Thyroid hormone and the cardiovascular system

B-type natriuretic peptide in patients with clinical hyperthyroidism

AIMS

To investigate the level and clinical significance of plasma B-type natriuretic peptide (BNP) in patients with hyperthyroidism.

METHODS

Plasma BNP was measured in 32 healthy subjects and 67 patients with clinical hyperthyroidism. Left ventricular anatomy and function was assessed with echocardiography.

RESULTS

The average BNP in hyperthyroid patients was higher than that in healthy subjects (186+/-140 vs 34+/-17 ng/l, p =0.001). The increase in BNP was mainly found in hyperthyroid patients who had clinical and echocardiographic evidence of left ventricular dysfunction (250+/-190 ng/l). The BNP level in patients with hyperthyroidism, but with normal left ventricular function, was similar to that of the controls (37+/-17 vs 34+/-17, ng/l, p>0.05). Multi-regression analysis showed that left atrial diameter and left ventricular ejection fraction were independently associated with the plasma levels of BNP.

CONCLUSIONS

there is a significant elevation in plasma BNP in patients with hyperthyroidism; the increase is largely due to hyperthyroidism-induced left ventricular dysfunction. Measurements of plasma BNP may help to detect heart failure in patients with clinical hyperthyroidism.

Decrease of arterial stiffness at common carotid artery in hypothyroid patients by normalization of thyroid function

This study examined the effect of hypothyroidism on arterial stiffening and the effect of levothyroxine (l-T(4)) replacement. The arterial stiffness index beta (stiffness beta) and intima-media thickness (IMT), a parameter of arterial stiffening and thickening, respectively, were determined in common carotid artery (CCA) by ultrasonography in 30 hypothyroid patients before and after 1 year of normalization of thyroid function by l-T(4) replacement. Baseline CCA stiffness beta and IMT was significantly higher in the hypothyroid patients than in age- and sex-matched normal controls [9.46 +/- 0.93 vs. 8.02 +/- 0.91 (mean +/- SE); P < 0.05, 0.635 +/- 0.018 mm vs. 0.541 +/- 0.019 mm; P < 0.005, respectively]. In multivariate analysis, baseline stiffness beta was significantly associated with baseline levels of IMT (r = 0.457, P = 0.0311), FT(4) (r = -0.413, P = 0.0169), and a plasma vascular injury marker, von Willebrand factor (vWF) (r = 0.412, P = 0.0261). During 1 year of euthyroidism, 22 and 29 out of 30 patients showed significant decreases of stiffness beta and IMT to normal respective level, from 9.46 +/- 0.93 to 7.58 +/- 0.34 and from 0.635 +/- 0.018 to 0.552 +/- 0.015 mm, respectively. Change in stiffness beta during l-T(4) therapy correlated significantly in a negative manner with baseline levels of age (r = -0.465, P = 0.011) and IMT (r = -0.406, P = 0.029). Stiffness beta after but not before l-T(4) therapy showed a tendency towards a positive correlation with age. This study suggested that increases of arterial thickening, and plasma vWF, and a reduction in serum FT(4) might have an important role independently in the increased arterial stiffening in hypothyroid patients. Furthermore, it was demonstrated that sustained euthyroidism might have the potential to reverse arterial stiffening in addition to thickening in hypothyroid patients.

Thyroid Hormone Analog, DITPA, Improves Endothelial Nitric Oxide and Beta-Adrenergic Mediated Vasorelaxation after Myocardial Infarction

This study was designed to determine if the thyroid hormone analog 3,5 diiodothyropropionic acid (DITPA), now in clinical trials for heart failure, alters endothelial function after myocardial infarction (MI). Three weeks after MI, adult Sprague-Dawley rats were randomly assigned to DITPA (375 microg/100 g subcutaneous) or no treatment of 3 weeks. In MI rats, left ventricular (LV) end-diastolic pressure and LV dP/dt decreased (P < 0.05). DITPA did not change MAP (87 +/- 10 versus 90 +/- 7 mm Hg) or LV end-diastolic pressure (23 +/- 3 versus 19 +/- 9 mm Hg) but did lower (P < 0.05) LV dP/dt (4,633 +/- 797 versus 3,650 +/- 1,236 mm Hg/s). In aortic segments from MI rats, DITPA enhanced the acetylcholine dependent vasorelaxation (59 +/- 11% at 10(-4) M, P < 0.05) and isoproterenol induced vasorelaxation (57 +/- 13% at 10(-4) M, P < 0.05). The increases in vasorelaxation were blocked with l-NAME and restored with L-arginine. Treatment with DITPA increased (P < 0.05) eNOS protein content in aortic tissue from sham rats (3.8 +/- 2.8 to 44.5 +/- 7.1 integrated intensity units (II)/microg) and in MI rats (5.3 +/- 3.4 to 28.3 +/- 8.9 II/microg). In endothelial cells, 24 hours' treatment with DITPA (10 microM) increased (P < 0.01) eNOS protein expression from 22.1 +/- 4.8 to 52.7 +/- 16.8 II/microg protein and DITPA (20 microM) increased eNOS to 49.1+/- 15.2 II/microg protein. The thyroid analog DITPA enhances endothelial nitric oxide and beta-adrenergic-mediated vasorelaxation by increasing nitric oxide in the vasculature.

Thyroid hormone and blood pressure regulation

Thyroid hormone has well-recognized effects on the cardiovascular system and blood pressure regulation. Blood pressure is altered across the entire spectrum of thyroid disease. The effects of hyperthyroidism include increased cardiac output, contractility, tachycardia, widened pulse pressure, decreased systemic vascular resistance, and increased basal metabolic rate. The manifestations of hypothyroidism are in marked contrast to those of hyperthyroidism and include decreased cardiac output, narrow pulse pressure, increased systemic vascular resistance, and decreased metabolic rate. Although thyroid hormone affects almost all tissues of the body and mediates changes in homeostasis, adaptations of the cardiovascular system can result in changes in blood pressure to accommodate the new demands on the system. In this paper, we review the direct and indirect thyroid hormone-mediated effects on blood pressure.

Effect of thyroid function on LDL oxidation in hypothyroidism and hyperthyroidism

Oxidized low-density lipoproteins (LDL) are highly suspected of initiating the atherosclerosis process. Hypothyroidism is frequently associated with hypercholesterolemia and carries increased risk for atherosclerosis. In contrast to hypothyroidism, hyperthyroidism is not associated with increased LDL cholesterol, but is associated with increased oxidized LDL. This study was designed to evaluate the changes in LDL oxidation in subjects with hypothyroidism or hyperthyroidism, and to reveal the effects of treatment in hypothyroidism and hyperthyroidism on LDL oxidation and lipid profiles. Thirty-two patients with hypothyroidism and 16 patients with hyperthyroidism were studied before the therapy and thereafter, when they were euthyroid with appropriate treatment. Plasma lipids and lipoproteins, and the oxidizability of LDL by determining the levels of malonaldehyde bis (dimethyacetyl) (MDA) and diene conjugation, were determined at baseline and after the patients were rendered euthyroid. The actual content of dienes in LDL particles was increased in hypothyroidism, with a decrease after T4 supplementation (p < .001). Dienes in LDL particles were increased in hyperthyroidism, with a decrease after treatment (p < .05). In hypothyroid patients, the lag phase was shorter in the pretreatment period than in the euthyroid period (p > .05). The lag phase of hyperthyroid patients was shorter in the pretreatment period than in the euthyroid period and hypothyroid state (p < .001). The Cu2+-catalyzed dienes of LDL and MDA oxidation in the hypothyroid state and the subsequent euthyroid states were decreased (p < .001). The Cu2+-catalyzed dienes of LDL (p < .01) and MDA oxidation (p < .001) in hyperthyroid patients after treatment were decreased. The enhanced LDL oxidation may play a role in the cardiac disease process in both hypothyroidism and hyperthyroidism.

Hemodynamic and tissue oxygenation responses to exercise and beta-adrenergic blockade in patients with hyperthyroidism

BACKGROUND

Exercise-induced dyspnea is a frequent feature in patients with hyperthyroidism.

HYPOTHESIS

Data from clinical studies to elucidate the origin of this symptom are lacking. In the current study, we examined the hemodynamic and oxygenation responses to exercise and beta-adrenergic blockade in patients with hyperthyroidism and their relationship with dyspnea.

METHODS

Hemodynamic studies were performed under resting conditions and after isotonic exercise in 15 patients with hyperthyroidism and 11 control subjects. Exercise was applied using a bicycle ergometer, with progressive loads. In the hyperthyroid group, measurements were repeated at rest and during supine exercise after administering 15 mg of intravenous metoprolol.

RESULTS

End-diastolic pulmonary artery pressure and cardiac index were higher in the hyperthyroid group than in controls (18.6 +/- 5.3 vs. 11.2 +/- 4.9 mmHg; p = 0.02, and 6.0 +/- 1.7 vs. 2.8 +/- 0.5 l/min/m2; p = 0.0001, respectively). After exercise, there was an increase in end-diastolic pulmonary artery pressure in the hyperthyroid group (18.6 +/- 5.3 to 25.5 +/- 9.9 mmHg; p = 0.02), revealing impaired cardiocirculatory reserve. Pulmonary arteriolar resistance increased significantly in parallel with end-diastolic pulmonary artery pressure after drug administration, suggesting an inadequate cardiovascular response after beta blockade in patients with hyperthyroidism.

CONCLUSION

We observed that functional left ventricular reserve is impaired in patients with hyperthyroidism, suggesting an explanation for the frequent symptom of dyspnea and impaired exercise tolerance. Moreover, we also suggest that beta-adrenergic blockade may adversely affect cardiovascular function in patients with hyperthyroidism.

Determination of LAG078, a lipid-lowering compound, in dog plasma using liquid chromatography-tandem mass spectrometry: application in a toxicokinetic study

A high throughput method was developed and validated for the quantitative determination of LAG078, a lipid-lowering compound, in dog plasma obtained during toxicokinetic studies. The method was based on reverse phase liquid chromatographic separation of the analyte from plasma extract followed by turbo-ionspray (TIS) in the negative ion mode and tandem mass spectrometry in the multiple reaction monitoring (MRM) mode. Extraction was performed using a combination of protein precipitation and liquid-liquid extraction in the 96-well plate format to increase the throughput of the method. Optimized chromatographic separation under basic condition (pH approximately 10) in a short polymer based column (50 mm x 2.0 mm i.d.) coupled with MRM mode of detection yielded clean chromatograms with minimal signal suppression. The standard curve was linear (r = 0.997) within the concentration range of 0.05 (lower limit of quantification; LLOQ) to 50 ng/ml using only 0.1 ml of dog plasma. The accuracy of the method varied from 95 to 100% with a precision (CV) of 3.04-10.8% over the concentration range. The method was simple, rapid, and robust.

Transient hyperthyroidism after withdrawal of antithyroid drugs in patients with Graves' disease

The development of silent thyroiditis in patients with a history of Graves' disease is common, especially in the postpartum period. We describe herein patients with Graves' disease who developed transient hyperthyroidism but not silent thyroiditis after withdrawal of antithyroid drug (ATD). If such patients are diagnosed as recurrence of Graves' disease, they may receive ATD or radioiodine therapy unnecessarily. We investigated the characteristics of these patients to prevent unnecessary therapy. We retrospectively studied 22 patients with Graves' disease who showed transient thyrotoxicosis after withdrawal of ATD. Two of 22 patients were male and the mean ages (+/- SD) were 33.7 +/- 12.6 yr. We observed these patients for 28.5 +/- 12.8 (mean +/- SD; range 12-53) months after transient thyrotoxicosis, and measured TSH, FT4, and TSH binding inhibitor immunoglobulin in sera. Radioiodine uptake was measured in 6 of them. The radioiodine uptake in the 4 patients was not suppressed (27.5%, 28.0%, 32.7%, 38.1%). These uptake levels indicate that their thyrotoxicosis was not caused by silent thyroiditis. Most of the 22 patients became euthyroid within 6 months. This study suggests a new therapeutic option as follows: in the case of young patients with mild thyrotoxicosis after withdrawal of ATD, physicians should follow them up for one month without medication unless they have unbearable symptoms or complications.

Effect of thyroid hormone on uncoupling protein-3 mRNA expression in rat heart and skeletal muscle

Thyroid hormones (triiodothyronine [T3] and thyroxine [T4]) stimulate UCP-3 expression in skeletal muscle. We examined whether thyroid hormone-induced changes in uncoupling protein (UCP)-3 mRNA expression are related to directs effects of T3 or reflect secondary effects of the hormone through stimulation of renin-angiotensin or beta-adrenergic systems. Hyperthyroidism was produced by three injections of 100 microg T3/100 g body weight on alternate days with or without concomitant treatment with either captopril (an angiotensin-converting enzyme [ACE] inhibitor), propranolol (a beta-blocker) or clenbuterol (a beta2-agonist). The relative abundance of UCP-3 mRNA was measured in ventricular myocardium and skeletal muscle (gastrocnemius and soleus). T3 resulted in a significant increase in the relative abundance of UCP-3 in heart and skeletal muscle (p < 0.05), and the effect was not altered by captopril or propanolol; the inhibitors alone had no effect of UCP-3 mRNA content. There was no synergistic or additive effect of T3 and clenbuterol on UCP-3 mRNA expression in skeletal muscle. Increased UCP-3 mRNA levels were associated with increased UCP-3 protein expression in skeletal muscle. We conclude that the effect of T3 on UCP-3 expression in cardiac and skeletal muscle is not dependent on either angiotensin II or the beta-adrenergic system and probably reflects a direct action of the hormone on UCP-3 gene expression.

Disfunções mínimas da tiróide: hipotiroidismo subclínico e hipertiroidismo subclínico

Hipotiroidismo subclínico (SHT) e hipertiroidismo subclínico (SCH) são definidos pelas concentrações normais de T4 e T3 livres séricos associadas com valores de TSH elevado (SHT) ou suprimido (SCH). As prevalências são baixas e sintomas e sinais de disfunção tiroideana escassos. No SHT, colesterol total e LDL-C estão ligeiramente elevados, e tratamento com levotiroxina pode influir nos valores dos lipídeos. Ocorre diminuição da contratilidade do miocárdio e aumento da resistência vascular periférica, que melhoram com o tratamento. Fibrilação atrial é mais freqüente no SCH, e há aumento do índice de massa do ventrículo esquerdo, da contratilidade cardíaca, disfunção diastólica e indução de batimentos atriais ectópicos que regridem com uso de beta-bloqueadores. No SCH, ocorre diminuição da densidade óssea. Depressão, doença do pânico e alterações de testes cognitivos são freqüentes no SHT. O tratamento do SHT é indicado com TSH sérico maior do que 8mU/L e presença de anticorpos antitiroideanos, e do SCH endógeno, quando existem sintomas, em idosos ou concentração de TSH menor do que 0,1mU/L.

Effect of thyroid hormone supplementation on survival of euthyroid dogs with congestive heart failure due to systolic myocardial dysfunction: a double-blind, placebo-controlled trial

Nineteen euthyroid dogs of 12 breeds with echocardiographic signs of dilated cardiomyopathy (DCM) and radiographic and clinical signs of congestive heart failure (CHF) were evaluated in a randomised, double-blind, and placebo-controlled study. The dogs received either thyroxine or placebo as an adjunct to digoxin, furosemide and propranolol. The group assignment of individual dogs and serum concentrations of thyroid hormones remained unknown to owners and investigators during the entire study period. Dogs were evaluated clinically and with electrocardiography (ECG), thoracic radiography, echocardiography and measurement of total thyroxine (tT4) and thyroid stimulating hormone (TSH) before beginning of the trial, and then one week, 2 months, 6 months and yearly after initial examination, and, when applicable, at the time of euthanasia. End-point of the study was euthanasia (n = 17) due to severe congestive heart failure or sudden death (n = 2). Survival times ranged from 17 to 1030 days (median 187 days) in the placebo group, and from 18 to 1000 days (median 73 days) in the treatment group. There was no statistically significant difference in survival times between the treatment group and the placebo group (p = 0.46). Post mortem and histopathologic examinations revealed the attenuated wavy fiber type of DCM in 11 dogs, and myocardial infarcts, arteriosclerosis and chronic valvular disease in one dog. In conclusion, there was a wide range in survival times of dogs treated with digoxin, furosemide and propranolol. Adding thyroid hormones to the treatment did not significantly influence survival.

Thyroxine-induced cardiac hypertrophy: influence of adrenergic nervous system versus renin-angiotensin system on myocyte remodeling

The present study assessed the possible involvement of the renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) in thyroxine (T4)-induced cardiac hypertrophy. Hemodynamic parameters, heart weight (HW), ratio of HW to body weight (HW/BW), and myocyte width were evaluated in absence of thyroid hormone (hypothyroidism) and after T4 administration. Male Wistar rats were used. Some were subjected to thyroidectomies, whereas hyperthyroidism was induced in others via daily intraperitoneal injection of T4 (25 or 100 microg x 100 g BW(-1) x day(-1)) for 7 days. In some cases, T4 administration was combined with the angiotensin I-converting enzyme inhibitor enalapril (Ena), with the angiotensin type 1 (AT1) receptor blocker losartan (Los) or with the beta-adrenergic blocker propanolol (Prop). Hemodynamics and morphology were then evaluated. Systolic blood pressure (SBP) was not altered by administration of either T4 alone or T4 in combination with the specific inhibitors. However, SBP decreased significantly in hypothyroid rats. An increased heart rate was seen after administration of either T4 alone or T4 in combination with either Los or Ena. Although the higher dose of T4 significantly increased HW, HW/BW increased in both T4-treated groups. Ena and Prop inhibited the increase in HW or HW/BW in hyperthyroid rats. Morphologically, both T4 dose levels significantly increased myocyte width, an occurrence prevented by RAS or SNS blockers. There was a good correlation between changes in HW/BW and myocyte width. These results indicate that T4-induced cardiac hypertrophy is associated with both the SNS and the RAS.

Cardiac changes in subclinical and overt hyperthyroid women: retrospective study

BACKGROUND

This retrospective and descriptive 4-year study was undertaken to describe cardiac changes in subclinical and overt hyperthyroidism.

METHODS

We revised the charts of 386 consecutive cardiopathic women whose blood samples were referred to the Radioimmunoassay Laboratory to evaluate thyroid function from 1 January 1997 through 31 December 2000.

RESULTS

After excluding women because euthyroid or hypothyroid, or taking amiodarone and women with hypertension, rheumatic disease, myocardial infarction, a total of 31 hyperthyroid women were thus selected for the study: 19 with subclinical hyperthyroidism and 12 with overt hyperthyroidism. The prevalence of atrial fibrillation did not differ between subclinical (48%) and overt (67%) hyperthyroid women, as well as left atrial dimension; the latter was larger in hyperthyroid (27.8+/-7.8 cm(2)/m(2)) than in control women (18.9+/-2.8 cm(2)/m(2)) (P<0.001). In the subclinical and overt hyperthyroidism, the heart rate (HR) was increased and left ventricular end diastolic (LVED) volume was reduced; in addition, only in overt hyperthyroidism, left ventricular (LV) mass was increased. A significant correlation between LV mass and free triiodothyronine was found.

CONCLUSION

HR increase and LVED decrease, both in subclinical and overt hyperthyroidism, indicate a global impairment of diastolic heart performance, complicated in overt hyperthyroidism by LV concentric hypertrophy. So, in our opinion, subclinical hyperthyroidism, far from being considered a simple laboratory finding, in clinical practice should be taken into serious consideration.

Increased pressor sensitivity to chronic nitric oxide deficiency in hyperthyroid rats

We studied the effects of a possible interaction between partial nitric oxide deficiency and thyroid hormone excess on the long-term control of blood pressure (BP) and morphological and renal variables and examined the role of the renin-angiotensin system in the increased BP of this interaction. Eight groups (n=8 each) of male Wistar rats were used: a control group; 3 groups that were treated with thyroxine (50 microg/d), Nw-nitro-L-arginine methyl ester (L-NAME; subpressor dose, 1.5 mg x kg(-1) d(-1)), or thyroxine plus L-NAME; and another 4 similarly treated groups that received losartan (20 mg x kg(-1) x d(-1)) in their drinking fluid. All treatments were maintained for 3 weeks. The time course of tail systolic BP was recorded once a week. At the end of the experimental period, we measured mean arterial pressure in conscious rats and assessed the morphological, metabolic, plasma, and renal variables. Thyroxine produced a mild BP increase from the second week of treatment and an increase in plasma angiotensin II and plasma nitrates/nitrites by the end of the study. Simultaneous administration of thyroxine and a subpressor dose of L-NAME produced a marked BP increase that reached significance from the first week of treatment. Losartan produced normotension in thyroxine-treated rats and attenuated the BP elevation in thyroxine+L-NAME-treated rats. Hyperthyroid rats showed relative renal and ventricular hypertrophy, absence of absolute left ventricular hypertrophy, and proteinuria. These alterations were not changed by losartan. We conclude that an impaired nitric oxide system might have a counterregulatory homeostatic role against the prohypertensive effects of thyroid hormone and that the renin-angiotensin system plays an important role in thyroxine+L-NAME hypertension.

Cardiovascular manifestations of thyroid storm: a case report

We present a case of thyroid storm manifesting as supraventricular tachycardia with cardiopulmonary dysfunction. Our patient presented with severe cardiopulmonary symptoms (tachycardia, respiratory distress, and pulmonary edema) refractory to standard medical treatment. When the diagnosis of thyroid storm was made and proper treatment initiated, our patient had a prompt and appropriate response.

Role of endothelium-derived relaxing factors in the renal response to vasoactive agents in hypothyroid rats

This study analyzed the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in the abnormal renal vascular reactivity of hypothyroid rats. Renal responses to vasoconstrictors [VC: phenylephrine (PHE) and ANG II] and vasodilators [VD: ACh, sodium nitroprusside (SNP), and papaverine (PV)] were studied in kidneys from control and hypothyroid rats under normal conditions and after NO or EDHF blockade. NO was blocked by the administration of Nomega-nitro-l-arginine methyl ester (l-NAME) and EDHF by the administration of tetraethylammonium (TEA) or by an increased extracellular K+. The response to VC was also evaluated after endothelium removal. Hypothyroid kidneys showed reduced responsiveness to PHE and a normal response to ANG II. l-NAME and TEA administration produced an increased sensitivity to PHE and to ANG II in control preparations. l-NAME also increased the response to PHE in hypothyroid kidneys, but the differences between control and hypothyroid kidneys were maintained. TEA administration did not change the response to either VC in hypothyroid preparations. In endothelium-removed preparations, TEA was unable to increase pressor responsiveness to VC. Hypothyroid kidneys showed reduced responsiveness to ACh and SNP and normal response to PV. The differences between hypothyroid and control preparations in the responses to ACh and SNP were maintained after l-NAME or increased K+. In conclusion, this study shows that 1) the attenuated response to PHE in hypothyroidism is not related to an increased production of endothelium-derived relaxing factors NO and EDHF; 2) the response to VC in hypothyroid preparations is insensitive to EDHF blockade; and 3) hypothyroid preparations have a reduced reactivity to the NO donor, and NO-independent vasodilatation remains unaffected.

Triiodothyronine-mediated myosin heavy chain gene transcription in the heart

We developed an RT-PCR assay to study both the time course and the mechanism for the triiodothyronine (T(3))-induced transcription of the alpha- and beta-myosin heavy chain (MHC) genes in vivo on the basis of the quantity of specific heterogeneous nuclear RNA (hnRNA). The temporal relationship of changes in transcriptional activity to the amount of alpha-MHC mRNA and the coordinated regulation of transcription of more than one gene in response to T(3) are demonstrated here for the first time. Quantitation of alpha-MHC hnRNA demonstrated that T(3) induced alpha-MHC transcription in hypothyroid rats within 30 min of a single injection of T(3) (0.5 microg/100 g body wt). Maximal transcription rates (135% +/- 15.8 of euthyroid values) occurred 6 h after injection and subsequently declined in parallel with serum T(3) levels. The transcription of beta-MHC was reduced to 86% of peak hypothyroid levels 6 h after a single T(3) injection and reached a nadir of 59% of hypothyroid levels at 36 h. Analysis of the time course of T(3)-mediated induction of alpha-MHC hnRNA and repression of beta-MHC hnRNA indicates that separate molecular mechanisms are involved in the coordinated regulation of these genes.

Subclinical thyroid disorders: the menace of the Trojan horse

This review aims at summarizing some new data regarding the so-called subclinical thyroid disease and incorporate the knowledge in order to provide a basis for a more careful approach to these morbidities. SHyper represents a considerable risk factor for atrial fibrillation in the elderly and also for osteoporosis, which is a major cause of morbidity in postmenopausal women. SHypo is not an innocuous condition. It progresses to thyroid failure in patients with positive thyroid antibodies, it affects neurobehavior, it may influence cardiac contractility at exercise and it is associated with an impaired lipid profile that may provoke atherosclerosis. Therefore, both conditions should be screened more carefully in the community and treatment should be more often considered.

Absolute configuration of the thyroid hormone analog KAT-2003 as determined by the1H NMR anisotropy method with a novel chiral auxiliary, M?NP acid

The absolute configuration of the chiral thyroid hormone analog KAT-2003 (+)-2, showing hypocholesterolemic activities, decreases of hepatic triglyceride contents with lowering cardiac side effects, and significant inhibitory effect for the second primary hepatocellular carcinoma, was determined as S by the (1)H NMR anisotropy method using a novel chiral auxiliary, 2-methoxy-2-(1-naphtyl)propionic acid (MalphaNP acid).

