COMBINED ADENOSINE AND LIDOCAINE ADMINISTRATION LIMITS MYOCARDIAL REPERFUSION INJURY

The endogenous compound adenosine may play a role in limiting myocardial ischemia-reperfusion injury through its ability to cause vasodilation, modulate cardiac adrenergic responses, inhibit neutrophil function, or modulate energy supply and demand of the myocardium. The local anesthetic lidocaine has been shown to be protective against myocardial ischemia-reperfusion injury, although its mechanism of action remains unresolved. We hypothesized that administration of exogenous adenosine during reperfusion would limit the size of the infarct that results from a period of ischemia and reperfusion only when the animals are treated with lidocaine. Male, mongrel dogs (13.0-20.0 kg) were anesthetized (30 mg/kg i.v. sodium pentobarbital), and a left thoracotomy was performed. The left circumflex coronary artery (LCx) was isolated and instrumented with an electromagnetic flow probe, a 25-gauge nonobstructing intracoronary catheter, and a critical stenosis. The dogs were allocated randomly to one of four groups: 1) control, n=13, (saline), 2) adenosine, n=13, (0.15 mg/kg/ml/min i.c. for the first hour of reperfusion), 3) lidocaine, n=9, (2.0 mg/kg i.v. given immediately before coronary artery occlusion and just before reperfusion), or 4) adenosine plus lidocaine, n=11. The LCx was occluded for 90 minutes and reperfused for 6 hours. Regional myocardial blood flow (RMBF) was determined (n=6 per group) at 80 minutes of occlusion and at 45 minutes of reperfusion with radiolabeled microspheres. RMBF determinations revealed an increase in blood flow to the inner two thirds of the myocardium at 45 minutes of reperfusion only in the presence of the combined treatment. Adenosine treatment alone or lidocaine treatment alone did not affect RMBF. Quantification of infarct size (triphenyltetrazolium method) expressed as a percent of the area at risk revealed a significant limitation of infarct size only in the group treated with both adenosine and lidocaine: control, 47.8±6.6%; adenosine, 45.0±3.2%; lidocaine, 46.9±6.0%; and adenosine and lidocaine, 20.8±5.6%. Statistical analyses were performed with two-way analysis of variance to account for the two individual drug treatments. The findings show that intracoronary administration of exogenous adenosine, at the dose used, is only effective at limiting myocardial infarct size when administered to lidocaine-treated animals.