The Effect Of Dexamethasone On Preventing Arachnoidal Fibrosis In Rat Model Of Subarachnoid Hemorrhage

Background: Chronic hydrocephalus, that was one of the common complication of subarachnoid hemorrhage ( SAH ) , severely influences patient's prognosis.The mechaniccsm of the chronic hydrocephalus caused by subarachnoid hemorrhage was still unclear, generally consists of cerebraspinal fluid(CSF) over-secretion, CSF circulation block, absorption disorders or both of them. Recent resources showed that chronic hydrocephalus caused by subarachnoid hemorrhage was in close relationship with arachnoidal fibrosis. Objective: To set up rat models of SAH by cisterna magna puncture and arterialblood injection; to study the relationship between arachnoid cell and arachnoidal fibrosis; and to clarify dexamethasone's (DXM) effects on preventing arachnoid fibrosis and chronic hydrocephalus. Method: The twice blood injection in cisterna magna was used for modeling. Andthe rats were divided into 3 groups: the group1 was subarachnoid hemorrhage treated without DXM (blank control), the group2 was subarachnoid hemorrhage treated with DXM intraperitone- ally, and the group3 was subarachnoidhemorrhage treated by DXM intrathecally. To detect hyaluronic acid, type IV collagen, laminin and type III precollagen in the arachnoid membrane by RIA method. The electron microscope was used to detect arachnoid cell's morphology and collagen distribution in the subarachnoid space. Result: The twice blood injection in cisterma magna could be a simple but effectivemethod in SAH modeling. The type III precollagen increased and 2 week later began to decrease, hyaluronic acid and type IV collagen fluctuated little, laminin decreased constantly; among these 3 groups, DXM group caused type III precollagen lower than the blank control group. For electron microscope observation we discovered arachnoid cells presented lower mitochondria density and less collagen in subarachnoid space in DXM treatment groups. Conclusion: The twice hemorrhage models was a simple and repeatable model for expe- rimental subarachnoid hemorrhage. One of the extracellular matrix (ECM), especially increased in both arachnoid cell plasma or subarachnoid space and hyaluronic acid, type IV collagen and laminin were almost stable, thatsuggested that type III collagen was one of the crucial factors on arachnoid fibrosis following the subarachnoid hemorrhage. Compared with the DXM ungiven group, the type III collagen in the DXM given group significantly decreased. It suggested that the DXM had effects on improving arachnoid fibrosis probably by easing nonspecific inflammatory reaction to improve CSF circulation and absorption.