Nitric oxide and thyroid gland: modulation of cardiovascular function in autonomic-blocked anaesthetized rats

Relationship between serum nitric oxide of patients with thyroid disorders and metabolic syndrome indices and nitrate concentration of water

This case-control study aimed to assess the effect of drinking water nitrate on serum nitric oxide concentration and the risk of metabolic syndrome (MetS) in the population in the Middle East. The study included 50 control and 50 thyroid disorder cases who were referred to two medical centers in 2021. In this study, serum nitric oxide concentration, drinking water nitrate, and metabolic syndrome components were measured in the two groups. The results showed there was a statistically significant difference between serum NO in the case and control groups (p-value < 0.001). There was a positive correlation between the concentration of nitrate in drinking water and serum nitric oxide in the case and control groups; however, this relationship was not significant statistically. A statistically significant difference was found between serum nitric oxide and systolic blood pressure in the cases (p-value < 0.05), but there was no significant difference between MetS and nitric oxide. Therefore, we concluded that the relationship between nitric oxide and nitrate in consuming water should be determined in thyroid patients. In addition to their water consumption, it is better to study the nitrate of foods, especially vegetables.

l-Thyroxine induces left ventricular remodeling and fibrosis in rats by upregulating miR-21 in a reactive oxygen-dependent mechanism: a protective role of N-acetylcysteine

miR-21 is the most studied pro-fibrotic marker in the majority of mammalian tissues. The precise mechanism by which hyperthyroidism induces left ventricular LV fibrosis and remodeling remains unclear. In this study, we have investigated the role of miR-21 on l-thyroxine (l-Thy)-induced cardiac fibrosis in rats. Adult male Sprague-Dawley rats were divided into four groups as control, l-Thy, l-Thy + miR antagomir (inhibitor), and l-Thy + N-acetylcysteine (NAC/glutathione (GSH) precursor). Administration of l-Thy significantly increased mRNA levels of miR-21 in the LVs of the treated rats. Also, it impaired the LV systolic and diastolic function and increased the production of reactive oxygen species (ROS), the transactivation of NF-κB p65, the expression of NRLP3 inflammasome, and levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in these LVs. Concomitantly, l-Thy increased the ventricular collagen deposition, and stimulated the expression of collagen 1/3, alpha-smooth actin (α-SMA), transforming growth factor-β1, and Smad3/p-Smad3 but suppressed the expression of Smad7. All these effects were reversed by pre-treatment with miR-21 antagomir or co-administration of NAC. In conclusion, l-Thy-induced LV remodeling and fibrosis include a ROS-dependent upregulation of miR-21 which in turns activates NF-κB/NRLP3 inflammasome and suppresses SMad7.

Association Between Serum Nitric Oxide Level and Changes in Thyroid Function Test in a Population-based Study: Tehran Thyroid Study Participants (TTS)

BACKGROUND

Nitric oxide (NO) plays a key role in thyroid function regulation through the inhibition of iodide (I) uptake at the thyroidal sodium-iodide symporter (NIS) and impacts on the thyroid vascularity and blood flow.

OBJECTIVES

This study aimed to evaluate the association between serum NO metabolites (NOx) and thyroid-stimulating hormone (TSH), free thyroxin (FT4), and anti-thyroid peroxidase (TPOAb) changes. Also, it aimed at evaluating the correlation between serum NOx and the incidence of clinical hypothyroidism, characterized by elevated TSH level and decreased FT4 concentration, and subclinical hypothyroidism, characterized by mildly elevated TSH level despite FT4 concentration within the normal range, over three years of follow-up.

METHODS

This study included 1,137 participants of the Tehran Thyroid study (TTS), aged > 20 years old, for whom data on serum TSH, FT4, and TPOAb in the third and fourth phases, and serum NOx in the third phase were available. Changes in TSH (ΔTSH), FT4 (ΔFT4), and TPOAb (ΔTPO) between the third and fourth phases were calculated, and the associations between serum NOx and ΔTSH, ΔFT4, and ΔTPOAb were assessed after multivariable adjustment using linear regression analysis.

RESULTS

No significant association was found between serum NOx and ΔTSH, ΔFT4, and ΔTPOAb after the multivariable adjustment; neither was any observed in TPOAb split groups after multivariable adjustment. No significant association was found between serum NOx tertiles and clinical and subclinical hypothyroidism incidence in the fourth phase of TTS.

