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

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Abstract
To determine the effects of adenosine on transmural myocardial blood flow distribution, 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 .mu.m) were used to determine regional coronary blood flow. Four experimental protocols were evaluated as follows: effects of maximal (1.00 mg.cntdot.kg-1.cntdot.min-1) and submaximal (0.45 mg.cntdot.kg-1.cntdot.min-1) vasodilatory levels of adenosine, the dose-response characteristics of adenosine, dose-response characteristics of dipyridamole and effects of adenosine in the presence of an increased arterial PO2 [O2 partial pressure]. Maximal vasodilatory doses of adenosine have little effect on the endocardial-to-epicardial blood flow ratio; 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. The vasodilator reactivity to adenosine infusion is greater in the endocardial layer.