Increased sensitivity to nitric oxide synthase inhibition in patients with heart failure: Potentiation of β-adrenergic inotropic responsiveness

Background - We previously showed that cardiac nitric oxide (NO) inhibits the positive inotropic response to β-adrenergic stimulation in humans with left ventricular (LV) dysfunction. Whether this effect is specific to heart failure per se or is a generalized feature of normal human myocardium is unknown. We therefore tested the hypothesis that inhibition of cardiac NO potentiates the positive inotropic response to β-adrenergic stimulation in patients with symptomatic LV failure but not in subjects with normal LV function. Methods and Results - We studied 11 patients with LV failure due to idiopathic dilated cardiomyopathy and 7 control subjects with normal LV function. The β-adrenergic agonist dobutamine was infused via a peripheral vein before and during concurrent intracoronary artery infusion of acetylcholine, which activates the agonist-coupled isoforms of NO synthase, and N(G)-monomethyl-L-arginine, which inhibits all isoforms of NO synthase. Changes in contractility were assessed by measuring the peak rate of rise of LV pressure (+dP/dt). Dobutamine increased +dP/dt by 40±6% and 73 ± 14% in patients with heart failure and control subjects, respectively. Acetylcholine inhibited the +dP/dt response to dobutamine to a similar degree in patients with heart failure and control subjects (-39 ± 8% and -31 ± 4%, respectively; P=NS). Infusion of N(G)-monomethyl-L-arginine potentiated the +dP/dt response to dobutamine by 51 ± 15% (P=.01 versus dobutamine) in patients with heart failure but had no effect in control subjects (-6 ± 4%; P=NS versus dobutamine; P=.0002 versus heart failure patients). Conclusions - Inhibition of cardiac NO augments the positive inotropic response to β- adrenergic receptor stimulation in patients with heart failure due to idiopathic dilated cardiomyopathy but not in control subjects with normal LV function.