Aim: To elucidate the involvement of the endothelin (ET) pathway in the pathogenesis of monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) and the therapeutic effect of CPU 86017 (p-chlorobenzyltetrahydroberberine chloride) in rats. Methods: Rats were injected with a single dose (60 mg/kg, sc) of MCT and given CPU 86017 (20,40, and 80 mg-kg~(-’)-d~(-’), po) or saline for 28 d. The hemodynamics, mRNA expression, and vascular activity were evaluated. Results: Right ventricular systolic pressure and central venous pressures were elevated markedly in the PAH model and decreased by CPU 86017. In the PAH group, the endothelin-1 (ET-1) in serum and lungs was dramatically increased by 54% (79.9 pg/ mL, P<0.01) and 93% (166.2 pg/mL, P<0.01), and mRNA levels of preproET-1, eNOS, and iNOS also increased dramatically compared with control. Compared with PAH group, CPU 86017 decreased the content of ET-1 to the normal level in lung tissue, but was less effective in serum. The level of NO was significantly increased in CPU 86017 at 80 and 40 mg-kg~(-’)-d~-1) groups in tissue, whereas the difference in serum was not significant. A significant reduction in MDA production and an increase in the SOD activity in the serum and lungs was observed in all three CPU 86017 groups. CPU 86017 80 mg-kg~(-’)-d~(-1) po increased the activity of cNOS by 33% (P<0.01). The up-regulation of eNOS and iNOS mRNA levels induced by MCT was significantly reversed in 3 CPU 86017 groups, and preproET-1 mRNA abundance was also reduced notably in CPU 86017 80 mg-kg~(-’)-d~(-1) group vs the PAH group. The KCl-induced vasoconstrictions in the calcium-free medium decreased markedly in PAH group but recovered partially after CPU 86017 intervention. The constrictions in the presence of Ca~(2+) was not improved by CPU 86017. The phenylephrine-induced vasoconstrictions in the calcium-free medium decreased markedly in PAH group but not recovered after CPU 86017 intervention. The constrictions in the presence of Ca~(2+) completely returned to the normal after CPU 86017 intervention. Conclusion: CPU 86017 suppressed MCT-induced PAH mainly through an indirect suppression of the ET-1 system, which was involved in the pathogenesis of the disease. Aim: To elucidate the involvement of the endothelin (ET) pathway in the pathogenesis of monocrotaline (MCT) -induced pulmonary arterial hypertension (PAH) and the therapeutic effect of CPU 86017 (p-chlorobenzyltetrahydroberberine chloride) in rats. Methods: Rats were injected (60 mg / kg, sc) of MCT and given CPU 86017 (20, 40, and 80 mg-kg ~ Results: Right ventricular systolic pressure and central venous pressures were elevated markedly in the PAH model and decreased by CPU 86017. In the PAH group, the endothelin-1 (ET-1) in serum and lungs was increased increased by 54% (79.9 pg / mL, P <0.01) and 93% (166.2 pg / mL, P <0.01), and mRNA levels of preproET-1, eNOS, and iNOS also increased dramatically compared with control . Compared with PAH group, CPU 86017 decreased the content of ET-1 to the normal level in lung tissue, but was less effective in serum. The level o f NO was significantly increased in CPU 86017 at 80 and 40 mg-kg ~ (- ’) - d ~ -1) in tissue, while the difference in serum was not significant. A significant reduction in MDA production and an increase in the SOD activity in the serum and lungs was observed in all three CPUs 86017 groups. CPU 86017 increased the activity of cNOS by 33% (P <0.01) 80 mg-kg ~ (- ’) - d ~ Up-regulation of eNOS and iNOS mRNA levels induced by MCT was drained in CPU 86017 groups, and preproET-1 mRNA abundance was also reduced significantly in CPU 86017 80 mg-kg ~ (- ’) - d ~ The KCl-induced vasoconstrictions in the calcium-free medium decreased markedly in PAH group but partially recovered after CPU 86017 intervention. The constrictions in the presence of Ca ~ (2+) were not improved by CPU 86017. The phenylephrine-induced vasoconstrictions in the calcium-free medium decreased markedly in PAH group but not recovered after CPU 86017 intervention. The constrictions in the pConclusion: CPU 86017 suppressed MCT-induced PAH mainly through an indirect suppression of the ET-1 system, which was involved in the pathogenesis of the disease.