Pharmacological Stress Thallium Scintigraphy With 2-Cyclohexylmethylidenehydrazinoadenosine (WRC-0470)

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Abstract
Background Pharmacological stress imaging with adenosine or dipyridamole is associated with a high incidence of side effects, including hypotension, chest pain, AV conduction abnormalities, and bronchospasm. Although the desired coronary vasodilatory response is mediated primarily by the adenosine A2A receptors, these side effects result from stimulation of the A1, A2B, or A3 adenosine receptors. We hypothesized that a selective adenosine A2A receptor agonist would induce coronary vasodilatation appropriate for pharmacological stress imaging, without evoking adenosine receptor–mediated side effects. Methods and Results Infusions of a potent and selective A2A adenosine receptor agonist, WRC-0470 (0.1 to 3 μg · kg−1 ·min−1 for 10 minutes), to five open-chest dogs produced dose-related left anterior descending (LAD) and left circumflex (LCx) coronary artery vasodilatation without altering mean arterial pressure, heart rate, left atrial pressure, or left ventricular dP/dt. In the same dogs, adenosine (300 μg · kg−1 · min−1 for 4 minutes) produced coronary vasodilatation that was limited by significant hypotension. To determine the utility of WRC-0470 for pharmacological stress imaging, the hemodynamic responses to WRC-0470 (0.6 μg · kg−1 · min−1 for 10 minutes) and adenosine (250 μg · kg−1 · min−1 for 4 minutes) were compared in dogs with critical LAD stenoses. 201Tl was injected at the peak WRC-0470 stress response. WRC-0470 increased LCx flow nearly fivefold but did not significantly lower mean arterial pressure. Anteroseptal defects were readily apparent in slice images from all dogs. The mean defect ratio (LAD/LCx) was 0.59±0.06. Conclusions The potent A2A-selective adenosine receptor agonist WRC-0470 is a short-acting coronary vasodilator with potential utility for pharmacological stress perfusion imaging.

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