Hypertension in thyroid disorders.

Hypertension is more common in hypothyroidic patients than in euthyroid controls in older age groups. Treatment of the thyroid deficiency alone lowers blood pressure in most patients. Hemodynamically, cardiac output is reduced and total peripheral resistance is elevated. The latter probably is secondary to an increase of sympathetic nervous tone and a relative increase in alpha-adrenergic response. In hyperthyroidism, elevation of diastolic blood pressure is uncommon. Systolic hypertension is more common in younger age groups. Treatment of the hyperthyroidism alone lowers systolic blood pressure in most patients. An increase in cardiac output and a decrease in total peripheral resistance accompany the hyperthyroidism. Potentiation of catecholamine action by an excess of thyroid hormone has been invoked as an explanation, because thyroid hormone excess is accompanied by increased beta-adrenergic receptors in some tissue, including heart.