Introduction

Article Abstract:

Thyroid hormones have effects on almost all tissues including the heart. Disease of the thyroid gland is associated with abnormalities of the heart and blood vessels. The complex changes in the cardiovascular system result from the direct effects of thyroid hormones on the heart muscle; combined effects of thyroid hormones and the adrenergic nervous system on heart function; indirect effects of thyroid hormones on heart function; and indirect effects of the adrenergic nervous system on blood vessels. (The adrenergic or sympathetic nervous system controls involuntary body functions under conditions of stress, such as aggression, fear and increased physical activity. Catecholamine hormones mediate the effects of the adrenergic nervous system.) Certain symptoms of thyroid gland disease may result from changes in basic cell processes. For example, thyroid hormones alter body temperature through an effect on the cell nucleus and protein production. In thyroid disease, changes in responsiveness of the adrenergic nervous system may be due to abnormal catecholamine metabolism or altered sensitivity of the tissues to catecholamines. Therapy directed at improving these changes in the adrenergic system is also beneficial in treating hyperthyroidism, or increased activity of the thyroid gland. A recent symposium in San Francisco, California focused on the interactions between thyroid hormones and the adrenergic nervous system in the heart. Some issues discussed at the symposium included the effects of thyroid hormones on heart muscle; the interaction between thyroid hormones and the adrenergic nervous system; the role of beta-adrenergic-blocking agents in treating hyperthyroidism; and clinical problems associated with thyroid gland disease. The symposium helped to clarify the normal effects of thyroid hormones on the heart and their interaction with the adrenergic nervous system; changes in cardiovascular function in thyroid disease; and treatment of thyroid gland diseases. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Catecholamine-thyroid hormone interactions and cardiovascular manifestations of hyperthyroidism

Article Abstract:

Hyperthyroidism, or increased activity of the thyroid gland, results in excessive levels of thyroid hormones and is associated with increased activity of the adrenergic nervous system. The sympathetic or adrenergic nervous system controls involuntary body functions under conditions of stress, such as aggression, fear, or increased physical activity. However, the blood and urine levels of catecholamine hormones, which mediate the effects of the adrenergic nervous system, were shown to be normal or less than normal in patients with hyperthyroidism. Hypothyroidism, or decreased activity of the thyroid gland, results in decreased levels of thyroid hormones and is associated with decreased activity of the adrenergic system. Catecholamine levels were shown to be increased in hypothyroidism. The paradox of increased activity of the adrenergic system associated with decreased levels of catecholamine hormones and vice versa is discussed. Hyperthyroidism is treated by drugs called beta blockers, which prevent the activation of the adrenergic nervous system and thereby improve symptoms associated with increased activity of the adrenergic nervous system. However, the recovery to normal thyroid function in hyperthyroid patients requires the long-term use of antithyroid agents. Hyperthyroidism can be managed effectively with knowledge of the interaction between heart-related and other symptoms of hyperthyroidism and understanding of the role of the adrenergic nervous system. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Drug therapy, Adrenergic beta blockers, Adrenergic beta-antagonists, Catecholamines

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Thyroid hormone and the cardiovascular system

Article Abstract:

Thyroid hormones have effects on both the heart and blood vessels. The administration of thyroid hormones decreases systemic vascular resistance, the pressure against which blood flows, and increases heart contraction and cardiac output, the amount of blood pumped by the heart. These changes are similar to heart and blood vessel responses to exercise and are associated with increased work in the left ventricle (the heart chamber that pumps blood into the systemic circulation). Although the heart adapts to changes in thyroid function, certain patients with thyroid disease have abnormalities of heart function. Hyperthyroidism, or increased activity of the thyroid gland, has been associated with atrial arrhythmias, or abnormal heart rhythms arising in the atria; decreased ability to withstand exercise; and congestive heart failure, the inability of the heart to pump blood. Heart disorders associated with hyperthyroidism are more common in older patients. Thyroid hormones are also involved in the control of blood pressure, and hypothyroidism, or decreased activity of the thyroid gland, is often accompanied by increased blood pressure during the diastolic or relaxation phase of heart contraction. Based on knowledge of the mechanisms of thyroid hormone effects on the heart and blood vessels, response to therapy for thyroid disease can be predicted. (Consumer Summary produced by Reliance Medical Information, Inc.)

Hypothyroidism

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