Thyroid hormones vascular effects

Increased metabolism, increased heat production, weight loss, protrusion of the eyes (exophthalmia), and an increase in bone and muscle turnover are the major symptoms. In addition, increased levels of thyroid hormone have detrimental effects on cardiac muscle and cardiac conduction, as well as on vascular smooth muscle function. 

The first measurable effect of TSH on thyroid hormone metabolism is increased secretion, which is detectable within minutes. AU phases of hormone synthesis and secretion are eventually stimulated iodide uptake and organification, endocytosis, and proteolysis of thyroglobulin. There also is increased vascularity of the gland and hypertrophy and hyperplasia of thyroid cells. 

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. 

Iodide therapy (usually saturated solution of potassium iodide) is useful in reducing thyroid hormone release and in decreasing the vascularity of the gland prior to surgery. However, escape from the inhibitory effect of iodide often occurs in Graves disease, and the increased iodine substrate made available by the therapy may actually accentuate the disease. 

Thyroid Hormone Action within the Heart and Vascular System from Cellular to Hemodynamic Effects... 

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. 

Iodides have. several poorly understood actions on the thyroid. They inhibit organitication and hormone release. In addition, iodide de-crca.scs the size and vascularity of the hyperplastic gland, effects which are useful in the preparation of patients for thyroidectomy. In phamia-cological dose.s. the main effect of iodides is to inhibit hnmtone release (possibly by inhibition of thywglobulin proteolysis) and. because thyrotoxic symptoms are reduced relatively quickly (2 7 days), iodine is valuable in the treatment of thyrotoxic crisis ( thyroid storm —a life-threatening acute exacerbation of all the symptoms of thyrotoxicosis). Iodine caimoi be used for the long-term treatment of hyperthyroidism because its antithyroid action tends to diminish. 

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