Effects of minute quantity of endogenous endotoxin from the lung on ventilator-induced lung injury in rats

Abstract

Objective To investigate the effects of minute quantity of endogenous endotoxin originating from the lung on ventilator-induced lung injury in rats. Methods Thirty-two pathogen-free male adult SD rats weighing 370-390 g were randomly divided into 4 groups ( n = 8 each): group I spontaneous breathing (group C) ; group Ⅱ spontaneous breathing + IPS (group CL) ; group IE mechanical ventilation (group M) and group IV mechanical ventilation + LPS (group ML). The animals were anesthetized with intraperitoneal 20% urethane 0.8 ml/100 g. Right common carotid artery and left femoral vein were cannulated for BP monitoring and fluid and drug administration. The animals were tracheostomized. In group CL and ML LPS 100μg /kg was instilled into trachea. In group M and ML the animals were mechanically ventilated (V_T 20 ml/kg, PEEP=0, I = E = 1:1). P_(ET) CO_2 was maintained at 35-45 nun Hg by adjusting respiratory rate. The animals were breathing or ventilated with room air,and ECG, BP, HR and P_(ET)CO_2 were continuously monitored. Blood gases were analyzed at the beginning and 1, 2 and 3 h of experiment. The animals were sacrificed at 3 h of experiment. The lungs were removed for microscopic examination. The pathological changes of the lung were scored (0 = normal,3 = severe change) . Wet/dry lung weight ratio was determined. The left lung was lavaged. The broncho-alveolar lavage fluid (BALF) was collected. WBCs in BALF were counted. Pulmonary albumin permeability (PAP) (BALF protein concentration/plasma protein concentration) was determined. Plasma TNF-a and macrophage inflammatory protein 2 (MIP-2) concentrations were detected with ELISA. The endotoxin receptor CD14 mRNA expression in lung tissue was determined by RT-PCR and the macrophage CD14 expression in BALF was determined by immuno histochemistry in group C and M. Results Wet/dry lung weight ratio and PAP were significantly higher in group ML than in group M and C. WBC count in BALF, the pathological score and plasma MIP-2 concentration were significantly higher in group M and ML than in group C and were significantly higher in group ML than in group M. TNF-a concentration was significantly higher in group CL and ML and was not detected in group C and M. CD14mRNA expression in the lung tissue and CD14 expression in BALF macrophage were significantly higher in group M than in group C. Conclusion Minute amount of endogenous endotoxin from the lung can aggravate ventilator-induced lung injury in rats. Mechanical ventilation with large tidal volume sensitizes the lung to LPS stimulation through up-regulation of CD14 exexpression. Key words: Endotoxins; Respiration, artificial; Respiratory distress syndrome, adult