Effects of thyroid replacement therapy on catecholamine plasma levels

Abstract

Plasma catecholamines (CA), total and free thyroid hormones (T₄, FT₄, T₃, FT₃) and thyrotropin (TSH) were measured before and during therapy in seven normotensive women with primary hypothyroidism lasting for more than 6 months. Twelve normal women matched for age were used as controls. In hypothyroid patients plasma norepinephrine (NE) was found increased in supine and upright position and plasma epinephrine (E) unchanged. After 30–60 days of therapy with dry thyroid extract, NE, T₃, and FT₃ levels were found in the normal range while T₄ and FT₄levels, although raised, were still significantly lower than those of controls. These results seem to demonstrate that low doses of replacement therapy can restore NE levels to normal and therefore suggest that severe hypothyroidism alone is able to affect the sympathetic function.