Different gene expression of potassium channels by thyroid hormone and an antithyroid drug between the atrium and ventricle of rats

Thyroid hormone has been shown to modulate the gene expression of cardiac potassium channels, however, it is not known if gene expression is different between the atrium and the ventricle. The long-term effects of thyroid hormone on nuclear thyroid hormone receptors are also not known. Triiodothyronine (T3) at 25 microg/100 g of body weight or propylthiouracil (PTU) at 4 mg/100 g of body weight was given to adult rats via a gastric tube for 14 days. The levels of mRNA of Kv1.2. Kv1.4, Kv1.5, Kv2.1, Kv4.2, erg, LQT1, and minK were assayed by RNase protection assay. The mRNA of nuclear T3-receptor-al and T3-receptor-beta1 were also assayed for 15 days. After T3 (or PTU), plasma free T3 and free T4 increased (or decreased) significantly. The mRNA levels of Kv1.2 and Kv1.4 were reduced after T3 in the atrium and the ventricle. while PTU increased the levels in both chambers. Kv1.5 was significantly up-regulated by T3 in the atrium and the ventricle (P < 0.02 for both) and PTU decreased its expression in the ventricle (P < 0.02). Kv2.1 and Kv4.2 were not affected by T3 or PTU. mRNA of erg was not affected by T3 in the atrium but decreased in the ventricle (P < 0.01). After PTU, erg mRNA was decreased in the atrium (P < 0.02) but increased in the ventricle (P < 0.01). LQT1 was decreased by T3 in both chambers (P < 0.01) and not affected by PTU. minK was not detectable in the control state and was up-regulated only in the atrium: a peak on the 4th day followed by a decline to the undetectable level on the 10-15th days. During T3 treatment, nuclear T3-receptor-alpha1 and beta1 mRNA were decreased in the initial 3 days but returned to control levels thereafter.

CONCLUSIONS

Between the atrium and ventricle of the adult rat heart, the responses of gene expression of voltage-gated potassium channels to T3 or PTU were quantitatively or qualitatively different and the differential responses may explain cardiac manifestations of hyperthyroidism, which is a frequent complication of supraventricular arrhythmia.

[Reference figures for pulmonary artery pressures after effective treatment of Graves' disease]

We report the case of a 48-year-old woman with a diagnosis of pulmonary hypertension and hyperthyroidism (Graves' disease) in whom pulmonary artery pressures became normal after treatment of thyroid disease. The possible pathogenic mechanisms involved in this association include the presence of hyperdynamic heart failure and/or the presence of immune alterations underlying both conditions.

Euthyroid sick syndrome in acute ischemic syndromes

The purposes of this study were to assess the occurrence of euthyroid sick syndrome in patients with acute myocardial infarction (AMI) or unstable angina (UA), and the relationship with beta-blocker or thrombolytic therapy. Plasma triiodothyronine (T3), reverse T3 (rT3), free T3 (FT3), thyroxine (T4), free T4 (FT4), thyroid-stimulating hormone (TSH), thyroxine-binding globulin (TBG), and albumin (ALB) levels were determined in 95 patients (59 males, 36 females, aged 58.4+/-9) with AMI and 19 patients (13 males, 6 females aged 54.7+/-12.3) with UA for 5 consecutive days from the onset of the acute syndrome and 1 month later. Patients were divided according to beta-blocker therapy and thrombolytic therapy. There was a significant T3 decrease and rT3 increase in all patients during the first 5 days following admission (p < 0.05). FT3 and FT4 remained unchanged during the study. In patients with complicated infarctions, the rT3 increase and the T3 decrease were significantly greater compared to those with uncomplicated infarctions (p<0.03). TSH, T4, TBG, and ALB were significantly (p<0.05) decreased only in complicated infarctions. No differences were observed between patients with or without thrombolysis or patients with or without beta-blocker treatment. The apparent decrease in T3, the increase in rT3 levels and the decreased TSH and T4 levels, show clearly that the euthyroid sick syndrome (low T3) occurs not only in AMI but also in UA. In addition, these hormonal changes are not affected by beta-blocker therapy and thrombolysis does not influence the occurrence of the syndrome. The degree of T3 decrease is proportional to the severity of cardiac damage and may have a possible prognostic value.

Thyroid hormone and cardiac function in mice deficient in thyroid hormone receptor-alpha or -beta: an echocardiograph study

We investigated the effect of thyroid hormone (TH) receptor (TR)alpha and -beta isoforms in TH action in the heart. Noninvasive echocardiographic measurements were made in mice homozygous for disruption of TRalpha (TRalpha(0/0)) or TRbeta (TRbeta(-/-)). Mice were studied at baseline, 4 wk after TH deprivation (using a low-iodine diet containing propylthiouracil), and after 4-wk treatment with TH. Baseline heart rates (HR) were similar in wild-type (WT) and TRalpha(0/0) mice but were greater in TRbeta(-/-) mice. With TH deprivation, HR decreased 49% in WT and 37% in TRbeta(-/-) mice and decreased only 5% in TRalpha(0/0) mice from baseline, whereas HR increased in all genotypes with TH treatment. Cardiac output (CO) and cardiac index (CI) in WT mice decreased (-31 and -32%, respectively) with TH deprivation and increased (+69 and +35%, respectively) with TH treatment. The effects of CO and CI were blunted with TH withdrawal in both TRalpha(0/0) (+8 and -2%, respectively) and TRbeta(-/-) mice (-17 and -18%, respectively). Treatment with TH resulted in a 64% increase in LV mass in WT and a 44% increase in TRalpha(0/0) mice but only a 6% increase in TRbeta(-/-) mice (ANOVA P < 0.05). Taken together, these data suggest that TRalpha and TRbeta play different roles in the physiology of TH action on the heart.

Methimazole interferes with the progression of experimental autoimmune myocarditis in rats

In order to ascertain whether methimazole, a drug commonly used for the treatment of hyperthyroidism, interferes with the progression of autoimmune-mediated myocardial injury, we investigated the effect of methimazole on experimental autoimmune myocarditis (EAM) in rats. EAM was induced by immunization with porcine cardiac myosin. Methimazole administration markedly slowed the body weight growth in both normal and EAM rats, but did not induce morphologic change of cardiac tissue in normal rats. In EAM rats, macroscopic examination revealed discoloration of the cardiac surface, and histopathological examination by light microscopy showed extensive myocardial necrosis, infiltration by inflammatory cells and myocardial fibrosis. In the EAM rats treated with methimazole, the discolored areas on the cardiac surface were markedly diminished in size, and the myocardial necrosis, cellular infiltration and fibrosis were significantly less severe. To identify the mechanism responsible of this effect, we investigated the change of regulatory lymphocyte subsets in peripheral blood using an immunofluorescence technique with a flow cytometer. A decrease in the helper/suppressor T cell ratio as a result of the increased proportion of suppressor T cells and a decrease in the proportion of B cells were observed in normal rats after methimazole administration, and similar findings were made in the EAM rats treated with methimazole. These results indicate that methimazole interferes with the progression of EAM, and immunosuppression may, at least in part, be involved in the inhibitory effect of methimazole on EAM in rats.

Management of patients with thyroid disease: oral health considerations

BACKGROUND

The thyroid gland and its hormones play an important role in the regulation of growth, development and metabolic functions of the body. Thyroid diseases include a group of conditions that can affect the delivery of dental care.

LITERATURE REVIEWED

The authors conducted a MEDLINE search of the medical and dental literature concerning thyroid disease and its management published between 1980 and 2000. The authors found eight published articles concerning this topic in the dental literature; a few of the articles specifically addressed thyroid disease and dental care. They reviewed the medical literature within the scope of provision of dental care.

CONCLUSIONS

The oral health care professional can play a role in the screening of dental patients who have undiagnosed thyroid disease. In addition, to treat patients who have thyroid disease, a thorough understanding of the many related pathological conditions, as well as the signs and symptoms that can occur, is needed. Specific dental treatment protocols for these patients are not found in the medicodental literature published between 1980 and 2000.

CLINICAL IMPLICATIONS

As part of a health care team, the dentist plays an important role in detecting thyroid abnormalities. Modifications of dental care must be considered when treating patients who have thyroid disease.

