SERUM ANGIOTENSIN CONVERTING ENZYME-ACTIVITY IN SARCOIDOSIS AS MEASURED BY A SIMPLE RADIOCHEMICAL ASSAY

Abstract

A new simple radiochemical assay for serum angiotensin converting enzyme based on the hydrolysis of [glycine-1-14C] hippuryl-L-histidyl-L-leucine was used to quantify serum angiotensin converting enzyme activity in normal control subjects and patients with sarcoidosis. Serum angiotensin converting enzyme concentrations were significantly higher (P < 0.0005) in 42 patients with active sarcoidosis (71.9 .+-. 19.2 units/ml) compared to 60 normal control subjects (40.2 .+-. 8.6 units/ml). Patients with Stage I sarcoidosis had a singificantly lower (P < 0.05) mean enzyme activity (66.1 .+-. 16.0 units/ml) than patients with Stage II or Stage III disease (77.1 .+-. 21.1 units/ml). Considering a serum angiotensin converting enzyme activity of 57 units/ml (2 SD above the mean control value) to be increased, 33 of 42 (79%) of the patients with active sarcoidosis had increased enzyme activity but only 3 of 60 (5%) of the control subjects had increased enzyme activity. Of the 9 patients with active sarcoidosis whose results were falsely negative by this criterion, 7 had Stage I disease. This diagnostic criterion was applicable only to adult subjects; normal subjects younger than 20 yr of age had markedly increased serum angiotensin converting enzyme activity. The mean enzyme activity of 45.0 .+-. 11.4 units/ml for 28 patients on prednisone therapy was significantly lower (P < 0.0005) than the mean value for patients with active disease. This and the dramatic decrease in serum angiotensin converting enzyme activity in 5 of 6 patients receiving prednisone who were studied longitudinally suggest that serum angiotensin converting enzyme activity reflects the activity of the disease. Serum angiotensin converting enzyme activity is apparently a sensitive diagnostic index for sarcoidosis; although it is somewhat less sensitive for patients with Stage I disease it may be useful for assessing the progress of the disease during treatment.