Abstract： Objective To investigate the effect of platelet-activating factor(PAF)on the production of Src-suppressed C kinase substrate(SSeCKS)mRNA in rat pulmonary microvascular endothelial cell (RPMVEC)and its signal transduction pathways.Methods Cellular in situ hybridization was performed to reveal changes in SSeCKS mRNA expression in the cultured RPMVECs after giving PAF stimulation.Results Normal RPMVECs expressed SSeCKS mRNA at a low level,which appeared throughout the cytoplasm with specific hybridization signals.1.5 hours of 10~(-10),10~(-9),10~(-8),10~(-7) mol/L PAF incubation induced a progressive increase in SSeCKS mRNA expression.When compared to the normal control group each difference had statistical significance(0.054 9±0.000 7,0.059 9±0.001 8,0.069 0±0.001 8,0.075 4±0.001 9 vs.0.036 8±0.003 7,respectively,all P＜0.05).Within 0.5,1.5,3,6,12,24 hours of 10~(-7) mol/L PAF challenge,the level of SSeCKS mRNA expression raised at 0.5 hour markedly (0.071 0±0.001 5),peaked at 1.5 hours(0.075 6±0.001 7),then began to decline gradually,and still persisted at a higher level than the normal control group until 24 hours(0.043 9±0.001 0 vs.0.038 2±0.004 1,all P ＜ 0.05).Pre-incubation of 10 μmol/L pyrrolidine dithiocarbamate(PDTC)that inhibits activity of nuclear factor-κB(NF-κB)in RPMVECs caused a conspicuous attenuation of PAF-induced SSeCKS mRNA expression(0.049 7±0.003 2 vs.0.071 9±0.001 9,P＜0.05),whereas no change of PAF-induced effect was found by pretreatment of protein kinase C(PKC)inhibitor bis-indolylmaleimide (BIM,0.069 7±0.002 1 vs.0.071 9±0.001 9,P＞0.05).Conclusion PAF can up regulate the expression of SSeCKS mRNA in a dose-and time-dependent manner in RPMVECs.It is NF-κB rather than PKC signal pathway that is involved in modulation of the intracellular signaling process.