Proliferation and apoptosis of lung smooth muscular cells in hypoxic pulmonary hypertension in neonatal pigs

Objective To study the effects of the proliferation and apoptosis of smooth muscular cells(SMC) in small pulmonary arteries on the pulmonary vascular remodeling in hypoxia induced pulmonary hypertensive neonatal pigs. Methods Forty two pigs aged from the birthday to 14 days were divided into the normal developmental group and hypoxic hypertensive group. Twenty of them were exposed to hypobaric hypoxia (50.8 kPa) for 3 or 11 days to establish a pulmonary hypertension model. The proliferation and apoptosis of SMC in the pulmonary small arteries were studied with the immunohistochemiscal method and terminal transferase mediated nick end labeling (TUNEL) method. Results SMC replication rates were high (5%)at birth, and followed by a burst of replication during the early period after birth. The shorter period hypoxia did not cause the increase of SMC proliferation; and the longer hypoxia induced the pulmonary vascular wall remodeling with apparent SMC proliferation. No signal of cell apoptosis in the pulmonary vascular wall was found during the neonatal period under either the normal condition or the hypoxic condition. Conclusion The pulmonary resistant vascular remodeling after birth is related to SMC proliferation and SMC proliferation plays a crucial role in the formation of severe pulmonary hypertension induced by hypoxia. The role of apoptosis in the pulmonary vascular remodeling needs further research.