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

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 VR 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 ERR. The findings support a protective role for nitric oxide in I/R, and offer an explanation for the greater resistance to YR of ileum.