| Objectives: Secondary brain insults(SBI) usually fellows traumatic brain injury in a few hours to several days, may further the aggravation of brain injury. The particularity of the marine environment and treatment delays, making SBI with seawater immersion easily, the injury is more complicated. In this study, the model of SBI with seawater immersion was created on the bassis of SBI.Then the changes of superoxide dismutase(SOD) and malondialdehyde(MDA) were observed to study possible mechanism of SBI with seawater immersion.Methods: Total of 163 male SD rats were randomly divided into four groups:control group(A,5 rats), SBI group(B,32 rats), SBI with saline immersion group(C,33 rats), SBI with seawater immersion group(D,93 rats). DBI was produced by acceleration-deceleration model of traumatic brain injury developed by Marmarou et al.15minutes following the impact injury,a secondary insults was produced by right carotid occlusion for 30minutes.dental drill is used to open the right skull, the dura mater was cut longitudinally.The brain is covered with cotton slice and used infusion set to infuse seawater over the cotton at room temperature, suture the head skin, so that local brain tissue was soaked in sea water continuously.Pathological changes of traumatic brain edema was observed by hematoxylin and eosin method at designed time points(1h, 3h, 6h, 12h, 24h, 48h).Thiobarbituric acid method and xanthine oxidase method were used to determine the contents of malondialdehyde(MDA) and the activities of total SOD in brain tissue,and analyses the relationship of them. Results: SBI model and SBI with seawater immersion model were construct ,injured brain tissue can be immersed by sea water after the dura mater cutted, the models can be satisfied the experiment.SBI with seawater immersion group mortality rate (45/93,48.93%)is much higher than B group(8/32,25.00%)and C group(9/33,27.27%).these were statistically significant (P <0.05). The brain edema of SBI with seawater immersion is earlier and much serious than other groups,the brain edema of SBI and SBI with saline immersion group were stabilized after 24hs, but SBI with seawater immersion group is much serious until 48hs(88.38±0.93%). Pathological change by HE method indicated that pre-injury traumatic edema was aggravated as a result of seawater immersion and became grid changed not the same as Spongiform change of SBI group.SOD level in seawater immersion group were significantly decreased at the beginging of 3h(212.09±22.29)U/mgprot,and lower than SBI group(245.31±21.26)U/mgprot;MDA level in seawater immersion group were incresed in seawater immersion group at the beginging of 3h(9.53±0.47)nmol/mgprot,and higher than SBI groups in 3h(6.16±0.34)nmol/mgprot.There is a inverse correlation in control groups of SOD and MDA in brain tissue,with the result(P<0.05) There is parallel relationship between MDA and brain water content in B group,C group and D group.Conclusion:①SBI with seawater immersion group is more serious than SBI group under the corresponding time window;②the deteriorism of traumatic condition in SBI with seawater immersion became more serious quickly;③The radical change of SBI with seawater immersion is closely with traumatic condition.
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