Tissue-specific modulation of angiotensin-converting enzyme (ACE) in hyperthyroidism

The Clinical Characteristics and Outcomes of COVID-19 Patients with Pre-Existing Thyroid Dysfunction: A Nationwide Study

To which extent the pre-existing hypothyroidism or hyperthyroidism has an impact on coronavirus infection 2019 (COVID-19) outcomes remains unclear. The objective of this study was to evaluate COVID-19 morbidity and mortality in patients with pre-existing thyroid dysfunction. A retrospective cohort of patients with a polymerase chain reaction (PCR)-confirmed COVID-19 infection (n=14 966) from March 11 to May 30, 2020, was established using the database of the Turkish Ministry of Health. We compared the morbidity and mortality rates of COVID-19 patients with pre-existing hypothyroidism (n=8813) and hyperthyroidism (n=1822) to those patients with normal thyroid function (n=4331). Univariate and multivariate regression analyses were performed to identify the factors associated with mortality. Mortality rates were higher in patients with hyperthyroidism (7.7%) and hypothyroidism (4.4%) than those with normal thyroid function (3.4%) (p<0.001 and p=0.008, respectively). Pre-existing hyperthyroidism was significantly associated with an increased risk of mortality (OR 1.54; 95% CI, 1.02-2.33; p=0.042) along with advanced age, male gender, lymphopenia and chronic kidney disease (p<0.001 for all). Although a potential trend was noted, the association between pre-existing hypothyroidism and mortality was not significant (OR 1.36; 95% CI, 0.99-1.86; p=0.055). In conclusion, this study showed an association between pre-existing hyperthyroidism with higher COVID-19 mortality. A potential trend towards increased mortality was also observed for hypothyroidism. The risk was more pronounced in patients with hyperthyroidism.

Prospective role of thyroid disorders in monitoring COVID-19 pandemic

COVID-19 pandemic has affected more than 200 countries and 1.3 million individuals have deceased within eleven months. Intense research on COVID-19 occurrence and prevalence enable us to understand that comorbidities play a crucial role in spread and severity of SARS-CoV-2 infection. Chronic kidney disease, diabetes, respiratory diseases and hypertension are among the various morbidities that are prevalent in symptomatic COVID-19 patients. However, the effect of altered thyroid-driven disorders cannot be ignored. Since thyroid hormone critically coordinate and regulate the major metabolism and biochemical pathways, this review is on the potential role of prevailing thyroid disorders in SARS-CoV-2 infection. Direct link of thyroid hormone with several disorders such as diabetes, vitamin D deficiency, obesity, kidney and liver disorders etc. suggests that the prevailing thyroid conditions may affect SARS-CoV-2 infection. Further, we discuss the oxidative stress-induced aging is associated with the degree of SARS-CoV-2 infection. Importantly, ACE2 protein which facilitates the host-cell entry of SARS-CoV-2 using the spike protein, are highly expressed in individuals with abnormal level of thyroid hormone. Altogether, we report that the malfunction of thyroid hormone synthesis may aggravate SARS-CoV-2 infection and thus monitoring the thyroid hormone may help in understanding the pathogenesis of COVID-19.

Clinical Features of Graves' Ophthalmopathy and Impact of Enalapril on the Course of Mild Graves' Ophthalmopathy: A Pilot Study

BACKGROUND

Inflammation, oxidative stress, and adipogenesis are associated with Graves' ophthalmopathy (GO) progression.

OBJECTIVE

We conducted a pilot study to investigate the effect of Enalapril on patients with mild ophthalmopathy.

METHOD

Based on the comprehensive eye examination, 12 patients with mild ophthalmopathy were selected from referred Graves' patients and treated with Enalapril (5 mg daily) for 6 months. Clinical and ophthalmological examination [IOP (Intraocular Pressure), vision, Margin reflex distance and exophthalmia measurement, CAS (clinical activity score) and VISA [V (vision); I (inflammation/ congestion); S (strabismus/motility restriction); and A (appearance/exposure] score assessment) was performed at the beginning, 3 months and 6 months of the study period. Quality of life was also evaluated using a standard questionnaire.

