Altered thyroidal status and the in vivo synthesis of atrial natriuretic peptide in the rat heart

Triad of palpitation, angina, and murmur in a non-cardiac patient

The triad of palpitation, angina, and murmur is a classical feature of cardiac pathology. However, their presence sometimes uncovers a thyroid etiology. Identification well in time decreases out-of-pocket expenditures on illness and suffering. We report a case of a 40-year-old woman who presented with fever with chills, vomiting, palpitations, and shortness of breath for the past month. Also, she described chest pain as typical of angina. Multiple diagnoses were made elsewhere, but none of the treatments resulted in the resolution of symptoms. ST changes were suggestive of ischemic pathology, cardiac MRI done showed up hypertrophied myocardium. After a negative blood culture for infective endocarditis and serology sought for fever work-up, suspicious cardiac examination with a murmur, and an abnormal thyroid profile with a thyroid scan, led to a diagnosis of Graves' disease. This case defines the triad in a noncardiac patient and emphasizes what a thyroid disease does to the heart.

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.

Oxidative stress and heart failure in altered thyroid States

Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism). The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.

Hyperthyroid heart disease

The heart is an organ sensitive to the action of thyroid hormone, and measurable changes in cardiac performance are detected with small variations in thyroid hormone serum concentrations. Most patients with hyperthyroidism experience cardiovascular manifestations, and the most serious complications of hyperthyroidism occur as a result of cardiac involvement. Recent studies provide important insights into the molecular pathways that mediate the action of thyroid hormone on the heart and allow a better understanding of the mechanisms that underlie the hemodynamic and clinical manifestations of hyperthyroidism. Several cardiovascular conditions and drugs can interfere with thyroid hormone levels and may pose a difficulty in interpretation of laboratory data in patients with suspected thyroid heart disease. The focus of this report is a review of the current knowledge of thyroid hormone action on the heart and the clinical and hemodynamic laboratory findings as well as therapeutic management of patients with hyperthyroid heart disease.

Role of thyroid hormones on the synthesis and release of atrial natriuretic peptide in rats with acute renal failure

BACKGROUND/AIMS

High atrial natriuretic peptide (ANP) serum levels are seen in acute renal failure (ARF) due to impaired ANP clearance, but the response of ANP to blood volume expansion is blunted. ARF-associated hypothyroidism influences ANP clearance but it may also play a role in the synthesis and release of ANP because in primary hypothyroidism both mechanisms are disturbed. The aim of this study is to analyze whether thyroxin (T4) supplementation improves the synthesis and release of ANP in ARF.

METHODS

Four groups of rats were studied: group C (control); group ARF; Group ARF-T4 (ARF supplemented with T4), and group Tx (thyroidectomized). Serum creatinine (SCr), creatinine clearance (CrCl), total T4, total triiodothyronin (T3), plasma ANP, ANP response to acute saline load and atrial content of mRNA-ANP were measured 5 days after ARF induction with potassium dichromate.

RESULTS

CrCl was 1.8 +/- 0.4 ml/min in group C, and it significantly dropped to 0.6 +/- 0.5 in ARF (p < 0.01), T4 improved it (1.7 +/- 0.7 in ARF-T4, p < 0.01) and Tx did not change it. Plasma ANP was higher in ARF as compared with C (152 +/- 23 vs. 52 +/- 21 fmol/l, p < 0.01). In ARF-T4, ANP was higher than in C but lower than in ARF (85 +/- 28 fmol/l, p < 0.01). No changes were observed in Tx rats (48 +/- 17 fmol/l). The atrial content of mRNA-ANP was 0.06 +/- 0.025 mRNA-ANP/mRNA-beta-actin ratio units in group C, it was higher in ARF (0.13 +/- 0.025, p < 0.01) and lower in Tx (0.04 +/- 0.01, p < 0.05) as compared to C. Supplementation with T4 increased the mRNA-ANF content (0.18 +/- 0.2 mRNA-ANP/mRNA-beta-actin ratio units, p < 0.05) over ARF. Plasma ANP response to saline load was 45 +/- 7% in C, but it was reduced in ARF and Tx (20 +/- 10 and 26 +/- 10%, p < 0.01). In ARF-T4 the response was restored (36 +/- 9%, p < 0.01 vs. ARF).

CONCLUSION

Thyroid hormones modulate the synthesis and release of ANP in ARF. Although the effect is probably direct, T4-induced amelioration of renal damage may also play a significant role by improving the uremic milieu.

Polyamine regulation of atrial natriuretic peptide in cultured cardiocytes

In the following investigation, we have studied the role of polyamines in the regulation of atrial natriuretic peptide (ANP) using ventricular cardiocytes which in culture synthesize and secrete ANP. Polyamines are cellular cations ubiquitous in eukaryotes, and ANP is a hormone synthesized and secreted by the cardiac atria in adult animal. The cardiocytes were isolated from neonatal rat hearts by enzymatic dissociation using trypsin and collagenase. The functional role of polyamines in regulation of ANP was assessed by exposing the cardiocytes to difluoromethylornithine (DFMO) which is an inhibitor of ornithine decarboxylase, an initial rate-limiting enzyme in the biosynthesis of polyamines. The results showed that DFMO reduced the levels of putrescine (diamine) and spermidine (triamine) in cultured cardiocytes, and it decreased the levels of ANP in media and cellular extracts of cardiocytes as a function of its dose. An addition of putrescine (100 microM) restored within 5-15 min the levels of ANP in media of both control and polyamine-depleted cardiocytes. These results suggest that polyamines are one of the cellular factors involved in regulation of ANP secretion in cultured cardiocytes.