Changes in distribution of three isoforms of nitric oxide synthase in ulcerative colitis

Background: Nitric oxide (NO) has an important role both in normal physiolo gy and pathological events of the colon. Our aim was to study possible chan ges of the three nitric oxide synthases in ulcerative colitis (UC). Methods : Tissue samples from normal colon and least and moderately affected region s of ulcerative colitis colon were obtained at surgery and immunostained fo r NOS-1, NOS-2, NOS-3, and GAP-43, a marker of nerve fibers. Quantitative a nalysis of NOS-1 immunoreactivity was performed on the circular muscle laye r. Results: NOS-1-immunoreactive fibers in the muscularis mucosae disappear ed in least affected and moderately affected UC colon. Quantitative analysi s of NOS-1-immunoreactive nerve fibers in the circular muscle showed no dif ferences between normal and diseased colon. NOS-2 immunoreactivity appeared apically in the epithelial cells. In normal colon some specimens showed im munoreactivity in lower parts of crypts. NOS-2 immunoreactivity increased a ccording to the severity of UC. NOS-3 immunoreactivity was exclusively loca lized in the vascular endothelium. The difference in NOS-3 staining intensi ty between the lamina propria and submucosa observed in normal tissue disap peared in moderately affected UC colon. The number of NOS-3-immunoreactive vascular profiles increased in the lamina propria of UC colon. Conclusions: All three NOS isoforms show specific changes in UC colon.