LPS-induced muscularis macrophage nitric oxide suppresses rat jejunal circular muscle activity

Cellular mechanisms of sepsis-induced ileus remain an enigma. The study aim was to determine the role of nitric oxide (NO) in mediating the suppressio n of rat jejunal circular smooth muscle activity during endotoxemia. Isolat ed muscularis inducible NO synthase (iNOS) mRNA was measured by RT-PCR, imm unohistochemistry was employed to localize iNOS protein, and contractile ac tivity was measured in an organ bath. The low basal expression of musculari s iNOS mRNA expression was increased in a time-dependent fashion after lipo polysaccharide (LPS), resulting in a 20-fold increase over controls 3 h aft er injection. Immunohistochemistry of muscularis whole mounts and dissociat ed muscularis cells for iNOS revealed staining only in the muscularis macro phages 12 h after LPS. LPS caused a 68% reduction in spontaneous muscle act ivity 12 h after injection, which improved by 53% after the in vitro applic ation of the selective iNOS inhibitor L-N-6-(1-iminoethyl)lysine. Similar r esults were obtained in C57BL/6 mice but not in iNOS knockout mice. These d ata demonstrate that macrophage iNOS plays an important role in mediating L PS-induced intestinal circular muscle suppression.