(Institute of Aviation Medicine,Beijing 100036,China)

CHEN Li-mingWEN Jing

(General Hospital of Air Force,PLA,Beijing 100036,China)

Abstract：Objective To observe the effects of repeated +10 Gz stress on cerebral lipid peroxidation，liver and renal function in rats and the prophylactic effects of antioxidant tea polyphenols(TP)．Method Twenty-four male Wistar rats were randomly divided into three groups(n=8 each):group A(control),group B(+10 Gz),and group C(TP).Group B and C were exposed to repeated +10 Gz stress(each for 30s，onset rate about 0.5 G/s,3 times/d with +1 Gz 1 min intervals,3 d/wk,4 weeks in total),but group A was only submitted to +1 Gz.TP(200 mg/kg) was given orally in group C about 1 h prior to the +Gz experiment,while distilled water was given in group A and B.Lipid peroxidation in the brain，liver and renal functions and serum lipids were determined．Results As compared with the control，lipid peroxidation in rat cerebral homogenate,mitochondria and cytoplasm was significantly increased( P＜0.05)，and serum creatinine concentration was markedly elevated after repeated +10 Gz stress(P＜0.01).But,TP had significant inhibitory effect on +10 Gz stress induced peroxidative injury in rat brain and reduced the serum creatinine level.There were no differences of serum triglyceride and total cholesterol concentrations and glutamic-pyruvic transaminase activity among the three groups．Conclusion These results indicated that repeated high +Gz stress could bring about peroxidative injury in brain and harmful effect on renal function,and natural antioxidant TP had signficant protective effects.

Key words:acceleration stress；lipid peroxidation；liver function;renal function；antioxidant；tea polyphenols；rat

摘要：目的 观察重复+10 Gz暴露对大鼠脑脂质过氧化反应和肝肾功能的影响以及天然抗氧化剂茶多酚(TP)的防护作用。方法 24只雄性Wistar大鼠随机等分为三组(n=8):A组(对照组)，B组(+10 Gz组)和C组(TP组)。B、C组重复+10 Gz暴露(每次30 s，G增长率约为0.5 G/s，3次/d，间隔+1 Gz 1min，3 d/wk，共4 wk)，而A组仅受+1 Gz作用。C组于+Gz实验前约1 h灌胃给予TP(200 mg/kg)，另外两组给予等量蒸馏水。测定脑脂质过氧化反应、肝肾功能和血脂水平。结果 与对照组相比，B组大脑皮层匀浆、线粒体和胞浆脂质过氧化反应明显增强(P＜0.05)，血浆肌酐水平明显升高(P＜0.01)；而TP对此过氧化反应具有显著抑制作用并明显降低血浆肌酐水平。各组间血清谷丙转氨酶活性、甘油三酯和总胆固醇水平无统计学差异。结论 重复高+Gz作用可引起脑自由基损伤并损害肾功能,而天然抗氧化剂茶多酚具有明显的保护作用。

中图法分类号：R852.21文献标识码：A文章编号：1002-0837(1999)01-0001-05

Many studies have shown the occurrence of free radical generation and lipid peroxidation in ischemic or injuried brain tissue,and the protective effects of antioxidants and free radical scavengers provide further evidence for the involvement of oxygen free radicals and lipid peroxidation in case of brain ischemia or trauma^［1,2］.It has been found that repeated +Gz exposure could bring about effects on brain tissue similar to ischemia and reperfusion or hypoxia and reoxygenetion^［3］，and induced brain injury^［4］.But,in aviation medicine,the role of free radical metabolism in +Gz exposure induced brain injury hasn't been systematically studied.In our previous study,it was shown that +10 Gz stress(3 times each for 3 min with 40 min intervals) could induce peroxidative injury in rat brain.Malondialdehyde(MDA) content in cerebral mitochondria was significantly increased after +10 Gz exposure,but in cytoplasm,there was no such difference in MDA concentration between the control and +10 Gz stressed rats^［5］.After pretreatment with antioxidant tea polyphenols(TP) at dose of 30 and 100 mg·kg^-1.d^-1(ip)，for three consecutive days,the mitochondrial lipid peroxidation was significantly inhibited.In addition,TP had remarkable protective effect on blood brain barrier injury induced by +10 Gz stress,as indicated by measuring the leakage of Evan's blue，and could substantially elevate mitochondrial adenosine triphosphatase(ATPase) activity^［6］.In this study,we further observed the changes of cerebral lipid peroxidation,liver and renal functions in rats after long-term,repeated +10 Gz stress and the prophylactic effects of antioxidant TP．

Materials and Methods

Experimental animal and drug administrationMale Wistar rats(193.1±14.2 g,n=24) from the Experimental Animal Center，Chinese Academy of Military Medical Sciences served as test subjects.These animals were randomly divided into three groups(n=8 each):group A(control),group B(+10 Gz) and group C(+10 Gz TP).TP (200 mg/kg) was given orally in group C about 1 h prior to the +Gz experiment,while distilled water was given in group A and B.TP with concentration ＞97% was produced by Hangzhou Dongya Tea Polyphenol Factory and provided by Professor YANG Xian-qiang of Zhejiang Agriculture University.

+Gz stress profileCentrifuge for small animals(radius of 2 m) in our institute was used .Rats(without anesthethia) were restrained in a special frame(3 cm in diameter,10 cm in length).The rate of +Gz onset was about 0.5 G/s.Both group B and C were exposed to repeated +Gz stress(each for 30 s，3 times/d with +1 Gz 1 min intervals,3 d/wk,4 weeks in total);the rats in group A were handled in the same way but only submitted to +1 Gz．

Determination of MDA concentration in rat brainThe rats were decapitated in the next day after the last centrifuge run,and the brains and serum were collected．Cerebral cortices were homogenized with 1/15 M phosphate buffer(pH 7.4，1∶10,W/V)．The homogenate was centrifuged at 2000 g for 5 min,then the supernatant was further centrifuged at 12500g for 20 min.The resulting supernatant and pellet of this centrifugation were the cytosolic and crude mitochondrial function,respectively^［7］.Malondialdehyde(MDA) contents in cerebral homogenate，mitochondria and cytoplasm were determined by thiobarbituric acid(TBA) reaction^［8］.Tissue sample was mixed with sodium dodecylsulfate,acetate buffer(pH 3.5) and aqueous solution of TBA.After heating at 95 ℃ for 60 min,the produced red pigment was estimated by the absorbance at 532 nm.1,1,3,3-tetraethoxy-propane(Fluka chemie AG) was used as an MDA standard．MDA content was expressed as nmol/mg protein.

Assay of superoxide dismutase(SOD) activityAbove mentioned cerebral homogenate,mitochondria and cytoplasm were used.Assaying of SOD activity was indirect and based on this enzymatic ability to scavenge superoxide radical() from the autoxidation of pyrogallol^［9］,but slight modification was made．Reaction system contained 4.5 ml of 50 mmol/L K₂HPO₄-KH₂PO₄ buffer(pH 8.3) and 10 μl of 50 mmol/L pyrogallol.The rate of autoxidation was taken from the increase in A325 per min.SOD activity was expressed as U/mg protein．

Measurment of liver and renal functions and serum lipid levelBUN(blood urea nitrogen) and serum creatinine levels，serum glutamic-pyruvic transaminase(GPT) activity,and serum triglyceride and total cholesterol concentration were analyzed by using ALCYON 300 full automatic biochemical analyzer．Reagent kits were purchased from Chinese High Technical Company(BUN) and Ausio Bioengineering limited Company(creatinine,GPT,triglyceride and total cholesterol) ．Serum GPT activity is an indicator of liver func