Intrapericardial delivery of L-arginine reduces the increased severity of ventricular arrhythmias during sympathetic stimulation in dogs with acute coronary occlusion: nitric oxide modulates sympathetic effects on ventricular electrophysiological properties.
BACKGROUND
Nitric oxide (NO) modulates autonomic effects on myocardial contractility and sinus and atrioventricular nodal function of the heart. Whether NO influences autonomic actions on ventricular electrophysiological properties and arrhythmogenesis is not known.


RESULTS
Four groups consisting of 43 autonomically denervated dogs were studied. To "superfuse" sympathetic nerves innervating the ventricles, test drugs were introduced into the pericardial sac for 30 minutes, and their effects on ventricular effective refractory period (ERP) and arrhythmia development were assessed before and during sympathetic stimulation (SS). In group 1 (n=12), ventricular ERPs showed no significant difference between control and superfusion with L-arginine, a NO precursor (222+/-20 versus 222+/-19 ms, P=.485). However, L-arginine significantly reduced SS-induced ERP shortening compared with control (9+/-7 versus 13+/-7 ms, P<.001). Simultaneous administration of N(G)-monomethyl-L-arginine (2 mg/mL) abolished the inhibitory effects of L-arginine (13+/-7 versus 13+/-7 ms, P=.885). In group 2 (n=15), the severity of ventricular arrhythmias significantly increased during SS. L-Arginine reduced this increase caused by SS. In group 3 (n=8), plasma norepinephrine spillover measured from the coronary sinus significantly increased during SS and was reduced by pericardial superfusion with L-arginine compared with control (6005.2+/-1525.6 versus 8503.4+/-2044.5 pg/min, P=.012). In group 4 (n=8), L-arginine pericardial superfusion significantly increased NO overflow measured from the coronary sinus during SS (93.25+/-59.20 versus 114.82+/-74.92 nmol/min, P=.043).


CONCLUSIONS
Pericardial L-arginine reduces ERP shortening and increased severity of ischemic ventricular arrhythmias during SS in dogs. NO-induced reduction of norepinephrine release in the heart may be one of the underlying mechanisms.
Fei
L
L
Department of Medicine, Indiana University School of Medicine, and the Roudebush Veterans Administration Medical Center, Indianapolis 46202-4800, USA.
Baron
A D
AD
Henry
D P
DP
Zipes
D P
DP
D000818:Animals; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D015986:Confounding Factors, Epidemiologic; D004195:Disease Models, Animal; D004285:Dogs; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D009203:Myocardial Infarction / Q000150:complications / Q000503:physiopathology*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000378:metabolism*; D010496:Pericardium; D012720:Severity of Illness Index; D017180:Tachycardia, Ventricular / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D009638:Norepinephrine