Serum Angiotensin Converting Enzyme Activity Measured by Angiotensin I Hydrolysis
A sensitive and specific assay method to determine serum angiotensin converting enzyme (ACE) was developed. Although hippuryl-his-leu is commonly used as substrate, Angiotensin I (AI) was the substrate used to measure ACE activity in this study. AI hydrolysis was measured by radioimmunoassay of angiotensin II. ACE activity was expressed as the amount of All formed from AI per minute. There was a positive correlation (p<0.01, r = 0.81) between the ACE activities determined by AI hydrolysis and by hippuryl-his-leu hydrolysis. The ACE activity in eighty-three normal subjects was 4.08 ±1.04 nmol/ml/min (normal range, from 2.00 to 6.16 nmol/ml/min). ACE activity was significantly suppressed after acute administration of captopril to seven normal subjects (0.40±0.12 nmol/ml/min, p<0.01), and significantly elevated in five with active pulmonary sarcoidosis (10.08 + 4.44 nmol/ml/min, p<0.05), compared with normal controls.