Adenosine attenuates in vivo myocardial stunning with minimal effects on cardiac energetics

Adenosine has been shown to modulate myocardial intermediary metabolism. The purpose of this study was to determine whether adenosine-mediated attenuation of in vivo myocardial stunning is associated with improved myocardial phosphorylation potential. Adult, open chest pigs were subjected to 10 minutes of regional myocardial ischemia and 90 minutes reperfusion. Regional ventricular function was assessed by measuring systolic wall thickening. Myocardial phosphorylation potential was estimated from the tissue (CrP/CrxPi) ratio determined in rapid-frozen tissue biopsy samples from normal and stunned myocardium. Control pigs were compared to animals treated prior to ischemia with intracoronary adenosine (50 micrograms/kg/min). Postischemic regional systolic wall thickening in adenosine treated pigs was significantly improved (40 +/- 3% of preischemic values) compared to control untreated pigs (26 +/- 3%). Myocardial stunning was associated with decreased ATP levels, but neither the total creatine pool (CrP + Cr) nor the (CrP/CrxPi) ratio was reduced. Adenosine pretreatment was associated with decreased Pi and Cr contents resulting in improved postischemic (CrP/CrxPi) ratio in the stunned bed compared to controls, but this effect occurred only after postischemic function had attained maximal improvement. These results suggest that adenosine attenuation of in vivo myocardial stunning is independent of elevated myocardial phosphorylation potential.