The Preliminary Studies On Biochemical Mechanisms Of Myocardial Injury Induced By Repetitive +Gz Stress In Rats And The Protective Effects Of Low-G Preconditioning And Tea Polyphenols

It is well known that high +Gz stress can produce somemal-effects on human body during aviation (aerospace) activities. With the development of aviation (aerospace) techniques and protective measures, pilots have to undertake high sustained-G acceleration stress. Especially, modern high-performance aircraft can develop +9 to +12Gz with 45 s, which produces loss of consciousness (G-LOC), even results in fatal flight accidents. Some important "G protective" methods such as anti~G devices and anti-G straining maneuvers (AGSM) have been used to maintain the bloodsupply of brain against G-LOC during +Gz acceleration.The heart, as one of important organs, works like a dynamic pump in the circulatory system. Many studies have been demonstrated the hostile effects of repeated +Gz stress on the cardiac structure and function. Meanwhile, some detrimental effects of "G protective" methods on the cardiac have also been observed. So far, few investigations have been systematically carried out on the biochemical mechanisms of cardiac injury induced by repetitive +Gz stress. Therefore, it is necessary to further investigate the mechanisms of myocardial damage induced by repetitive +Gz acceleration stress.Preconditioning (PC) is a kind of phenomenon that some brief episodes of ischemia/reperfusion results in less infarction after a sustained ischemic period than controls. In some way, the previous short ischemic periods initiate a powerful protection for the following sustained ischemic period. Numerous studies have shown that many various stimuli can induce the cardiac preconditioned status. Moreover, some antioxidants such as vitamine E, vitamine C and tea polyphenols (TP) have been proved to protect myocardium from ischemia-reperfusion injury and inhibit the occurrence of myocardial stunning. But whether the precondtionging and TP have similar protective effects on the myocardial injury and dysfunction induced by repeated +Gz stress will be worth studying.In this study, Wistar rats served as experimental subjects. Experimental group was exposed to five plateaus of 30s at +10Gz with 1 min interval, three times a week, for three weeks. Some methods of biochemistry, immunohisto-chemistry and molecular biology are used to explore the mechanisms of myocardial injury. The main results are as follow:1. Compared with control group, the adrenalin (AD) content in myocardial tissue of rats was elevated significantly in repetitive+10Gz stress group, which indicated some detrimental effects of catecholamine on the cardiac structure and function. But there were no marked changes of myocardial noradrenal in (NA), dopamine (DA) and 5-HT contents after +10Gz stress.2. After repeated +10Gz exposures, mitochondrial MDA concentration was significantly increased and SOD activity tended to decline. Also, iNOS enzymatic content was higher in myocardial tissue of +10Gz stress rats than that in control rats. But there were no significant changes of MDA concentration, SOD activity and Cu-ZnSOD protein expression in hearts after +10Gz exposures. These alterations demonstrated that exposures to repeated +10Gz stress could induce the cardiac oxidative damage.3. As for SDH and CCO, the marker enzyme of mitochondrial endomembrane, their activities decreased significantly after the rats were exposed to repetitive +10Gz stress. But there was no remarkable alteration of myocardial ATPase activity in each group of rats. These results suggest that the obstacle of energetic production in heart is also involved in the cardiac injury after -10Gz exposures.4. ICAM-1 protein expression in endothelium of myocardial stroma was enhanced obviously after repetitive +10Gz stress, which indicated that the infiltrating of leukocytes and following inflammation mediated by ICAM-1 would take part in myocardial damage.5. No significant difference of apoptosis-related gene bcl-2 and p53 mRNA expression was found in each group after repeated +10Gz exposures.On the other hand, low-G preconditioning (+2Gz for 5min about 1h prior to+10...