RESULTS

Mean exophthalmia at the first visit was 18.75 ± 2.39, 3 months later 18.53 ± 2.39 and 6 months later was 17.92 ± 2.31, respectively. Mean CAS was 0.71 ± 0.82 (first visit), 0.57 ± 0.54 (3 months) and 0.14 ± 0.36 (6 months), respectively. Mean Margin reflex distance was 9.09 ± 4.36 (first visit) and 9.60 ± 4.40 (6 months), respectively. There were significant differences in the case of exophthalmia (P=0.002), CAS (P=0.006), and Margin reflex distance (P=0.029) between the first visit and 6 months after treatment. The difference between the score of quality of life in patients with GO after 6 months of follow up was statistically significant (P = 0.006).

CONCLUSION

Our results showed that Enalapril treatment could ameliorate the clinical course of GO according to the ophthalmologic examinations and subjective parameters of disease progression. However, further studies should be performed to determine the efficacy of Enalapril in Graves' ophthalmopathy treatment.

The Role of Thyroid Diseases and their Medications in Cardiovascular Disorders: A Review of the Literature

The association between thyroid disease and cardiovascular manifestations is significant and undeniable. Previous studies have explained several aspects of the effects of thyroid hormone on the heart and cardiovascular system. Accordingly, both hyper and hypothyroidism can cause important alterations in cardiac rhythm, output and contractility as well as vascular resistance and blood pressure. Since treating the thyroid abnormality, especially in its initial stages, could lead to a significant improvement in most of its resultant cardiovascular disturbances, early suspicion and recognition of thyroid dysfunction, is necessary in patients with cardiovascular manifestations. In this in-depth review, we discuss the physiological roles as well as the effects of abnormal levels of thyroid hormones on the cardiovascular system. We also review the effects of the medications used for the treatment of hyper and hypothyroidism on cardiac function. In the end, we discuss the association between thyroid function and amiodarone, an effective and frequently-used antiarrhythmic drug, because of its well-known effects on the thyroid.

Aliskiren, Fosinopril, and Their Outcome on Renin-Angiotensin-Aldosterone System (RAAS) in Rats with Thyroid Dysfunction

BACKGROUND AND OBJECTIVES

Thyroid hormones have an important role in the growth and development of various tissues including the kidney, which is the major site of renin release and the consequent angiotensin and aldosterone formation. Therefore any derangement in thyroid function can result in abnormal functioning in the renin-angiotensin-aldosterone system. The current study was undertaken to find the impact of using a direct renin inhibitor (Aliskiren) and an angiotensin-converting enzyme inhibitor (Fosinopril) on the components of the renin-angiotensin-aldosterone system (RAAS) in rats with thyroid dysfunctions.

METHOD

Forty-two male albino rats were divided into three subgroups. First group (6 rats) served as control. Second group (18 rats) served as hyperthyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Third group (18 rats) served as hypothyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Induction of hyperthyroidism and hypothyroidism was done through daily oral administration of L-Thyroxine and Propylthiouracil, respectively. On day 40 of the study, the rats were sacrificed and blood was collected for estimation of renin, angiotensin I, angiotensin II, aldosterone, TSH, T₃, and T₄. The collected blood samples were also used for estimation of levels blood urea, serum creatinine, liver enzymes, and serum electrolytes. Blood pressure and urine collection were done on days 1 and 40. The collected urine was used for estimation of urine flow, sodium excretion, and potassium excretion rates.

RESULTS

In hypothyroid induced rats, serum renin level dropped as expected, while the use of Aliskiren and Fosinopril on these hypothyroid rats raised renin level due to the feedback mechanism. Both angiotensin I and II were significantly (P <0.05) lower than normal levels in the hypothyroid rats, unlike the level of aldosterone, which was higher than normal level. There was nonsignificant lowering in BP (systolic, diastolic, and mean BP) in the hypothyroid rats. Treatment of these rats with Aliskiren and Fosinopril did not lower the blood pressure more than normal when compared to the hypothyroid group. The hypothyroid rats also showed a decrease in level of serum creatinine. In hyperthyroid rats, there was a rise in levels of serum renin, angiotensin II, and aldosterone; nevertheless, the increase in angiotensin I level was significant. The use of Aliskiren and Fosinopril increased the level of renin nonsignificantly (decreased angiotensin I significantly). Hyperthyroid rats showed a significant increase in systolic, diastolic, and mean blood pressure. Both Aliskiren and Fosinopril increased urine flow, Na⁺ excretion, and K⁺ excretion rates. Aliskiren was better at reducing the high blood pressure.

