Effect of nitrate and l-arginine therapy on nitric oxide levels in serum, heart, and aorta of fetal hypothyroid rats

Region-specific effects of antenatal/early postnatal hypothyroidism on endothelial NO-pathway activity in systemic circulation

Background

Antenatal/early postnatal hypothyroidism weakens NO-mediated anticontractile influence of endothelium in coronary arteries of adult rats, but it remains unclear whether this occurs in other vascular regions. We hypothesized that developmental thyroid deficiency is followed by region-specific changes in the endothelial NO-pathway activity in systemic vasculature. To explore this, we estimated the effects of antenatal/early postnatal hypothyroidism on NO-pathway activity and its potential local control mechanisms in rat mesenteric and skeletal muscle (sural) arteries.

Methods

Dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%) during pregnancy and 2 weeks postpartum; control (CON) females received PTU-free water. Adult offspring (10–12-weeks) arteries were studied by wire myography, qPCR, and Western blotting.

Results

Endothelium removal or inhibition of NO-synthase with L-NNA augmented contractile responses to α₁-adrenoceptor agonist methoxamine. In PTU compared to CON group, these effects were stronger in sural arteries, but did not differ in mesenteric arteries. The responses of both arteries to NO-donor DEA/NO were similar in CON and PTU rats. mRNA contents of deiodinase 2 and thyroid hormone receptor α were similar in mesenteric arteries of two groups but were elevated in sural arteries of PTU group compared to CON. The abundance of eNOS protein was higher in sural arteries of PTU compared to CON rats.

Conclusion

Antenatal/early postnatal hypothyroidism is followed by an increase in NO-mediated anticontractile influence in sural, but not in mesenteric arteries of adult animals. The diversity of hypothyroidism effects may be due to different alterations of local T3 synthesis/reception in different vascular beds.

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Antenatal hypothyroidism increases anticontractile NO-effect in sural arteries.

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Antenatal hypothyroidism doesn't change anticontractile effect in mesenteric arteries.

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Diverse hypothyroidism effects may be due to the differences in local T3 signaling.

Thyroxine Induces Acute Relaxation of Rat Skeletal Muscle Arteries via Integrin αvβ3, ERK1/2 and Integrin-Linked Kinase

Aim: Hyperthyroidism is associated with a decreased peripheral vascular resistance, which could be caused by the vasodilator genomic or non-genomic effects of thyroid hormones (TH). Non-genomic, or acute, effects develop within several minutes and involve a wide tissue-specific spectrum of molecular pathways poorly studied in vasculature. We aimed to investigate the mechanisms of acute effects of TH on rat skeletal muscle arteries.

Methods: Sural arteries from male Wistar rats were used for isometric force recording (wire myography) and phosphorylated protein content measurement (Western blotting).

Results: Both triiodothyronine (T3) and thyroxine (T4) reduced contractile response of sural arteries to α₁-adrenoceptor agonist methoxamine. The effect of T4 was more prominent than T3 and not affected by iopanoic acid, an inhibitor of deiodinase 2. Endothelium denudation abolished the effect of T3, but not T4. Integrin αvβ3 inhibitor tetrac abolished the effect of T4 in endothelium-denuded arteries. T4 weakened methoxamine-induced elevation of phospho-MLC2 (Ser19) content in arterial samples. The effect of T4 in endothelium-denuded arteries was abolished by inhibiting ERK1/2 activation with U0126 as well as by ILK inhibitor Cpd22 but persisted in the presence of Src- or Rho-kinase inhibitors (PP2 and Y27632, respectively).

Conclusion: Acute non-genomic relaxation of sural arteries induced by T3 is endothelium-dependent and that induced by T4 is endothelium-independent. The effect of T4 on α₁-adrenergic contraction is stronger compared to T3 and involves the suppression of extracellular matrix signaling via integrin αvβ3, ERK1/2 and ILK with subsequent decrease of MLC2 (Ser19) phosphorylation.

