Mesenteric Nitric Oxide and Superoxide Production in Experimental Necrotizing Enterocolitis

BackgroundA proposed mechanism of intestinal injury in necrotizing enterocolitis (NEC) involves vascular dysfunction through altered nitric oxide synthase (NOS) activity. We hypothesize that this dysfunction results in an imbalance in nitric oxide (
• NO) and superoxide (O2
• –) production by the intestinal vascular endothelium, which contributes to the intestinal injury seen in NEC.Materials and MethodsNeonatal rat pups were divided into two groups. Control pups were breast fed and housed with their mother. Experimental NEC pups were housed separately and either exposed to formula feeding and 5% to 10% hypoxia alone (FF/H) or with the addition of lipopolysaccharide (FF/H/LPS). Mesenteries from each group were analyzed for
• NO and O2
• – production with and without NOS inhibition by NG-monomethyl-L-arginine (L-NMMA). Western blot analysis for eNOS, phosphorylated eNOS (phospho-eNOS), and inducible NOS (iNOS) was performed, and each terminal ileum was graded for intestinal injury by histology.ResultsHistology revealed mild intestinal injury (grade 1–2 on a 4-point scale) in the FF/H group and severe injury (grade 3–4) in the FF/H/LPS group. The FF/H cohort had significantly increased
• NO and lower O2
• – production, while the FF/H/LPS group shifted to significantly decreased
• NO and increased O2
• – production. L-NMMA inhibited >50% of O2
• – production in all three groups but only inhibited
• NO production in control and FF/H pups. Western blot analysis revealed increased levels of phospho-eNOS in FF/H pups and increased iNOS in FF/H/LPS pups.ConclusionsThis study demonstrates in the progression of NEC, intestinal ischemia is associated with a shift from
• NO to O2
• – production, which is NOS-dependent. Potentially greater injury results from impaired vasodilatation and over-production of reactive oxygen species.