NITRIC-OXIDE - A MEDIATOR IN RAT TUBULAR HYPOXIA REOXYGENATION INJURY/

Nitric oxide (NO), among several other functions, may play a role in h ypoxia and reoxygenation injury due to its free radical nature and hig h reactivity with the superoxide radical to yield peroxynitrite, an ox idant molecule. The present study was undertaken to evaluate a potenti al role for NO, either endogenous or exogenous, in a model of hypoxia/ reoxygenation (H/R) in freshly isolated rat proximal tubules. NO synth ase activity, as assessed by conversion of L-[H-3]arginine to L-[H-3]c itrulline, was detected in normoxic tubules. This activity could be in hibited by N-nitro-L-arginine methyl ester (L-NAME), a NO synthase inh ibitor, and was stimulated by 15 min of hypoxia. The injury in proxima l tubules caused by 15 min of hypoxia followed by 35 min of reoxygenat ion was completely prevented by L-NAME as assessed by release of lacta te dehydrogenase, whereas D-NAME, which does not inhibit NO synthase, had no effect. In contrast, L-arginine (NO substrate) enhanced the H/R injury. These effects were paralleled by nitrite/nitrate production. In separate experiments, the addition of sodium nitroprusside, a NO do nor, to proximal tubules enhanced the H/R injury; this effect could be blocked by hemoglobin, a NO scavenger. Also, addition of nitroprussid e reversed L-NAME protection against H/R injury. These results demonst rate that NO is synthesized in rat proximal tubules and participates a s one of the mediators in rat tubular H/R injury.