It has been postulated that the
adenosine A1 receptor subtype, but also A2a receptors, are involved in mediating the beneficial properties of
adenosine during
ischemia and reperfusion. We investigated the effects of the selective A1
adenosine receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA), the selective A2A
adenosine receptor agonists, 2-[
p-(2-carboxyethyl)phenetylamino]-
5'-N-ethylcarboxamidoadenosine (
CGS 21680),
2-hexynyl-5'-N-ethylcarboxamidoadenosine (2HE-NECA), and the non selective agonist,
5'-N-ethylcarboxamidoadenosine (
NECA), on
ischemia-reperfusion injury in Langendorff-perfused rat hearts. Global
ischemia was induced for 15 min in paced hearts followed by 60 min reperfusion. Control hearts developed
left ventricular dysfunction, as indicated by the increase in end diastolic pressure to 40.8 +/- 5.1 vs 5.9 +/- 1.0 mm Hg baseline, and in coronary perfusion pressure to 57.6 +/- 8.4 vs 28.8 +/- 2.2 mm Hg before
ischemia. After 15 min of reperfusion, ventricular function (LVDP) recovered by 83%, but
creatine kinase levels were still significantly increased (294 +/- 55 IUl(-1) vs basal), indicating the occurrence of myocardial injury. All
adenosine agonists added to the perfusion medium 15 min prior to
ischemia exerted protective effects against myocardial dysfunction and
reperfusion injury. Thus, 2HE-NECA (100 nM),
CGS 21680 (10 nM), CCPA (3 nM) and
NECA (100 nM) significantly (P < 0.05) decreased end diastolic pressure by 50-75% as compared with the control group. Similarly, all compounds significantly (P < 0.05) reduced coronary perfusion pressure by 30-45% vs control. For all drugs, recovery of LVDP occurred immediately after restoration of coronary flow. At 15-min reperfusion the
adenosine agonists decreased
myocardial creatine kinase release by 80-95% (P < 0.05 vs control). These findings indicate that both A1 and A2A
adenosine receptors are involved in protecting the myocardium against
ischemia and reperfusion in isolated rat heart, even if through different mechanisms.