Fetal Hypothyroidism Impairs Aortic Vasorelaxation Responses in Adulthood: Involvement of Hydrogen Sulfide and Nitric Oxide Cross talk

ABSTRACT

Thyroid hormones have a wide range of effects on growth, differentiation, evolution, metabolism, and physiological function of all tissues, including the vascular bed. In this study, the effect of fetal hypothyroidism on impairment of aortic vasorelaxation responses in adulthood was investigated with emphasis on possible involvement of hydrogen sulfide (H2S)/nitric oxide interaction. Two groups of female rats were selected. After mating and observation of vaginal plaque, one group received propylthiouracil (200 ppm in drinking water) until the end of pregnancy and another group had no propylthiouracil treatment during the fetal period. In adult rats, aortic relaxation responses to l-arginine and GYY4137 were assessed in the presence or absence of Nω-nitro-L-arginine methyl ester hydrochloride and dl-propargylglycine in addition to the biochemical measurement of thyroid hormones and some related factors. Obtained findings showed a lower vasorelaxation response for GYY4137 and l-arginine in the fetal hypothyroidism group, and preincubation with Nω-nitro-L-arginine methyl ester hydrochloride or dl-propargylglycine did not significantly aggravate this weakened relaxation response. In addition, aortic levels of sirtuin 3, endothelial nitric oxide synthase, cystathionine gamma-lyase, and H2S were significantly lower in the fetal hypothyroidism group. Meanwhile, no significant changes were obtained regarding serum levels of thyroid hormones including free triiodothyronine;, total triiodothyronine, free thyroxine, total thyroxine, and thyroid-stimulating hormone in adult rats. It can be concluded that hypothyroidism in the fetal period has inappropriate effects on the differentiation and development of vascular bed with subsequent functional abnormality that persists into adulthood, and part of this vascular abnormality is mediated through weakened interaction and/or cross talk between H2S and nitric oxide.

Changes in nitric oxide synthase levels are associated with impaired cardiac function and tolerance to ischemia-reperfusion injury in male rats with transient congenital hypothyroidism

Transient congenital hypothyroidism (TCH) has long-lasting consequences on the cardiovascular system during adulthood. The aim of this study was to determine whether nitric oxide (NO) and NO-producing enzymes are involved in impaired cardiac function as well as decreased tolerance to ischemia-reperfusion (IR) injury in adult male rats with TCH. Pregnant rats were divided into control and hypothyroid groups. Male offspring rats were categorized in control and hypothyroid (TCH) groups at week 16. Levels of NOx (nitrate+nitrite) and neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS) were measured in hearts of rats and isolated perfused hearts from both groups were subjected to IR. Levels of NOx and NOSs were also measured in both groups after ischemia. Compared with controls, heart NOx levels were higher at baseline (48.0 ± 4.9 vs. 35.0 ± 2.6 μmol/L; P = 0.034) and following IR (103.6 ± 4.2 vs. 70.2 ± 2.7 μmol/L; P < 0.001) in rat with TCH. At baseline, compared with controls, heart iNOS and nNOS levels were significantly higher in rats with TCH (6.12 ± 0.34 vs. 4.78 ± 0.27 ng/mg protein; P = 0.008 for iNOS and 4.87 ± 0.28 vs. 3.55 ± 0.23 ng/mg protein; P = 0.003 for nNOS). Following IR, in rats with TCH, heart iNOS levels increased (11.75 ± 2.02 vs. 6.12 ± 0.34, ng/mg protein; P = 0.015) whereas nNOS level decreased (4.10 ± 0.25 vs. 4.87 ± 0.28 ng/mg protein; P = 0.063). Adverse effects of TCH on cardiac function are associated with increased ratio of iNOS/eNOS; in addition, increased heart nNOS levels are involved in impaired cardiac function while its decrease is associated with decreased tolerance to IR injury.

