Effects of Thyroid Hormone on the Cardiovascular System

Abstract

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 overt hyperthyroidism induces a hyperdynamic cardiovascular state (high cardiac output with low systemic vascular resistance), which is associated with a faster heart rate, enhanced left ventricular (LV) systolic and diastolic function, and increased prevalence of supraventricular tachyarrhythmias -namely, atrial fibrillation -whereas overt hypothyroidism is characterized by the opposite changes. However, whether changes in cardiac performance associated with overt thyroid dysfunction are due mainly to alterations of myocardial contractility or to loading conditions remains unclear. Extensive evidence indicates that the cardiovascular system responds to the minimal but persistent changes in circulating thyroid hormone levels, which are typical of individuals with subclinical thyroid dysfunction. Subclinical hyperthyroidism is associated with increased heart rate, atrial arrhythmias, increased LV mass, impaired ventricular relaxation, reduced exercise performance, and increased risk of cardiovascular mortality. Subclinical hypothyroidism is associated with impaired LV diastolic function and subtle systolic dysfunction and an enhanced risk for atherosclerosis and myocardial infarction. Because all cardiovascular abnormalities are reversed by restoration of euthyroidism ("subclinical hypothyroidism") or blunted by ␤-blockade and L-thyroxine (L-T4) dose tailoring ("subclinical hyperthyroidism"), timely treatment is advisable in an attempt to avoid adverse cardiovascular effects. Interestingly, some data indicate that patients with acute and chronic cardiovascular disorders and those undergoing cardiac surgery may have altered peripheral thyroid hormone metabolism that, in turn, may contribute to altered cardiac function. Preliminary clinical investigations suggest that administration of thyroid hormone or its analogue 3,5-diiodothyropropionic acid greatly benefits these patients, highlighting the potential role of thyroid hormone treatment in patients with acute and chronic cardiovascular disease.

Effect of chronic hypoxia during embryonic development on physiological functioning and on hatching and post-hatching parameters related to ascites syndrome in broiler chickens

“…However, Olkowski et al (1999) and Olkowski and Classen (1998) have published results indicating that RVH and right ventricular failure are secondary to left ventricular failure. This may be brought into relation with changed thyroid function and the lower thyroid hormone levels in postnatal birds when incubated at high altitude because subclinical hypothyroidism causes left ventricle dysfunction, at least in mammals (Fazio et al, 2004).…”

Influência do exercício físico nas alterações cardiovasculares induzidas pelo hipotireoidismo

“…(33) Devido à presença de receptores específicos de T3 nas células cardíacas e vasculares (34) , alterações promovidas pela redução da produção dos hormônios tireoidianos implicam em diminuição do débito cardíaco, aumento da resistência vascular periférica, disfunção sistólica e diastólica. Isso ocorre, em grande parte, devido à contratilidade miocárdica comprometida.…”

Comparison of therapeutic effects of L-Thyroxin, apelin and a combination of both on antioxidant enzymes in the heart of PTU-induced hypothyroid rats

“…Some studies reported that apelin increase mRNA expression and activity of SOD, catalase and glutathion peroxidase and decreased MDA (it is the end stage of the lipid peroxidation process and identify for lipid peroxidation evaluation) in cardiac cell and tissue (Aikawa et al 2001;Foussal et al 2010). An absence of thyroid hormones causes morphological and structural changes in cardiac myocytes that brings about changes in hemodynamic characteristics which hypothyroid patient suffering from them (Fazio et al 2004;Klein and Danzi 2007). The oxidant-antioxidant imbalance is one of the reasons in pathogenesis of tissue damage (Halliwell1994).…”