Objective   To investigate the protective effect and mechanism of naloxone preconditioning (NP) for rats with cerebral hemorrhage.   Methods   Totally 30 healthy male Sprague Dawley (SD) rats were randomly separated into Sham operatopm group

intracerebral hemorrhage (ICH) and NP treatment groups (n=10). Before the establishment of rat cerebral hemorrhage model

rats in the NP group were given an intraperitoneal injection of naloxone hydrochloride (2.0 mg/kg)

and those of ICH group received an injection of normal saline at same volume. Then

the ICH model was made by injecting 0.4 IU collagen Ⅶ into caudate nucleus while. The brain tissue samples around cerebral hemorrhagic focus after ICH were collected. RT-PCR and Western blotting were used to detect the transcriptional level and protein level of aquaporin protein 4 (AQP4) in the brain tissue

respectively. Meanwhile

immunohistochemistry was employed to determine the expression of matrix metalloproteinase 9 (MMP-9) in the rat brain tissue.   Results   Brain water content in ICH group was larger than that in Sham group (P0.05). However

NP preconditioning effectively decreased the brain water content (P0.05) compared with the other 2 groups. Compared with the ICH group

NP group had significantly decreased mRNA and protein levels of AQP4 in brain tissue (P0.01

P0.01). Meanwhile

the positive expression percentage of MMP-9 in the brain tissue was also significantly down-regulated after naloxone hydrochloride preconditioning.   Conclusion   Naloxone hydrochloride preconditioning exerts its effective protective effect by decreasing AQP4 expression at mRNA and protein levels and thus leads to attenuate and down-regulate MMP-9 in the ICH brain tissue.