Selective A2A Adenosine Receptor Agonist As a Coronary Vasodilator in Conscious Dogs: Potential for Use in Myocardial Perfusion Imaging

The authors sought to demonstrate the advantages of a selective, potent, short-acting A adenosine receptor agonist, CVT-3146 (2-(N-pyrazolyl)Ado derivative), for potential clinical use as a coronary vasodilator during myocardial perfusion imaging. The use of adenosine in a pharmacological stress test during myocardial imaging is limited by side effects mediated by A1 and A2B adenosine receptors and by its ultrashort duration of action. CVT-3146 (0.1-5 microg/kg) and adenosine (13-267 microg/kg) were given as peripheral intravenous injections in 10 awake dogs instrumented for measurement of coronary blood flow (CBF). CVT-3146 caused a dose-dependent increase of CBF (ED50 = 0.34 +/- 0.08 microg/kg, maximal increase = 221 +/- 18%, n = 6). Adenosine was less potent (ED = 51 +/- 15 microg/kg, p < 0.05) but equieffective (maximal increase in CBF = 227 +/- 11%). The increase in CBF caused by 2.5 microg/kg CVT-3146 reached 84 +/- 5% of the maximal reactive hyperemia following 20 s of coronary occlusion (n = 4). After a 10-s injection of CVT-3146 (2.5 microg/kg), the increase in CBF remained at least twofold above baseline for 97 +/- 14 s, whereas for adenosine (267 microg/kg), the twofold increase in CBF lasted only 24 +/- 2 s (p < 0.01, n = 6). A 30-s injection of 2.5 microg/kg CVT-3146 prolonged the twofold increase in CBF up to 221 +/- 20 s. No atrioventricular block was noted. At 2.5 microg/kg, the peak effect of CVT-3146 on CBF was associated with a short-lasting (20 +/- 6 s) increase in heart rate (78 +/- 9 bpm) and decrease in mean arterial blood pressure (13 +/- 6 mm Hg, p < 0.05, n = 6). CVT-3146 is a potent coronary vasodilator. Its short duration of action, minimal and transient systemic hemodynamic effects, and ease of administration may make this agonist suitable for pharmacological coronary vasodilation during myocardial perfusion imaging for noninvasive detection of subcritical arterial stenosis.