Increased stiffness in common carotid artery in hyperthyroid Graves' disease patients

The present study was undertaken to assess the effect of hyperthyroidism on stiffness in the common carotid artery (CCA) in patients with Graves' disease (GD) and elucidate the mechanism by which arterial stiffness is increased in hyperthyroidism. The arterial stiffness index beta (stiffness beta) was evaluated in the CCA using an ultrasonic phase-locked echo-tracking system. Stiffness beta was defined as the logarithm of the ratio of systolic to diastolic blood pressure divided by the fractional diameter increase during the cardiac cycle and thus established as a measure of arterial stiffness uninfluenced by the change in blood pressure. Seventy euthyroid GD patients were measured for CCA stiffness beta to determine its relationship to retinal blood flow and plasma levels of vascular injury markers. To investigate the effect of hyperthyroidism, 27 GD patients were measured for changes during antithyroid drug (ATD) therapy in stiffness beta and in hemodynamic parameters, retinal blood flow and plasma vascular injury markers. In euthyroid GD patients, stiffness beta in the CCA showed a significant and positive correlation with systolic blood pressure and pulse pressure, but not with peripheral blood flow in the central retinal artery. ATD therapy significantly reduced stiffness beta from 5.23 +/- 2.10 to 4.36 +/- 1.48. The fractional reduction of stiffness beta during ATD therapy correlated significantly with reductions in pulse pressure and retinal blood flow, but not with the reductions in systolic and mean blood pressure, or any of the plasma injury markers. In summary, the significant increase in stiffness beta in the hyperthyroid state may reflect the harmful effect of hyperthyroidism on the arterial wall, which may in turn result from increased stroke volume.

Hyperthyroidism and the management of atrial fibrillation

Atrial fibrillation is often induced in patients with hyperthyroidism and may trigger heart failure. Its prevalence and outcome were examined to obtain up-to-date information. Persistent atrial fibrillation was observed in approximately 1.7% of new hyperthyroid patients. It occurs more frequently in males (2.86%) than in females (1.36%), even though the number of male hyperthyroid patients is only one fifth of female patients. The rate increased with age, being 8% in the patients older than 70 years old. The initial treatment is to control the heart rate with routine pharmacologic therapy and to start antithyroid therapy as quickly as possible. Attempted cardioversion should be deferred until approximately the fourth month of maintaining a euthyroid state, because more than 56% of atrial fibrillation spontaneously reverts to sinus rhythm when the thyroid hormone levels start to decline. Elective cardioversion for those whose atrial fibrillation persists is highly effective and sinus rhythm maintenance rates were 56.7% and 47.6% at the 10th and the 14th year, respectively, even though the duration of atrial fibrillation prior to cardioversion was extremely long (35.0 +/- 29.0 months).

The role of thyroid hormone in blood pressure homeostasis: evidence from short-term hypothyroidism in humans

Arterial hypertension is known to be frequently associated with thyroid dysfunction, with a particularly high prevalence in chronic hypothyroidism. However, to our knowledge no comprehensive study addressed causal mechanisms possibly involved in this association. We here report the physiological relationships between blood pressure and neuro-humoral modifications induced by acute hypothyroidism in normotensive subjects. Twelve normotensive patients with previous total thyroidectomy were studied. Ambulatory 24-h blood pressure monitoring was performed, and free T(3), free T(4), TSH, PRA, aldosterone, cortisol, adrenaline, and noradrenaline were assayed 6 wk after oral L-T(4) withdrawal (phase 1) and 2 months after resumption of treatment (phase 2). During the hypothyroid state (TSH, 68.1 +/- 27.7 microIU/ml; mean +/- SD), daytime arterial systolic levels slightly, but significantly, increased (125.5 +/- 9.7 vs. 120.4 +/- 10.8 mm Hg; P < 0.05), and daytime diastolic levels (84.6 +/- 7.9 vs. 76.4 +/- 6.8 mm Hg; P < 0.001), noradrenaline (2954 +/- 1578 vs. 1574 +/- 962 pmol/liter; P < 0.001), and adrenaline (228.4 +/- 160 vs. 111.3 +/- 46.1 pmol/liter; P < 0.05) also increased. PRA remained unchanged (0.49 +/- 0.37 vs. 0.35 +/- 0.21 ng/ml.h; P = NS), whereas both aldosterone (310.3 +/- 151 vs. 156.9 +/- 67.5 pmol/liter; P < 0.005) and cortisol (409.2 +/- 239 vs. 250.9 +/- 113 pmol/liter; P < 0.02) significantly increased. By using univariate logistic regression daytime arterial diastolic values, noradrenaline and aldosterone were found to be significantly related to the hypothyroid state (P < 0.02, P < 0.036, and P < 0.024, respectively). In conclusion, our data show that thyroid hormones participate in the control of systemic arterial blood pressure homeostasis in normotensive subjects. The observed sympathetic and adrenal activation in hypothyroidism, which is reversible with thyroid hormone treatment, may also contribute to the development of arterial hypertension in human hypothyroidism.

Hyperthyroidism and pulmonary hypertension

In recent years, many authors have described several cases revealing an association between hyperthyroidism and pulmonary hypertension (PH). This observational study was designed to evaluate the incidence of PH in hyperthyroidism and was set in a department of internal medicine and pulmonary diseases with an out-patients department of endocrinology. Thirty-four patients, 25 women and nine men, with a mean age of 38 +/- 15 SD years participated. Twenty had Graves' disease and 14 had a nodular goitre. The patients were divided into two equally matched groups: those with a recently diagnosed hyperthyroidism, taking no drugs (group 1; n = 17) and those in a euthyroid state taking methimazole (group 2; n= 17). Transthoracic Doppler echocardiography was performed and systolic pulmonary artery pressurements of (PAPs) was determined by the tricuspid regurgitation method using the Bernoulli equation. Measurements of triiodothyronine, tetraiodothyronine, free thyroxine (Ft4), thyroid-stimulating hormone (TSH) and antithyroglobulin and antimicrosomal antibodies were also taken. We found a mild PH in seven patients of group 1 and in none of group 2. The mean +/- SD systolic pulmonaryartery pressurewas 28.88 +/- 6.41 in group 1 and 22.53 +/- 1.84 ingroup 2 (P<0.0001). A correlation was found between the TSH value and PAPs (r = -082;P < 0.001) and Ft4 and PAPs (r = 0 85; P < 0.001) in group 1. These findings indicate the presence of a frequent association between PH and hyperthyroidism. We suggest that hyperthyroidism be included in the differential diagnosis of PH.

Thyroid disease and lipids

The composition and the transport of lipoproteins are seriously disturbed in thyroid diseases. Overt hypothyroidism is characterized by hypercholesterolaemia and a marked increase in low-density lipoproteins (LDL) and apolipoprotein B (apo A) because of a decreased fractional clearance of LDL by a reduced number of LDL receptors in the liver. The high-density lipoprotein (HDL) levels are normal or even elevated in severe hypothyroidism because of decreased activity of cholesteryl-ester transfer protein (CETP) and hepatic lipase (HL), which are enzymes regulated by thyroid hormones. The low activity of CETP, and more specifically of HL, results in reduced transport of cholesteryl esters from HDL(2) to very low-density lipoproteins (VLDL) and intermediate low-density lipoprotein (IDL), and reduced transport of HDL(2) to HDL(3). Moreover, hypothyroidism increases the oxidation of plasma cholesterol mainly because of an altered pattern of binding and to the increased levels of cholesterol, which presents a substrate for the oxidative stress. Cardiac oxygen consumption is reduced in hypothyroidism. This reduction is associated with increased peripheral resistance and reduced contractility. Hypothyroidism is often accompanied by diastolic hypertension that, in conjunction with the dyslipidemia, may promote atherosclerosis. However, thyroxine therapy, in a thyrotropin (TSH)-suppressive dose, usually leads to a considerable improvement of the lipid profile. The changes in lipoproteins are correlated with changes in free thyroxine (FT(4)) levels. Hyperthyroidism exhibits an enhanced excretion of cholesterol and an increased turnover of LDL resulting in a decrease of total and LDL cholesterol, whereas HDL are decreased or not affected. The action of thyroid hormone on Lp(a) lipoprotein is still debated, because both decrease or no changes have been reported. The discrepancies are mostly because of genetic polymorphism of apo(a) and to the differences between the various study groups. Subclinical hypothyroidism (SH) is associated with lipid disorders that are characterized by normal or slightly elevated total cholesterol levels, increased LDL, and lower HDL. Moreover, SH has been associated with endothelium dysfunction, aortic atherosclerosis, and myocardial infarction. Lipid disorders exhibit great individual variability. Nevertheless, they might be a link, although it has not been proved, between SH and atherosclerosis.

Association between increased levels of reverse triiodothyronine and mortality after acute myocardial infarction

PURPOSE

The thyroid hormone system may be downregulated temporarily in patients who are severely ill. This "euthyroid sick syndrome" may be an adaptive response to conserve energy. However, thyroid hormone also has beneficial effects on the cardiovascular system, such as improving cardiac function, reducing systemic vascular resistance, and lowering serum cholesterol levels. We investigated whether thyroid hormone levels obtained at the time of myocardial infarction are associated with subsequent mortality.

PATIENTS AND METHODS

Serum levels of thyroid hormones (triiodothyronine [T3], reverse T3, free thyroxine [T4], and thyroid-stimulating hormone) were measured in 331 consecutive patients with acute myocardial infarction (mean age [+/- SD], 68 +/- 12 years), from samples obtained at the time of admission.

