Nitrite is protective against renal
ischemia/reperfusion injury (IRI); an effect due to its reduction to
nitric oxide (NO). In addition to other
reductase pathways, endothelial
NO synthase (eNOS) may also facilitate
nitrite reduction in ischemic environments. We investigated the role of eNOS in
sodium nitrite (60 microM, 10 ml/kg applied topically 1 min before reperfusion)-induced protection against renal IRI in C57/BL6 wild-type (WT) and eNOS knockout (eNOS KO) mice subjected to bilateral renal
ischemia (30 min) and reperfusion (24h). Markers of renal dysfunction (plasma [
creatinine] and [
urea]), damage (tubular histology) and
inflammation (cell recruitment) were elevated following IRI in WT mice; effects significantly reduced following
nitrite treatment. Chemiluminescence analysis of cortical and medullary sections of the kidney demonstrated rapid (within 1 min) distribution of
nitrite following application. Whilst IRI caused a significant (albeit substantially reduced compared to WT mice) elevation of markers of renal dysfunction and damage in eNOS KO mice, the beneficial effects of
nitrite were absent or reduced, respectively. Moreover,
nitrite treatment enhanced renal dysfunction in the form of increased plasma [
creatinine] in eNOS KO mice. Confirmation of
nitrite reductase activity of eNOS was provided by demonstration of
nitrite (100 microM)-derived NO production by kidney homogenates of WT mice, that was significantly reduced by
L-NMMA.
L-NMMA was without effect using kidney homogenates of eNOS KO mice. These results support a role for eNOS in the pathways activated during renal IRI and also identify eNOS as a
nitrite reductase in ischemic conditions; activity which in part underlies the protective effects of
nitrite.