Upregulation of iNOS by COX-2 in muscularis resident macrophage of rat intestine stimulated with LPS

We investigated the effect of lipopolysaccharide (LPS) on the induction of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in musc ularis resident macrophages of rat intestine in situ. When the tissue was i ncubated with LPS for 4 h, mRNA levels of iNOS and COX-2 were increased. Th e majority of iNOS and COX-2 proteins appeared to be localized to the dense network of muscularis resident macrophages immunoreactive to ED2. LPS trea tment also increased the production of nitric oxide (NO), PGE(2), and PGI(2 ). The increased expression of iNOS mRNA by LPS was suppressed by indometha cin but not by N-G-monomethyl-L-arginine (L-NMMA). The increased expression of COX-2 mRNA by LPS was affected neither by indomethacin nor by L-NMMA. M uscle contractility stimulated by 3 muM carbachol was significantly inhibit ed in the LPS-treated muscle, which was restored by treatment of the tissue with L-NMMA, aminoguanidine, indomethacin, or NS-398. Together, these find ings show that LPS increases iNOS expression and stimulates NO production i n muscularis resident macrophages to inhibit smooth muscle contraction. LPS -induced iNOS gene expression may be mediated by autocrine regulation of PG s through the induction of COX-2 gene expression.