Prostacyclin prevents pulmonary
vascular injury and
shock by inhibiting increases in lung tissue levels of TNF in rats administered
endotoxin. We previously reported that NO derived from eNOS increases endothelial production of
prostacyclin. Because
neutrophil elastase has been shown to decrease endothelial production of
prostacyclin by inhibiting NOS activity, we examined whether
neutrophil elastase inhibitors reduce pulmonary
vascular injury and
hypotension by inhibiting the decrease in pulmonary endothelial production of
prostacyclin in rats administered
endotoxin. Animals were pretreated with
sivelestat or
L-658,758,
neutrophil elastase inhibitors, before
endotoxin administration. Lung tissue levels of 6-keto-prostaglandin F1alpha were markedly increased after
endotoxin administration, followed by a rapid decrease to baseline levels.
Sivelestat and
L-658,758 inhibited these decreases as well as inhibiting increases in lung tissue levels of TNF and
lung wet-to-dry weight ratios in animals administered
endotoxin. These inhibitors also reduced
hypotension and inhibited increases in lung tissue levels of
mRNA of the inducible form of NOS in animals administered
endotoxin. The effects of
neutrophil elastase inhibitors were completely reversed by pretreatment with nitro-
L-arginine methyl ester, an inhibitor of NOS, or
indomethacin, a nonspecific
cyclooxygenase inhibitor. These observations suggested that
neutrophil elastase might decrease the pulmonary endothelial production of
prostacyclin by inhibiting endothelial NO production, thereby contributing to the development of pulmonary
vascular injury and
shock through increases in lung tissue levels of TNF in rats administered
endotoxin.