Epinephrine-stimulated contractile and metabolic reserve in postischemic rat myocardium

Recovery of contractile function and of fatty acid oxidation may be delayed in viable postischemic myocardium. To determine whether a metabolic reserve is preserved after reperfusion of reversibly injured myocardium, we studied the effect of epinephrine on myocardial fatty acid oxidation in isolated rat hearts perfused retrogradely with erythrocyte enriched buffer containing albumin 0.4 mM, palmitate 0.4 mM, and glucose 11 mM. Hearts were subjected to 60 min of low-flow ischemia (5% of control flow) followed by 60 min of reperfusion. Five minutes following the onset of reperfusion, developed left ventricular pressure (DLVP) and oxidation of palmitate were reduced to 53% (p less than 0.01) and 46% (p less than 0.01), respectively, of values measured in nonischemic control hearts. Subsequently, DLVP and oxidation of palmitate gradually recovered to 78% (NS) and 91% (NS) by 60 min of reperfusion. Epinephrine 5.10(-1) M elicited an immediate stimulation of both contractile function and palmitate oxidation. Early after reperfusion stimulated DLVP and palmitate oxidation were still lower compared to values measured in control hearts exposed to the same concentration of epinephrine. Later than 15 min after the onset of reperfusion the response of DLVP and of palmitate oxidation to epinephrine no longer differed between control and reperfused hearts. These results indicate that viable postischemic myocardium exhibits a remarkable oxidative metabolic reserve. The observation provides further evidence for the view that impairment of myocardial energy production is not responsible for contractile dysfunction early after reperfusion.