Effect of theophylline on adenosine production in the canine myocardium.

Adenosine is thought to participate in local regulation of coronary blood flow. However, competitive antagonists of adenosine fail to block myocardial active hyperemia. We examined the effect of locally administered theophylline on active hyperemia and myocardial adenosine production during intracoronary isoproterenol infusion in the dog heart. Isoproterenol decreased coronary resistance and increased myocardial adenosine production. Infusion of theophylline at a rate that attenuated the vasodilator response to exogenously administered adenosine failed to attenuate the increase in coronary blood flow produced by isoproterenol. However, theophylline plus isoproterenol produced greater increases in myocardial adenosine production than isoproterenol alone. The curves relating resistance and adenosine in the presence of theophylline fell to the right of those in the absence of theophylline. These findings suggest that the failure of theophylline to attenuate isoproterenol hyperemia in the dog heart results at least in part from an increase in adenosine concentration at the arteriole to a level beyond that blocked by this competitive antagonist and that adenosine may in fact play a role in isoproterenol-induced active hyperemia.