OBJECTIVE: METHODS: Thirty guinea pigs (1.5 months old and weighed 200 - 225 g) were sensitized by exposure to aerosolized ovalbumin and challenged with the same antigen to establish asthma model. These animals were divided randomly into dexamethasone-treatment group and non- dexamethasone-treatment group (15 guinea pigs in each group). Normal control group animals (n = 15) were treated with normal saline (NS) instead of aerosolized ovalbumin. The guinea pigs in the dexamethasone-treatment group were treated with dexamethasone (5.0 mg/kg, intraperitoneal injection) one day before asthma-inducement, on the day of inducement and 24 h after inducement. The non- dexamethasone-treatment group animals were treated with NS (5.0 mg/kg, intraperitoneal injection) on the same days as the dexamethasone-treatment group was treated. The normal control group animals were treated with NS (5.0 mg/kg, intraperitoneal injection). The contents of NKA in the plasma and lung tissues were detected by ELISA; the expression of NKA mRNA in lung tissues was examined by RT-PCR. RESULTS: (1) The contents of NKA in the plasma (2.20 +/- 0.46 ng/ml), lung tissues (5.02 +/- 2.11 ng/g x protein) and the NKA mRNA expression in the lung tissues (1.10 +/- 0.06) of guinea pigs with induced asthma were significantly higher than those of the normal control group (plasma 0.84 +/- 0.33 ng/ml, lung tissues 2.56 +/- 0.80 ng/g x protein, mRNA 0.30 +/- 0.04; P < 0.001, respectively). (2) The contents of NKA in the plasma, lung tissues and the NKA mRNA expression in the lung tissues of guinea pigs with induced asthma were significantly lower in dexamethasone-treatment group (plasma 0.98 +/- 0.23 ng/ml, lung tissues 2.71 +/- 0.50 ng/g x protein, mRNA 0.35 +/- 0.07) than those in the non- dexamethasone-treatment group (plasma 2.20 +/- 0.46 ng/ml, lung tissues 5.02 +/- 2.11 ng/g x protein, mRNA 1.10 +/- 0.06; P < 0.001, respectively). No significant difference was found between the dexamethasone-treatment group and the normal control group (P > 0.05, respectively). CONCLUSIONS: (1) NKA mRNA expression in the lungs of guinea pigs with asthma was up-regulated and NKA contents were higher in plasma and lungs; (2) Glucocorticoid could significantly decrease the contents of NKA in plasma, lung tissues of guinea pigs with induced asthma; the mechanism of the effect may be related to down-regulation of NKA mRNA expression in lung tissues caused by glucocorticoid.
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