Vagal stimulation suppresses ischemia-induced myocardial interstitial norepinephrine release

Although electrical vagal stimulation exerts beneficial effects on the ischemic heart such as an antiarrhythmic effect, whether it modulates norepinephrine (NE) and acetylcholine (ACh) releases in the ischemic myocardium remains unknown. To clarify the neural modulation in the ischemic region during vagal stimulation, we examined ischemia-induced NE and ACh releases in anesthetized and vagotomized cats. In a control group (VX, n = 8), occlusion of the left anterior descending coronary artery increased myocardial interstitial NE level from 0.46 ± 0.09 to 83.2 ± 17.6 nM at 30–45 min of ischemia (mean ± SE). Vagal stimulation at 5 Hz (VS, n = 8) decreased heart rate by approximately 80 beats/min during the ischemic period and suppressed the NE release to 24.4 ± 10.6 nM (P < 0.05 from the VX group). Fixed-rate ventricular pacing (VSP, n = 8) abolished this vagally mediated suppression of ischemia-induced NE release. The vagal stimulation augmented ischemia-induced ACh release at 0–15 min of ischemia (VX: 11.1 ± 2.1 vs. VS: 20.7 ± 3.9 nM, P < 0.05). In the VSP group, the ACh release was not augmented. In conclusion, vagal stimulation suppressed the ischemia-induced NE release and augmented the initial increase in the ACh level. These modulations of NE and ACh levels in the ischemic myocardium may contribute to the beneficial effects of vagal stimulation on the heart during acute myocardial ischemia.