Phikud Navakot Modulates the Level of Pro-Inflammatory Mediators and the Protein Expression of SOD1 and 2 and the Nrf2/HO-1 Signaling Pathway in Rats with Acute Myocardial Infarction

Phikud Navakot (PN) is nine major herbs in a famous traditional Thai recipe namely “Yahom Navakot” used to treat cardiovascular disorders. This study investigated the cardioprotective effects of PN formula on isoproterenol-induced myocardial infarction (IMI) in Sprague-Dawley rats. Forty-five rats were randomly divided into nine groups (n = 5 per group): the control, the IMI, the IMI + propranolol, the control or the IMI + PN formula (PN ethanolic extract at doses of 64, 127, or 255 mg/kg) by oroesophageal gavage for 28 days. The ST segment and serum troponin T levels were significantly increased in IMI rats. PN did not eliminate tissue necrosis, infiltration of inflammatory cells, or interstitial edema in IMI rats. All doses of PN decreased (p < 0.001) serum TNF-α and IL-6 levels. PN (127 and 255 mg/kg) up-regulated (p < 0.05) heme oxygenase (HO)-1 expression, whereas PN (255 mg/kg) significantly increased superoxide dismutase (SOD) 1 and 2 expression, compared with IMI rats. Nuclear factor erythroid 2-related factor 2 (Nrf2) and HO-1 expression significantly increased in IMI rats and IMI rats that received PN. PN formula possesses potential anti-inflammatory and antioxidant properties by modulating the levels of TNF-α, IL-6 and antioxidant enzymes. Our study reveals a novel cardioprotective effect of PN in IMI rats through the Nrf2/HO-1 signaling.

Changes in Endothelial Nitric Oxide Production in Systemic Vessels during Early Ontogenesis-A Key Mechanism for the Perinatal Adaptation of the Circulatory System

Nitric oxide (NO) produced in the wall of blood vessels is necessary for the regulation of vascular tone to ensure an adequate blood supply of organs and tissues. In this review, we present evidence that the functioning of endothelial NO-synthase (eNOS) changes considerably during postnatal maturation. Alterations in NO-ergic vasoregulation in early ontogeny vary between vascular beds and correlate with the functional reorganization of a particular organ. Importantly, the anticontractile effect of NO can be an important mechanism responsible for the protectively low blood pressure in the immature circulatory system. The activity of eNOS is regulated by a number of hormones, including thyroid hormones which are key regulators of the perinatal developmental processes. Maternal thyroid hormone deficiency suppresses the anticontractile effect of NO at perinatal age. Such alterations disturb perinatal cardiovascular homeostasis and lead to delayed occurring cardiovascular pathologies in adulthood. The newly discovered role of thyroid hormones may have broad implications in cardiovascular medicine, considering the extremely high prevalence of maternal hypothyroidism in human society.

Radioactive Iodine Therapy and Glucose Tolerance

Radioactive iodine therapy is commonly used as an adjuvant therapy in follicular and papillary thyroid carcinoma (PTC) and in the treatment of Graves’ disease (GD). The basis of this therapy is the accumulation of radioactive iodine by the sodium-iodide symporter (NIS) in the thyroid gland. Expression of NIS by extrathyroidal tissues such as islets of pancreas has been reported. Radioactive iodine uptake by pancreatic beta-cells can potentially damage these cells. In this study, we discuss the possible associations between radioactive iodine and glucose intolerance. Overall, radioactive iodine uptake by the pancreas may damage beta-cells and predispose patients to glucose intolerance or type 2 diabetes, particularly in patients exposed to radioactive iodine therapy following total thyroidectomy. Further studies are needed to clarify and confirm this association.

NO-mediated anticontractile effect of the endothelium is abolished in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism

INTRODUCTION

Thyroid hormones are essential for proper development of many systems and organs, including circulatory system. Thyroid deficiency during pregnancy may affect the cardiovascular function in children early on and later in adulthood. However, long-term effects of early thyroid deficiency are poorly understood. We hypothesized that antenatal/early postnatal hypothyroidism will influence anticontractile effect of NO in coronary arteries of adult rats.

DESIGN AND METHODS

To model antenatal/early postnatal hypothyroidism dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%, w/v) from the first day of pregnancy till 2 weeks after delivery. Control females were supplied with pure water. Their male offspring was grown up till the age of 10-12 weeks. Systolic blood pressure was measured using tail cuff method. Septal coronary arteries were isolated and studied in wire myograph. Blood serum thyroid hormones concentrations (ELISA) and NO metabolites level (Griess method) were evaluated.

