Presence of nitrotyrosine with minimal inducible nitric oxide synthase induction in lipopolysaccharide-treated pigs

The production of large amounts of nitric oxide (NO) by the inducible form of nitric oxide synthase (iNOS) and the subsequent production of peroxynitr ite (OONO-) are believed to be major factors in the hemodynamic abnormaliti es of sepsis. This finding is based on data from rats and mice but has not been established in other species. Therefore, we examined the role of iNOS in lipopolysaccharide (LPS)-treated pigs, which have a hemodynamic pattern with sepsis that is more similar to humans than rats. Pigs were anesthetize d, ventilated, and given LPS (n = 12), 20 mug/kg over 2 h, or saline (n = 7 ). They were killed after 2 (n = 8 LPS, 7 control) or 4 h (4 LPS). We measu red cardiac output (CO), mean arterial (Part), and pulmonary and central ve nous pressures. We evaluated NO production by measuring expired NO, and pla sma nitrate/nitrite concentration, NOS activity (in lung tissue), and iNOS protein by Western analysis, and immunohistochemistry (lung and liver), as well as iNOS mRNA by Northern analysis (liver and lung). We also measured n itrotyrosine as evidence of OONO- production by slot blot, Western analysis , and immunohistochemistry. By 2 h, Part fell and CO did not change so that systemic vascular resistance decreased from 21.5 +/- 2.9 to 12.7 +/- 3.1 m mHg (.) L-1 (.) min (P < 0.05) and remained at 11.3 +/- 1.7 mmHg (.) L-1 (. ) min in the animals observed for 4 h. Plasma nitrate/nitrite, expired NO, and NOS activity did not change. We found no iNOS in tissues by Western ana lysis with 5 different antibodies but detected a small amount of iNOS by im munohistochemistry in inflammatory cells and small vessels. There was a sma ll increase in iNOS mRNA in liver and lung. Despite the minimal increase in iNOS, nitrotyrosine was increased in small vessels and in inflammatory cel ls. In conclusion, caution should be used when extrapolating the septic res ponse in rodents to other species, for the pattern of iNOS induction is ver y different.