CONCLUSION

Aliskiren and Fosinopril in hyperthyroid rats decreased serum angiotensin I, angiotensin II, and aldosterone. Blockade of renin and inhibition of angiotensin-converting enzyme both resulted in a rebound increase in level of renin in hypothyroid rats. Aliskiren is better at controlling blood pressure in hyperthyroid rats. Urine flow, sodium excretion, and potassium excretion rates were improved by the use of Aliskiren and Fosinopril in hyperthyroid rats.

Angiotensin-(1–7) reduces cardiac effects of thyroid hormone by GSK3Β/NFATc3 signaling pathway

Patients with hyperthyroidism exhibit increased risk of development and progression of cardiac diseases. The activation of the renin–angiotensin system (RAS) has been indirectly implicated in these cardiac effects observed in hyperthyroidism. Angiotensin-(1–7) (Ang-(1–7)) has previously been shown to counterbalance pathological effects of angiotensin II (Ang II). The aim of the present study was to investigate the effects of elevated circulating Ang-(1–7) levels on cardiac effects promoted by hyperthyroidism in a transgenic rat (TG) model that constitutively overexpresses an Ang-(1–7)-producing fusion protein [TGR(A1-7)3292]. TG and wild-type (WT) rats received daily injections (i.p.) of triiodothyronine (T3; 7 µg/100 g of body weight (BW)) or vehicle for 14 days. In contrast with WT rats, the TG rats did not develop cardiac hypertrophy after T3 treatment. Indeed, TG rats displayed reduced systolic blood pressure (SBP) and cardiac hyperdynamic condition induced by hyperthyroidism. Moreover, increased plasma levels of Ang II observed in hyperthyroid WT rats were prevented in TG rats. TG rats were protected from glycogen synthase kinase 3β (GSK3β) inactivation and nuclear factor of activated T cells (NFAT) nuclear accumulation induced by T3. In vitro studies evidenced that Ang-(1–7) prevented cardiomyocyte hypertrophy and GSK3β inactivation induced by T3. Taken together, these data reveal an important cardioprotective action of Ang-(1–7) in experimental model of hyperthyroidism.

Cardiac ACE2/angiotensin 1-7/Mas receptor axis is activated in thyroid hormone-induced cardiac hypertrophy

OBJECTIVES

Thyroid hormone (TH) promotes marked effects on the cardiovascular system, including the development of cardiac hypertrophy. Some studies have demonstrated that the renin-angiotensin system (RAS) is a key mediator of the cardiac growth in response to elevated TH levels. Although some of the main RAS components are changed in cardiac tissue on hyperthyroid state, the potential modulation of the counter regulatory components of the RAS, such as angiotensin-converting enzyme type 2 (ACE2), angiotensin 1-7 (Ang 1-7) levels and Mas receptor induced by hyperthyroidism is unknown. The aim of this study was to investigate the effect of hyperthyroidism on cardiac Ang 1-7, ACE2 and Mas receptor levels.

METHODS

Hyperthyroidism was induced in Wistar rats by daily intraperitoneal injections of T4 for 14 days.

RESULTS

Although plasma Ang 1-7 levels were unchanged by hyperthyroidism, cardiac Ang 1-7 levels were increased in TH-induced cardiac hypertrophy. ACE2 enzymatic activity was significantly increased in hearts from hyperthyroid animals, which may be contributing to the higher Ang 1-7 levels observed in the T4 group. Furthermore, elevated cardiac levels of Ang 1-7 levels were accompanied by increased Mas receptor protein levels.

CONCLUSION

The counter-regulatory components of the RAS are activated in hyperthyroidism and may be contributing to modulate the cardiac hypertrophy in response to TH.

