Spleen damage in endotoxaemic mice: The involvement of nitric oxide

either nitric oxide synthase inhibitor, L-N G -nitroarginine methyl ester (L-NAME, 20 mg kg -1 , i.p.) or inducible nitric oxide synthase expression inhibitor, dexamethasone (5 mg kg -1 , i.p.) or the inhibitor of murine inducible nitric oxide synthase in vivo, 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT, 1 mg kg -1 , i.p.). 5 h after endotoxin treatment, electrochemically detected concentration of nitric oxide was significantly elevated (nM, endotoxin: 716.6 ± 178.2 ,n=1 0vs saline: 209.4 ± 127.8 ,n=9 , P= 0.0312, unpaired Student’s t-test) and remained so throughout the 30 min monitorization period. Neither dexamethasone nor AMT blocked the endotoxin-induced overproduction of nitric oxide indicating that the enhanced inducible nitric oxide synthase activity cannot be the only explanation. When dexamethasone and L-NAME combination was used to block both the constitutive and the inducible isoforms, nitric oxide production was virtually abolished, indicating a significant contribution from the constituve isoform of nitric oxide synthase. The results of nitrotyrosine immunohistochemistry and the conventional light microscopy were also in agreement with the amperometric method while immunoblotting revealed the expression of both the endothelial and the inducible isoforms of nitric oxide synthase were induced in endotoxaemic animals. Thus, we conclude that endotoxin-induced splenic damage in endotoxaemia can be explained by enhanced production of nitric oxide due to the induction of both endothelial and inducible nitric oxide synthases while causal relationship and the roles of other deleterious mediators such as oxygen-derived free radicals are yet to be established.