In the present study, by comparing the responses in wild-type mice (+/+) and mice lacking (-/-) the inducible (or type 2)
nitric oxide synthase (iNOS), we investigated the role played by iNOS in the development of non-
septic shock. A severe inflammatory response characterized by peritoneal exudation, high peritoneal levels of
nitrate/
nitrite, and leukocyte infiltration into peritoneal exudate was induced by
zymosan administration in iNOS +/+ mice. This inflammatory process coincided with the damage of lung, liver, and small intestine, as assessed by histological examination. Lung, small intestine, and liver
myeloperoxidase (MPO) activity, indicative of neutrophil infiltration and lipid peroxidation, were significantly increased in
zymosan-treated iNOS +/+ mice. Peritoneal administration of
zymosan in the iNOS +/+ mice induced also a significant increase in the plasma levels of
nitrite/
nitrate and in the levels of
peroxynitrite at 18 h after
zymosan challenge. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to
nitrotyrosine and to
poly ADP-ribose synthetase (PARS) in the lung, liver, and intestine of
zymosan-treated iNOS +/+ mice. The intensity and degree of
nitrotyrosine and PARS were markedly reduced in tissue section from
zymosan-iNOS -/- mice.
Zymosan-treated iNOS -/- mice showed a significantly decreased mortality and inhibition of the development of
peritonitis. In addition, iNOS -/- mice showed a significant protection on the development of organ failure since tissue injury and MPO were reduced in lung, small intestine, and liver. Furthermore, a significant reduction of suppression of mitochondrial respiration,
DNA strand breakage, and reduction of cellular levels of NAD+ was observed in ex vivo macrophages harvested from the peritoneal cavity of iNOS -/- mice subjected to
zymosan-induced non-
septic shock. In vivo treatment with
aminoguanidine (300 mg/kg 1 and 6 h after
zymosan administration) significantly prevents the inflammatory process. Taken together, our results clearly demonstrate that iNOS plays an important role in
zymosan-induced non-
septic shock.