Effects of hemodialysis on inhibition of angiotensin converting enzyme (ACE) by normal solutes of human plasma

Plasma solutes that inhibit ACE physiologically are dialyzable, which questions effects of hemodialysis on ACE activities. Commercial ACE assays use substrate at >K m , which obscures effects of the inhibitors. Still, such assays reveal that plasma ACE activities are increased by hemodialysis. We assayed ACE of plasmas (54 patients) taken at the beginning of dialysis (PRE) and at the end (POST). The commercial hippuryl‐Gly‐Gly kit was used (substrate >K m ). Results ( mean ±SD): PRE 109±27.4 units; POST 121±28.6 units; p=0.029. To distinguish loss of inhibitors from a true increase in ACE content (a possible membrane effect), we used the first order [ 3 H]hippuryl‐His‐Leu assay described in the accompanying abstract. Plasmas of 37 healthy adults were used as controls (C). Total ACE was not increased by dialysis: PRE 0.387±0.118/min v. POST 0.431±0.147/min, p>0.1, and did not differ from C: 0.3755±0.098/min, p>0.1. However, net ACE activities and % inhibition differed: PRE net ACE 0.022±0.006/min, POST 0.0402±0.0125/min, p<0.001; C 0.045±0.003/min (p<0.001 v. PRE and POST); % inhibition PRE 94.1±1.54, POST 90.4±2.46, p<0.001, C 88.23±5.04, p<0.001 v. PRE and POST. Dialysis nearly doubled net ACE but not to normal. Clearly, ACE is heavily inhibited in hemodialysis patients, an inhibition partially relieved by dialysis. Does this help explain why dialysis patients are highly sensitive to ACE inhibitor medications?