Heart protection by combination therapy with esmolol and milrinone at late-ischemia and early reperfusion

Introduction: The present study determined whether late-ischemia/early reperfusion therapy with the β₁-adrenergic receptor (AR) blocker esmolol and phosphodiesterase III inhibitor milrinone reduced left ventricular (LV) myocardial infarct size (IS). Methods and Results: In an ischemia/reperfusion rat model (30-min ischemia/4-hr reperfusion), esmolol, milrinone or esmolol + milrinone were intravenous (IV) infused over 10 min (from the last 5min of ischemia to the first 5min of reperfusion). LV-IS were 48.9±8.9%, 41.5±5.4%, 25.8±7.7% and 16.8±7.3% for saline, esmolol, milrinone, and esmolol + milrinone, respectively (n=12/group). Esmolol + milrinone further reduced LV-IS compared with esmolol or milrinone alone (p<0.05). LV-IS-reduction induced by esmolol + milrinone was eliminated in the presence of protein kinase A-(PKA)-inhibitor (Rp-cAMPS) or Akt-inhibitor (AKT 1/2 kinase inhibitor). In mixed rat ventricular cardiomyocyte cultures, intra-ischemic application of esmolol, milrinone or esmolol + milrinone reduced myocyte death rates by 5.5%, 13.3%, and 16.8%, respectively, compared with saline (p<0.01). This cell protective effect by esmolol + milrinone was abrogated in the presence of PKA-inhibitor or Akt-inhibitor. Esmolol, milrinone or esmolol + milrinone increased myocardial PKA activity by 22%, 28% and 59%, respectively, compared with saline (n=6, p<0.01). No non-specific adverse effect of Rp-cAMPS on myocytes was identified in a purified myocyte preparation during hypoxia/re-oxygenation. Antiapoptotic pathways were assessed by measuring myocardial phosphorylated Akt (pAkt) levels combined with terminal dUTP nick-end labelling staining analysis. Ten minutes following infusion of esmolol, milrinone or esmolol + milrinone, there were 1.7-, 2.7-, and 6-fold increase in tissue pAkt levels, respectively. This esmolol + milrinone induced pAkt activation was abolished in the presence of PKA inhibitor. Esmolol, milrinone and esmolol + milrinone reduced myocyte apoptosis rates by 22%, 37% and 60%, respectively, compared with saline (p<0.01). Conclusions: Late-ischemia/early reperfusion therapy with esmolol+milrinone additively reduces LV-IS associated with robust activation of myocardial PKA and subsequent Akt-antiapoptotic pathway.