Abstract: To investigate the effects of mechanical ventilation on endotoxin receptor CD14 in alveolar macrophages in rats. Methods: Eighteen clean adult male SD rats were respectively dealt with autonomous breathing (A group，n=6), small tidal volume mechanical ventilation (S group, n=6)and large tidal volume mechanical ventilation （L group, n=6）at random. Four hours later, the experiment was terminated and the rats were executed by bloodletting. Then the pulmonary pathomorphology integral, the pulmonary tissue wet/dry weight ratio, WBC in bronchial lavage fluid（BALF）, and the pulmonary albumin permeability （PAP）were determined. The expression of AM endotoxin receptor CD14 mRNA was determined by reverse transcriptionpolymerase chain reaction (RTPCR), of AM CD14 protein by immunohistochemistry. Result： Compared with A group, pulmonary pathomorphology integral, W/D ratio, WBC, PAP, AM CD14 protein expression, and AM CD14 mRNA expression were not significantly changed in the S group（P＞0.05）；but the above values were significantly increased in the L group（P＜0.01). Conclusion: Large tidal volume mechanical ventilation can induce the injury of lungs and upregulate the CD14 expression in alveolar macrophages inrats. Small tidal volume mechanical ventilation can avoide the abovementioned changes.

Key words: Mechanical ventilation, Mechanoreceptors, Endotoxins, Alveolar macrophages