Acadesine increases blood flow in the collateralized heart during exercise

Acadesine, an adenosine-regulating agent, has been shown to increase coronary flow and exert cardioprotective effects in acutely ischemic myocardium, but a beneficial effect on coronary collateral flow during exercise has not been demonstrated. We examined the effect of acadesine, 100 μmol/min, i.v., on myocardial blood flow during treadmill exercise in six normal dogs and seven dogs with moderately well-developed coronary collateral vessels. Collateral vessel growth was produced with 2-min intermittent occlusions of the left circumflex coronary artery followed by permanent occlusion. During resting conditions, myocardial blood flow in the collateral zone was not significantly less than in the normal zone, but during exercise, blood flow increased by only 79 ± 21% (from 0.98 ± 0.29 ml/min/g to 1.64 ± 0.19 ml/min/g; p < 0.05) in the collateral zone as compared with 118 ± 32% (from 1.09 ± 0.28 ml/min/g to 2.14 ± 0.2 ml/min/g; p < 0.01) in the normal zone. During exercise, acadesine further increased mean blood flow in the collateral-dependent region by 24 ± 5% (to 2.04 ± 0.26 ml/min/g; p < 0.05) with no change in the transmural distribution of perfusion. The increase in collateral zone blood flow in response to acadesine resulted from a decrease in both transcollateral resistance from 25.1 ± 2.7 mm Hg/min/g/ml to 18.8 ± 8 mm Hg/min/g/ml (p < 0.05) and small-vessel resistance in the collateral- dependent myocardium from 45.3 ± 6.6 mm Hg/min/g/ml to 36.4 ± 5.8 mm Hg/min/g/ml (p < 0.05). Acadesine also significantly increased normal-zone flow in the collateralized dogs (to 2.62 ± 0.33 ml/min/g; p < 0.05). In contrast, acadesine had no effect on coronary blood flow in normal dogs. In dogs with moderately well-developed collateral vessels, acadesine increased blood flow in both the collateral-dependent and normal myocardial zones during exercise. In contrast, acadesine did not increase blood flow in normal dogs. These findings suggest that adenosine metabolism is altered not only in the collateral-dependent region but also in the normal region of hearts with a coronary artery occlusion.