Effects of adenosine on intrarenal oxygenation

Although generally a vasodilator, adenosine vasoconstricts cortical vessels in the kidney, reduces glomerular filtration rate (GFR), and increases medullary blood flow, effects likely to improve the medullary O₂ deficiency characteristic of mammalian kidneys. To evaluate a possible role of adenosine in medullary O₂ balance, we investigated the effect of adenosine upon cortical and medullary tissue Po₂. Adenosine was infused into renal interstitium through chronically implanted capsules. Cortical and medullary Po₂ were measured using sensitive dark-type O₂ microelectrodes inserted into kidneys of anesthetized rats at the respective depths of 1.8 and 3.7 mm. Infusion of adenosine (0.1-0.5 μmol/min) increased medullary Po₂ from 17 ± 3 (SE) to 40 ± 5 mmHg (P < 0.001) and decreased cortical Po₂ from 64 ± 4 to 47 ± 3 mmHg (P < 0.001). After the infusion was stopped, Po₂ returned to baseline at both sites. Coadministration of adenosine receptor antagonist 8-phenyltheophylline (0.01 μmol/min) prevented both cortical and medullary effects of adenosine. We concluded that adenosine could play an important protective and regulatory role in renal medullary O₂ balance.