Thyroid hormone and myocardial ischaemia

Influence of carvedilol and thyroid hormones on inflammatory proteins and cardioprotective factor HIF-1α in the infarcted heart

Inflammatory pathways of Toll-like receptor 4 (TLR4) and NLRP3 inflammasome contribute to acute myocardial infarction (AMI) pathophysiology. The hypoxia-inducible factor 1α (HIF-1α), however, is a key transcription factor related to cardioprotection. This study aimed to compare the influence of carvedilol and thyroid hormones (TH) on inflammatory and HIF-1α proteins and on cardiac haemodynamics in the infarcted heart. Male Wistar rats were allocated into five groups: sham-operated group (SHAM), infarcted group (MI), infarcted treated with the carvedilol group (MI + C), infarcted treated with the TH group (MI + TH), and infarcted co-treated with the carvedilol and TH group (MI + C + TH). Haemodynamic analysis was assessed 15 days post-AMI. The left ventricle (LV) was collected for morphometric and Western blot analysis. The MI group presented LV systolic pressure reduction, LV end-diastolic pressure elevation, and contractility index decrease compared to the SHAM group. The MI + C, MI + TH, and MI + C + TH groups did not reveal such alterations compared to the SHAM group. The MI + TH and MI + C + TH groups presented reduced MyD88 and NLRP3 and increased HIF-1α levels. In conclusion, all treatments preserve the cardiac haemodynamic, and only TH, as isolated treatment or in co-treatment with carvedilol, was able to reduce MyD88 and NLRP3 and increase HIF-1α in the infarcted heart.

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.

Effects of thyroid hormones on aortic tissue after myocardial infarction in rats

Studies have shown a cardioprotective role of thyroid hormones (THs) in cardiac remodeling after acute myocardial infarction (MI). However, there is no data in the literature examining the influence of TH administration on the aortic tissue in an animal model of MI. This study aimed to evaluate the effects of thyroid hormones on the aorta after MI. Male Wistar rats were divided into a sham group (SHAM), infarcted group (AMI), sham+TH (SHAMT) and AMI+TH (AMIT). After MI, the animals received T3 and T4 (2 and 8μg/100g/day, respectively) by oral gavage for 12 days. Later, the animals underwent echocardiography and euthanasia and the aorta was collected for molecular and biochemical analysis. T3 and T4 administration increased the expression of the pro-angiogenic proteins vascular endothelial growth factor (VEGF) and hypoxia inducible factor 1α (HIF-1α) in the aorta of AMIT rats when compared with AMI. With respect to TH receptors, AMI rats presented a decrease in TRβ levels, which was prevented by the hormonal administration. In AMIT rats, both TRα and TRβ levels were increased when compared with the AMI group. Reactive oxygen species levels and NADPH oxidase activity were decreased in both treated groups when compared with the non-treated animals. TH administration after MI may improve angiogenic signaling in the aorta as well as the responsiveness of this vessel to T3 and T4. These positive effects in the aorta may result in additional protection for the cardiovascular system in the context of cardiac ischaemic injury.

Anesthesia and thyroid surgery: The never ending challenges

Thyroidectomy is the most common endocrine surgical procedure being carried out throughout the world. Besides, many patients who have deranged thyroid physiology, namely hyperthyroidism and hypothyroidism, have to undergo various elective and emergency surgical procedures at some stage of their life. The attending anesthesiologist has to face numerous daunting tasks while administering anesthesia to such patients. The challenging scenarios can be encountered at any stage, be it preoperative, intra-op or postoperative period. Preoperatively, deranged thyroid physiology warrants optimal preparation, while anticipated difficult airway due to enlarged thyroid gland further adds to the anesthetic challenges. Cardiac complications are equally challenging as also the presence of various co-morbidities which make the task of anesthesiologist extremely difficult. Thyroid storm can occur during intra-op and post-op period in inadequately prepared surgical patients. Postoperatively, numerous complications can develop that include hemorrhage, laryngeal edema, nerve palsies, tracheomalacia, hypocalcemic tetany, pneumothorax, etc., The present review aims at an in-depth analysis of potential risk factors and challenges during administration of anesthesia and possible complications in patients with thyroid disease.

The difficult patient: drug interaction and the influence of concomitant diseases on the treatment of hypothyroidism

Although most hypothyroid patients do well with one single tablet of thyroxine daily, approximately 10% are dissatisfied and another important group of patients is difficult to control. We reviewed the most common causes for frequent-dose adjustment or high-dose requirement, including poor compliance with therapy and inadequate medication. Since these two causes have been ruled out, drug interaction and other concomitant diseases need to be investigated. Requirements of thyroxine increase in all conditions characterized by impaired gastric acid secretion. Proton-pump inhibitors, antacids and a long list of drugs may decrease thyroxine absorption. In addition, a series of diseases including celiac disease and chronic inflammatory intestinal diseases, as well as nutritional habits may be important in patient control. Finally, we mention the effects of a growing list of drugs and thyroid disruptors that may also affect thyroid hormone metabolism at many levels.

