Renal interstitial adenosine metabolism during ischemia in dogs

Abstract

The present study was conducted to determine the metabolism of renal interstitial adenosine under resting conditions and during ischemia. By using a microdialysis method with HPLC-fluorometric analysis, renal interstitial concentrations of adenosine, inosine, and hypoxanthine were assessed in pentobarbital-anesthetized dogs. Average basal renal interstitial concentrations of adenosine, inosine, and hypoxanthine were 0.18 ± 0.04, 0.31 ± 0.05, and 0.35 ± 0.05 μmol/l, respectively. Local inhibition of adenosine kinase with iodotubercidin (10 μmol/l in perfusate) or inhibition of adenosine deaminase with erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; 100 μmol/l in perfusate) did not change adenosine concentrations in the nonischemic kidneys (0.18 ± 0.04 and 0.24 ± 0.05 μmol/l, respectively). On the other hand, treatment with iodotubercidin+EHNA significantly increased adenosine concentration (0.52 ± 0.07 μmol/l) with significant decreases in inosine and hypoxanthine levels (0.13 ± 0.03 and 0.19 ± 0.04 μmol/l, respectively). During 30 min of ischemia, adenosine, inosine, and hypoxanthine were significantly increased to 0.76 ± 0.29, 2.14 ± 0.45, and 21.8 ± 4.7 μmol/l, respectively. The treatment with iodotubercidin did not alter ischemia-induced increase in adenosine (0.84 ± 0.18 μmol/l); however, EHNA alone markedly enhanced adenosine accumulation (13.54 ± 2.16 μmol/l), the value of which was not augmented by an addition of iodotubercidin (15.80 ± 1.24 μmol/l). In contrast, ischemia-induced increases in inosine and hypoxanthine were inversely diminished by the treatment with iodotubercidin+EHNA (0.90 ± 0.20 and 9.86 ± 1.96 μmol/l, respectively). These results suggest that both adenosine kinase and adenosine deaminase contribute to the metabolism of renal interstitial adenosine under resting conditions, whereas adenosine produced during ischemia is mainly metabolized by adenosine deaminase and the rephosphorylation of adenosine by adenosine kinase is small.