Difference in the time course between increases in coronary flow and in effluent adenosine concentration during...

The isolated rat heart was perfused by Langendorff's technique with either an oxygenated (95% O2 and 5% CO2) or an anoxic (95% N2 and 5% CO2) solution. Anoxia increased coronary flow and effluent adenosine concentration, but the time course of these changes was discordant; coronary flow increased transiently (the maximum increase in flow was observed within 1-2 min after the onset of anoxia), whereas the effluent adenosine concentration increased as a function of the time during anoxia. The concentration of effluent adenosine reached 3 microM 10 min after anoxia. The tissue (myocardial) adenosine content changed in parallel with the effluent adenosine concentration. An infusion of adenosine increased coronary flow dose-dependently, and the maximum increase was obtained when 0.27 microM of adenosine was infused. Effluent adenosine concentration was 0.05-0.3 microM in both anoxia and adenosine infusion experiments at the time when the maximum increase in coronary flow occurred. An increase in concentrations of adenosine above 0.05-0.03 microM in the effluent was not accompanied by an increase in coronary flow. These results raise a question about the role of adenosine in regulating coronary circulation during anoxic perfusion, though there is a possibility of vasodilatory function of adenosine in early period of anoxic perfusion.