3-isobutyl-1-methylxanthine decreases renal cortical interstitial levels of adenosine and inosine.

The purpose of this study was to test the hypothesis that endogenous cyclic AMP, via metabolism by phosphodiesterase, contributes to interstitial levels of adenosine in the renal cortex in vivo. This hypothesis was tested by determining the effects of 3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor, on renal cortical interstitial levels of adenosine and inosine. Changes in renal cortical interstitial adenosine and inosine levels were assessed in rats by implanting microdialysis probes into the renal cortex and measuring adenosine and inosine levels in the dialysate exiting the kidney using high performance liquid chromatography. When added to the dialysate entering the kidney at concentrations of 0.5, 1 and 2.5 mM, 3-isobutyl-1-methylxanthine significantly and dose-dependently decreased interstitial levels of both adenosine and inosine. The percentage changes from baseline of interstitial levels of adenosine and inosine were: -39 +/- 6% and -19 +/- 6%, respectively, with 0.5 mM 3-isobutyl-1-methylxanthine; -45 +/- 7% and -24 +/- 8%, respectively, with 1 mM 3-isobutyl-1-methylxanthine; and -56 +/- 12% and -38 +/- 8%, respectively, with 2.5 mM 3-isobutyl-1-methylxanthine. These data suggest that in the renal cortex, cyclic AMP metabolism via phosphodiesterase is an important source of renal interstitial adenosine.