Inhibition of Endogenous Nitric Oxide Synthase Augments Contractile Response to Adenylyl Cyclase Stimulation Without Altering Mechanical Efficiency in Patients With Idiopathic Dilated Cardiomyopathy

Abstract

Background Increased nitric oxide (NO) in the failing heart attenuates the myocardial contractile response to β-adrenergic receptor stimulation. However, the physiological effects of NO on the β-adrenergic post-receptor signaling system are unknown. The objective of the present study was to examine the effects of cardiac NO synthase (NOS) inhibition on left ventricular (LV) hemodynamics and mechanoenergetics in response to adenylyl cyclase stimulation in human heart failure. Methods and Results The study group comprised 13 patients with heart failure because of idiopathic cardiomyopathy (IDC). E_max was examined as an index of LV contractility, LV external work (EW), pressure - volume area (PVA), myocardial oxygen consumption (MVO₂), and mechanical efficiency (EW/MVO₂) with the use of conductance and coronary sinus thermodilution catheters before and during colforsin daropate infusion, and during concurrent infusion of colforsin daropate with the NOS inhibitor, N^G-monomethyl-L-arginine (L-NMMA; 200 μmol). Colforsin daropate increased E_max by 53% and EW by 18%, and reduced PVA by 14%, without altering MVO₂ or mechanical efficiency. The combination of colforsin daropate with L-NMMA further increased E_max by 26% and reduced PVA by 9%, without altering MVO₂ or mechanical efficiency. Conclusions These findings suggest endogenous NO may modulate β-adrenergic post-receptor pathways and preserve myocardial efficiency in patients with IDC. (Circ J 2007; 71: 1268 - 1273)