Objective: To investigate the pharmacological role of 95% ethanol extract of Rhodiola algida var. tangutica on hypoxic pulmonary hypertension (HPH) and the related molecular mechanism. Method: Seventy-five male Sprague Dawley rats were randomly divided into five groups: control group

hypoxic control group(HC)

hypoxic and physiological saline group(HS)

hypoxic and low dose herb group(1.25 g·kg-1·day-1)

hypoxic and high dose herb group(2.5 g·kg-1·d-1).The rats were kept in a hypobaric chamber which simulated the environment of a 4 500 m altitude except the control animals.Every 24 h

the hypobaric chamber was opened for 30 min to administrate the herb and the treatment was lasted for 30 days.After that

the hemodynamic changes were recorded and right ventricular hypertrophy index were [RV/(LV+S)

%] calculated.The lung tissues were stained in HE and morphological parameter of vascular wall thickness(WT

%) was used to assess the remodeling of small pulmonary arteries.The levels of endothelin 1(ET-1) and endothelial nitric oxide synthase(eNOS)mRNA were measured by real-time PCR analysis.The levels of ET-1 and eNOS protein were measured by ELISA method. Result: Compared with the HC and HS group

the high dose of R. algida var.tangutica showed the pharmacologic actions as follows: ① The development of mean pulmonary arterial pressure(mPAP)

RV/LV+S

hemoglobin(Hb)

haematocrit(Hct) (%) were inhibited(p<0.01); ② The muscularization and WT of pulmonary small artery were decreased(P<0.05); ③ The level of ET-1 mRNA was decreased and the level of eNOS mRNA was increased in lung(P<0.05).④ The level of ET-1 protein content was decreased and the level of eNOS protein content was increased in sera(P<0.05). Conclusion: R. algida var.tangutica attenuates hypoxic pulmonary hypertension and remodeling of pulmonary small artery in HPH rats.The mechanisms are likely related to increase in level of eNOS mRNA and protein and decrease in level of ET-1mRNA and protein.