Estimates of Interstitial Adenosine in Isolated Rat Hearts from Surface Exudates During Rapid Pacing and EHNA Infusion

Summary

When isolated hearts are perfused with colloid-free salt solution, fluid filters from the vascular bed through the interstitial space and accumulates on the epicardial surface. We suggest that under steady-state conditions, the composition of this exudate is equivalent to that of the extracellular fluid. We have developed techniques to collect samples of this surface exudate (_s) and have used HPLC methods to determine the adenosine (ADO) and inosine (INO) concentrations which can be compared to those of the venous effluent (_v). Under steady-state conditions, [ADO]_v and [ADO]_s were 23 ± 3 and 130 ± 8 nM, respectively, and [INO]_v and [INO]_s were 38 ± 5 and 119 ± 13, respectively. An increase in pacing from 3 Hz to 6 Hz was associated with a transient increase in [ADO]_v but no increase in [ADO]_s. After 10 min rapid pacing, [ADO]_s and [ADO]_V were below the prerapid pacing values. Both [INO]_S and [INO]_V, however, increased and remained elevated throughout the 10 min period of rapid pacing. The data suggest that coronary vascular tone decreased during rapid pacing. Addition of the adenosine deaminase inhibitor, EHNA (10⁻⁵ M), was associated with an increase in the [ADO] and a decrease in [INO] of both fluid samples and a decrease in the coronary vascular resistance under steady-state conditions. The [ADO]_v and [ADO]_s of EHNA-treated hearts were increased significantly during the period of rapid pacing. Furthermore, the data indicate that the decrease in coronary vascular tone during rapid pacing was greater in EHNA-treated hearts than in control hearts. The results of these experiments suggest that interstitial levels of adenosine in these hearts is nearly six-fold greater than that of the venous effluent and that there is significant endogenous adenosine deaminase activity that may prevent interstitial levels from rising significantly during rapid pacing.