BACKGROUND: The signal pathways and their precise roles for acute respiratory distress syndrome caused by endotoxin (ETX) has not been established. Since there has been several in vitro experiments suggesting that activation of protein kinase C (PKC) pathway may be responsible for endotoxin-induced inflammatory reaction, we performed in vivo experiments in the rats with the hypothesis that PKC-inhibition can effectively prevent endotoxin-induced acute lung injury. METHODS: We studied the role of PKC in ETX-induced ALl using PKC inhibitor (staurosporine, 5Th) in the rat. Specific pathogen free male Sprague-Dawley weighted from 165 to 270g were used for the study. Animals were divided into the normal control (NC)-, vehicle control (VC)-, ETX-, PMA (phorbolmyristateacetate)-, STP+PMA-, and STP+ETX-group. PMA (50mg/kg) or ETX (7mg/kg) was instilled through polyethylen catheter after aseptic tracheostomy with and without STP (0.2mg/kg) pretreatment. STP was injected via tail vein 30mm before intratracheal injection (IT) of PMA or ETX. Bronchoalveolar lavage (BAL) was done 3- or 6-hrs after IT of PMA or FTX respectively, to measure protein concentration, total and differential cell counts. RESULTS The results were as follows. The protein concentrations in BALF in the PMA- and ETX-group were very higher than that of VC-group (p<0.001). When animals were pretreated with STP, the %reduction of the protein concentration in BALF was 64.8 8.5 and 30.4 2.5% in the STP+PMA- and STP+ETX-group, respectively (p=0.028). There was no difference in the total cell counts between the PMA-and VC-group (p = 0.26). However the ETX-group showed markedly increased total cell counts as compared to the VC- (p=0.003) and PMA group (p=0.0027), respectively. The total cell counts in BALF were not changed after pretreatment with STP compared to the PMA- (p=0.22) and ETX-group (p=0.46). The percentage of PMN, but not alveolar macrophage, was significantly elevated in the PMA-, and ETX-group. Especially in the ETX-group, the percentage of PMN was 17 times higher than that of PMA (p<0.001). The differential cell counts was not different between the PMA and STP+PMA. On the contrary the STP+ETX-group showed decreased percentage of PMN (p = 0.016). There was no significant relationship between the protein concentration and the total or differential cell counts in each group. CONCLUSION: Pretreatment with PKC-inhibitor (staurosporine) partially but significantly inhibited ETX-in-duced ALI.