Objective    To observe the changes of aquaporin 9 (AQP9) expression and its role in rat brain after intracerebral hemorrhage (ICH).     Methods    Collagenase was infused into the right caudate nucleus to establish ICH model in adult Wistar rats. HE staining was used to detect the pathological changes. The protein expression of AQP9 was detected by immunohistochemical method and immunofluorescence

and the content of AQP9 mRNA was detected by RT-PCR.     Results    The area of ICH was gradually increased

and reached the peak at 24 h

then showed no more change. The content of AQP9 mRNA increased in 1 h after ICH

then decreased in 2-6 h and reached the lowest at 6 h

dramatically increased again after 24 h and reached the maximum at 48 h

compared with normal controls and sham operation group. The areas where AQP9 expressed were various in different time periods

especially at 48 h the content of AQP9 in circumventricular organs and osmoreceptor was excessive.     Conclusion    In the early stage of ICH

the decreased expression of AQP9 delays the cytotoxic edema

and in the later stage the increased expression of AQP9 is involved in water-ion homeostasis and energy metabolism.