Zymosan induces nitric oxide production by peritoneal mesothelial cells

Introduction: The production of nitric oxide is an important peritoneal defense mechanism. We have evaluated the effect of various putative stimulants on nitric oxide production by peritoneal mesothelial cells. Methods: Wistar rats were randomized to either a control group or a peritonitis group (5 mg zymosan intraperitoneally). Groups of five animals were sacrificed at 4, 18, 24, 48 and 96 h after the induction of peritonitis and their peritoneal fluid was harvested for assay. Cultures of peritoneal mesothelial cells were stimulated with lipopolysaccharide, myeloperoxidase, TNFα, zymosan, peritoneal fluid from a control animal and peritoneal fluid from a peritonitis animal. Supernatants were collected after incubation for 4, 24 and 48 h for assay. The assay for nitric oxide was based upon the nitrite content of the samples. Results: The intraperitoneal administration of zymosan was associated with an increased production of nitric oxide (NO) when compared with control animals (P < 0.01). In cultures of peritoneal mesothelial cells, zymosan, but not the other putative stimulants, was associated with a marked output of nitric oxide (P < 0.001). Conclusion: Zymosan has a direct effect on peritoneal mesothelial cells, which are able to generate nitric oxide in the absence of co‐stimulatory molecules. This suggests that it may be possible to use some form of external stimulation to up‐regulate the NO response by peritoneal mesothelial cells.