Parachuting:A Preliminary Investigation^*

WU Tang-chun¹, XIONG Yi-li²,CHEN Sheng¹,LENG Shun-tang²,HAI Tao,Robert M.Tanguay³

(1.Institute of Occupational Medicine, Tongji Medical University, Wuhan 430030；2. Hankou Airplane Hospital (No.457), Wuhan 430012；3.Lab of Cellular and Developmental Genetics, Life and Health Sciences Research Center, Laval University, Quebec, Canada G1K 7P4)

Abstract:Objective To study whether physiological and psychological stresses during parachuting jumps may result in biochemical changes of plasma in parachutists.Method Differences in the levels of hormones (cortisol, growth hormone, insulin, pancreatic glucagon, endothelin, angiotonin I and II, aldosterone), activities of enzymes (superoxide dismutase, glutathione peroxidase, glutathione S transferase), levels of the free radical damage indicator malondialdehyde (MDA), tumor necrosis factor alpha (TNF-α), and the main heat stress protein, HSP70,in the plasma and serum were investigated in control (non-parachuting) and parachuting paratroops.Result Significantly higher levels of serum hormones such as growth hormone, insulin, angiotonin I, renin activities, as well as MDA and plasma TNF-α and HSP70 were observed in the parachuting group.Conclusion Whether these changes can potentially serve as useful biomarkers to assess possible abnormal stress in parachutists and to evaluate the health condition and to select parachutists remains to be further studied.

Key words: parachutists; parachuting; stress(physiology); hormones;HSP70;malondialdehyde

摘要：目的 探讨跳伞期间空降兵经历的生理和心理应激是否会改变空降兵血浆的生化指标。方法 调查了对照组（未跳伞组）和跳伞组空降兵血浆和血清中激素水平（皮质醇、生长激素、胰岛素、胰高血糖素、类皮素、血管紧张素I和 II、醛固酮）、酶活性（超氧化物岐化酶、谷胱甘肽过氧化氢酶和谷胱甘肽硫转移酶）、自由基损伤指标水平（丙二醛，）、肿瘤坏死因子α(TNF-α)和主要热应激蛋白（HSP70）的差异性。结果 跳伞组血清中生长激素、胰岛素、血管紧张素I、肾素活性和血浆中丙二醛、TNF-α、HSP70等的水平比对照值显著高。结论 这些变化有可能作为评估空降兵是否经历异常应激、评价他们的健康状况和选择空降兵的有用生物标志物，但需进一步研究。

中图分类号：R851.3文献标识码：A文章编号：1002-0837(1999)04-0235-05

Parachuting has long been a subject of military interest,and is used to insert troops rapidly into a drop zone by air^［1］.During parachuting,paratroops may experience both physiological and psychological stresses caused by such environmental factors as high ambient temperature,altitude hypoxia,noise,vibration,and by such inherent psychogenic and emotional states as anxiety,fear,feeling of insecurity,and self-imposed stressors^［2,3］.These complex stressors can result in the stress response,but the biochemical changes in plasma of paratroops caused by these combined stresses and their possible significance in evaluating the health condition and selection of parachutists are unknown.It is known that organisms ranging from bacteria to human respond to high temperatures by inducing the synthesis of a group of proteins known as heat shock or heat stress protein (HSPs) and by reducing the rate of synthesis of most other proteins^［4～6］.The synthesis of HSPs is not only induced by heat but also by a variety of other physiological stresses such as ischemia and low pH,and by environmental stressors such as ethanol,carbon monoxide,nicotine,H₂O₂,benzene,mutagens,carcinogens,teratogens,dusts,drugs,ultraviolet light,amino acid analogs,heavy metals,free radicals,and others^［4～7］.HSP70 is the main heat stress protein and has been shown to have many important biological functions^［8］.For example,HSP70 may confer to organisms the ability to recover from stress,and it also protects organisms against the damage from heat or other harmful factors by raising the cellular resistance to these harmful factors^［8～10］.Moreover,HSP70 functions as a molecular chaperone,facilitating the synthesis,folding,assembly and intracellular transport of many proteins; this ability has been linked to thermotolerance and resistance to toxicants^［11,12］.To examine the stress response of paratroops,we investigated the levels of a number of factors.The levels of hormones (cortisol,growth hormone,insulin,pancreatic glucagon,endothelin,angiotonin I and II,aldosterone),activities of antioxidant enzymes ［superoxide dismutase (SOD),glutathione peroxidase (GST-Px),glutathione S transferase (GST)］,oxidative damage ［malondialdehyde (MDA)］,tumor necrosis factor alpha (TNF-α),and levels of the main heat stress protein,HSP70,were determined in serum and plasma of paratroops after parachuting and the results were compared with those in paratroops that had not parachuted within the last 6 months.The potential biomedical significance of the observed changes was discussed.

Method

Subjects118 healthy male paratroopers aged 18～23 years (mean: 20 years)were selected as the subjects.All subjects were in excellent physical condition.Fifty of them,who had not jumped within the last 6 months,served as control.The other 68,were subjected to three parachute jump exercises (once a day for three consecutive days),and served as the test group.

Determination of Environmental ConditionsDry wet and black bulb temperatures were determined.The wind velocity was determined using an anemometer.The temperature and wind velocity were measured six times between 9:00～11:00 a.m.on three consecutive days.

Collection of blood samplesVenous blood samples(5 ml) were obtained from both parachuting and control subjects at the same time on the last day of the experiment.Half of each sample was used for collecting sera (not heparinised),while the other half was heparinised for collecting plasma.

Determination of serum hormone levelsThe concentrations of serum cortisol,growth hormone,insulin,pancreatic glucagon,endothelin,angiotonin I and II ,and aldosterone were determined using the corresponding radioimmune reagent kit (all from the Institute of Northern Biotechnique,Beijing,except for the endothelin reagent kit which was from the Institute of Eastern-Asia Immunotechnique,Beijing).

Activities of SOD,GST-Px,GST and level of MDAThe activities of SOD,GST-Px,GST,and the levels of MDA were determined with the corresponding reagent kits (Jiancheng Bioengineering Company,Nanjing).

Levels of TNF-α and HSP70The concentration of TNF-α was determined using an ELISA Kit (Bangding Biomedical Company,Beijing).Plasma HSP70 was detected using an immunodot blot assay^［13,14］.Recombinant human HSP70,purified through the expression of the corresponding cDNA in E.coli BL2(DE3) cells using a pET vector as described earlier^［15］,was used as a standard reference.In this assay,antibodies against human HSP70 which were produced by the immunization of a rabbit with human HSP70 fusion protein in the pET-3c expression vector were used at a dilution of 1:5000^［16］.Immunoblot analysis was performed with a horseradish peroxidase conjugated goat anti-rabbit immunoglobin G (Sigma) and DAB (3,3-diaminobenzidine tetrahydrochloride).The density of each spot was determined by the absorbance read at 460 nm using a CS-930 Image Analyser (Japan).

Statistical