Difference in the time course between increases in coronary flow and in effluent adenosine concentration during anoxia in the perfused rat heart.

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.