1 Erythropoietin secretion is increased by T3, which can explain the normochromic, normocytic anemia often found in hypothyroidism. This results in diastolic hypertension that is often sodium sensitive. Thus, in a hypothyroid state, diastolic blood pressure increases, pulse pressure narrows, and renin levels decrease. Renin substrates are synthesized in the liver under the stimulus of T3. Thyroid hormones also impact the renin-angiotensin-aldosterone system. On a molecular level, these alterations result from reduced expression of sarcoplasmic reticulum Ca 2+-ATPase and increased expression of phospholamban, which inhibits ATPase. This produces a cascade effect of increased arterial stiffness that leads to increased systemic vascular resistance. Hypothyroidism is associated with decreased cardiac output due to impaired relaxation of vascular smooth muscle and decreased availability of endothelial nitric oxide. Thyroid hormones have a variety of effects on the cardiovascular system that can greatly impact cardiac function ( Figure 1). Cardiometabolic Changes in Hypothyroidism
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