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Objective:To investigate the effect of Rhynchophylline（Rhy） on hypoxic pulmonary hypertension（HPH） and its mechanisms.Methods:1.Forty male healthy SD rats were randomly divided into 4 groups:（1） normal control group（C group）;（2） HPH model group（P group）;（3） HPH treated by Rhy group（P+Rhy group,PR group）;（4） HPH treated by Rhy and TEA group （P+Rhy+TEA group,PRT group）;each had 10 rats.The rats in C group were fed nonnal conditions.The rats in p groups were fed in hypoxic environment（oxygen concentration was10.0±1%）,8h/d,6d/w,continued 28 days.The rats in PR group were treated with Rhy（30mg/kg/d,for 5 days） by intraperitoneal injection after hypcxic for 28 days.The rats in PRT group were treated with TEA（5mg/kg） by intravenous injection,and treated with Rhy（30mg/kg/d,for 5 days） 3 hours later. Mean pulmonary arterial pressure（mPAP） and mean carotid pressure（mCAP） were measared by a cardiac catheterization.The right ventricle（RV） and left ventricle plus septum（VL+S） of rat were weighed respectively,and the RV/（VL+S） was caleulated.2.Tension of rat pulmonary artery ring（RPAR） was recorded in vitro,and the RPAR were divided into 3 groups:①control group（NE+Krebs）;②Rhy treated goups（NE+Rhy group）;③antagonist treated group（NE+Rhy+TEA group）.The effect of Rhy on the 10-5 mol/L NE preconstricted RPAR.was observed.Results:（1） Compared with control rats,the mPAP of P group rats had been markedly elevated after hypoxic for 28 days（P＜0.01）.The mPAP of PR group rats had been decreased significantly compared with those of P group rats（P＜0.01）.The mPAP of PRT group rats had been increased significantly compared with those of PR group rats （P＜0.01）.The mCAP of C group,P group,PR group and PRT grpop were（101.35±2.13）mmHg,（104.76±2.01）mmHg,（105.05±2.15）mmHg and（103.89±1.88） mmHg repectively.Thers is not significant difference of mCAP among those group （P＞0.05）.（2） The maximum tension of RPAR precontricted with 10-5mol/L NE was 2.334±0.65g.Rhy（15,30,45,60umol/L） could relax the RPAR precontricted with 10-5mol/L NE significantly（P＜0.01）,co-treated with TEA,the the relaxation of Rhy was inhibited markedly（P＜0.01）.Conclusion:（1） Rhy could decrease mPAP of HPH model rat significantly,and the TEA may abolish the relaxation response of Rhy to RPAR.（2） The mechanism of Rhy has related to its aciviting of the KCa.
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