| Abstrakt: |
The metabolism of inosine (Ino) and guanosine (Guo) was studied in rat blood and plasma in vitro. Nucleoside levels were determined using a modification of the HPLC method of Hartwick and Brown (1977). When heparinized whole blood was spiked with Ino and maintained at room temperature, the level of Ino declined in a linear manner from an initial concentration of 9.9 to 1.6 µg/ml after 60 min., giving a plasma half-life of 23.7 min. Blood spiked with Guo showed a similar linear decline in Guo levels, but in a faster manner (11.0 to 0.1 µg/ml at 60 min., half-life = 8.9 min.). The decline in nucleoside concentration was greatly retarded by maintaining blood and plasma on ice. Addition of dipyridamole (100 nmoles/ml) to whole blood, to block nucleoside uptake, retarded the disappearance of Ino and Guo 1.2 and 2.8-fold, respectively. Addition of 8-aminoguanosine (8-AG, 100 nmoles/ml), an inhibitor of purine nucleoside phosphorylase (PNP), had a slightly greater effect, increasing the half-lives of Ino and Guo 2.5 and 4.4-fold, respectively. Dipyridamole and 8-AG had an additive effect in whole blood. When rat plasma was spiked at room temperature with Ino and Guo (each at 1 µg/ml), neither nucleoside was detectable after 30 min. However, addition of 8-AG to spiked rat plasma totally inhibited the reduction in the levels of each nucleoside for at least 60 min. Thus, membrane transport and especially catabolism by PNP cause disappearance of Ino and Guo from rat blood in vitro. |
