Investigation of Possible Participation of Nucleoside Transport Systems in the Postischemic Release of Purines and Pyrimidines from Cold Stored Liver

The aim of the study was to elucidate the role of nucleoside transport systems in the postischemic release of nucleosides and nucleobases accumulated by the rat liver during cold storage. Livers were preserved for 24 h in Euro-Collins (EC) or in a lactobionate-based solution (LBS) without exogenous adenosine. The rates of release of uric acid, xanthine, hypoxanthine, inosine, adenosine, uridine, and cytidine were monitored during early reperfusion. The greater part of the purines and pyrimidines (up to 80%) was lost in the first 2 min of reperfusion. After storage in EC, uric acid and xanthine formed more than 90% of the total purines released; nucleosides did not exceed 5% of the total. After storage in LBS, hypoxanthine formed more than 80% of purine efflux and the release of inosine and uridine was increased 5-10 times. These changes were shown to be due to the presence of allopurinol in LBS. Dipyridamole (an inhibitor of equilibrative nucleoside transporters) decreased the efflux of uric acid after storage in EC but residual release remained high. Dipyridamole exerted the most pronounced effect on the release of nucleosides (inosine and uridine) from livers stored in LBS. The use of sodium-free media for liver preservation and reperfusion did not alter the rates of purine and pyrimidine release. We conclude that equilibrative nucleoside transporters mediate the postischemic release of nucleosides and also, but to a less degree, of uric acid. Simple diffusion is an important factor in the release of nucleobases. Active Na(+)/nucleoside cotransport does not play an important role in early reperfusion.