Thyroid Hormone and Vascular Remodeling

Both hyperthyroidism and hypothyroidism affect the cardiovascular system. Hypothyroidism is known to be associated with enhanced atherosclerosis and ischemic heart diseases. The accelerated atherosclerosis in the hypothyroid state has been traditionally ascribed to atherogenic lipid profile, diastolic hypertension, and impaired endothelial function. However, recent studies indicate that thyroid hormone has direct anti-atherosclerotic effects, such as production of nitric oxide and suppression of smooth muscle cell proliferation. These data suggest that thyroid hormone inhibits atherogenesis through direct effects on the vasculature as well as modification of risk factors for atherosclerosis. This review summarizes the basic and clinical studies on the role of thyroid hormone in vascular remodeling. The possible application of thyroid hormone mimetics to the therapy of hypercholesterolemia and atherosclerosis is also discussed.

Cardiac microvascular rarefaction in hyperthyroidism-induced left ventricle dysfunction

OBJECTIVE

The pathophysiology underlying hyperthyroidism-induced left ventricle (LV) dysfunction and hypertrophy directly involves the heart and indirectly involves the neuroendocrine systems. The effects of hyperthyroidism on the microcirculation are still controversial in experimental models. We investigated the effects of hyperthyroidism on the cardiac function and microcirculation of an experimental rat model.

METHODS

Male Wistar rats (170-250 g) were divided into two groups: the euthyroid group (n = 10), which was treated with 0.9% saline solution, and the hyperthyroid group (n = 10), which was treated with l-thyroxine (600 μg/kg/day, i.p.) during 14 days. An echocardiographic study was performed to evaluate the alterations in cardiac function, structure and geometry. The structural capillary density and the expression of angiotensin II AT1 receptor in the LV were analyzed using histochemistry and immunohistochemistry, respectively.

RESULTS

Hyperthyroidism was found to induce profound cardiovascular alterations, such as systolic hypertension, tachycardia, LV dysfunction, cardiac hypertrophy, and myocardial fibrosis. This study demonstrates the existence of structural capillary rarefaction and the down-regulation of the cardiac angiotensin II AT1 receptor in the myocardium of hyperthyroid rats in comparison with euthyroid rats.

CONCLUSIONS

Microvascular rarefaction may be involved in the pathophysiology of hyperthyroidism-induced cardiovascular alterations.

Local thyroid renin-angiotensin system in experimental breast cancer

An association between breast cancer and thyroid dysfunction exists although the underlying mechanisms remain to be elucidated. Numerous studies have characterized the role of thyroid hormones in controlling the synthesis and secretion of renin-angiotensin system (RAS) components, but little information is available on the putative role of the local RAS on thyroid function.

AIMS

Here we analyze several soluble and membrane-bound RAS-regulating aminopeptidase activities in thyroid gland from rats with mammary tumors and the relationship with the circulating levels of thyroid stimulating hormone (TSH) and free thyroxin (fT4).

MAIN METHODS

We analyze soluble and membrane-bound RAS-regulating aminopeptidase activities fluorometrically using their corresponding aminoacyl-β-naphthylamide as the substrate.

KEY FINDINGS

We have found in rats with mammary tumors a concomitant change of thyroid RAS-regulating enzymes and thyroid hormone production.

SIGNIFICANCE

We suggest that existence of alterations in the regulatory mechanisms mediated by the angiotensins of the local tissue RAS as a consequence of the carcinogenic process which could act alone or in combination with alterations at a higher level of regulation such as the hypothalamus-pituitary axis.

Maternal hyperthyroidism alters the pattern of expression of cardiac renin-angiotensin system components in rat offspring

INTRODUCTION

Changes in perinatal environment can lead to physiological, morphological, or metabolic alterations in adult life. It is well known that thyroid hormones (TH) are critical for the development, growth, and maturation of organs and systems. In addition, TH interact with the renin-angiotensin system (RAS), and both play a critical role in adult cardiovascular function. The objective of this study was to evaluate the effect of maternal hyperthyroidism on cardiac RAS components in pups during development.

MATERIALS AND METHODS

From gestational day nine (GD9), pregnant Wistar rats received thyroxine (T4, 12 mg/l in tap water; Hyper group) or vehicle (control group). Dams and pups were killed on GD18 and GD20.

