Measurements of coronary plasma and pericardial infusate adenosine concentrations during exercise in conscious dog: Relationship to myocardial oxygen consumption and coronary blood flow

A conscious dog model was employed to evaluate the relationships among myocardial oxygen consumption (MV̇O₂), myocardial adenosine release and coronary blood flow (CBF) during graded treadmill exercise. Two methods were utilized simultaneously as indexes of changes in interstitial adenosine concentrations, (1) a pericardial infusate technique and (2) the measurement of arterial-coronary sinus plasma adenosine concentration differences. Graded exercise was associated with graded increases in MV̇O₂, CBF, pericardial infusate adenosine concentration (PI Ado) and adenosine washout in coronary plasma. Regression analysis demonstrated significant linear relationships for MV̇O₂ v. CBF (r = 0.78, P < 0.01), MV̇O₂ v. PI Ado (r = 0.52, P < 0.01), and PI Ado v. CBF (r = 0.76, P < 0.01). Coronary plasma adenosine arterio-sinus differences, sinus plasma concentrations, and net washout of adenosine also increased with graded exercise, however, a significant inter-animal variance was noted. These data suggest that the plasma adenosine assay is capable of detecting directional (qualitative) changes associated with changes in cardiac metabolism, however, it may not be reliable as a quantitative indicator of interstitial adenosine concentrations due to multiple factors which may influence the plasma adenosine pool. The pericardial infusate technique, which presumably represents a model of diffusion, is relatively invariant by comparison. The results demonstrate a significant correlation among MV̇O₂, PI Ado and CBF, and thereby provide support to the hypothesis that adenosine is a major factor in the coupling of myocardial oxygen demand to oxygen supply under physiological conditions.