the clinical importance of our findings.

Bone Loss in Thyroid Disease

More than 10% of postmenopausal women in the United States receive thyroid hormone replacement therapy and up to 20% of these women are over-replaced inducing subclinical hyperthyroidism. Because hyperthyroidism and post menopausal osteoporosis overlap in women of advancing age, it is urgent to understand the effect of thyroid hormone excess on bone. We can now provide results that not thyroid hormones but also TSH itself has an equally important role to play in bone remodeling.

Fetal Loss Associated With Excess Thyroid Hormone Exposure

ContextMaternal hypothyroidism and hyperthyroidism have deleterious effects on the outcome of pregnancy. While the effects of thyroid hormone (TH) deprivation on the fetus, independently from that on the mother, can be studied in infants with congenital hypothyroidism, this is not the case in those with fetal thyrotoxicosis.ObjectiveTo study the effects of TH excess on fetuses carried by mothers with resistance to TH (RTH) who are euthyroid despite high TH levels but who may carry normal fetuses that are exposed to high maternal hormone levels.Design, Setting, and ParticipantsRetrospective study of 167 members of an Azorean family with RTH. Affected individuals had the RTH phenotype (high serum concentration of free thyroxine and triiodothyronine without suppressed thyrotropin) confirmed by genotyping to identify the Arg243→Gln mutation in the TH receptor β gene.Main Outcome MeasuresPregnancy outcome of affected mothers vs that of unaffected mothers carrying fetuses conceived by affected fathers, as well as that of unaffected first-degree relatives and outcomes from the general island population. Comparison of birth weights and blood concentrations of thyrotropin (TSH) obtained during routine neonatal screening of infants born to these 3 groups.ResultsThirty-six couples with complete information belonged to 1 of 3 groups: affected mothers (n = 9), affected fathers (n = 9), and unaffected relatives (n = 18). Mean miscarriage rates were 22.9%, 2.0%, and 4.4%, respectively (χ2 = 8.66, P = .01). Affected mothers had an increased rate of miscarriage (z = 3.10, P = .002, by Wilcoxon rank-sum test). They had marginally higher than expected numbers of affected offspring, ie, 20 affected and 11 unaffected children (P = .07), while affected fathers had 15 affected and 12 unaffected children (P = .35). Unaffected infants born to affected mothers were significantly smaller than affected infants, having a mean SD score for gestational age of –1.79 (SD, 0.86) vs −0.06 (SD, 1.11) to –0.22 (SD, 0.70) for all other groups (P<.001). Only unaffected infants born to affected mothers had undetectable blood levels of TSH.ConclusionThere was a higher rate of miscarriage in mothers affected by RTH that may have involved predominantly unaffected fetuses. The lower birth weight and suppressed levels of TSH in unaffected infants born to affected mothers indicates that the high maternal TH levels produce fetal thyrotoxicosis. These data indicate a direct toxic effect of TH excess on the fetus.

Fetal loss associated with excess thyroid hormone exposure.

