Background. Endotoxin modulates esophageal motor function by increasing nitric oxide (NO) production. The aims of this study were to examine inducible nitric oxide synthase (iNOS) induction in the lower esophageal sphincter (LES) of endotoxemic opossums and to investigate the effects of aminoguanidine (AG), a selective inhibitor of iNOS, on plasma nitrite/nitrate levels and on iNOS protein and mRNA expression after exposure to lipopolysaccharide (LPS). Methods. Before and 12h after the intravenous administration of LPS and/or AG, plasma nitrite/nitrate levels were determined. The iNOS protein and mRNA expression were investigated in the tissues taken from the LES by Western blot and reverse-transcriptase polymerase chain reaction (RT-PCR). Results. Plasma nitrite/nitrate levels were significantly increased by LPS. The increase in plasma nitrite/nitrate produced by LPS was significantly decreased by AG. Western blot and RT-PCR demonstrated that iNOS expression was markedly increased by LPS, and attenuated slightly by AG. Conclusions. These studies support the hypothesis that endotoxin increases NO production by the induction of iNOS protein and mRNA.
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