Protective Effects And Mechanism Of Dexmedetomidine On The Brain Of Endotoxin-induced Shock Rats

Objective:To investigate the protective effects and possible mechanism of the dexmedetomidine (Dex) on the brain of endotoxin-induced shock rats.Methods:Fifty-six Sprague-Dawley rats were randomly divided into four groups of14rats each:normal saline (NS) group (NS0.5ml/kg+NS0.5ml/kg), lipopolysaccharide (LPS) model group (NS0.5ml/kg+LPS5mg/kg), Dex low-dose group (Dex0.5μg/kg+LPS5mg/kg) and Dex high-dose group (Dex4.5μg/kg+LPS5mg/kg). Fasting consisted of withholding solid food, but not water, for12h. All rats were weighed. Rats in low-and high-dose group were given doses of Dex0.5μg/kg and4.5μg/kg respectively within10min through tail intravenous injection. Rats in the NS and LPS model groups were given tail intravenous injection of NS0.5ml/kg. After a5-min interval, rats in the NS group were intravenously injected NS0.5ml/kg, and the remaining rats were given LPS5mg/kg (soluble in the NS,0.5ml) slowly through tail vein injection (10min).6h later, rats were intraperitoneally injected1%sodium pentobarbital (30mg/kg), and the cerebrospinal fluid and blood were obtained, then the rats were immediately sacrificed, and the brain was taken out for the experimental observation. Of each group7rats’ brain fifth segment were moved out to measure expression of nNOS and c-fos in hippocampal formation (hippocampus and dentate gyrus) by immunohistochemical methods. The brain tissues in addition to the fifth segment of the rat brain were prepared for10%homogenate, and the supernatant was collected. Contents of TNF-alpha, IL-1μ and NO in homogenate, cerebrospinal fluid and serum were detected by ELISA and Griess Reagent method.Seven rats’brains in each group were divided into left and right parts. The left part of hippocampal formation was for the expression of nNOS mRNA by RT-PCR, and the right part of hippocampal formation was for expression of nNOS protein using Western blot. The brain tissues outside of the hippocampal formation in7rats were placed in the oven to weigh the wet weight, and72h later to weigh dry weight, thus the brain water content was determined.Results:(1)Compared with NS group, cerebral water content in LPS group was evidently increased(P<0.01);Compared with LPS group, brain edema in high-and low-dose Dex group were obviously decreased (P<0.01or P<0.05).The Dex lightened brain edema. (2)Compared with NS group, the concentrations of TNF-a, IL-1β and NO in brain tissues, serum and cerebrospinal fluid in LPS group were obviously increased (P<0.01); Compared with LPS group, the concentrations of TNF-a, IL-1(3and NO in brain tissues, serum and cerebrospinal fluid in high-dose Dex group were obviously decreased (P<0.05or P<0.01). Compared with LPS group, the concentrations of TNF-a, IL-1β and NO in brain tissues, those of TNF-a and IL-1β in serum and that of NO in cerebrospinal fluid in low-dose Dex group were obviously decreased (P<0.05or P<0.01); Compared with low-dose group, the concentration of NO of cerebrospinal fluid in high dose group was significantly decreased (P<0.05).(3)The study using immnohistochemistry and image analysis method showed that there were nNOS and c-fos positive cells in hippocampal CA1, CA2, CA3areas and the dentate gyrus (DG) in NS group, but the c-fos was faintly expressed. Compared with NS group, the expression of nNOS and c-fos positive cells in hippocampal CA1, CA2, CA3areas and the DG in LPS group was increased evidently (P<0.01). Compared with LPS group, the expression of nNOS positive cells in hippocampal CA1, CA2, CA3areas and the DG in high-and low-dose group was decreased significantly (P<0.05or P<0.01). Compared with LPS group, the expression of c-fos positive cells in hippocampal CA1, CA2, CA3areas and the DG in high-dose group was decreased significantly (P<0.05or P<0.01), the expression of c-fos positive cells in hippocampal CA2and CA3areas and the DG in low-dose group was decreased significantly (P<0.05or P<0.01) Compared with low-dose group, the expression of c-fos positive cells in hippocampal CA1, CA2, and CA3areas and the DG and the expression of nNOS positive cells in hippocampal CA3areas in high-dose group was decreased significantly (P<0.05or P<0.01).(4)The mRNA expression levels of nNOS in hippocampal formation were examined by RT-PCR. The results showed that the expression of nNOS mRNA in hippocampal formation was significantly higher in LPS group than that in NS group (P<0.01). Compared with LPS group, the level of mRNA was obviously decreased in high-and low-dose groups (P<0.01).(5)The nNOS protein expression in hippocampal formation was studied using Western blot. The results showed that the protein expression of nNOS in hippocampal formation was significantly higher in LPS group than that in NS group (P<0.01).Compared with LPS group, the levels of protein were obviously decreased in high-and low-dose groups (P<0.01).Conclusion:LPS induces the expression of nNOS mRNA, increases the protein expression of nNOS and c-fos in hippocampal formation, and increases the synthesis and releasing of TNF-a, IL-1β and NO in serum, cerebrospinal fluid and brain tissues. LPS leads to acute brain edema and brain injury. Dex lightens brain edema induced by LPS. Dex significantly decreases expression of nNOS mRNA, nNOS and c-fos protein in the hippocampal formation, inhibits the synthesis and releasing of TNF-a, IL-1β and NO in serum, cerebrospinal fluid and brain tissues. By inhibiting oxidative stress and excess mediators of inflammation of endotoxin shock, Dex contributes to brain protection.