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

Objective: To 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. Design: Experimental study. Setting: Institute of Pharmacology and Toxicology, 2(nd) University of Naples, Naples, Italy. Subjects: Male 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 Results: Peritoneal 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. 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 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 a levels were significantly reduced in animals shocked by zymosan and treated with HBO. Conclusions: Our findings suggest that HBO may also be an efficacious treatment in zymosan-induced experimental shock model.