OBJECTIVE: To observe the effect of breviscapine on the pulmonary artery pressure and the Rho-kinase and Rho-kinase mRNA in pulmonary arterioles of rats treated with hypoxia, and therefore to explore the mechanisms of breviscapine on hypoxic pulmonary hypertension. METHODS: Eighteen adult male SD rats were randomly divided into 3 groups. One group was exposed to air (normal group), the second group was exposed to isobaric hypoxia for 3 weeks (hypoxic group), and the third group was exposed to hypoxia for 3 weeks and treated with breviscapine (preventive group). Cardiac catheterization was used to measure the mean pulmonary arterial pressure (mPAP). The heart was isolated, and the right ventricle (RV), left ventricle plus ventricular septum (LV + S) were weighed to calculate the ratio RV/(LV + S). The ratio of vascular wall thickness/vascular external diameter (WT%) and the ratio of vascular wall area/total vascular area (WA%) were measured by image analysis. The quantity of Rho-kinase and Rho-kinase mRNA in rat pulmonary arterioles were determined by immunohistochemistry and in situ hybridization respectively. RESULTS: The mPAP in the preventive group [(19.83 +/- 1.47) mm Hg, 1 mm Hg = 0.133 kPa] was significantly lower than that of the hypoxic group [(27.3 +/- 5.0) mm Hg], t = 4.28, P < 0.05. The RV/(LV + S) in the preventive group (0.29 +/- 0.03) was significantly lower than that in the hypoxic group (0.34 +/- 0.05, t = 2.39, P < 0.05). The WT% and WA% in the preventive group (25 +/- 5 and 45 +/- 5, respectively) were significantly lower than those in the hypoxic group (36 +/- 12 and 59 +/- 13, respectively, t = 4.89, 5.89, P < 0.05). The positive staining of ROCKI and ROCKII on pulmonary arterioles in the preventive group (1.18 +/- 0.10 and 1.30 +/- 0.12, respectively) were significantly lower than those in the hypoxic group (1.29 +/- 0.08 and 1.63 +/- 0.24, respectively, t = 3.90, 5.82, P < 0.05). The positive staining of ROCKI mRNA and ROCKII mRNA in the preventive group (1.23 +/- 0.13 and 1.22 +/- 0.06, respectively) were significantly lower than those in the hypoxic group (1.37 +/- 0.13 and 1.59 +/- 0.31, respectively, t = 3.94, 5.83, P < 0.05). CONCLUSION: Breviscapine was shown to prevent hypoxic pulmonary hypertension and decrease Rho-kinase and Rho-kinase mRNA.