RESULTS

Fifty-three patients (16%) died within 1 year. Ten percent (16 of 165) of patients with reverse T3 levels (an inactive metabolite) >0.41 nmol/L (the median value) died within the first week after myocardial infarction, compared with none of the 166 patients with lower levels (P <0.0004). After 1 year, the corresponding figures were 24% (40 of 165) versus 7.8% (13 of 166; P <0.0001). Reverse T3 levels >0.41 nmol/L were associated with an increased risk of 1-year mortality (hazard ratio = 3.0; 95% confidence interval: 1.4 to 6.3; P = 0.005), independent of age, previous myocardial infarction, prior angina, heart failure, serum creatinine level, and peak serum creatine kinase-MB fraction levels.

CONCLUSION

Determination of reverse T3 levels may be a valuable and simple aid to improve identification of patients with myocardial infarction who are at high risk of subsequent mortality.

Dehydroepiandrosterone sulphate is increased and dehydroepiandrosterone-response to corticotrophin-releasing hormone is decreased in the hyperthyroid state compared with the euthyroid state

OBJECTIVE

Dehydroepiandrosterone (DHEA) and DHEA-sulphate (S) have been suggested to play protective roles in many pathological states, some of which are observed in hyperthyroidism. If DHEA and DHEA-S levels change in hyperthyroidism, they might participate as a possible causative link with such pathophysiological changes in hyperthyroidism. However, the CRH-ACTH-DHEA system in hyperthyroidism has not been clearly defined. We examined plasma levels of DHEA and DHEA-S together with ACTH and cortisol in both hyperthyroid (Hyper) and euthyroid states (Eu).

METHODS

Eighteen patients (5 men and 13 women, aged 46.9 +/- 2.8 years) with Graves' disease were studied before treatment and again in the euthyroid state following treatment with methimazole. A 100 microg hCRH stimulation test and a low-dose (0.5 microg) 1-24 ACTH stimulation test were performed on separate days. Basal levels and A area under the response curve (AUC) were compared between Hyper and Eu.

RESULTS

DHEA-S was higher in Hyper than in Eu. However, basal DHEA did not differ between Hyper and Eu. The ratio of DHEA to DHEA-S was lower in Hyper than in Eu. AAUC of DHEA during a CRH test was lower in Hyper than in Eu. However, AAUC of DHEA during an ACTH test was similar in both Hyper and Eu. Basal ACTH was higher in Hyper than in Eu. In both CRH and ACTH tests, AAUC of cortisol response was lower in Hyper than in Eu, although the basal cortisol level was not different.

CONCLUSION

The balance of the conversion between DHEA-S and DHEA in the hyperthyroid state favoured DHEA-S. Similar to cortisol, the DHEA response in the CRH test in hyperthyroidism seemed to be insufficiently compensated for by increased ACTH, although the DHEA response to low-dose ACTH was similar in the hyperthyroid and euthyroid states. Increased DHEA-S might play some role in the pathological states in many organs in hyperthyroidism.

Triiodothyronine supplementation in patients undergoing cardiopulmonary bypass

Patients undergoing cardiopulmonary bypass may develop clinically significant physiologic alterations in the perioperative period, including alteration of thyroid hormone concentrations. Alterations in the concentration of thyroid hormones are of concern due to the effects of these hormones on cardiac function. Hypothyroidism is associated with a decrease in cardiac performance; therefore, supplementation with the active thyroid hormone triiodothyronine (T3) in patients undergoing cardiopulmonary bypass has been investigated to improve outcomes. In addition, T3 has been studied as an agent to reduce the frequency of atrial fibrillation after cardiopulmonary bypass.

Estrogen and tamoxifen interplay with T(3) in male rats: pharmacologically distinct classes of estrogen responses affecting growth, bone, and lipid metabolism, and their relation to serum GH and IGF-I

Estrogen (E) and T(3) regulate gene expression by receptor mechanisms that may enable hormonal interplay affecting growth and metabolism. Prior studies of E and tamoxifen (TM) interplay with T(3) in female rats identified a subset of E responses that required T(3) for expression and exhibited large agonist responses to TM. In contrast, TM acted more like an antagonist in most T(3)-independent E responses. This study used male rats to further explore the role of T(3) in E effects on growth and metabolism, and the relation of such effects to changes in serum GH and IGF-I. Orchidectomized, hypothyroid rats were treated 6 wk with vehicle, E2 benzoate (E2B), or TM with or without T(3). The following parameters were measured: body weight change; tibia length and bone mineral density; heart and kidney weight; food intake and body temperature; serum levels of glucose, cholesterol, triglycerides, GH, and IGF-I; seminal vesicle weight; and anterior pituitary levels of GH, PRL, glandular kallikrein, and total protein. Interplay with T(3) contributed to multiple E effects on growth and metabolism, and some E responses involved both T(3)-dependent and T(3)-independent components. Both E2B and TM increased serum GH, but the increases were poorly coupled to IGF-I. Correlation/regression analysis of individual rat data sets suggested distinct roles for GH and IGF-I in specific E effects. E2B and TM effects on somatic growth exhibited positive correlations with IGF-I and negative correlations with GH; effects on bone mineral density and triglycerides exhibited positive correlations with GH and negative correlations with IGF-I. Three pharmacologically distinct classes of in vivo E responses were identified in this study, and TM displayed a profile of biological activity that may be useful for men undergoing androgen-deprivation therapy.

Negative functional effects of cGMP mediated by cGMP protein kinase are reduced in T4 cardiac myocytes

We tested the hypothesis that in isolated rabbit cardiac myocytes, the negative functional effects of cyclic GMP are partly mediated by cyclic GMP-dependent protein kinase activity, and that these effects are altered in thyroxine (T4, 0.5 mg/kg/day for 16 days)-induced hypertrophic myocytes. Using isolated ventricular myocytes from control (N=8) and T4 (N=8) hypertrophic hearts, data for percent cell shortening (%) and maximum rate of contraction (microm/s) were collected using a video edge detector at baseline, after the addition of 10(-6) M 8-bromo-cyclic GMP (8-Br-cGMP), 10(-5) M 8-Br-cGMP, and 10(-6) M KT5823 (10-methoxy-10-methoxycarbonyl-9, 10, 11, 12-tetrahydro-9, 12-epoxy-(1H)-diinidolo [1, 2, 3, f-g: 3', 2', 1'-k-j]-pyrrolidino-[3,4-i] [1,6]-benzodiazocin-2-methyl-1-one, cyclic GMP protein kinase inhibitor). Protein phosphorylation was determined autoradiographically after gel electrophoresis. In both control and T(4) myocytes, 8-Br-cGMP caused a significant decrease in percent shortening (5.56+/-0.49% to 3.02+/-0.47% in control and 4.34+/-0.33% to 3.13+/-0.17% in T4 myocytes) and maximal rate of contraction 57.35+/-6.05 to 36.82+/-3.17 microm/s in control and 58.49+/-3.28 to 42.88+/-2.29 microm/s in T4 myocytes). KT5823 significantly increased percent shortening to 3.77+/-0.28% and rate to 48.68+/-4.71 microm/s after 8-Br-cGMP only in control myocytes. In T4 myocytes, the changes in percent shortening and rate after KT5823 were not significant. Protein phosphorylation was increased by 8-Br-cGMP in control and to a lesser extent in T4 myocytes, but the increment was reduced by KT-5823 in control only. These data demonstrated that cyclic GMP had negative functional effects partially mediated by cyclic GMP protein kinase in control myocytes. Cyclic GMP also exerted negative functional effects in thyroxine-induced hypertrophic myocytes, but cyclic GMP protein kinase activity was not an important regulator of these effects in T4 ventricular myocytes.

Re-evaluation of the thyroxine binding to human plasma lipoproteins using three techniques

Using gel filtration chromatography (GFC), we found that human VLDL, LDL and HDL transport approximately 0.03, 0.2 and 3% of plasma T4. As T4 could dissociate from carriers during GFC, we evaluated [125I]T4 transport to lipoproteins (Lp) in 50 normolipidemic and euthyroid subjects by GFC and 2 independent methods: zone electrophoresis (ZE) and radioimmunoprecipitation (RIP). At GFC, VLDL+LDL transported less T4 (approximately 0.3%) than either ZE (approximately 1.3%) or RIP (approximately 1.5-2.0%). In contrast, GFC values for the HDL (approximately 3%) were close to the RIP values (approximately 3.5%), but lower than ZE (approximately 8.5%) because of partial co-migration with TBG. In conclusion, GFC underestimates T4 binding to VLDL and LDL, which, indeed, is of the same magnitude as binding of some steroid hormones to CBG and SHBG. Hence, the anti-atherosclerotic effects of T4 resulting from binding to the LDL should be greater than anticipated based on GFC data.

