The Thyroid and the Circulation

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Abstract
The thyroid hormone, stimulating metabolism, increases the work of the heart and by its metabolic effect upon the heart muscle engenders tachycardia which persists in the isolated heart together with an increased responsiveness to epinephrine and norepinephrine. Myxedema increases the water content of the myocardium and produces degenerative changes in the muscle fibers. With this the function of the heart and circulation is indolent. Cardiac failure results when other heart disease accompanies myxedema. In the presence of coronary insufficiency or intractable congestive failure suppression of thyroid function in euthyroid individuals is accompanied by clinical improvement in most instances. Although it has been demonstrated in animals that diminished thyroid function seems to enhance the development of atherosclerosis when a high cholesterol diet is admd., the evidence that hypothyroidism is nvariably accompanied by precocious or advanced atherosclerosis in man is not sufficient to interdict the treatment of intractable cardiac failure by lowering the metabolic rate.