Thyroid hormone cardiovascular effects

Cardiovascular Effects. Thyroid hormones appear to increase heart rate and myocardial contractility, thus leading to an increase in cardiac output. It is unclear, however, if this occurrence is a direct effect of these hormones or if the thyroid hormones increase myocardial sensitivity to other hormones (norepinephrine and epinephrine). 

Thyroid hormone has multiple effects on the cardiovascular system with various physiological consequences. Several genes that encode important regulatory and structural proteins in the heart have been shown to be thyroid hormone responsive. Thyroid hormone increases cardiac contractility, induces vasorelaxation and angiogenesis, prevents fibrosis and has favorable effects on lipid metabolism (reviewed by Pantos73). 

Cardiovascular Effects Thyroid hormones directly and indirectly influence cardiac function, and cardiovascular manifestations are prominent clinical consequences of thyroid disease. In hyperthyroidism, there is tachycardia, increased stroke volume, increased cardiac index, cardiac hypertrophy, decreased peripheral vascular resistance, and increased pulse pressure. In hypothyroidism, there is bradycardia, decreased cardiac index, pericardial effusion, increased peripheral vascular resistance, decreased pulse pressure, and elevation of mean arterial pressure. 

In vivo effects of thyroid hormone and iodine intake on the cardiovascular system... 

The thyroid hormones, T4 and T3, play numerous, profound roles in regulating metabolism, growth, and development and in maintaining homeostasis. Their reactions and products influence carbohydrate metabolism, protein synthesis and breakdown, and cardiovascular, renal, and brain function. It generally is believed that these actions result from effects of thyroid hormones on protein synthesis. 

I. Mechanism of toxicity. Excessive thyroid hormone potentiates adrenergic activity in the cardiovascular, gastrointestinal, and neurologic systems. The effects of T3 overdose are manifested within the first 6 hours after ingestion. In contrast, symptoms of T4 overdose may be delayed 2-5 days after ingestion while metabolic conversion to T3 occurs. 

The heart, as an endocrine organ itself, secretes the atrial natriuretic peptide, which has several important influences on the cardiovascular system. In addition to atrial natriuretic peptide, catecholamines, thyroid hormones, mineralocorticoids, sex steroids, and angiotensin II are other hormones also known to exert their effects on the cardiovascular functions and blood pressure. Hormones regulate the contraction and dilatation of the vascular bed. They may also affect the contraction of other smooth muscles other than the vascular smooth muscle. Oxytocin stimulates contraction of the myoepithelium in the mammary gland that is necessary for milk ejection. 

Uses Thyroid hormones (levothyroxine, T4, and liothyronine, T3) are used to treat overt hypothyroidism. In addition, supra-physiological doses of levothyroxine are widely used to reduce the risk of thyroid cancer recurrence by suppressing serum TSH concentrations. The use of levothyroxine suppressive therapy to induce shrinkage of benign thjnoid nodules remains controversial and its routine use is not recommended in view of its low efficacy and potential long-term effects on the cardiovascular system and the skeleton caused by the induction of subchnical hjrper-thyroidism [5 ]. 

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