CONCLUSIONS

There was no association between serum NOx levels and changes in TSH, FT4, and TPOAb and clinical and subclinical hypothyroidism incidence.

The effect of 131I-induced hypothyroidism on the levels of nitric oxide (NO), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), total nitric oxide synthase (NOS) activity, and expression of NOS isoforms in rats

Accumulating evidence has shown that hypothyroidism affects the cardiovascular system, significantly increasing the incidence of cardiovascular diseases. In the present study we investigated the effect of radioactive iodine (I-131)-induced hypothyroidism on several parameters of vascular function, such as nitric oxide (NO), total nitric oxide synthase (NOS) activity and expression of NOS isoforms, as well as on interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) as indicators of inflammation, in rats. A dose of 150 µCi of 131-I was determined as optimal for establishing the model of hypothyroidism in rats. After administration of 131-I, at the end of month 1, 2, and 4 (n = 3 for each time point), NO, IL-6, and TNF-α in the serum and total NOS activity in the aorta were determined in 150 µCi group, compared to controls. The mRNA and protein expression of endothelial, neuronal, and inducible NOS (eNOS, nNOS, and iNOS) in the rat aorta was also estimated, using quantitative reverse transcription polymerase chain reaction and Western blot, respectively. The levels of IL-6 and TNF-α increased in 150 µCi group; the results were significant at the end of month 2 and 4 for IL-6, and at all time points for TNF-α. The levels of NO decreased significantly at the end of month 2 and 4 in 150 µCi group. The total NOS activity increased significantly in 150 µCi group, at all three time points. Significant changes in the mRNA and protein expression of all three NOS isoforms were observed in 150 µCi group compared to controls. NO, IL-6, TNF-α levels and NOS activity and expression are altered in hypothyroid state, and the underlying mechanism should be further investigated.

Cardiovascular and metabolic consequences of the association between chronic stress and high-fat diet in rats

Obesity and chronic stress are considered independent risk factors for the development of cardiovascular diseases and changes in autonomic system activity. However, the cardiovascular consequences induced by the association between high-fat diet (HFD) and chronic stress are not fully understood. We hypothesized that the association between HFD and exposure to a chronic variable stress (CVS) protocol for four weeks might exacerbate the cardiovascular and metabolic disturbances in rats when compared to these factors singly. To test this hypothesis, male Wistar rats were divided into four groups: control-standard chow diet (SD; n = 8); control-HFD (n = 8); CVS-SD (n = 8); and CVS-HFD (n = 8). The CVS consisted of repeated exposure of the rats to different inescapable and unpredictable stressors (restraint tress; damp sawdust, cold, swim stress and light cycle inversion). We evaluated cardiovascular function, autonomic activity, dietary intake, adiposity and metabolism. The HFD increased body weight, adiposity and blood glucose concentration (∼15%) in both control and CVS rats. The CVS-HFD rats showed decreased insulin sensitivity (25%) compared to CVS-SD rats. The control-HFD and CVS-HFD rats presented increased intrinsic heart rate (HR) values (∼8%). CVS increased cardiac sympathetic activity (∼65%) in both SD- and HFD-fed rats. The HFD increased basal HR (∼10%). Blood pressure and baroreflex analyzes showed no differences among the experimental groups. In conclusion, the present data indicate absence of interaction on autonomic imbalance evoked by either CVS or HFD. Additionally, HFD increased HR and evoked metabolic disruptions which are independent of stress exposure.

Neonatal hypothyroidism does not increase Sertoli cell proliferation in iNOS−/− mice

