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

OBJECTIVE: To observe the influence of mechanical ventilation (MV) on rat's lung and the expression changes of lung endotoxin receptor CD14 mRNA. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.