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