The effects of chronic hypobaric hypoxia on pulmonary vasoreactivity in rat and the role of prostaglandin were studied. The results showed: ① The response of intrapulmonary artery rings to acute hypoxia consisted of a transient contraction followed by a relaxation and a sustained contraction. The transient contraction reactivity was significantly attenuated and the relaxation reactivity significantly potentiated by exposure of the rats to chronic hypobaric hypoxia for 15 d (CH15 group) and for 30 d (CH30 gr...