21. Phenylephrine Induces Delayed Cardioprotection Against Necrosis in the Globally Ischemic Myocardium Without Amelioration of Stunning

Kourosh Baghelai, Laura J. Graham, Emma R. Jakoi, Andrew S. Wechsler

Medical College of Virginia/Virginia Commonwealth University

Richmond, Va.

Alpha-adrenergic stimulation can precondition against postischemic dysfunction. It is not known whether the improved recovery is due to decreased necrosis or amelioration of stunning. We tested the hypothesis that alpha-adrenergic stimulation produces delayed preconditioning by limiting infarction but not stunning. Rabbits (n=34) were pretreated with either phenylephrine (PE) (n=12) or vehicle (n=12). Twenty-four hours later, hearts were isolated and perfused with a bovine erythrocyte suspension. The PE and vehicle pretreated hearts underwent either 45 (infarction protocol, n=6) or 20 (stunning protocol, n=6) minutes of global ischemia and two hours of reperfusion. Infarct size was measured by TTC staining. In the infarction protocol, the developed pressures (DP) for the PE and vehicle treated groups were 56.8±4.9 and 36.2±3.9 mmHg (p=0.008). The improved DP of the PE pretreated hearts was due to better diastolic recovery without systolic improvement. The percent infarct areas for the PE and vehicle treated groups were 9.9±2.4 percent and 42.6±2.6 percent (p=2.002). In contrast, PE pretreatment did not improve recovery of the stunned hearts and minimal infarction (less than 1 percent). In conclusion, PE pretreatment improves functional recovery after global ischemia 24 hours later by limiting infarct size. PE-mediated delayed cardioprotection has no effect on stunned myocardium in the absence of infarction.