Role of inducible nitric oxide synthase in leukocyte extravasation in vivo

Several recent studies have suggested that nitric oxide (NO) derived from the inducible isoform of NO synthase (NOS) may act as an endogenous modulator of the inflammatory response by inhibiting adhesion of leukocytes to endothelial cells in vitro. Few studies have addressed specifically the role of iNOS in regulating leukocyte recruitment in vivo in a model of acute inflammation. Thus, the objective of this study was to assess the role of iNOS in modulating neutrophil (PMN) extravasation in an oyster glycogen-induced model of acute peritonitis in rats. Data obtained in the present study demonstrates that injection (IP) of oyster glycogen induces massive and selective PMN recruitment into the peritoneal cavity of rats at 6 hrs following OG administration. These extravasated cells were found to contain significant amounts of iNOS protein as assessed by Western blot analysis. Treatment of rats with the selective iNOS inhibitor L-iminoethyl-lysine (L-NIL) dramatically reduced NO levels in lavage fluid as measured by de. creases in nitrate and nitrite concentrations without significantly affecting iNOS protein levels. Although L-NIL inhibited NO production by >70%, it did not alter oyster glycogen-induced PMN recruitment when compared to vehicle-treated rats. We conclude that PMN-associated, iNOS-derived NO does not play an important role in modulating extravasation of these leukocytes in this model of acute inflammation. (C) 1999 Academic Press.