Effect of adenosine on transmural myocardial blood flow distribution in the awake dog

Studies were conducted to determine the effects of adenosine on transmural myocardial blood flow distribution. Both maximal and submaximal vasodilatory doses of adenosine were infused into awake resting dogs chronically instrumented with coronary flow probes and aortic and left atrial pressure catheters. Radioactive microspheres (8-10 micron) were used to determine regional coronary blood flow. Four experimental protocols were evaluated: 1) the effects of maximal (1.00 mg . kg-1 . min-1) as well as submaximal (0.45 mg . kg-1 . min-1) vasodilatory levels of adenosine, 2) the dose-response characteristics of adenosine, 3) the dose-response characteristics of dipyridamole, and 4) the effects of adenosine in the presence of an increased arterial PO2. The data indicate that maximal vasodilatory doses of adenosine have little effect on the endocardial-to-epicardial blood flow ratio, whereas submaximal doses result in a marked preferential endocardial perfusion. This relative increase in endocardial perfusion was not altered by hyperoxia. Dipyridamole, in submaximal doses, produced a similar preferential flow to the endocardial layer. These data demonstrate that the vasodilator reactivity to adenosine infusion is greater in the endocardial layer,