Comparison of serum angiotensin-converting enzyme in Graves' disease, toxic nodular goiter, and other thyroid conditions.

Angiotensin-converting enzyme (ACE) was measured in plasma of patients with Graves' disease and with toxic nodular goiter, as well as in their treated counterparts and in normal controls. A significant elevation of ACE levels and a positive correlation between ACE, thyroxine, and triiodothyronine levels was found in both groups of thyrotoxicosis. Parallel fluctuations of triiodothyronine and ACE levels, albeit with a certain lag of the latter, was observed in patients in whom multiple measurements were taken. ACE levels, which were also determined in hypothyroid patients and in patients with euthyroid goiter on suppression therapy, were in the same range as normal controls and as in treated thyrotoxic patients. We conclude that the pathogenesis of thyrotoxicosis does not play a role in ACE elevation but that increased thyroid hormone seems to induce elevation of ACE. ACE elevation in thyrotoxicosis may constitute an integral part of the renin-angiotensin axis.