Role of adenosine in the regulation of coronary blood flow in swine at rest and during treadmill exercise

A pivotal role for adenosine in the regulation of coronary blood flow is still controversial. Consequently, we investigated its role in the regulation of coronary vasomotor tone in swine at rest and during graded treadmill exercise. During exercise, myocardial O2 consumption increased from 167 +/- 18 micromol/min at rest to 399 +/- 27 micromol/min at 5 km/h (P </= 0.05), which was paralleled by an increase in O2 delivery, so that myocardial O2 extraction (76 +/- 1 and 78 +/- 1% at rest and 5 km/h, respectively) and coronary venous PO2 (24.5 +/- 1.0 and 22.8 +/- 0.3 mmHg at rest and 5 km/h, respectively) remained unchanged. After adenosine receptor blockade with 8-phenyltheophylline (5 mg/kg iv), the relation between myocardial O2 consumption and coronary vascular resistance was shifted toward higher resistance, whereas myocardial O2 extraction rose to 81 +/- 1 and 83 +/- 1% at rest and 5 km/h and coronary venous PO2 fell to 19.2 +/- 0.8 and 18.9 +/- 0.8 mmHg at rest and 5 km/h, respectively (all P </= 0.05). Thus, although adenosine is not mandatory for the exercise-induced coronary vasodilation, it exerts a vasodilator influence on the coronary resistance vessels in swine at rest and during exercise.