Increased cardiac endothelial nitric oxide synthase expression in patients taking angiotensin‐converting enzyme inhibitor therapy

Background  The efficacy of angiotensin-converting enzyme (ACE) inhibitors has been demonstrated in large clinical trials, but knowledge of the underlying mechanisms remains incomplete. Therefore, this study investigated the impact of ACE inhibitor therapy on cardiac nitric oxide (NO) synthases in patients with coronary artery disease (CAD) or heart failure. Patients and methods  The mRNA expression was quantified by standard calibrated competitive RT-PCR, protein expression by Western blotting and NOS activity by monitoring the conversion of [3H]arginine to [3H]citrulline during enzymatic formation of NO in tissue homogenates of myocardium of patients with, or without, ACE inhibitor treatment before elective coronary artery bypass grafting or heart transplantation. Results  The mRNA expression (amol µg−1 RNA) of endothelial NO synthase (eNOS) was higher (22·5 ± 4·8, n = 23) in the atrial myocardium of patients taking ACE inhibitor treatment, before elective coronary artery bypass grafting, compared with patients not taking this therapy (8·9 ± 0·7, n = 33, P < 0·0001). The ACE inhibitor therapy increased eNOS protein expression from [(9 ± 0·7) relative units (RUs) to (12 ± 0·9) RUs, P < 0·05, respectively] and cardiac NOS activity from 17·6 ± 1·3 to 23·7 ± 1·1 pmol mg protein−1 min−1 (P < 0·001, respectively). Inducible and neuronal NO synthase expression was not changed by the ACE inhibition. A similar up-regulation of eNOS by ACE inhibition was found in the left ventricles of patients with heart failure. The augmented endothelial NOS expression and activity was not the result of differences in clinical characteristics and concomitant therapy between the patient groups. Conclusion  Increased eNOS expression and activity might contribute to the beneficial effects of ACE inhibitor therapy in the treatment of CAD and heart failure.