The Effect of Dexamethasone on Gene Expression and Total Amount of Surfactant Protein A

Background Surfactant protein A (SP-A) is importanpt for regulating surfactant secretion, synthesis and recycling. However, It's regulation in vivo is unclear. SP-A has important roles in regulating surfactant met abolism as well as determining its physical properties. Glucocorticoid accelerates the morphologic differentiation of epithelial cells into type II cells and increase the rate of phosphatidylcholine synthesis. Methods The authors investigated the effects of glucocorticoid on the accumulation of mRAN encoding SPA and SP-A protein content. A dult rats were given various doses of subcutaneous dexamethasone and sacrificed after 24 hours and one week. SP-A mRNA was measured using a filter hybridization method. The lung SP-A protein content was determined using a double sandwich ELISA assay with polyclonal antiserum raised in rabbits against purified rat SP-A. Results 1) The accumulation of SP-A mRNA in the dexamethasone treated group 24 hours after 0.2 mg/kg dexamethasone treatment was increased 38.8% compared to the control group. 2) The accumulation of SP-A mRNA in the dexamethasone treated group 1 week after 2 mg/kg dexamethasone treatment was 49.7% higher than the control group(P<0.01). 3)The total lung SP-A level was not altered after 24 hours by the 0.2 mg/kg treatment. The total lung SP-A content one week after 2 mg/kg dexamethasone administration was 373.7% higher than the control group(P<0.005). Conclusions Dexamethasone treatment results in an increase in the SP-A mRNA and SP-A protein levels, suggesting that the pretranslational events in vivo may in part contribute to this process.