Adenosine A2 receptor activation attenuates reperfusion injury by inhibiting neutrophil accumulation, superoxide generation and coronary endothelial adherence.

This study tests the hypothesis that adenosine A2 receptor activation reduces reperfusion injury by inhibiting neutrophils in a canine model of ischemia and reperfusion. In 16 anesthetized, open-chest dogs, the left anterior descending coronary artery was ligated for 60 min and reperfused for 3 hr. An intracoronary infusion of either the selective adenosine A2 agonist CGS-21680 at 0.2 microgram/kg/min (n = 8) or vehicle (n = 8) was started 5 min before reperfusion and discontinued after 60 min. The area at risk was comparable between vehicle-treated and CGS-21680-treated groups (39.6 +/- 4.1 vs. 37.1 +/- 2.5% of left ventricle). Infarction size, determined with triphenyltetrazolium chloride, was smaller in the CGS-21680-treated group than in the vehicle-treated group (15.4 +/- 2.9 vs. 29.8 +/- 2.3% of area at risk, P < .05 vs. vehicle-treated group). CGS-21680 significantly reduced neutrophil accumulation (myeloperoxidase activity) in the nonnecrotic area at risk tissue, compared with the vehicle-treated group (2.12 +/- 0.5 vs. 6.47 +/- 0.6 U/g of tissue, P < .05 vs. vehicle-treated group). In in vitro studies, CGS-21680 reduced platelet-activating factor (PAF)-activated canine neutrophil adherence to the endothelial surface of normal homologous coronary artery segments. Compared with PAF-stimulated neutrophils (188.4 +/- 9.4 adhered neutrophils/mm2), CGS-21680 reduced adherence close to base-line levels (46.6 +/- 5.8 adhered neutrophils/mm2) at concentrations of 10 microM (65.6 +/- 8.2 adhered neutrophils/mm2, P < .05 vs. PAF-stimulated group) and 50 microM (56.6 +/- 4.6 adhered neutrophils/mm2, P < .05 vs. PAF-stimulated group). Superoxide anion production (cytochrome c reduction) by activated neutrophils was reduced by CGS-21680 from 33.8 +/- 5.0 to 8.9 +/- 3.6 nmol/5 min/5 x 10(5) cells (P < .05 vs. PAF-stimulated group). We conclude that specific A2 receptor stimulation with CGS-21680 at reflow reduces reperfusion injury by inhibiting neutrophil-related processes.