Effects of hyperbaric oxygen exposure on a zymosan-induced shock model

Objective: To evaluate the effects of hyperbaric oxygen (HBO) therapy on zy mosan induced shock in rats. Zymosan, a cell wall component of the yeast Sa ccharomyces cerevisiae, induces inflammation by causing the production of v arious cytokines and pro-inflammatory mediators. The administration of zymo san to rats represents a new experimental shock model by inducing acute per itonitis, severe hypotension, and signs of systemic illness. However, it ha s been recently proposed that the zymosan induced shock, like septic shock, may be mediated by overproduction of nitric oxide. Design: Experimental study. Setting: Institute of Pharmacology and Toxicology, 2(nd) University of Napl es, Naples, Italy. Subjects: Male rats were treated with zymosan (500 mg/kg) by intraperitonea l route, with HBO (2 Absolute Atmosphere) or with zymosan and HBO (2 Absolu te Atmosphere). Measurements and Main Results: Peritoneal exudate, plasma, and peritoneal n itric oxide metabolites (NOx) and zymosan determined a time dependent incre ase in peritoneal and plasma NOx concentrations, and peritoneal leukocytes were determined. More over, 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 a n acute peritonitis, producing turbid exudate. Zymosan determined a time de pendent increase in peritoneal, plasma NOx, and tumor necrosis factor (TNF) -alpha concentrations. Morbidity of zymosan shocked rats has been attenuate d 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 a leve ls were significantly reduced in animals shocked by zymosan and treated wit h HBO. Conclusions: Our findings suggest that HBO may also be an efficacious treat ment in zymosan-induced experimental shock model.