RESULTS

Serum concentrations of triiodothyronine (T3) and T4 were higher in the Hyper group than in the control group dams. Cardiac hypertrophy was observed in Hyper pups on GD20. Cardiac angiotensin-converting enzyme (ACE) activity was significantly lower in Hyper pups on both GD18 and GD20, but there was no difference in Ang I/Ang II levels. Ang II receptors expression was higher in the Hyper pup heart on GD18.

CONCLUSIONS

Maternal hyperthyroidism is associated with alterations in fetal development and altered pattern of expression in RAS components, which in addition to cardiac hypertrophy observed on GD20 may represent an important predisposing factor to cardiovascular diseases in adult life.

Thyroid hormones are involved in 5'-nucleotidase modulation in soluble fraction of cardiac tissue

AIMS

To investigate the role of TH (thyroid hormones) in 5'-nucleotidase activity and expression in cardiac soluble fraction (SF).

MAIN METHODS

Male Wistar rats received daily injections of T4 (10, 25 or 50 μg T4/100g body weight) for 14 days to develop a hyperthyroidism condition. Thyroidectomy was performed in other animals to mimic hypothyroidism, and 14 days after surgery they were submitted to TH replacement therapy.

KEY FINDINGS

T4 reduced the 5'-nucleotidase activity (T4-25, P<0.05 and T4-50, P<0.01) in the SF. Conversely, hypothyroidism significantly increased the 5'-nucleotidase activity in this fraction (P<0.001) and TH replacement therapy reversed the latter result (P<0.001 compared to hypothyroid group). The analysis of protein expression in the SF showed that 5'-nucleotidase was more expressed in hypothyroid than in the control group and that the phosphorylated state of PKC observed in this condition may contribute to a possible mechanism of 5'-nucleotidase modulation by thyroid status.

SIGNIFICANCE

Taken together, these data reveal that TH can influence adenosine production by modulating 5'-nucleotidase activity and expression, which may contribute to the cardioprotective effect and the maintenance of cardiac function under TH privation.

Decreased number of circulating endothelial progenitor cells in patients with Graves' hyperthyroidism

OBJECTIVE

A relevant biological role of circulating endothelial progenitor cells (EPC) was recently demonstrated. EPC are generated in the bone marrow, and interact with damaged endothelium, restoring the integrity of the monolayer. Therefore, aim of the present study was to evaluate EPC in the blood of patients with untreated Graves' hyperthyroidism (GD), in whom an increased oxidative stress was observed.

DESIGN AND METHODS

Twenty-three patients with untreated active GD and 18 matched normal controls (NC) were included in the study. Circulating EPC were isolated from peripheral blood. Mononuclear cells were cultured with endothelial basal medium supplemented with EGM SingleQuots, and were identified by positive double staining after 7 days in culture. Circulating levels of C reactive protein, total antioxidant power, interleukin (IL)-6, IL- 18, monocyte chemoattractant protein-1, tumor necrosis facotr- α, soluble vascular cell adhesion molecule (VCAM) and intracellular adhesion molecule were evaluated by enzymelinked immunosorbent assay kit. EPC number was also evaluated in a subgroup of GD patients after restoration of euthyroidism.

RESULTS

Systolic blood pressure resulted increased in GD patients compared with control subjects whereas diastolic blood pressure was not significantly different. Patients with GD showed an increase in circulating levels of IL-18 and VCAM-1 and a reduction of total antioxidant power (p<0.05) compared to NC. Moreover, a reduced number of EPC was observed in patients with GD compared to NC (p<0.05) which turned to NC values after restoring euthyroidism.

CONCLUSION

Patients with GD showed a reduction in the physiological protective mechanisms against endothelial damage, probably induced by increased inflammation and oxidative stress.

