The Impact Of Glucocorticoids On Sprague-Dawley Rats Model Infected With Mycoplasma Pneumoniae

Objective: Mice model infected with Mycoplasma pneumoniae is developed in Sprague-Dawley rats,which simulates human pneumonia infected with M. pneumoniae in order to observe the treatment effect of glucocorticoids on M. pneumoniae pneumonia.This experiment could provide animal model for investigating the pathogenesis and the therapy of M. pneumoniae. Moreover,it provide experimental basis of glucocorticoids used in M. pneumoniae treatment.Methods:(1)Development of Mice model:30 healthy male Sprague-Dawley rats were divided into M. pneumoniae infection group and culture control group at random.Infection group and control group were inoculated with 100μl of 106CFU/ml M. pneumoniae and 100μ1 liquid culture for four days,respectively.Mice were evaluated after 1,3,5,8 and 10 days of inoculation.BAL specimens were determined using real-time PCR,and lung histopathology were assessed by histopathologic score.(2)Treatment effect of glucocorticoids:After successful developoment of mice model with M. pneumoniae.A total of 95 mice were divided into Azithromycin group(25),Dexamethasone group(25), Combined group (25)and Placebo group(20).Besides, Azithromycin(10mg/kg) was administered subcutaneously once daily. Dexamethasone (0.5mg/kg) was administered intraperitoneally once daily. For the combined group,mice received Azithromycin(10mg/kg) and Dexamethasone (0.5mg/kg) once daily.Placebo group received sterile dextrose water. Mice were evaluated after 1,3,5,8 and10 days of treatment.BALF specimens were determined using real-time PCR,and lung histopathology were assessed by histopathologic score.Results:(1)Infection group:Wistar rats in infection group had inflammatory reaction 1 day later,and it turned severe at the 3 day with the highest HPS 16.The HPS of the 8 day and the 10 day were 8.1 and 7.1,respectively.No significant difference was found for HPS of the 8 day and the 10 day.However,Other HPS between different days had significant differences. No significant difference was found for DNA detected by real-time between days.Control group:There is no abnormal manigestation in animals.No obvious inflammation was identified by HPS.And no M. pneumoniae was shown by real-time PCR.(2)Treatment effect of glucocorticoids:Lung HPS in mice treated with combined therapy was significantly reduced after 3 days compared with other 3 group(P<0.05). After 3 days of Azithromycin therapy,HPS was significantly lower compared with the placebo treated mice. After 5 days of therapy, HPS was significantly lower with Dexamethasone compared with the placebo group(P<0.05).In addition, HPS was significantly higher with Dexamethasone compared with the Azithromycin and the combined group at the 3 day(P<0.05).No significant difference of HPS was shown between Azithromycin and Dexamethasone group at the 5,8 and 10 days(P>0.05).The DNA of M. pneumoniae in combined group reduced at the 5,8,10 days. In addition, DNA in Azithromycin group reduced at the 3 day,but no significant difference was found in DNA of Azithromycin group and placebo group. And no DNA decrease in BALF was shown in Dexamethasone groupConclusion:(1)Mice model with were successful developed in the experiment. Furthermore,it could provide animal model for investigating the pathogenesis and antimicrobial susceptibility of M. pneumoniae.(2) Dexamethasone alone did not significantly reduce DNA of in BALF,so it had no effect on M. pneumoniae.However, Dexamethasone could reduce histologic pulmonary inflammation by immune regulation.Thus, glucocorticoids should be invovled in severe M. pneumoniae pneumonia.(3) Resistance to Azithromycin in M. pneumoniae had been found in Wistar rats.However,there was decrease of HPS in group,which indicated that Azithromycin had certain immune regulation in addition to clinical resistance.