RESULTS

At the age of 10-12 weeks thyroid hormones, TSH concentrations, NO metabolites and systolic blood pressure level didn't differ between groups. Arterial responses to acetylcholine and exogenous NO-donor DEA/NO were similar in control and PTU groups. Along with that, in control rats endothelium denudation strongly potentiated basal tone of arteries and their contractile responses to thromboxane A2 receptor agonist U46619. The effects of endothelium denudation were absent in PTU rats indicating that anticontractile effect of endothelium is abolished in their arteries. Further, NO-synthase inhibitor L-NNA (100 μM) caused significant elevation of basal tone and increased U46619-induced contraction of endothelium-intact arteries only in control rats, while had no effect in PTU group.

CONCLUSIONS

Our data demonstrate that NO-mediated anticontractile effect of endothelium is eliminated in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. Therefore, maternal thyroid hormones deficiency may have detrimental consequences in adult offspring including coronary circulation pathologies, despite normal blood levels of thyroid hormones.

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.

Comparison of the effects of fetal hypothyroidism on glucose tolerance in male and female rat offspring

Thyroid hormones are vital for survival of mammalian species and play critical roles in growth, development, and metabolism. Both fetal hypothyroidism and sex can affect carbohydrate metabolism during adult life. This study aims to assess carbohydrate metabolism in male and female offspring born from mothers who were hypothyroid during pregnancy. Pregnant rats were divided into two groups; the controls consumed water and the hypothyroid group received water containing 0.025 % 6-propyl-2-thiouracial throughout gestation. The intravenous glucose tolerance test (0.5 g/kg glucose) was carried out in 3-month-old offspring. Findings showed that compared to controls, male fetal hypothyroid rats during adulthood had glucose intolerance (area under the curve: 446.4 ± 9.7 vs. 486.4 ± 8.8, p < 0.01 in control and fetal hypothyroid groups, respectively) whereas females had improved glucose tolerance (478.1 ± 7.0 vs. 455.9 ± 8.5, p < 0.01). In conclusion, sex could modulate the effects of fetal hypothyroidism on glucose tolerance in rats.

Effects of ischemic postconditioning on the hemodynamic parameters and heart nitric oxide levels of hypothyroid rats

Background

Ischemic postconditioning (IPost) is a method of protecting the heart against ischemia-reperfusion (IR) injury. However, the effectiveness of IPost in cases of ischemic heart disease accompanied by co-morbidities such as hypothyroidism remains unclear.

Objective

The aim of this study was to determine the effect of IPost on myocardial IR injury in hypothyroid male rats.

Methods

Propylthiouracil in drinking water (500 mg/L) was administered to male rats for 21 days to induce hypothyroidism. The hearts from control and hypothyroid rats were perfused in a Langendorff apparatus and exposed to 30 min of global ischemia, followed by 120 min of reperfusion. IPost was induced immediately following ischemia.

Results

Hypothyroidism and IPost significantly improved the left ventricular developed pressure (LVDP) and peak rates of positive and negative changes in left ventricular pressure (±dp/dt) during reperfusion in control rats (p < 0.05). However, IPost had no add-on effect on the recovery of LVDP and ±dp/dt in hypothyroid rats. Furthermore, hypothyroidism significantly decreased the basal NO metabolite (NO_x) levels of the serum (72.5 ± 4.2 vs. 102.8 ± 3.7 μmol/L; p < 0.05) and heart (7.9 ± 1.6 vs. 18.8 ± 3.2 μmol/L; p < 0.05). Heart NO_x concentration in the hypothyroid groups did not change after IR and IPost, whereas these were significantly (p < 0.05) higher and lower after IR and IPost, respectively, in the control groups.

Conclusion

Hypothyroidism protects the heart from IR injury, which may be due to a decrease in basal nitric oxide (NO) levels in the serum and heart and a decrease in NO after IR. IPost did not decrease the NO level and did not provide further cardioprotection in the hypothyroid group.