Text Box: HEMODYNAMICS ANALYSIS OF RATS WITH PULMONARY HYPERTENSION SECONDARY TO LEFT-TO-RIGHT SHUNT WEI B, DU J-B, QI JG Department of Pediatrics, First Hospital, Peking University, China Objective: To analyze pulmonary hemodynamics in rats with hypertension secondary to left-to-right shunt. Methods: Twenty-four male Sprague-Dawley rats (150-200g) were randomly divided into 6-week control group, 6-week shunt group, 11-week control group and 11-week shunt group. By producing shunt between the abdominal aorta and inferior vena cava, a left-to-right shunt was formed in 6-week and 11-week shunt groups, where pulmonary artery pressure, oxygen saturation, the weight of right ventricle and the weight of left ventricle with septum were measured. The endothelium-dependentcyclic guanosine monophosphate-mediated relaxation (response to acetylcholine) and the endothelium-independent cyclic guanosine monophosphate-mediated relaxation (response to sodium nitroprusside) of the isolated pulmonary artery rings were also studied. Results: Pulmonary artery pressure and RV/LV+S elevated obviously in 6-week and 11-week shunting group (p<0.01). By 11 weeks of high pulmonary flow, acetylcholine (ACH) did not produce relaxation versus 61.6%±21.9% in control animals, whereas sodium nitroprusside(SNP) produced 99.2%±5.0% relaxation versus 100% in control group. Conclusions: Dysfunction of pulmonary endothelium-dependent vasorelaxation caused by high pulmonary flow played an important part in pulmonary hypertension. 2128