Excessive thyroxine enhances susceptibility to apoptosis and decreases contractility of cardiomyocytes

Excessive thyroid hormone induces cardiac hypertrophy and promotes heart failure in patients with hyperthyroidism, but the mechanism remains elusive. Rats were orally administered with levothyroxine (100 microg/kg, T(4)) for 4 weeks to induce hyperthyroidism. The calculated stroke volume decreased and the shortening amplitude-frequency relationship in unloaded contraction of isolated cardiomyocytes was negative in T(4)-treated rats. Apoptotic rates increased and DNA laddering was also detectable in T(4)-treated rat hearts. By contrast, in primary cultured cardiomyocytes, T(3) induced dose-dependent hypertrophy but did not affect the apoptotic rate. Angiotensin II further increased the apoptotic rate of T(3)-induced hypertrophied cardiomyocytes. The apoptotic rate was dependent on the extent of cardiomyocyte hypertrophy. These results suggest that cardiac contractility is enhanced during the early stage of hyperthyroidism, but decreased during the late stage of hyperthyroidism. The hypertrophied cardiomyocytes were also susceptible to apoptotic stimulation by angiotensin II. Depressed cardiac contractility and enhanced apoptosis may lead to heart failure in hypertrophied myocardium.

The crosstalk between thyroid hormones and the Renin-Angiotensin System

Thyroid hormones (THs) exert multiple effects on the heart and vascular system. As a consequence, altered cardiovascular function observed in the thyroid diseases corresponds to one of the most important and clinically relevant aspects found in both hyperthyroidism and hypothyroidism. Besides THs' direct effects on the heart and vascular system, in the last three decades several studies have implicated the Renin-Angiotensin System (RAS) in some of the cardiovascular effects of THs, with this interaction suggesting that RAS may be an important mediator of THs actions. In the present review, we discuss the alterations in the circulating RAS, as well as modifications in cardiac and vascular RAS which are involved in the cardiovascular alterations found during the modulation of TH levels. In addition, considering the important role that both systems present during fetal and neonatal periods, we also review the interaction between THs and the RAS in the development of cardiovascular system. A greater understanding of the role of the RAS in hyperthyroidism and hypothyroidism, during early or adult life will presumably facilitate the evolution of newer, targeted therapies.

Angiotensin type 1 receptor mediates thyroid hormone-induced cardiomyocyte hypertrophy through the Akt/GSK-3beta/mTOR signaling pathway

Several studies have implicated the renin angiotensin system in the cardiac hypertrophy induced by thyroid hormone. However, whether Angiotensin type 1 receptor (AT1R) is critically required to the development of T3-induced cardiomyocyte hypertrophy as well as whether the intracellular mechanisms that are triggered by AT1R are able to contribute to this hypertrophy model is unknown. To address these questions, we employed a selective small interfering RNA (siRNA, 50 nM) or an AT1R blocker (Losartan, 1 microM) to evaluate the specific role of this receptor in primary cultures of neonatal cardiomyocytes submitted to T3 (10 nM) treatment. The cardiomyocytes transfected with the AT1R siRNA presented reduced mRNA (90%, P < 0.001) and protein (70%, P < 0.001) expression of AT1R. The AT1R silencing and the AT1R blockade totally prevented the T3-induced cardiomyocyte hypertrophy, as evidenced by lower mRNA expression of atrial natriuretic factor (66%, P < 0.01) and skeletal alpha-actin (170%, P < 0.01) as well as by reduction in protein synthesis (85%, P < 0.001). The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3beta/mTOR signaling pathway, which was completely inhibited by the use of PI3K inhibitors (LY294002, 10 microM and Wortmannin, 200 nM). In addition, we demonstrated that the AT1R mediated the T3-induced activation of Akt/GSK-3beta/mTOR signaling pathway, since the AT1R silencing and the AT1R blockade attenuated or totally prevented the activation of this signaling pathway. We also reported that local Angiotensin I/II (Ang I/II) levels (120%, P < 0.05) and the AT1R expression (180%, P < 0.05) were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy as well as to the activation of Akt/GSK-3beta/mTOR signaling pathway. These results represent a new insight into the mechanism of T3-induced cardiomyocyte hypertrophy, indicating that the Ang I/II-AT1R-Akt/GSK-3beta/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

V2 vasopressin receptor deficiency causes changes in expression and function of renal and hypothalamic components involved in electrolyte and water homeostasis

Polyuria, hypernatremia, and hypovolemia are the major clinical signs of inherited nephrogenic diabetes insipidus (NDI). Hypernatremia is commonly considered a secondary sign caused by the net loss of water due to insufficient insertion of aquaporin-2 water channels into the apical membrane of the collecting duct cells. In the present study, we employed transcriptome-wide expression analysis to study gene expression in V2 vasopressin receptor (Avpr2)-deficient mice, an animal model for X-linked NDI. Gene expression changes in NDI mice indicate increased proximal tubular sodium reabsorption. Expression of several key genes including Na+-K+-ATPase and carbonic anhydrases was increased at the mRNA levels and accompanied by enhanced enzyme activities. In addition, altered expression was also observed for components of the eicosanoid and thyroid hormone pathways, including cyclooxygenases and deiodinases, in both kidney and hypothalamus. These effects are likely to contribute to the clinical NDI phenotype. Finally, our data highlight the involvement of the renin-angiotensin-aldosterone system in NDI pathophysiology and provide clues to explain the effectiveness of diuretics and indomethacin in the treatment of NDI.

Cardiovascular and Renal Manifestations of Hyperthyroidism

In the simplest terms, hyperthyroidism is the clinical syndrome that results from an excess of thyroid hormones. This review considers the effects of hyperthyroidism on the cardiovascular and renal systems by reviewing the available literature on the clinical manifestations of this syndrome in the cat and also considering experimental studies and experience in other species, including human beings.

Cardiac angiotensin II type I and type II receptors are increased in rats submitted to experimental hypothyroidism

This study assessed the behaviour of angiotensin II (Ang II) receptors in an experimental hypothyroidism model in male Wistar rats. Animals were subjected to thyroidectomy and resting for 14 days. The alteration of cardiac mass was evaluated by total heart weight (HW), right ventricle weight (RVW), left ventricle weight (LVW), ratio of HW, RVW and LVW to body weight (BW) and atrial natriuretic factor (ANF) expression. Cardiac and plasma Ang II levels and serum T3 and T4 were determined. The mRNA and protein levels of Ang II receptors were investigated by RT-PCR and Western blotting, respectively. Functional analyses were performed using binding assays. T3 and T4 levels and the haemodynamic parameters confirmed the hypothyroid state. HW/BW, RVW/BW and LVW/BW ratios and the ANF expression were lower than those of control animals. No change was observed in cardiac or plasma Ang II levels. Both AT1/AT2 mRNA and protein levels were increased in the heart of hypothyroid animals due to a significant increase of these receptors in the RV. Experiments performed in cardiomyocytes showed a direct effect promoted by low thyroid hormone levels upon AT1 and AT2 receptors, discarding possible influence of haemodynamic parameters. Functional assays showed that both receptors are able to bind Ang II. Herein, we have identified, for the first time, a close and direct relation of elevated Ang II receptor levels in hypothyroidism. Whether the increase in these receptors in hypothyroidism is an alternative mechanism to compensate the atrophic state of heart or whether it may represent a potential means to the progression of heart failure remains unknown.

Angiotensin type 1 (AT1) and type 2 (AT2) receptors mediate the increase in TGF-β1 in thyroid hormone-induced cardiac hypertrophy

Increased thyroid hormone (TH) levels are known to induce cardiac hypertrophy. Some studies have provided evidence for a functional link between angiotensin II (ANG II) and transforming growth factor beta1 (TGF-beta1) in the heart, both being able to also induce cardiac hypertrophy. However, the contribution of this growth factor activated directly by TH or indirectly by ANG II in cardiac hypertrophy development remains unknown. To analyze the possible role of TGF-beta1 in cardiac hypertrophy induced by TH and also to evaluate if the TGF-beta1 effect is mediated by ANG II receptors, we employed Wistar rats separated into control, hypothyroid (hypo) and hyperthyroid (T4 - 10) groups combined or not with ANG II receptor blockers (losartan or PD123319). Serum levels of T3 and T4, systolic pressure and heart rate confirmed the thyroid state of the groups. The T4 - 10 group presented a significant increase in cardiac TGF-beta1 levels; however, TGF-beta1 levels in the hypo group did not change in relation to the control. Inhibition of the increase in cardiac TGF-beta1 levels was observed in the groups treated with T4 in association with losartan or PD123319 when compared to the T4 - 10 group. These results demonstrate for the first time the TH-modulated induction of cardiac TGF-beta1 in cardiac hypertrophy, and that this effect is mediated by ANG II receptors.