Detrimental effects of thyroid hormone analog DITPA in the mouse heart: increased mortality with in vivo acute myocardial ischemia-reperfusion

There is emerging evidence that treatment with thyroid hormone (TH) can improve postischemic cardiac function. 3,5-Diiodothyropropionic acid (DITPA), a TH analog, has been proposed to be a safer therapeutic agent than TH because of its negligible effects on cardiac metabolism and heart rate. However, conflicting results have been reported for the cardiac effects of DITPA. Importantly, recent clinical trials demonstrated no symptomatic benefit in patients with DITPA despite some improved hemodynamic and metabolic parameters. To address these issues, dose-dependent effects of DITPA were investigated in mice for baseline cardiovascular effects and postischemic myocardial function and/or salvage. Mice were treated with subcutaneous DITPA at 0.937, 1.875, 3.75, or 7.5 mg·kg(-1)·day(-1) for 7 days, and the results were compared with untreated mice for ex vivo and/or in vivo myocardial ischemia-reperfusion (I/R). DITPA had no effects on baseline body temperature, body weight, or heart rate; however, it mildly increased blood pressure. In isolated hearts, baseline contractile function was significantly impaired in DITPA-pretreated mice; however, postischemic recovery was comparable between untreated and DITPA-treated groups. In vivo baseline cardiac parameters were significantly affected by DITPA, with increased ventricular dimensions and decreased contractile function. Importantly, DITPA-treated mice demonstrated high prevalence of fatal cardiac rhythm abnormalities during in vivo ischemia and/or reperfusion. There were no improvements in myocardial infarction and postischemic fractional shortening with DITPA. Myocardial sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), phospholamban (PLB), and heat shock protein (HSP) levels remained unchanged with DITPA treatment. Thus DITPA administration impairs baseline cardiac parameters in mice and can be fatal during in vivo acute myocardial I/R.

Non-genomic effects of thyroid hormone in adult cardiac myocytes: relevance to gene expression and cell growth

Besides the well-characterized genomic action of thyroid hormone (TH), mediated by thyroid hormone receptors (TRs), accumulating data support the so-called non-genomic action of TH, which is often related to activation of signalling pathways. In this study, we sought to determine whether TH activates intracellular signalling pathways in the adult cardiac myocytes and whether such activation modulates cell growth and the expression of target proteins important in cardiac function. We demonstrate that TH promotes a rapid increase in the phosphorylation of several kinases, ERK1/2, PKCdelta, p38-MAPK and Akt. This activation is inhibited by triiodothyroacetic acid (triac), which is a TH analogue known to displace the hormone from membrane bound receptors, indicating that this TH effect is mediated through a cell membrane-initiated mechanism. Furthermore, using specific inhibitors of the TH-activated kinases, we show that the long-term effects of TH on the expression of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), alpha- and beta-myosin heavy chain (MHC) and cell growth are reverted, implying that what is initiated as a non-genomic action of the hormone interfaces with genomic effects. These data provide further insights into the underlying mechanisms of TH action in the heart with potentially important implications in the management of cardiac pathology.

Thyroid hormone improves postischaemic recovery of function while limiting apoptosis: a new therapeutic approach to support hemodynamics in the setting of ischaemia-reperfusion?

Although it has long been recognized that thyroid hormone is an effective positive inotrope, its efficacy in supporting hemodynamics in the acute setting of ischaemia and reperfusion (R) without worsening reperfusion injury remains largely unknown. Thus, we investigated the effects of triiodothyronine (T3) on reperfusion injury in a Langendorff-perfused rat heart model of 30 min zero-flow ischaemia and 60 min of (R) with or without T3 (40 microg/l) at R, T3-R60, n = 11 and CNT-R60, n = 10, respectively. Furthermore, phosphorylated levels of intracellular kinases were measured at 5, 15 and 60 min of R. T3 markedly improved postischaemic recovery of left ventricular developed pressure (LVDP%); 56.0% (SEM, 4.4) in T3-R60 versus 38.8% (3.1) in CNT-R60, P < 0.05. Furthermore, LDH release was significantly lower in T3-R60. Apoptosis detection by fluorescent probe optical imaging showed increased fluorescent signal in CNT-R60 hearts, while the signal was hardly detectable in T3-R60 hearts. Similarly, caspase-3 activity was found to be 78.2 (8.2) in CNT-R60 vs 40.5 (7.1) in T3-R60 hearts, P < 0.05. This response was associated with significantly lower levels of phospho-p38 MAPK at any time point of R. No significant changes in phospho- ERK1/2 and JNK levels were observed between groups. Phospho-Akt levels were significantly lower in T3 treated group at 5 min and no change in phospho-Akt levels were observed at 15 and 60 min between groups. In conclusion, T3 administration at reperfusion can improve postischaemic recovery of function while limiting apoptosis. This may constitute a paradigm of a positive inotropic agent with anti-apoptotic action suitable for supporting hemodynamics in the clinical setting of ischaemia-reperfusion.