Nitric oxide synthase-independent pathway(s) of nitric oxide formation after intestinal ischaemia–reperfusion

Abstract

Abstract Background Recent evidence suggests that nitric oxide produced in the gastrointestinal tract, in concert with other vasoactive mediators, plays an essential role in the regulation of splanchnic circulation. Methods To determine the sites and pathways of nitric oxide formation, electron paramagnetic resonance spectroscopy and the nitric oxide trap diethyldithiocarbamate-Fe were used to detect directly nitric oxide formed in intestine, liver and lungs of rats subjected to local intestinal ischaemia–reperfusion (I/R), in the presence or absence of nitric oxide donors or inhibitors. In addition, the role of nitric oxide in control of the gastrointestinal circulation was determined by means of a coloured microsphere technique employing N-(G)-Monomethyl-L-arginine (L-NMMA) in rats subjected to haemorrhagic shock followed by resuscitation. Results In contrast to remote organs lung and liver (no change), intestinal I/R resulted in an increase in nitric oxide formation in intestinal tissues. Administration of the non-specific nitric oxide inhibitor L-NMMA caused a decrease in I/R-independent basal nitric oxide levels in lung and liver but did not influence the I/R-induced increase in nitric oxide formation in intestinal tissues. In support of this, reverse transcriptase–polymerase chain reaction analyses showed inducible nitric oxide synthase (NOS) expression in the lung but not in intestinal tissues. In the microsphere experiment, a moderate and therapeutic dose of L-NMMA administered after the completion of resuscitation, which improved haemodynamic conditions and outcome, did not alter the intestinal circulation. Conclusion The data suggest that the early-phase I/R-induced nitric oxide formation in ischaemic intestinal tissue is probably NOS independent, while nitric oxide formation in normoxic remote tissues is partially NOS dependent. In addition, the authors' nitric oxide-related therapeutic approaches reveal that only the regulation of nitric oxide (e.g. nitric oxide supplementation during resuscitation or reperfusion and/or nitric oxide inhibition or modulation after resuscitation) may protect against hypovolaemic insults.