Sertoli cell (SC) proliferation in mice occurs until two weeks after birth and is mainly regulated by FSH and thyroid hormones. Previous studies have shown that transient neonatal hypothyroidism in laboratory rodents is able to extend SC mitotic activity, leading ultimately to higher testis size and daily sperm production (DSP) in adult animals. Moreover, we have shown that due to higher SC proliferation and lower germ cell apoptosis, iNOS deficiency in mice also results in higher testis size and DSP. Although the cell size was smaller, the Leydig cells (LCs) number per testis also significantly increased in iNOS−/−mice. Our aims in the present study were to investigate if the combination of neonatal hypothyroidism and iNOS deficiency promotes additive effects in SC number, testis size and DSP. Hypothyroidism was induced in wild-type (WT) and iNOS−/−mice using 6-propyl-2-thiouracil (PTU) through the mother’s drinking water from 0 to 20 days of age, and were sacrificed at adulthood. Our results showed that, in contrast to the WT mice in which testis size, DSP and SC numbers increased significantly by 20, 40 and 70% respectively, after PTU treatment, no additive effects were observed for these parameters in treated iNOS−/−mice, as well as for LC. No alterations were observed in spermatogenesis in any group evaluated. Although we still do not have an explanation for these intriguing findings, we are currently investigating whether thyroid hormones influence iNOS levels and/or counterbalance physiological effects of iNOS deficiency in testis function and spermatogenesis.

Thyroid disorders and nitric oxide in cardiovascular adaptation to hypovolemia

This study aimed to investigate whether nitric oxide participates in the cardiovascular function and haemodynamic adaptation to acute haemorrhage in animals with thyroid disorders. Sprague-Dawley rats aged 2months old treated with T3 (hyper, 20μg/100g body weight) or 0.02% methimazole (hypo, w/v) during 28days were pre-treated with N(G) nitro-l-arginine methyl ester (L-NAME) and submitted to 20% blood loss. Heart function was evaluated by echocardiography. Measurements of arterial blood pressure, heart rate, nitric oxide synthase activity and protein levels were performed. We found that hypo decreased fractional shortening and ejection fraction and increased left ventricle internal diameter. Hyper decreased ventricle diameter and no changes in cardiac contractility. Haemorrhage elicited a hypotension of similar magnitude within 10min. Then, this parameter was stabilized at about 30-40min and maintained until finalized, 120min. L-NAME rats showed that the immediate hypotension would be independent of nitric oxide. Nitric oxide synthase inhibition blunted the changes of heart rate induced by blood loss. Hyper and hypo had lower atrial enzyme activity associated with a decreased enzyme isoform in hypo. In ventricle, hyper and hypo had a higher enzyme activity, which was not correlated with changes in protein levels. Haemorrhage induced an increased heart nitric oxide production. We concluded that thyroid disorders were associated with hypertrophic remodelling which impacted differently on cardiac function and its adaptation to a hypovolemia. Hypovolemia triggered a nitric oxide synthase activation modulating the heart function to maintain haemodynamic homeostasis. This involvement depends on a specific enzyme isoform, cardiac chamber and thyroid state.

Association between serum nitric oxide metabolites and thyroid hormones in a general population: Tehran Thyroid Study

Nitric oxide participates in the regulation of thyroid function.

AIMS

The purpose of this study was to determine whether there is an association between serum nitric oxide metabolites (NOx) and free thyroxine (free T4), anti-thyroid peroxidase (anti-TPO), and thyroid-stimulating hormone (TSH) levels.

METHODS

Study subjects were adults, aged ≥20 years, who participated in the Tehran Thyroid Study (TTS). In a cross-sectional study, in the third phase of TTS, serum NOx concentrations were measured in 1974 adult participants; pregnant women and subjects who had chronic diarrhea, cancer, weight loss, and hospitalization within the past 3 months were excluded, as were those taking medicines that affect thyroid function; the remaining 1771 subjects were grouped according to tertiles of free T4, anti-TPO, and TSH. Spearman's correlation coefficients and multivariable linear regression analysis were used to determine the relationship between serum NOx levels and free T4, anti-TPO, and TSH.

RESULTS

Serum NOx levels were negatively correlated with free T4 in men (r = -0.083; p = 0.029). An inverse association between the third tertile of free T4 and NOx levels was found in both non-adjusted (β = -0.095, p = 0.031) and multivariable-adjusted (β = -0.094, p = 0.039) analyses, only in men. After multivariable adjustment, the third tertile of anti-TPO was significantly associated with NOx levels in women (β = -0.067, p = 0.050).

CONCLUSIONS

Based on the result, serum NOx concentration was found to be associated with free T4 in men and anti-TPO in women.