Renin-angiotensin system contribution to cardiac hypertrophy in experimental hyperthyroidism: an echocardiographic study

The objective of this study was to evaluate, using echocardiography, the involvement of the renin-angiotensin system (RAS) in left ventricular (LV) hypertrophy development in experimental hyperthyroidism. Thyrotoxicosis was produced by a daily intraperitoneal injection of L-thyroxine (T4), 0.1 mg/kg per day for 15 days in Wistar rats. Control (euthyroid) rats received intraperitoneal daily injection of the thyroxine solvent. Two series of experiments were performed. In the first series, euthyroid (n = 10) and hyperthyroid (n = 14) rats were surgically prepared with a femoral artery catheter. After a 3-day recovery period, blood pressure and heart rate were measured and blood samples were collected in conscious and unrestrained rats. In the second series of experiment, measurement of LV geometry was realized with two-dimensional time-movement echocardiography on the 15th day of treatment in control conditions and after long-term treatment with the angiotensin II type I receptor antagonist valsartan (10 mg/kg per day for 15 days) in both euthyroid and hyperthyroid rats. The dose and duration of T4 treatment was sufficient to induce a significant degree of hyperthyroidism with characteristic features including tachycardia, systolic hypertension, myocardial hypertrophy, hyperthermia, and weight loss. In addition, we measured an increase in free fractions of thyroid hormones, and a threefold increase in plasma renin activity. Echocardiographic examinations in rats revealed a strong correlation between LV weight and echocardiographic LV mass. Hyperthyroid rats exhibited an increased LV mass with a marked increase in the LV end-diastolic posterior wall and septal thickness. Chronic treatment with valsartan prevented this concentric LV hypertrophy (p < 0.01), with full prevention of the LV posterior wall hypertrophy (p < 0.001) and decreased LV septal hypertrophy (p < 0.05). In conclusion, the cardiovascular alterations of hyperthyroidism were reproduced with thyroid hormone injections in rats. Activation of the RAS in hyperthyroid rats was accompanied by increased LV mass. Using valsartan, we demonstrated that the RAS impinged on the LV remodelling in our experimental hyperthyroidism model. A chronic treatment with an angiotensin II type I receptor antagonist prevented the development of the concentric LV hypertrophy associated with thyrotoxicosis.

Cardiac ion channel expression and contractile function in mice with deletion of thyroid hormone receptor alpha or beta

Cardiac myocytes express the two thyroid hormone receptors (T(3)Rs), T(3)Ralpha and T(3)Rbeta. However, which isoform contributes to specific, T(3)-induced alterations of cardiac function remains unclear. Here, we used individual T(3)R isoform knockout (KO) mice to study the effects of T(3)Ralpha and T(3)Rbeta in the heart. Our findings indicate that potassium channel genes that code for K(+) channels involved in action potential repolarization, like KV 4.2 and minK, are T(3)Ralpha targets. Both are markedly regulated by thyroid status. The recently identified cyclic nucleotide-gated channels, HCN2 and HCN4, are targets of T(3)Ralpha and are unchanged in a euthyroid T(3)Rbeta KO. However, these transcripts respond markedly to altered T(3) signaling concomitant with bradycardia in T(3)Ralpha KO and hypothyroid animals, as well as tachycardia in hyperthyroid T(3)Rss KO mice. SERCA2a and myosins are T(3) regulated and were also targets of T(3)Ralpha, and the papillary muscles of alphaKO animals showed a slowed rate of force development. Because of the absence of significant cardiac effects in euthyroid T(3)Rss KO mice, we determined messenger RNA levels for both T(3)Ralpha and T(3)Rss in the heart. We found that T(3)Rss is present at a 1:3 ratio to T(3)Ralpha1. We conclude that the cardiac phenotype regulated by T(3) is predominantly mediated by T(3)Ralpha and that the lack of T(3)Ralpha cannot be compensated by T(3)Rss in the heart.

Effect of thyroid hormones on mitochondrial oxygen free radical production and DNA oxidative damage in the rat heart

Mitochondria seem to be involved in oxygen radical damage and aging. However, the possible relationships between oxygen consumption and oxygen radical production by functional mitochondria, and oxidative DNA damage, have not been studied previously. In order to analyze these relationships, male Wistar rats of 12 weeks of age were rendered hyper- and hypothyroid by chronic T(3) and 6-n-propyl-2-thiouracil treatments, respectively. Hypothyroidism decreased heart mitochondrial H(2)O(2) production in States 4 (to 51% of controls; P<0.05) and 3 (to 21% of controls; P<0.05). In agreement with this, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) decreased in the heart genomic DNA of hypothyroid animals to 40% of controls (P<0.001). Studies with respiratory inhibitors showed that the decrease in oxygen radical generation observed in hypothyroidism occurred at Complex III (mainly) and at Complex I; that decrease was due to the presence of a lower free radical leak in the respiratory chain (P<0.05). Hyperthyroidism did not significantly change heart mitochondrial H(2)O(2) production since the increase in State 4 oxygen consumption in comparison with control and hypothyroid animals (P<0.05) was compensated by a decrease in the free radical leak in relation to control animals (P<0.05). In agreement with this, heart 8-oxodG was not changed in hyperthyroid animals. The lack of increase in H(2)O(2) production per unit of mitochondrial protein will protect mitochondria themselves against self-inflicted damage during hyperthyroidism.

Ultrasonic myocardial textural analysis in subclinical hypothyroidism

BACKGROUND

In subclinical hypothyroidism (sHT), a condition in which impaired hormone synthesis is compensated by thyroid-stimulating hormone (TSH) hypersecretion, previous studies have suggested the presence of disturbances in left ventricular (LV) function.

OBJECTIVES

Our goal was to investigate LV structure and function through the combined use of conventional Doppler echocardiography and ultrasonic videodensitometry.

METHODS

We studied 16 patients with sHT (aged 32+/-12 [mean +/- SD] years) who had raised TSH levels (> 3.6 mIU/L) but normal levels of free thyroid hormones (free thyroxine [FT(4)] and free triiodothyro-nine [FT(3)]), and 16 carefully age- and sex-matched euthyroid subjects. Transmitral flow Doppler analysis and quantitative analysis of the echocardiographic digitized images were performed in all study subjects. Textural parameters of the septum and posterior wall were obtained as mean gray levels, which were then used to calculate the cyclic variation index (CVI), that is, the percent change in mean gray levels between diastole and systole.

RESULTS

Patients with sHT had a significantly higher LV mass index (92 +/- 16 versus 76 +/- 16 g.m(2), P<.01) and isovolumic relaxation time corrected for heart rate (IVRTc) (2.9 +/- 0.6 versus 2.5 +/- 0.6, P<.04) than did controls. On videodensitometry, patients had lower CVIs both for the septum (-5% +/- 22% versus 33% +/- 9%, P<.0001) and the posterior wall (10% +/- 26% versus 49% +/- 18%, P<.0001). IVRTc discriminated only 25% of the patients from the controls, whereas CVI analysis correctly identified 85% of the patients with sHT (P<.002). Furthermore, CVI values were found to be significantly related to serum FT(4) and FT(3) concentrations in a direct fashion, and to serum TSH levels in an inverse fashion.

CONCLUSIONS

Subclinical hypothyroidism is associated with changes in videodensitometric myocardial structure. These changes, which are not accurately detected by conventional or Doppler echocardiography, are quantitatively related to loss of thyroid function and could represent an early sign of myocardial damage in hypothyroidism.

Tri-iodothyronine treatment in children after cardiac surgery: a double-blind, randomised, placebo-controlled study

BACKGROUND

Serum thyroid hormone concentrations decline transiently during critical illness and after surgical procedures. We investigated prospectively the endocrine and haemodynamic effects of tri-iodothyronine treatment after cardiopulmonary bypass operations in children with congenital cardiac malformations.

METHODS

We did a randomised, double-blind, placebo-controlled trial, in which 40 children (median age 0.6 years; range 2 days to 10.4 years) were randomly assigned placebo (saline) or one daily infusion of tri-iodothyronine (2 microg/kg bodyweight on day 1 after surgery and 1 microg/kg bodyweight on subsequent postoperative days up to 12 days after surgery. Before and 2 h, 24 h, and 72 h after the first infusion, plasma concentrations of thyroid hormones were measured by RIA, and systolic cardiac function was evaluated by echocardiography. During the postoperative course intensive-care measures were assessed by use of the therapeutic intervention scoring system.

