Plasma Renin Activity in Hyper- and Hypothyroidism: Effect of Adrenergic Blocking Agents

Abstract

Plasma renin activity (PRA) levels and pressor response to the infusion of angiotensin II (AT II) were studied in normal, hyperthroid, and hypothyroid subjects before and after the administration of adrenergic blocking drugs. The mean PRA levels of the hyperthyroid subjects were significantly greater than that of normal subjects which were greater than that of hypothyroid patients. In the hyperthyroid patients there was a decreased sensitivity to the AT II infusion while the hypothyroid patients exhibited increased sensitivity to the AT II infusion. Successful treatment of the hyper- and hypothyroidism was followed by normalization of the PRA levels and a normal response to the AT II infusion. Successful treatment of the hyper- and hypothyroidism was followed by normalization of the PRA levels and a normal response to the AT II infusion. The administration of propranolol or dibenzylene produced a fall in PRA levels in the normal volunteers and in the hyperthyroid patients. With dibenzylene treatment, a significantly increased sensitivity to the AT II was observed while propranolol treatment produced a markedly decreased sensitivity to the AT II infusion. These findings lend additional support to the concept of adrenergic mediation of renin secretion. The elevated levels of PRA in hyperthyroidism are another manifestation of increased adrenergic activity in thyrotoxicosis.