Role of Oxidative Stress in Thyroid Hormone-Induced Cardiomyocyte Hypertrophy and Associated Cardiac Dysfunction: An Undisclosed Story

Cardiac hypertrophy is the most documented cardiomyopathy following hyperthyroidism in experimental animals. Thyroid hormone-induced cardiac hypertrophy is described as a relative ventricular hypertrophy that encompasses the whole heart and is linked with contractile abnormalities in both right and left ventricles. The increase in oxidative stress that takes place in experimental hyperthyroidism proposes that reactive oxygen species are key players in the cardiomyopathy frequently reported in this endocrine disorder. The goal of this review is to shed light on the effects of thyroid hormones on the development of oxidative stress in the heart along with the subsequent cellular and molecular changes. In particular, we will review the role of thyroid hormone-induced oxidative stress in the development of cardiomyocyte hypertrophy and associated cardiac dysfunction, as well as the potential effectiveness of antioxidant treatments in attenuating these hyperthyroidism-induced abnormalities in experimental animal models.

Neonatal hyperthyroidism on rat heart: interrelation with nitric oxide and sex

PURPOSE

To clarify the mechanism mediating the effect of hyperthyroidism on cardiac function during the second month of life in rats.

METHODS

Male and female Sprague-Dawley rats were assigned to a control or to a triiodothyronine (T3)-treated group. Treatment of each group was started on the third day after birth. Control rats (Eut) received 0.9 NaCl [0.1 ml/100 g body weight (BW)] every second day during 60 days and T3-treated rats (Hyper) received subcutaneous (SC) T3 injections every second day during 60 days.

RESULTS

Hyperthyroidism decreased left ventricle volume only in male rats. Female euthyroid rats presented higher atrial nitric oxide synthase (NOS) activity than male rats and hormonal treatment decreased this enzyme's activity in both sexes. Euthyroid male and female rats had similar atrial NOS protein levels, but females had higher caveolin (cav) 3 protein levels. T3 treatment increased this protein only in males. Female rats had lower ventricular NOS activity than male rats; hyperthyroidism increased NOS activity in both sexes but this effect was associated with lower cav 3 protein levels. Hyperthyroidism did not change cav 1 protein levels in both male and female rats.

CONCLUSIONS

The results of this study demonstrating clinically relevant sex-related differences in the pathophysiology of the hyperthyroid heart have raised new questions regarding the mechanisms responsible for the observed differences. This study suggests that sex-related intrinsic factors such as nitric oxide may modulate the response to hyperthyroidism that leads to cardiovascular dysfunction.

Nitric oxide and AQP2 in hypothyroid rats: a link between aging and water homeostasis

OBJECTIVE

Hypothyroid state and aging are associated with impairment in water reabsorption and changes in aquaporin water channel type 2 (AQP2). Nitric oxide (NO) is involved in AQP2 trafficking to the apical plasma membrane in medullary collecting duct cells. The purpose of this study was to investigate whether aging and hypothyroidism alter renal function, and whether medullary NO and AQP2 are implicated in maintaining water homeostasis.

MATERIALS/METHODS

Sprague-Dawley rats aged 2 and 18months old were treated with 0.02% methimazole (w/v) during 28days. Renal function was examined and NO synthase (NOS) activity ([(14)C (U)]-L-arginine to [(14)C (U)]-L-citrulline assays), NOS, caveolin-1 and -3 and AQP2 protein levels were determined in medullary tissue (Western blot). Plasma membrane fraction and intracellular vesicle fraction of AQP2 were evaluated by Western blot and immunohistochemistry.

RESULTS

A divergent response was observed in hypothyroid rats: while young rats exhibited polyuria with decreased medullary NOS activity, adult rats exhibited a decrease in urine output with increased NOS activity. AQP2 was increased with hypothyroidism, but while young rats exhibited increased AQP2 in plasma membrane, adult rats did so in the cytosolic site.

CONCLUSIONS

Hypothyroidism contributes in a differential way to aging-induced changes in renal function, and medullary NO and AQP2 would be implicated in maintaining water homeostasis.

