Effects Of Ventilation On Lung Tissue Apoptosis In A Rat Model Of Oleic Acid-induced Acute Lung Injury

Objective: To investigate the effect of different tidal volume and positive end expiratory pressure on early apoptosis of lung tissue cells.Methods: Forty healthy male Sprague-Dawley rats were randomly divided into five groups. 1. low tidal volume group (LV, VT 8ml/kg) 2. high tidal volume group (HV, VT 30ml/kg) 3. low tidal volume group and PEEP 2cmH2O (LV2P, VT 8ml/kg,PEEP 2cmH2O ) 4. low tidal volume group and PEEP 5cmH2O (LV5P, VT 8ml/kg,PEEP 5cmH2O) 5. low tidal volume group and PEEP 8cmH2O (LV8P, VT 8ml/kg,PEEP 8cmH2O). After infused by oleic acid (OA, 0.1ml/kg), the rat model of acute lung injury was built. Mechanical ventilation was employed in the experiment groups. Rats were killed after 2 hours ventilation when the serum and the whole lungs were acquired and weighted, to calculate the lung index(LI, wet/body weight×100). The supernatant of BALF was analyzed for TNF-α.The transferase d-UTP end labeling assay (TUNEL) was used to define the extent and distribution of apoptosis in bronchus and lung tissues. The expression of caspase-3 was determined by immunohistochemistry. Results:1 After different tidal volume ventilation, as the increasing of the tidal volume, the lung hyperaemia is more remarkable, the structure is more confused on the pathological section, the inflammatory cell is increasing, the thrombogenesis is find in capillary. With PEEP ventilation, the pathological changes are obviously to lessen.2 The changes of lung index: The lung index is higher in HV group than in LV group(p<0.01). It is higher in LV2P and LV8P than in LV5P group (p < 0.01),but there is no significant difference between LV2P and LV8P groups (p>0.05).3 The changes of TNF-αcontent of serum and BALF:3.1 The changes of TNF-αcontent of serum: The TNF-αcontent of serum is higher in HV group than in LV group(p<0.01). It is higher in LV2P than in LV5P and LV8P group (p<0.01), but there is no significant difference between LV5P and LV8P groups (p>0.05).3.2 The changes of TNF-αcontent of BALF: The TNF-αcontent of BALF is higher in HV group than in LV group(p<0.01). It is higher in LV8P than in LV2P and LV5P group (p<0.01), but there is no significant difference between LV2P and LV5P groups (p>0.05).4 The results of TUNEL assay: As the increasing of the tidal volume, TUNEL assay also exhibited the apoptotic index on both alveolar septum cell and bronchial epithelial cells. After with PEEP ventilation, the apoptotic masccline cells is obviously decrease in LV5P than in LV,LV2P and LV8P group(p<0.01).5 The expression of caspase-3 protein: As the increasing of the tidal volume, caspase-3 protein was strongly expressed in the bronchial epithelial cells. The caspase-3 protein was decreased expressed in LV,LV2P,LV8P groups, the masccline was expressed in the vascular endothelial cells and bronchiole cells. There is on significant difference in the three groups (p>0.05). It is least expressed in LV5P group than in three groups(p<0.01).Conclusions:1 The high tidal volume ventilation exacerbated the lung injury. The low tidal volume and with PEEP ventilation have protective effects.2 The high tidal volume ventilation enhanced the apoptotic index and the expression of caspase-3 protein. But it is obviously decreased in the low tidal volume and with PEEP ventilation.3 The distributions of apoptosis cell and the expression of caspase-3 protein were incomplete identical. We supposed that there have the other apoptotic pathway or controlling genes of the pathogenesis on ventilator-induced lung injury in the model of acute lung injury.