Cardiac nitric oxide production due to angiotensin-converting enzyme inhibition decreases beta-adrenergic myocardial contractility in patients with dilated cardiomyopathy

OBJECTIVES This study tested the hypothesis that angiotensin-converting enzyme (ACE) inhibitors attenuate beta-adrenergic contractility in patients with idiopathic dilated cardiomyopathy (DCM) through nitric oxide (NO) myocardial signaling. BACKGROUND The ACE inhibitors increase bradykinin, an agonist of NO synthase (NOS). Nitric oxide inhibits beta-adrenergic myocardial contractility in patients with heart failure. METHODS The study patients were given the angiotensin-1 (AT-1) receptor antagonist losartan for one week. The hemodynamic responses to intravenous dobutamine were determined before and during intracoronary infusion of enalaprilat (0.2 mg/min) with and without the NOS inhibitor NG-monomethyl-image-arginine (image-NMMA, 5 mg/min). RESULTS In patients with DCM (n = 8), dobutamine increased the peak rate of rise of left ventricular pressure (+dP/dt) by 49 ± 8% (p < 0.001) and ventricular elastance (Ees) by 53 ± 16% (p < 0.03). Co-infusion with enalaprilat decreased +dP/dt to 26 ± 12% and Ees to −2 ± 17% above baseline (p < 0.05), and this anti-adrenergic effect was reversed by image-NMMA co-infusion (p < 0.05 vs. enalaprilat). In addition, intracoronary enalaprilat reduced left ventricular end-diastolic pressure (LVEDP), but not left ventricular end-diastolic volume, consistent with increased left ventricular distensibility. Infusion with image-NMMA before enalaprilat in patients with DCM (n = 5) prevented the reduction in +dP/dt, Ees and LVEDP. In patients with normal left ventricular function (n = 5), enalaprilat did not inhibit contractility or reduce LVEDP during dobutamine infusion. CONCLUSIONS Enalaprilat attenuates beta-adrenergic contractility and enhances left ventricular distensibility in patients with DCM, but not in subjects with normal left ventricular function. This response is NO modulated and occurs in the presence of angiotensin receptor blockade. These findings may have important clinical and pharmacologic implications for the use of ACE inhibitors, AT-1 receptor antagonists and their combination in the treatment of heart failure.