Expression Of Aquaporin-4 In Brain From Rats With Subarachnoid Hemorrhagic Edema

[Objective] Brain edema and serious neuron damage may take place through different mechanisms, resulting from cerebral vasospasm and intracranial hypertension after aneurismal subarachnoid hemorrhage. However, people know little of the mechanism of brain edema. Aquaproins are special water permeable proteins which are found extensively existing in the cell membrane of animals and plants in recent years. Among them, aquaproin 4 is widespread in the brain, which is concerned with the reabsorption of cerebrospinal fluid , brain edema and other metabolism of water. This study was taken to explore the relation of aquaproin 4 with brain edema after SAH , by observing the mRNA expression of aquaproin 4 in cerebral cortex ,thalamus and hippocampus at different times after multiple rats received autologous blood injection into cisterna magna.[Methods] 62 adult Wistar rats were randomly divided into the following groups: control, sham operation and SAH group. In the operation group 0.3ml autologous blood was obtained from the cut-off tail of the rats and subarachnoid hemorrhage was induced by injection of the autologous blood into the cisterna magna. In the sham operation group, 0.3ml saline instead of autologous blood was injected into the cisterna magna of the rats, and in the control group the animals were normal rats. The SAH group and the sham operation group were divided into 7 groups by different postoperative time intervals(lh, 8h,ld,2d,3d,5d and 7d after operation). The changes of brain water content (BWC) was measuered by the wet and dry weight methods. In situ hybridization was used to determine the expression changes of AQP4mRNA in the cerebral cortex, thalamus and hippocampus at different times .[ Results ] In both control group and sham operation groups, only a few cells with expression of AQP4 mRNA appeared, showing no significant difference(P>0.05). In SAH group, both BWC and AQP4mRNA expression in rat cortex, thalamus and hippocampus were increased at 8 hours after SAH and reached a peak at 2 days. In one week following SAH it declined to the normal level. At 8h, Id, 2d, 3d and 5d after SAH show significantly higher at 0.05 level than those in the control and sham operation groups (P<0.05) . The expression of AQP4mRNA was positively correlated with BWC (r=0.9105-0.9457 , p<0.01).[Conclusion] The expression of AQP4mRNA was positively correlated with the brain edema after SAH. It suggests that AQP4 may play an important role in the pathophysiology of brain edema after SAH.