Elevation of serum angiotensin-converting enzyme activity in patients with hyperthyroidism

The activity of serum angiotensin-converting enzyme (S-ACE) was determined spectrophotometrically in 45 patients with hyperthyroidism (30 untreated and 15 treated and euthyroid patients), 14 patients with hypothyroidism, and 135 normotensive healthy subjects. S-ACE was significantly higher in the patients with untreated hyperthyroidism (51.6 +/- 1.9 less than SE greater than nmol.min/ml) than in the healthy controls (28.6 +/- 0.6 nmol.min/ml; P less than 0.001). On the other hand, S-ACE was found to be within the normal range in patients with hypothyroidism (23.2 +/- 1.3 nmol.min/ml). In patients with hyperthyroidism, S-ACE gradually fell into the normal range as the thyroid function became normalized, and there were significant positive correlations between S-ACE and the plasma T3 or T4 concentration (r = 0.60 and P less than 0.001; r = 0.61 and P less than 0.001, respectively ). S-ACE had no definite relation to blood pressure, serum glutamic oxaloacetic acid transaminase, or glutamic pyruvic acid transaminase. When the physicochemical characteristics of the enzyme in the sera of hyperthyroidism patients were compared with those in sarcoidosis patients, similar peak activities of S-ACE on gel chromatography and identical Michaelis constants were obtained; the effects of ethyldiaminetetraacetic acid, SQ14225, and pH on the enzymatic reaction were also similar in both diseases. Thus, hyperthyroidism is considered to be one of the diseases in which S-ACE is elevated. The elevation of S-ACE might be directly or indirectly related to the hyperthyroid state. In addition, it is suggested that the enzyme characteristics are identical in hyperthyroidism and sarcoidosis.