Role of nitric oxide in intestinal ischaemia-reperfusion injury studied using electron paramagnetic resonance

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Abstract
Background: The role of nitric oxide in intestinal ischaemia–reperfusion (I/R) remains poorly defined, partly because of difficulty in detecting the nitric oxide free radical. In this study nitric oxide production was assessed during intestinal I/R by direct measurement using electron paramagnetic resonance (EPR), and the production of nitric oxide in jejunum and ileum was correlated with their different abilities to resist I/R injury. Methods: Rats were given an electron spin trapper (diethyldithiocarbamate/ferrous citrate) by intraperitoneal injection. Thirty-six segments each of jejunum and ileum were subjected to 15–90 min of ischaemia and 25 min of reperfusion. Tissue samples were analysed for EPR signals using a spectrometer. Results: Mean(s.d.) basal nitric oxide level was significantly higher in ileum (3·39(1·42) units) than jejunum (0·65(0·05) units) (P = 0·0005). Increasing ischaemic times in the ileum resulted in decreasing nitric oxide levels (85, 32 and 13 per cent of basal level at 30, 60 and 90 min respectively); reperfusion resulted in further nitric oxide reduction (mean decrease 26 per cent). Severe (grade 3) histological damage was observed in low nitric oxide states (after 15 min of I/R in jejunum, 60 min of I/R in ileum). Conclusion: Nitric oxide can be measured in intestinal tissues directly by EPR. The findings support a protective role for nitric oxide in I/R, and offer an explanation for the greater resistance to I/R of ileum.