Angiotensin-converting enzyme. I. Activity and correlation with serum lysozyme in sarcoidosis, other chest or lymph node diseases and healthy persons.

Serum angiotensin-converting enzyme (ACE) activity was studied in healthy controls, in 57 untreated sarcoidosis patients, and in 164 patients with other chest or lymph node diseases. The serum ACE activity of healthy persons was independent of sex, intake of meals, and smoking habits. There were no diurnal variations. Healthy children had a significantly higher ACE mean value than adults, whose ACE activity was not affected by age. The sarcoidosis patients had the highest ACE mean values, but those of patients with silicosis and asbestosis were also significantly elevated. Pulmonary cancer patients had decreased serum ACE activity, which was probably due to antimitotic treatment. Serum lysozyme (LZM) concentrations did not correlate with normal ACE activity, but the correlation between elevated ACE and LZM was significant in sarcoidosis and silicosis, and the trend was clearly the same for asbestosis. This indicates separate sources for these enzymes when ACE activity is normal, and a common source, i.e. macrophages, when ACE activity is increased. ACE production in certain diseases involving macrophages may be due to the bradykinin inhibiting effect of this enzyme.