Effect Of High Tidal Volume Ventilation And Lipopolysaccharide On Mitogen-activated Protein Kinase Pathway In Rat Lung Tissue

PartⅠ Time course of the activation of mitogen-activated protein kinase in rat lung tissue after high tidal volume ventilationObjective: To investigate the time course of the activation of mitogen-activated protein kinase (MAPK) in rat lung tissue after high tidal volume ventilation. Methods: Eighteen Sprague-Dawley rats were divided into six groups (n=3): control group and 15min, 30min, 45min, 60min and 120min (after high tidal volume ventilation) group. Rats were mechanically ventilated with volume controlled ventilation (tidal volume 25ml/kg, positive end-expiratory pressure 3cmH2O, inspiratory-expiratory ratio 1:2, ventilatory frequency 20 breaths/min, and 100% oxygen). The phosphorylated MAPK [extracellular signal-regulated kinase (ERK), p38 and c-jun N-terminal kinase (JNK)] in rat lung tissues were assessed by Western immunoblot. Results: The expression of phospho-ERK1/2 of lung tissue was higher in 30min group (331.5±25.8) than thoses in control and 15min group (69.8±1.1 and 94.2±3.1, all P(0.05). The expression of phospho-ERK1/2 in 45min, 60min and 120min group decreased gradually, but the expression was still higher in 120min group (149.4±31.4) than those in control and 15min group (P(0.05). In addition, the expression of phospho-p38 in lung tissue was higher in 15min group (83±10) when compared to the control group (51±4, P(0.05), and the peak expression was at 30min (107±6). The expression of phospho-p38 in 45min, 60min and 120min group decreased gradually, and returned to the control group level at 60min and 120min(62±6 and 65±8). Moreover, JNK in lung tissue of all groups was not activated. Conclusions: High tidal volume ventilation may contribute to the time-dependent activation of ERK1/2 and p38 in lung tissue.PartⅡ Activation of mitogen-activated protein kinase inrat lung tissue after high tidal volume ventilation androle of lipopolysaccharide in high-sensitivityObjective: To investigate the activation of mitogen-activated protein kinase (MAPK) in rat lung tissue after high tidal volume ventilation and the role of lipopolysaccharide (LPS) in high-sensitivity. Methods: Fifty-six Sprague-Dawley rats were divided into four groups: (1) High-tidal volume group (HV): tidal volume (VT) 25ml/kg, positive end-expiratory pressure (PEEP) 3cmH2O, ventilatory frequency (f) 20 breaths/min, inspiratory -expiratory ratio (I:E) 1:2, and 100% oxygen. (2) Normal tidal volume group (LV): VT 8ml/kg, PEEP 3cmH2O, f 50 breaths/min, I:E 1:2, and 100% oxygen. (3) High -tidal volume + LPS group (HVL): The animals received 6mg/kg LPS administered intravenously before mechanical ventilation, and ventilated with the same mode as HV group. (4) Normal tidal volume + LPS group (LVL): The animals received 6mg/kg LPS administered intravenously before mechanical ventilation, and ventilated with the same mode as LV group. Each group was divided into two subgroups: mechanical ventilation for 15min (n=6) and 30min (n=8) subgroup. Protein was extracted from lung tissues for determination of MAPK [extracellular signal-regulated kinase (ERK), p38 and c-jun N-terminal kinase (JNK)] phosphorylation by Western immunoblot analysis. Macrophage inflammatory protein (MIP)-2 and tumor necrosis factor (TNF)-( mRNA expression in lung tissues was detected by reverse transcription polymerase chain reaction (RT-PCR).Results: (1) High tidal volume ventilation may accelerate the activation of ERK1/2 and p38. Expression of phospho-ERK1/2 of lung tissue in HV group of 30min subgroup (221±25) was higher significantly than LV group (135±20, P(0.05). Expression of phospho–p38 of lung tissue in HV group of 30min subgroup was 268±109, which was higher markedly than LV group (182±44, P(0.05). Two groups had the similar results of 15min subgroup (P>0.05). Moreover, JNK in lung tissue of HV and LV group was not activated.(2) LPS could enhance the sensitivity of ERK1/2 and p38 activation induced by high tidal volume ventilation.In LVL group of 15min subgroup, phospho-ERK1/2 e...