ObjectiveTo evaluate the effects of hyperbaric oxygen (HBO) therapy on zymosan-induced shock in rats. Zymosan, a cell wall component of the yeast Saccharomyces cerevisiae, induces inflammation by causing the production of various cytokines and pro-inflammatory mediators. The administration of zymosan to rats represents a new experimental shock model by inducing acute peritonitis, severe hypotension, and signs of systemic illness. However, it has been recently proposed that the zymosan-induced shock, like septic shock, may be mediated by overproduction of nitric oxide.DesignExperimental study.SettingInstitute of Pharmacology and Toxicology, 2ndUniversity of Naples, Naples, Italy.SubjectsMale rats were treated with zymosan (500 mg/kg) by intraperitoneal route, with HBO (2 Absolute Atmosphere) or with zymosan and HBO (2 Absolute Atmosphere).Measurements and Main ResultsPeritoneal exudate, plasma, and peritoneal nitric oxide metabolites (NOx) and zymosan determined a time-dependent increase in peritoneal and plasma NOx concentrations, and peritoneal leukocytes were determined. Moreover, symptomatology was observed.The administration of zymosan caused the appearance of a severe illness in the rats characterized by ruffled fur, lethargy, conjunctivitis, diarrhea, and a significant loss of body weight.All zymosan-treated rats developed an acute peritonitis, producing turbid exudate. Zymosan determined a time-dependent increase in peritoneal, plasma NOx, and tumor necrosis factor (TNF)-alpha concentrations. Morbidity of zymosan shocked rats has been attenuated and no mortality was observed by treatment with HBO. These findings were associated with a significant reduction either of peritoneal leukocytes and exudate, or plasma and peritoneal NOx concentrations. Moreover, TNF-alpha levels were significantly reduced in animals shocked by zymosan and treated with HBO.ConclusionsOur findings suggest that HBO may also be an efficacious treatment in zymosan-induced experimental shock model. (Crit Care Med 1998; 26:1972-1976)