Influence of various ventilation manier on rat's lung and the expression of lung endotoxin receptor CD14 mRNA

Abstract

To observe the influence of mechanical ventilation (MV) on rat's lung and the expression changes of lung endotoxin receptor CD14 mRNA. Forty-eight male SD rats weighing 330-360 g were randomly divided into 4 groups (n = 12 each): group R received no mechanical ventilation, group P received small MV (VT = 6 ml/kg, PEEP = 8 mm Hg), group M received conventional MV (VT = 12 ml/kg, PEEP = 0 mm Hg), and group N received large tidal volume mechanical ventilation (VT = 40 ml/kg, PEEP = 0 mm Hg). The animals were anesthetized with intraperitoneal pentobarbital 100 mg x kg(-1), tracheotomized and mechanically ventilated (I:E = 1:1, FiO2 = 21%). The respiratory rate (RR) of MV was adjusted to maintain the end-tidal carbon dioxide in the rang of 35-45 mm Hg throughout the procedure. Right carotid artery and left femoral vein were cannulated for BP monitoring and fluid and drug administration. 6 rats in each group were injected 50 mg/kg Evans Blue (EB). The experiment was culminated in 3 hours, then the rats were killed by exsanguination via arteria carotis interna. Morphologic change scores of the rats' lungs, wet/dry weight ratio of lung tissue (W/D), bronchial lavage fluid (BALF) inflammatory cell population, and permeability of vessel wall were evaluated. The concentration of TNF-alpha and MIP-2 in the plasma were determined by enzyme immunoassay method (ELISA). The expressions of lung tissue endotoxin receptor CD14 were detected by RT-PCR, macrophage CD14 in BALF was also detected by immunohistochemistry. pulmonary pathomorphology scores: there were no alteration in R group and P group, but it were slightly increased in M group, there was significantly elevated in N group as compare to M group (F = 8.0, P = 0.000). Pulmonary tissue wet/dry weight ratio (W/D): Compare with R group, There was no statistically significant difference in P group and M group; the elevation in N group (t = 4.103, P = 0.02), EB: Compare with R group, There was no statistically significant difference in P group and M group; the obviously elevation in N group (t = 36.634, P = 0.000). WBC in BALF: Compare with R group, there was no change in P group, the elevation in M group (t = 4.272, P = 0.02), there was significantly elevated in N group (F = 26.68, P = 0.000). TNF-alpha had no manifest variation in 4 groups. MIP-2: compare with R group (31.5 +/- 2.4), There was no statistically significant difference in P group (35.4 +/- 5.3), the elevation in M group (44.7 +/- 6.9, t = 7.85, P = 0.04), there was significantly elevated in N group (167.7 +/- 11.8, t = 27.779, P = 0.000). The expressions of macrophage CD14 protein in BALF and lung tissue CD14 mRNA were fundamentally coincident in R group and P group; the expressions of CD14 mRNA were elevated, but the expressions of CD14 protein were no change in M group; the expressions of CD14 in N group manifestly elevated (P = 0.000). Conventional MV induces minor injury in rat's lung and can up regulate the expression of CD14 mRNA in the lung, but not up regulate the expression of CD14 protein; large tidal volume MV induces injury of rat's lung and evidently up regulates CD14 expression in the lung. Protective MV can avoid the above mentioned variations in rat's lung.