Phenylephrine induces delayed cardioprotection against necrosis without amelioration of stunning

Background. α-Adrenergic stimulation induces protection in reperfused ischemic (I/R) myocardium 24 hours later. We tested the hypothesis that phenylephrine improves dysfunction after global I/R by limiting cell death not stunning. Methods. Rabbits were pretreated with either phenylephrine or vehicle. Twenty-four hours later, isolated hearts underwent either 45 (infarction protocol) or 20 minutes (stunning protocol) of global ischemia before 2 hours of reperfusion (n = 6 per group). Cell death was determined by triphenyl tetrazolium chloride staining (infarction) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) (apoptosis). Results. Compared with vehicle, phenylephrine pretreatment improved post-I/R-developed pressures in hearts after infarction (53.2 ± 4.0 vs 35.8 ± 4.1 mm Hg, p = 0.01) but not stunning protocol (64.3 ± 8.9 vs 57.7 ± 6.2 mm Hg, p = NS). The improved developed pressure was due to better diastolic recovery. Systolic pressures were similar between groups. Phenylephrine markedly decreased infarction (9.0 ± 1.9% vs 40.8 ± 1.8% for vehicle, p< 0.001) and TUNEL-positive staining. Stunned hearts of either group had less than 3% infarction and no apoptosis. Conclusions. Phenylephrine pretreatment 24 hours before global I/R improves function by limiting infarction but not stunning.