| Objective The present study was initiated to assess the therapeutic effect of bilobalide on experiment rats with Pneumocystis carinii pneumonia, and to determine the mechanism of bilobalide against Pneumocystis carinii.Methods PCP rat models were established by hypodermic injection of dexamethasone twice a week for 6 weeks. The PCP rats were divided into five groups casually①Immunosuppressed control group, none therapy was administered. ②Menstruun control group, alcohol was administered intraperitoneally at dose of 0.4/mg/kg/d for 8 days.③Bilobalide 20mg/kg therapy group, bilobalide was administered intraperitoneally at dose of 20mg/kg /d for 8 days. ④Bilobalide 30mg/kg therapy group, bilobalide was administered intraperitoneally at dose of 30mg/kg /d for 8 days. ⑤SMZCo therapy control group, SMZCo was administered orally at dose of TMP20mg/kg/d+SMZ100mg/kg/d for 8 days. The therapeutic effect was evaluated by survival rate, lung weight/body weight ratio and mean cyst number per field of lung print smear, and the pathological changes. The ultrastructural change of Pneumocystis carinii after treating with bilobalide were investigated by transmission electronic microscope.Results ①The lung weight/body weight ratio of rats treated with bilobalide 20mg/kg,30mg/kg ((0.97±0.33)%,(1.02±0.21)%)was lower than that of immunosuppressed rats and menstruun control rats((1.46±0.34)%,(1.50±0.51)%,P<0.05), but was close to that of the rats treated with SMZCo((0.98±0.51)%, P>0.05)②Mean cyst number per field of lung print smear of rats treated with bilobalide 20mg/kg,30mg/kg was 2.31±0.88,1.95±0.57,which was lower than that of immunosuppressed rats and menstruun control rats (7.39±2.33,7.08±3.57,P<0.01), but was close to that of the rats treated with SMZCo( 1.05±0.44, P>0.05). ③Pathological change like pulmonary consolidation and inflammation were absorbed apparently in the rats treated with bilobalide .④The investigation of thinner lung tissue section by transmission electronic microscope showed that the Pneumocystis carinii treated with bilobalide had formation of vacuoles in trophozoites and cysts, swelling and destroying of cell organ, rupture of cytomembrane and some high density electronic granulae were investigated in the cytoplasm.Conclusion ①PCP rat models can be established by hypodermic injection with dexamethasone for 6 weeks.②Pulmonary inflammation produced by PC absorbed apparently after treating by bilobalide.③The quantity of Pneumocystis carinii in the lung of the rats treated with bilobalide decreased dramatically. ④The curative effect of bilobalide anti-PCP was similar to that of SMZCo on experiment rats. At the same time, none side effect had been found in our experiment.⑤Bilobalide could destroy ultrastructures of Pneumocystis carinii ,The membrane system of PC may be the aim of the drug.
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