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1 Department of Pharmacology and 3 Research Equipment Center, Kagawa Medical University, Kagawa 761-0793; and 2 Department of Pharmacology, Osaka City University Medical School, Osaka 545-8585, Japan
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.
renal interstitium; adenosine deaminase; adenosine kinase
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