Modulation of the myocardial redox state by vagal nerve stimulation after experimental myocardial infarction

Aims: Redox alteration plays a major role in the pathogenesis of heart failure (HF). Since vagal nerve stimulation (VNS) is known to improve survival and attenuate cardiac remodelling, we hypothesized that VNS may modulate the myocardial redox state. Methods and results: Using a chronic HF mouse model, we applied VNS for 15 min and measured myocardial redox status using in vivo electron spin resonance spectroscopy. Signal decay rate of the nitroxyl probe, an index of redox status, was enhanced in HF compared with sham (0.16 ± 0.01 vs. 0.13 ± 0.01 min^-1, P < 0.05; n = 6), and VNS normalized this enhancement (0.13 ± 0.01 min^-1, P < 0.05). Atropine sulphate abolished the VNS effects, indicating that the VNS modulates myocardial redox state via muscarinic receptors. N_ω-Nitro-L- arginine methyl ester treatment and fixed-rate atrial pacing showed a trend to suppress the VNS effects, suggesting the involvement of nitric oxide-based signalling and myocardial oxygen consumption. Moreover, VNS decreased the myocardial norepinephrine (NE) level (0.25 ± 0.07 vs. 0.60 ± 0.12 ng/mL, P < 0.05; n = 6). Reactive oxygen species production from cultured cardiomyocytes was enhanced by β-adrenergic activation, which was partially antagonized by 10 μmol/L acetylcholine (ACh) (relative value compared with control: NE 3.7 ± 0.5, NE + ACh 2.5 ± 0.3, P < 0.05; n = 12). Conclusion: The present study suggests that VNS modulates the cardiac redox status and adrenergic drive, and thereby suppresses free radical generation in the failing heart.