Histopathological and immunohistochemical alterations in rat heart after thyroidectomy and the role of hemin and ketoconazole in treatment

The heart is a major target organ for thyroid hormone action and marked changes occur in cardiac function in the case of hypo- or hyperthyroidism. Also, thyroid hormone has a significant regulatory effect on the rate of heme oxidation in the liver. Heme oxygenase (HO) is a heme-catabolizing enzyme that converts heme into biliverdin, iron and carbon monoxide. HO(-1) and its reaction products protect the heart and vasculature in pathological conditions. We studied the changes in the heart structure of thyroidectomized rat at the post-pubertal stage, in addition to the role of hemin as HO inducer and ketoconazole (KTZ) as HO inhibitor in treatment. 35 male Wistar rats were equally divided into seven groups; the first and second groups were the control and Sham-operated groups respectively while the 3rd and 4th groups were subjected to sham operation then treated with hemin (G(3)) and KTZ (G(4)). The 5th group (G(5)) was thyroidectomized group. The 6th and 7th groups were subjected to thyroidectomy then treated with hemin (G(5)) and KTZ (G(6)) respectively. Serum T(3) & TSH levels in thyroidectomized rats were significantly decreased and increased respectively when compared with the control group. Left ventricle section in the heart of thyroidectomized rats showed many of abnormalities as hydrophobic changes of myofibrillar structure with striations, myocardial atrophy and edema, focal haemorrhage when compared with that in control and sham groups. The iNOS label index was significantly decreased in thyroidectomized rat heart (grade 1) and their levels were significantly increased in treated thyroidectomized rats with hemin and KTZ (grades 3 & 2 respectively) when compared with control and sham rat groups (grade 4). Treatment of thyroidectomized rat with hemin improves the histopathological alternation and the intensity of iNOS immunoreactive cells demonstrating the recovery of some injury.

Hypothyroidism: age-related influence on cardiovascular nitric oxide system in rats

This study investigates whether changes in nitric oxide (NO) production participate in the cardiovascular manifestations of hypothyroidism and whether these changes are age-related. Sprague-Dawley rats aged 2 and 18 months old were treated with 0.02% methimazole (wt/vol) during 28 days. Left ventricular function was evaluated by echocardiography. Measurements of arterial blood pressure, heart rate, nitric oxide synthase (NOS) activity and NOS/caveolin-1 and -3 protein levels were performed. Hypothyroidism enhanced the age-related changes in heart function. Hypothyroid state decreased atrial NOS activity in both young and adult rats, associated with a reduction in protein levels of the three NOS isoforms in young animals and increased caveolin (cav) 1 expression in adult rats. Ventricle and aorta NOS activity increased in young and adult hypothyroid animals. In ventricle, changes in NOS activity were accompanied by an increase in inducible NOS isoform in young rats and by an increase in caveolins expression in adult rats. Greater aorta NOS activity level in young and in adult Hypo rats would derive from the inducible and the endothelial NOS isoform, respectively. Thyroid hormones would be one of the factors involved in the modulation of cardiovascular NO production and caveolin-1 and -3 tissue-specific abundance, regardless of age. Hypothyroidism appears to contribute in a differential way to aging-induced changes in the myocardium and aorta tissues. Low thyroid hormones levels would enhance the aging effect on the heart. Age-related changes in NO production participate in the cardiovascular manifestations of hypothyroidism.

Boveris A, T. Arranz C, Balaszczuk AM. Cardiac mitochondrial nitric oxide: a regulator of heart rate?

Alterations in autonomic control and myocardial nitric-oxide (NO) production are likely linked to the development and progression of heart dysfunction. By focusing on heart rate, the complexity of the actions of NO at distinct levels throughout the autonomic nervous system and its relationship with other regulators can be demonstrated. Given the multiple and opposing actions of NO on cardiac control, it is difficult to interpret a response after a global intervention in the NO system. The diversity of intracellular pathways activated by NO, and their differing sensitivities to different levels of NO, might account for some aspects of reported specific but opposite effects. We discuss factors that might contribute to this diversity of actions. A proper elucidation of the effects of NO on metabolic pathways and on energy generation could lead to novel therapeutic strategies aimed at the early treatment of heart dysfunction.