Maternal hypothyroidism and hyperthyroidism have deleterious effects on the outcome of pregnancy. While the effects of thyroid hormone (TH) deprivation on the fetus, independently from that on the mother, can be studied in infants with congenital hypothyroidism, this is not the case in those with fetal thyrotoxicosis. To study the effects of TH excess on fetuses carried by mothers with resistance to TH (RTH) who are euthyroid despite high TH levels but who may carry normal fetuses that are exposed to high maternal hormone levels. Retrospective study of 167 members of an Azorean family with RTH. Affected individuals had the RTH phenotype (high serum concentration of free thyroxine and triiodothyronine without suppressed thyrotropin) confirmed by genotyping to identify the Arg243-->Gln mutation in the TH receptor beta gene. Pregnancy outcome of affected mothers vs that of unaffected mothers carrying fetuses conceived by affected fathers, as well as that of unaffected first-degree relatives and outcomes from the general island population. Comparison of birth weights and blood concentrations of thyrotropin (TSH) obtained during routine neonatal screening of infants born to these 3 groups. Thirty-six couples with complete information belonged to 1 of 3 groups: affected mothers (n = 9), affected fathers (n = 9), and unaffected relatives (n = 18). Mean miscarriage rates were 22.9%, 2.0%, and 4.4%, respectively (chi2 = 8.66, P =.01). Affected mothers had an increased rate of miscarriage (z = 3.10, P =.002, by Wilcoxon rank-sum test). They had marginally higher than expected numbers of affected offspring, ie, 20 affected and 11 unaffected children (P =.07), while affected fathers had 15 affected and 12 unaffected children (P =.35). Unaffected infants born to affected mothers were significantly smaller than affected infants, having a mean SD score for gestational age of -1.79 (SD, 0.86) vs -0.06 (SD, 1.11) to -0.22 (SD, 0.70) for all other groups (P<.001). Only unaffected infants born to affected mothers had undetectable blood levels of TSH. There was a higher rate of miscarriage in mothers affected by RTH that may have involved predominantly unaffected fetuses. The lower birth weight and suppressed levels of TSH in unaffected infants born to affected mothers indicates that the high maternal TH levels produce fetal thyrotoxicosis. These data indicate a direct toxic effect of TH excess on the fetus.

The metabolic and cardiovascular effects of hyperthyroidism are largely independent of beta-adrenergic stimulation.

Hyperthyroidism and states of adrenergic hyperactivity have many common clinical features, suggesting similar pathogenic mechanisms of action. The widespread use of beta-adrenergic receptor (betaAR) antagonists (beta-blockers) to treat hyperthyroidism has led to the belief that the physiological consequences of thyroid hormone (TH) excess are mediated in part via catecholamine signaling through betaARs. To test this hypothesis, we compared the response to TH excess in mice lacking the three known betaARs (beta-less) vs. wild-type (WT) mice. Although beta-less mice had a lower heart rate at baseline in comparison to WT mice, the metabolic and cardiovascular responses to hyperthyroidism were equivalent in both WT and beta-less mice. These data indicate that the metabolic and cardiovascular effects of TH excess are largely independent of betaARs. These findings suggest that the efficacy of clinical treatment of hyperthyroidism with beta-blockers is due to antagonism of sympathetic signaling, and that this process functions independently of TH action.

High Urinary Corticoid/Creatinine Ratios in Cats with Hyperthyroidism

Measurement of the urinary corticoid: creatinine (C: C) ratio provides an assessment of cortisol secretion over a period of time. Therefore, this test is a very sensitive measure of adrenocortical function. The stress of the diagnostic procedure and nonadrenal disease may increase the urinary C: C ratio. In addition, diseases such as hyperthyroidism may influence the metabolic clearance of cortisol. To evaluate the effect of thyroid hormone excess, urinary C: C ratios were measured in 32 cats with hyperthyroidism and 45 healthy household cats. In 7 cats, urinary C: C ratios were measured both before and after treatment for hyperthyroidism. With data from the healthy cats, the reference range for the urinary C:C ratio was determined to be 8.0 to 42.0 × 10‐6. The urinary C:C ratios in the cats with hyperthyroidism (median, 37.5 × 10‐6; range, 5.9–169.5 × 10‐6) were significantly (P =.001) higher than those in the healthy cats (median, 16 × 10‐6; range, 4.8–52.5 × 10‐6). In 15 cats with hyperthyroidism, the urinary C: C ratios exceeded the upper limit of the reference range. Treatment for hyperthyroidism led to a marked decrease in urinary C: C ratios. The results of this study demonstrate that the urinary C: C ratio may be abnormally high in cats with hyperthyroidism, probably because of increased metabolic clearance of cortisol and activation of the pituitary‐adrenocortical axis by disease. Although the clinical features of hyperthyroidism and hyperadrenocorticism in cats are different, hyperthyroidism should be ruled out when cats are suspected of hyperadrenocorticism on the basis of abnormally high urinary C: C ratios.