OBJECTIVETo study the changes of pulmonary vascular remodeling in the pathogenesis of hypoxia-induced pulmonary hypertension (HPH) in neonatal rats.

METHODSNinety-six newborn Wistar rats were randomly divided into an HPH group (hypoxia exposure) and a control group (room air exposure). The mean pulmonary arteria pressure (mPAP), right ventricle hypertrophy index (RVHI), and vascular remodeling indexes MT% and MA% were measured 3, 5, 7, 10, 14 and 21 days after exposure (n=8 each time point). The ultrastructure of pulmonary vascular was observed under a transmission electron microscope.

RESULTSmPAP in the HPH group 3, 5, 7, 10, 14 and 21 days after hypoxia exposure increased compared with the control group (P<0.05). With the prolonged hypoxia time, mPAP in the HPH group increased more significantly. MT%, MA% and RVHI increased significantly in the HPH group after 7 days of hypoxia exposure in a time-dependent manner compared with the control group (P<0.05). The transmission electron microscopy demonstrated that small pulmonary arterials became thickened, endothelial cell hyperplasia and degeneration, and organelles increased in the HPH group after 7 days of hypoxia exposure. Besides, collagen deposition in the extracellular matrix and the changes of pulmonary vascular remodeling were observed.

CONCLUSIONSmPAP increases between 3 and 5 days of hypoxia exposure, resulting from pulmonary vascular spasm caused by hypoxia. After hypoxia of 7 days, the mPAP increases more significantly, pulmonary vascular remodeling occurs, and right ventricle becomes irreversibly hypertrophic. These changes may be intensified as the prolonged hypoxia time.