Ameliorative effect of adenosine on hypoxia-reoxygenation injury in LLC-PK1, a porcine kidney cell line

We studied the effects of adenosine on injury caused by hypoxia and reoxygenation in LLC-PK1 cells. Lactate dehydrogenase and gamma-glutamyltranspeptidase were released from cells exposed to hypoxia for 6 hr and then reoxygenation for 1 hr. The addition of adenosine at 100 mu M to the medium before hypoxia began significantly decreased enzyme leakage into medium during both hypoxia and reoxygenation. The adenosine A(1)-receptor agonist, R(-)-N-6-(2-phenylisopropyl)adenosine (R-PIA), at the concentration of 100 mu M, did not affect enzyme release, but the adenosine A(2)-receptor agonist 2-p-[2-carboxyethyl]phenethyl-amino-5'-N-ethylcarboxamido-adenosine hydrochloride (CGS 21680) at the concentration of 100 nM, suppressed the injury caused by hypoxia and reoxygenation. There were decreases in cAMP contents and ATP levels in LLC-PK1 cells injured by hypoxia and reoxygenation. Adenosine (100 mu M) restored ATP levels in the cells during reoxygenation. With adenosine, the intracellular cAMP level was increased prominently during reoxygenation. These results suggest that adenosine protects LLC-PK1 cells from injury caused by hypoxia and reoxygenation by increasing the intracellular cAMP level via adenosine A(2) receptor.