Abstract
The mixed A1/A2a-adenosine agonist AMP579 given at reperfusion is protective in animal models of myocardial infarction. Receptor-blocking studies have indicated that the protection came from an adenosine receptor (AR), but neither A1- nor A2a-selective agonists could duplicate its protection. We recently found that A2b-selective agonists given at reperfusion are protective, and, therefore, tested whether AMP579 might also be an A2b agonist. We used human embryonic kidney cells overexpressing human A2b receptors as an assay system. In these cells, A2b receptor occupancy causes phosphorylation of ERK. AMP579 induced ERK phosphorylation with an EC50 of 250 nM and this phosphorylation could be blocked by MRS1754 or PSB1115, two highly selective blockers of human A2b receptors. We attempted to confirm our A2b hypothesis in a rabbit heart model of ischemia-reperfusion. AMP579 (500 nM) for 1 h starting at reperfusion reduced infarct size in isolated rabbit hearts exposed to 30 min of regional ischemia and 2 h of reperfusion (12.9 +/- 2.2% infarction of risk zone vs. 32.0 +/- 1.9% in untreated hearts). PSB1115 (500 nM) given for the first 15 min of reperfusion blocked AMP579's protection (32.2 +/- 3.1% infarction) which is consistent with an A2b mechanism. We conclude that AMP579 is a non-selective, but potent A2b-AR agonist, and that its protection against infarction is through that receptor.