Free fatty acid metabolism in "stunned" myocardium

To assess whether myocardial lipid metabolism is altered in the “stunned” myocardium we have studied the metabolism of (1-14C)-palmitate during reperfusion in a modified rat heart preparation. Hearts were perfused retrogradely at a physiological flow rate (2 ml/min) in a non-recirculating system with erythrocyte-enhanced Krebs-Henseleit buffer containing albumin 0.4 mM, glucose 11 mM, palmitate 0.4 mM and trace amounts of (1-14C)-palmitate. Left ventricular pressure was measured by a latex balloon in the left ventricular cavity. Control hearts were perfused at constant flow for 120 min. To achieve reversible ischaemic damage, myocardial perfusion was reduced by 95% for 40 min, followed by reperfusion at the control flow rate for 60 min (reperfusion group). For comparison, irreversible damage was produced by calcium free perfusion (calcium paradox group). In the reperfusion group, the developed pressure was severely depressed 5 min after reperfusion to 23% of the value in the control group (p < 0.05) but recovered to 84% (NS) at 60 min. In the calcium paradox group, mechanical activity ceased completely without recovery. Myocardial uptake of (1-14C)-palmitate in the reperfusion group was similar to the control experiments for the entire reperfusion period, whereas a marked depression was observed in the calcium paradox group. 14CO2 production was severely depressed at the onset of reperfusion in both the reperfusion and calcium paradox group to 42% (p < 0.05) and 29% (p < 0.05) respectively. In contrast to the calcium paradox group, 14CO2 production in the reperfusion group recovered progressively to 70% (NS) of the control value during the 60 min of reperfusion. The results suggest that in the myocardium exhibiting a reversible depression of mechanical function following transient ischaemia (“stunning”), extraction of free fatty acid is normal during early reperfusion, whereas oxidation of free fatty acid recovers more slowly at a rate comparable to the recovery of mechanical performance.