Interstitial adenosine in guinea pig hearts: an index obtained by epicardial disks

Epicardial porous disks were used to estimate left ventricular interstitial fluid adenosine in the isolated guinea pig heart perfused at constant flow. To validate this technique, adenosine was infused with 0.5 microM dipyridamole and 5 microM erythro-4-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA) to inhibit adenosine uptake and deamination, respectively. Under these conditions, with 6 or 12 microM adenosine in the arterial infusate, the venous and steady-state left ventricular disk adenosine values equaled those of the perfusion fluid, reflecting the expected equilibration between vascular and left ventricular interstitial fluid (disk) compartments. The concentration of endogenous adenosine in the interstitial fluid as estimated by the epicardial disks under control conditions was 0.28 +/- 0.03 microM with a concomitant coronary sinus concentration of 0.004 +/- 0.001 microM. We conclude that a marked adenosine gradient exists between the interstitial fluid and the vascular space and that disk adenosine measurements provide a useful index of left ventricular interstitial fluid adenosine.