Pericardial superfusion to measure cardiac interstitial adenosine concentration

The steady-state concentration of adenosine in pericardial superfusates, [Ado]SS, may estimate the concentration in the cardiac interstitium. As reaching a steady state may sometimes require many minutes, the concentration at an earlier time is often used as an index of [Ado]SS. The latter assumes that the rate of approach to [Ado]SS is uniform and insensitive to perturbations of cardiac oxygen usage (MVO2). In 11 open-chest dogs superfusate adenosine rose at a rate (+/- SD) of 0.53 +/- 0.99/min to an [Ado]SS of 68 +/- 32. The mean rate of equilibration has a very large coefficient of variation, indicating substantial dog-to-dog variation. In five dogs the rate of equilibration during the second of successive superfusions was significantly lower than the first. Raising MVO2 by cardiac pacing or isoproterenol infusion changed neither the rate of equilibration nor [Ado]SS. Aortic constriction or propranolol slowed equilibration but had no effect on [Ado]SS. Thus superfusate adenosine concentration early in the course of equilibration seems an unreliable index of [Ado]SS. That interventions that change MVO2 do not change [Ado]SS from control means either that [Ado]SS fails to reflect the concentration in the vicinity of the coronary resistance vessels or, alternatively, that adenosine does not regulate coronary blood flow.