Effects of Ischemic preconditioning on the Post-ischemic Myocardial Dysfunction and Coronary Flow in the Isolated Rat Hearts

ABSTRACT

BACKGROUND: Brief episodic ischemias prior to subsequent prolonged ischemia limit infarct size and attenuate the reperfusion arrythmia. But the effect of ischemic preconditioning on post-ischemic myocardial dysfunction, coronary flow and nitric oxide (NO) remains unclear. METHODS: To investigate the effect of ischemic preconditioning on myocardial function and coronary flow during reperfusion after 15 minutes of global myocardial ischemia, 30 isolated hearts of Sprague-Dowley rats were perfused under constant pressure. Two episodes of three minutes global ischemia followed by 12 minutes of reflow were employed to precondition the hearts. The hearts were randomized to one of three groups group I had no preconditioning, group II had preconditioning, group III had preconditioning as well as L-arginine pretreatment. Left ventricular developed pressure (LVDP), LV dp/dt, perfused coronary flow, concentration of NO and heart rate were continuously measured. RESULTS: In preconditioning groups (Group II, Group III), LVDP decreased during reflow and was lower than that of the control group. LV dp/dt decreased after reflow and gradually recovered with time but recovered was less in preconditioning groups. Coronary flow increased in the first few minutes after reflow in all groups, but decreased gradually. The decrease of coronary flow was greater in preconditioning groups. NO increased during the first 10 minutes after reflow and then decreased. In preconditioning groups, NO tends to be lower than that in the non-preconditioning group. CONCLUSION: Ischemic preconditioning was not beneficial to post-ischemic myocardial dysfunction, coronary flow and NO concentration in the flow. Cummulative effect of stunning due to repetitive ischemia for preconditioning may be an explanation for worse post-ischemic myocardial dysfunction and coronary flow in preconditioning groups.