FINDINGS

In all patients, postoperative plasma concentrations of thyrotropin, thyroxine, free thyroxine, tri-iodothyronine were abnormally low and plasma concentrations of reverse tri-iodothyronine were raised. After start of treatment, tri-iodothyronine was significantly higher in patients given tri-iodothyronine than in those receiving placebo, whereas thyrotropin, thyroxine, free thyroxine, and reverse tri-iodothyronine remained similar in the two groups. At discharge, thyroid hormones of all patients were within the normal range, but thyrotropin secretion increased to plasma concentrations higher than those seen before treatment. The mean change of cardiac index was significantly higher in children given tri-iodothyronine (20.4% [SD 19.6] vs 10.0% [15.2]; p=0.004). Systolic cardiac function improved most in patients given tri-iodothyronine after longer cardiopulmonary bypass operations. Overall, patients given tri-iodothyronine had significantly lower mean treatment scores.

INTERPRETATION

Treatment of children with tri-iodothyronine after cardiopulmonary bypass operations raises tri-iodothyronine plasma concentrations and improves myocardial function especially in patients with low postoperative cardiac output without adverse events, and without delaying postoperative recovery of thyroid function. Furthermore, tri-iodothyronine reduces the need for postoperative intensive care.

Synthesis and biological activity of phenoxyphenyl oxamic acid derivatives related to L-thyronine

The synthesis of substituted phenoxyphenyl oxamic acid derivatives related to L-thyronine (L-T3) is described. The in vitro and in vivo cholesterol lowering and cardiovascular effects of these compounds are presented and discussed.

Cardiac dysfunction caused by myocardium-specific expression of a mutant thyroid hormone receptor

Thyroid hormone deficiency has profound effects on the cardiovascular system, resulting in decreased cardiac contractility, adrenergic responsiveness, and vascular volume and increased peripheral vascular resistance. To determine the importance of direct cardiac effects in the genesis of hypothyroid cardiac dysfunction, the cardiac myocyte was specifically targeted with a mutant thyroid hormone receptor (TR)-beta (Delta337T-TR-beta(1)) driven by the alpha-myosin heavy chain (alpha-MHC) gene promoter. As a control in these experiments, a wild-type (Wt) TR-beta(1) was also targeted to the heart by using the same promoter. Transgenic mice expressing the mutant TR displayed an mRNA expression pattern consistent with cardiac hypothyroidism, even though their peripheral thyroid hormone levels were normal. When these animals were rendered hypothyroid or thyrotoxic, mRNA expression of MHC isoforms remained unchanged in the hearts of the Delta337T transgenic animals, in contrast to Wt controls or transgenic animals expressing Wt TR-beta(1), which exhibited the expected changes in steady-state MHC mRNA levels. Studies in Langendorff heart preparations from mutant TR-beta(1) transgenic animals revealed evidence of heart failure with a significant reduction in +dP/dT, -dP/dT, and force-frequency responses compared with values in Wt controls and transgenic mice overexpressing the Wt TR-beta(1). In contrast, in vivo measures of cardiac performance were similar between Wt and mutant animals, indicating that the diminished performance of the mutant transgenic heart in vitro was compensated for by other mechanisms in vivo. This is the first demonstration indicating that isolated cardiac hypothyroidism causes cardiac dysfunction in the absence of changes in the adrenergic or peripheral vascular system.

Isometric force and endurance in soleus muscle of thyroid hormone receptor-alpha(1)- or -beta-deficient mice

The specific role of each subtype of thyroid hormone receptor (TR) on skeletal muscle function is unclear. We have therefore studied kinetics of isometric twitches and tetani as well as fatigue resistance in isolated soleus muscles of R-alpha(1)- or -beta-deficient mice. The results show 20-40% longer contraction and relaxation times of twitches and tetani in soleus muscles from TR-alpha(1)-deficient mice compared with their wild-type controls. TR-beta-deficient mice, which have high thyroid hormone levels, were less fatigue resistant than their wild-type controls, but contraction and relaxation times were not different. Western blot analyses showed a reduced concentration of the fast-type sarcoplasmic reticulum Ca(2+)-ATPase (SERCa1) in TR-alpha(1)-deficient mice, but no changes were observed in TR-beta-deficient mice compared with their respective controls. We conclude that in skeletal muscle, both TR-alpha(1) and TR-beta are required to get a normal thyroid hormone response.

Effects of thyroid hormone on action potential and repolarizing currents in rat ventricular myocytes

Thyroid hormones play an important role in cardiac electrophysiology through both genomic and nongenomic mechanisms of action. The effects of triiodothyronine (T(3)) on the electrophysiological properties of ventricular myocytes isolated from euthyroid and hypothyroid rats were studied using whole cell patch clamp techniques. Hypothyroid ventricular myocytes showed significantly prolonged action potential duration (APD(90)) compared with euthyroid myocytes, APD(90) of 151 +/- 5 vs. 51 +/- 8 ms, respectively. Treatment of hypothyroid ventricular myocytes with T(3) (0.1 microM) for 5 min significantly shortened APD by 24% to 115 +/- 10 ms. T(3) similarly shortened APD in euthyroid ventricular myocytes, but only in the presence of 4-aminopyridine (4-AP), an inhibitor of the transient outward current (I(to)), which prolonged the APD by threefold. Transient outward current (I(to)) was not affected by the acute application of T(3) to either euthyroid or hypothyroid myocytes; however, I(to) density was significantly reduced in hypothyroid compared with euthyroid ventricular myocytes.

Triiodothyronine: a link between the insulin resistance syndrome and blood pressure?

OBJECTIVE

Overall obesity is associated with elevated serum triiodothyronine concentrations and insulin resistance. Oral triiodothyronine is known to induce hypertension in laboratory rats, while triiodothyronine also increases the expression of genes encoding for enzymes involved in the synthesis and secretion of insulin by pancreatic beta cells. We investigated the hypothesis that central obesity and insulin resistance are linked with an increased blood pressure and insulin production through elevated free serum triiodothyronine concentrations.

DESIGN

A cross-sectional study of 47 healthy euthyroid subjects (17 men, 30 women; 34 +/- 15 years, mean +/- SD).

METHODS

The waist:hip ratio was used as measure of central obesity, and insulin-stimulated glucose disposal during a hyperinsulinaemic euglycaemic clamp was used as measure of insulin sensitivity. Insulin production was calculated from the insulin clearance during the clamp and fasting insulin concentrations.

RESULTS

Free serum triiodothyronine concentrations correlated, independent of age and gender, positively with systolic and diastolic blood pressure, insulin production and fasting insulin. There was only a borderline significant correlation of free serum triiodothyronine with the waist-to-hip ratio, and no correlation with insulin sensitivity as assessed during the clamp. The correlations of free serum triiodothyronine with blood pressure, insulin production and fasting insulin were independent of the waist:hip ratio and insulin sensitivity.

CONCLUSION

Our hypothesis of free serum triiodothyronine as an intermediate factor in the insulin resistance syndrome is refuted by these data, but we identified free serum triiodothyronine concentrations as a new determinant of blood pressure, insulin production, and fasting insulin in healthy euthyroid subjects.

Pulmonary hypertension caused by Graves' thyrotoxicosis: normal pulmonary hemodynamics restored by (131)I treatment

We describe a case of pulmonary hypertension, initially thought to be idiopathic, which resolved after treatment of Graves' hyperthyroidism. Results of pulmonary artery catheterization before and after treatment are reported, and the effects of thyrotoxicosis on hemodynamics and pulmonary function are briefly reviewed. Possible mechanisms for development of pulmonary hypertension caused by hyperthyroidism include pulmonary vascular endothelial dysfunction or damage because of autoimmunity or the high cardiac output state, or increased metabolism of intrinsic pulmonary vasodilators.

Endothelial membrane potential regulates production of both nitric oxide and superoxide--a fundamental determinant of vascular health

There is recent evidence that the membrane potential of vascular endothelium regulates not only nitric oxide (NO) synthesis, but also superoxide generation, such that hyperpolarization stimulates NO production while suppressing that of superoxide. Given that NO works in a variety of ways to inhibit atherothrombotic disease and hypertension, whereas superoxide not only vetoes the benefits of NO but also disrupts endothelial metabolism and promotes LDL oxidation through its oxidant activity, it is thus evident that endothelium membrane potential is a crucial determinant of cardiovascular risk. Membrane polarization can be enhanced by measures which increase the synthesis or availability of the Na+-K+-ATPase, moderately enhance serum K+ and increase the conductance of membrane K+ channels. Such measures may include high-K+/low-Na+ natural diets, insulin sensitizing modalities, 'euthyroid replacement therapy' and ACE inhibitors. Epidemiological correlations of insulin resistance with hypertension and cardiovascular risk may reflect the low membrane potential of insulin-resistant vascular endothelium. Adjunctive measures for suppressing the generation or half-life of endothelial superoxide are suggested.