K_ATP⁺ channels, nitric oxide, and adenosine are not required for local metabolic coronary vasodilation

The role of ATP-sensitive K⁺ (K_ATP⁺) channels, nitric oxide, and adenosine in coronary exercise hyperemia was investigated. Dogs (n = 10) were chronically instrumented with catheters in the aorta and coronary sinus and instrumented with a flow transducer on the circumflex coronary artery. Cardiac interstitial adenosine concentration was estimated from arterial and coronary venous plasma concentrations using a previously tested mathematical model. Experiments were conducted at rest and during graded treadmill exercise with and without combined inhibition of K_ATP⁺ channels (glibenclamide, 1 mg/kg iv), nitric oxide synthesis (Nω-nitro-L-arginine, 35 mg/kg iv), and adenosine receptors (8-phenyltheophylline, 3 mg/kg iv). During control exercise, myocardial oxygen consumption increased ∼2.9-fold, coronary blood flow increased ∼2.6-fold, and coronary venous oxygen tension decreased from 19.9 ± 0.4 to 13.7 ± 0.6 mmHg. Triple blockade did not significantly change the myocardial oxygen consumption or coronary blood flow response during exercise but lowered the resting coronary venous oxygen tension to 10.0 ± 0.4 mmHg and during exercise to 6.2 ± 0.5 mmHg. Cardiac adenosine levels did not increase sufficiently to overcome the adenosine receptor blockade. These results indicate that combined inhibition of K_ATP⁺ channels, nitric oxide synthesis, and adenosine receptors lowers the balance between total oxygen supply and consumption at rest but that these factors are not required for local metabolic coronary vasodilation during exercise.