Effects of dipyridamole, soluflazine and related molecules on adenosine uptake and metabolism by isolated human red blood cells

Summary— The suggestion that adenosine may have beneficial effects on post reperfusion survival following cardiac ischaemia has led to the search for agents which increase the concentration of this substance in the ischemic region as a possible therapeutic approach to the treatment of angina and myocardial infarction. In the present study, dipyridamole, soluflazine and lidoflazine, known inhibitors of the nucleotide exchange system, have been shown using an HPLC method to prevent the decrease in the concentration od added adenosine outside human red blood cells in vitro. However, the results suggest that this effect was due to inhibition of adenosine deaminase rather than inhibition of nucleotide exchange as had previously been suggested. The selective inhibitor of adenosine deaminase erythro-9-(2 hydroxy-3-nonyl adenosine) exhibited the same profile of activity in the human red blood cell assay. pIC₅₀ values for the four compounds named above were found to be 6.80 ± 0.09, 6.95 ± .03, 6.10 ± 0.14 and 7.39 ± 0.05 vs adenosine disapearance observed in the extracellular incubation medium respectively. Thus, as the disappearance of adenosine outside the cells was not due to its uptake but to its catabolism, this in vitro method does not appear to be predictive for the ability of compounds to act on adenosine uptake into cardiac myocytes. Any antiischemic action of these agents is more readily explained by an inhibition of the catabolism of adenosine and not by the inhibition of its transport across the membrane of cardiac myocytes.