3 mongrel dogs (weight 21.3±1.5 kg) were anesthetized with 25 mk/kg pentobarbital i.v. and instrumented with femoral arterial and venous catheters. Anesthesia was maintained with additional pentobarbital (5 mg/kg iv every hour and when indicated) and muscle relaxation provided by pancuronium (3 mg bolus and 0.5 mg hourly iv). A 39 or 41 french double-lumen endobronchial tube was placed via a tracheostomy and position confirmed by fiberoptic bronchoscopy. The animals were ventilated with a “dual piston” large animal ventilator, permitting independent control of tidal volume (Vt), inspired oxygen fraction (FiO2), and positive end-expiratory pressure (PEEP), and measurement of airway opening pressure (Paw) and end-tidal partial pressure of carbon dioxide (ETPCO2) for each lung. Oxygen saturation (SaO2) was continuously measured using a pulse oximeter applied to the tongue or ear and ETPCO2, arterial blood pressure (Pa), Paw, and esophageal pressure (Pes) were continuously recorded. An infusion of lactated ringers (LR, 5-10 ml/kg/hr) was given for maintenance fluid replacement. Rectal or PA temperature was maintained at 36±1?C with radiant heat lamps. At the conclusion of the study, the animals were sacrificed by exsanguination after supplemental pentobarbital (10 mg/kg i.v.). After instrumentation, the individual lung Vt !Sample_description =were adjusted to provide an ETPCO2 of 30-35 mmHg at a respiratory rate of 25 breaths/min. The left lung was then mildly injured by repeated lavage with warmed saline, 20 ml/kg repeated 4 times. Ventilation continued at baseline settings, with the addition of 5 cm H2O PEEP to the control right lung, for 5 hours. At that time the animal was sacrificed by exsanguination, the chest opened, and 10 tissue samples taken from 5 corresponding regions in both lungs (apex- dependent and non-dependent, base- non dependent, mid, and dependent). The lung tissue samples were immersed in RNAlater (Ambion, Austin, Texas) and frozen for subsequent analysis. In some animals, additional tissue samples were taken and stored in 10% formalin for immunohistochemistry. Sample_hybridization: total RNA was converted to first-strand cDNA using a hybrid reverse transcription primer consisting of oligo-dT and T7 RNA polymerase promoter sequences. The single-stranded cDNA was then converted to double-stranded cDNA. Complementary DNA corresponding to 5-10 µg of total RNA was used in a cRNA amplification step using T7 RNA polymerase and two biotinylated nucleotide precursors. The resulting biotinylated cRNA was fragmented to a size of approximately 50 bp, and approximately 20-30 µg of the biotinylated cRNA was hybridized to the Human HG_U133A GeneChip (Affymetrix, Santa Clara, CA). The bound cRNA was visualized by binding of streptavidin/phycoerythrin conjugates to the hybridized GeneChip, followed by laser scanning of bound phycoerythrin. Sample_RNA_Isolation: Tissues (~50 mg) were taken frozen and directly solubilized in chaotropic solubilization buffer using a Brinkman Polytron tissue disruptor. Larger tissue fragments (>100mg) were pulverized into frozen powder with a mortar and pestle, pre-chilled to liquid nitrogen temperature, and then the frozen powder was solubilized with the Polytron. RNA was purified using Trizol LS (Life Technologies) and an additional RNA purification step was conducted using the RNAeasy purification kit (Qiagen Inc., Valencia, CA). Approximately 10 µg of purified, total RNA was used for analyses. Sample_strain: Mongrel Keywords = unilateral canine lung injury model, microarray, gene expression, mechanical ventilation
