Direct radioimmunoassay of angiotensin-converting enzyme in sera from patients with pulmonary diseases.

Abstract

The concentration of angiotensin-converting enzyme (ACE) was measured in the sera of 47 normal subjects and 108 patients with various pulmonary diseases by radioimmunoassay (RIA) using antiserum to human kidney ACE and homogeneous human kidney ACE as a tracer. The immunologic identity of ACE in the sera from a normal subject and a patient with active sarcoidosis was demonstrated by parallel logit-log transformation of displacement curves in the RIA. The activity and the enzyme concentration in normal and clinical samples correlated well (r=0.78,P<0.001). The mean concentration of ACE in normal serum was 320.9±105.2 ng/ml (mean ±1 SD, n=47). Serum ACE concentration in patients with active sarcoidosis (823.4±209.7, n=13) and in patients with silicosis (569.5±183.8, n=21) was significantly higher than in normals, and the ACE activity in the serum of both groups increased parallel to the concentration. In contrast, patients with active pulmonary tuberculosis (508.5±159.4, n=11) and with lung cancer (481.1±169.5, n=12) had significantly higher serum ACE concentrations (P<0.005) although the serum ACE activity did not increase. The specific activity of both groups (40.4±7.0 and 39.6±7.1 µmol/min/mg, respectively) was lower than that of normal subjects (50.0±12.8). A low ACE activity and a normal ACE concentration in patients with diffuse panbronchiolitis (n=8) and chronic bronchitis (n=6) resulted in a significantly low specific activity (37.4±13.0 and 36.2±7.3, respectively).