Effect of exogenous adenosine on resistance, capillary permeability-surface area and flow in ischemic canine myocardium.

The effects of adenosine on capillary-tissue exchange have not been evaluated. Although adenosine is a known vasodilator, its effects on nutritive flow are unknown. We therefore measured the influence of adenosine on resistance and capillary exchange in normal and mildly ischemic myocardium in 11 anesthetized, heparinized dogs. Flow to the left anterior descending artery was measured and controlled through an extracorporeal shunt from the carotid artery. Capillary permeability-surface area for sucrose (PS) was determined using the multiple-tracer technique in which mixtures of isotopes were injected into the coronary arterial shunt. We found that in the normal myocardium, intracoronary infusion of adenosine at 8 +/- 2 (S.E.M.) micrograms/ml of plasma significantly lowered resistance and increased PS. In the ischemic myocardium, however, large doses of adenosine (200 +/- micrograms/ml of plasma) lowered resistance but failed to increase PS. We interpret these results to mean that in mild, flow-reduction ischemia, adenosine did not lead to a recovery of capillary surface area for exchange, but simply increased flow through capillaries which had already been functioning. Nutritional flow was not enhanced.