Intracoronary infusion of the nitric oxide synthase inhibitor L-NMMA reduced vagal inhibition of the dobutamine-stimulated inotropic response by 44-62% in normal dogs.
Does nitric oxide mediate parasympathetic inhibition of beta-adrenergic myocardial contractility in normal dogs?
Nitric oxide plays a role in the normal physiologic regulation of myocardial autonomic responses by mediating vagal inhibition of beta-adrenergic stimulation.
Effect estimate: 44-62% reduction
p-value: p=<0.001
In vitro studies indicate that muscarinic cholinergic inhibition of beta-adrenergic cardiac responses may be modulated in part by nitric oxide (NO). To evaluate the role of NO in parasympathetic inhibition of the beta-adrenergic contractile response in vivo, we assessed the inotropic response to dobutamine before and during bilateral vagus nerve stimulation in closed-chest dogs. Dobutamine administration and vagal stimulation were repeated during intracoronary infusion of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 10 mumol/min) and again following infusion of L-arginine (100 mg/kg). In eight dogs, intracoronary dobutamine infusion at rates of 25 and 50 micrograms/min increased peak +dP/dt by 131 +/- 24 and 168 +/- 22%, respectively (P < 0.0001). Vagal stimulation (2.5 Hz) attenuated the responses to dobutamine (25 and 50 micrograms/min) by 23 +/- 4 and 21 +/- 4%, respectively (P < 0.001). L-NMMA reduced (by 44-62%; P < 0.001) and L-arginine restored vagal inhibition of the dobutamine-stimulated inotropic response. In a second group of nine dogs, dobutamine was administered systemically to assure a constant concentration in the coronary circulation. Vagal stimulation (2.5 Hz) attenuated the dobutamine-stimulated inotropic response (2.5 and 5.0 micrograms/kg per min) by 40 +/- 12% and 57 +/- 8%, respectively (P < 0.004). As with intracoronary dobutamine, L-NMMA diminished and L-arginine restored vagal inhibition of the inotropic response to dobutamine. Intracoronary infusion of atropine (12 micrograms/min) abolished the vagal inhibitory effect, and intracoronary infusion of 8-bromo-cyclic GMP (1 and 10 mM) caused a dose-dependent attenuation of the dobutamine-stimulated increase in +dP/dt. These data suggest that NO mediates, at least in part, vagal inhibition of the inotropic response to beta-adrenergic stimulation by dobutamine, and thus may play a role in normal physiologic regulation of myocardial autonomic responses.
Hare et al. (1995) studied Normal dogs (animal model) (n=18). L-NMMA (NO synthase inhibitor) vs. Baseline (without L-NMMA) was evaluated on Vagal inhibition of dobutamine-stimulated inotropic response (+dP/dt) (44-62% reduction, p=<0.001). Intracoronary infusion of the nitric oxide synthase inhibitor L-NMMA reduced vagal inhibition of the dobutamine-stimulated inotropic response by 44-62% in normal dogs.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: