Abstract
Background
Myocardial infarction (MI) is a major cause of death in western countries and Japan, and hypertension is a major risk factor of MI. In hypertensive heart, acute myocardial infarction often leads to lethal ventricular arrhythmia. Nicorandil, an ATP sensitive potassium channel (KATP) opener, is usually used in the treatment of acute myocardial infarction. The effects of nicorandil on ischemic myocyte are fully defined. On the other hand, KATP in neuroterminals is known to regulate norepinephrine release, but the effect of nicorandil on ischemic norepinephrine release in cardiac tissue has remained unexplored.
Purpose
We examined whether nicorandil suppressed norepinephrine release via neuronal KATP and ventricular arrhythmia during acute ischemia in pressure overload-induced hypertrophic hearts.
Methods
SD Rats were divided into two groups; abdominal aortic constriction (AAC) group and sham-operated (Sham) group. Four weeks after constriction, cardiac geometry and function were examined using echocardiography. Then, myocardial ischemia was induced by the left anterior descending artery occlusion for 100 minutes in the presence or absence of intravenous infusion of nicorandil. Cardiac interstitial norepinephrine concentration in ischemic region was measured using the microdialysis method and concentration of cyclic AMP, a second messenger of norepinephrine, in cardiac tissue was measured by ELISA. Ventricular arrhythmias were monitered by ECG during whole ischemic period.
Results
Four weeks after constriction, remarkable left ventricular wall thickening was observed in AAC group. Before ischemia, ventricular arrhythmia was not found in both groups. Number of ventricular arrhythmia, including ventricular tachycardia and ventricular fibrillation, was increased in early ischemic period (- 40 min) in both groups, and was grater in AAC group. Before ischemia, interstitial norepinephrine concentration in cardiac tissue was higher level in AAC group than in Sham group. Ischemia obviously increased norepinephrine concentration in both groups time dependently and AAC further increased norepinephrine than Sham group. Concentration of cyclic AMP in cardiac tissue was raised in early ischemic period (- 40 min) and then gradually decreased. Nicorandil significantly suppressed the number of ventricular arrhythmias, and abolished the ventricular tachycardia and fibrillation without hemodynamic alterations. Nicorandil also attenuated norepinephrine and cAMP enhancement in acute ischemic period in both groups.
Conclusion
Ischemia-induced ventricular arrhythmia was more frequent and severe in hypertrophic hearts and interstitial norepinephrine enhancement may play a role in this ischemic arrhythmia. Nicorandil suppressed ischemia-induced interstitial norepinephrine release by neuronal KATP opening, which attenuated ventricular arrhythmias in normal and hypertrophic hearts.
Polymorphous ventricular tachycardia associated with acute myocardial infarction.