Nitric oxide and cardiac function

Nitric oxide (NO) participates in the control of contractility and heart rate, limits cardiac remodeling after an infarction and contributes to the protective effect of ischemic pre- and postconditioning. Low concentrations of NO, with production of small amounts of cGMP, inhibit phosphodiesterase III, thus preventing the hydrolysis of cAMP. The subsequent activation of a protein-kinase A causes the opening of sarcolemmal voltage-operated and sarcoplasmic ryanodin receptor Ca(2+) channels, thus increasing myocardial contractility. High concentrations of NO induce the production of larger amounts of cGMP which are responsible for a cardiodepression in response to an activation of protein kinase G (PKG) with blockade of sarcolemmal Ca(2+) channels. NO is also involved in reduced contractile response to adrenergic stimulation in heart failure. A reduction of heart rate is an evident effect of NO-synthase (NOS) inhibition. It is noteworthy that the direct effect of NOS inhibition can be altered if baroreceptors are stimulated by increases in blood pressure. Finally, NO can limit the deleterious effects of cardiac remodeling after myocardial infarction possibly via the cGMP pathway. The protective effect of NO is mainly mediated by the guanylyl cyclase-cGMP pathway resulting in activation of PKG with opening of mitochondrial ATP-sensitive potassium channels and inhibition of the mitochondrial permeability transition pores. NO acting on heart is produced by vascular and endocardial endothelial NOS, as well as neuronal and inducible synthases. In particular, while in the basal control of contractility, endothelial synthase has a predominant role, the inducible isoform is mainly responsible for the cardiodepression in septic shock.

Effect of acute inhibition of nitric oxide synthesis by l-NAME on cardiovascular responses following peripheral autonomic blockade in rabbits

The pressor and chronotropic responses to acute inhibition of nitric oxide synthase enzyme by N(G)-nitro-L-arginine methyl ester (L-NAME) were studied in anaesthetized rabbits with intact autonomic nervous system (ANS) activity. Also, they were investigated when administration of L-NAME was preceded by peripheral autonomic blockade. Autonomic blockade had different forms: ganglionic (hexamethonium-induced), post-ganglionic beta-adrenergic blockade (propranolol induced), parasympathetic blockade (atropine induced), and complete autonomic blockade by coadministration of hexamethonium and atropine simultaneously. L-NAME injected intravenously (10 mg/kg) in animals with intact and blocked autonomic activity induced a pressor response. This pressor response was accompanied by bradycardia in rabbits with either intact autonomic activity or hexamethonium-induced ganglionic blockade. L-NAME exerted no effect on heart rate in animals with beta-adrenergic blockade or parasympathetic blockade. In rabbits with complete autonomic blockade, L-NAME evoked tachycardia. These experiments indicate that L-NAME-induced hypertension is not relying only on ANS. Also, L-NAME-induced tachycardia in rabbits treated with atropine plus hexamethonium suggests other humoral mechanisms that may be involved in the L-NAME induced chronotropic response.

Autonomic regulation of pacemaker activity: role of heart nitric oxide synthases

In autonomic-blocked rats treated with NG-nitro-L-arginine methyl ester (L-NAME, 7.5 mg/kg), heart rate increased 18% and mean arterial pressure increased 48%. Thyroidectomy, along with autonomic blockade, hampered the chronotropic response but did not modify the effect on blood pressure. After 150 min of autonomic blockade, the experimental end point, total nitric oxide (NO) production by heart NO synthases (NOS) decreased 61%: from 54 to 21 nmol NO.min-1.g heart-1. Mitochondrial NOS (mtNOS) and sarcoplasmic reticulum endothelial NOS activities decreased 74% and 52%, respectively. Mitochondria isolated from whole heart showed a well-coupled oxidative phosphorylation with high respiratory control and ADP-to-O ratios, decreased mtNOS activity (55-60%), and decreased mtNOS protein expression (70%). Immunohistochemistry with anti-inducible NOS antibody linked to gold particles localized mtNOS at the inner mitochondrial membranes. Histochemical right atrial NOS (NADPH-diaphorase) decreased 55% after heart denervation. The effects of autonomic denervation on the NO system were partially prevented by thyroidectomy performed simultaneously with autonomic blockade. Western blot analysis indicated a very rapid mtNOS protein turnover (half time=120 min) with a process of protein expression that was upregulated by thyroidectomy and a degradation process that was downregulated by the autonomic nervous system. The observations suggest that NO-mediated pathways contribute to pacemaker heart activity, likely through the NO steady-state levels in the right atrium and the whole heart.