| Living in a weightless environment often produces some adaptational and pathophysiological changes refered to as adverse effects. Among them, much attention has been paid to such problems like muscle atrophy, bone loss, cardiovascular deconditioning, and decreases in plasma-testosterone-concentration. These adverse effects would greatly impair the effectiveness of extravehicular activities, the safety and health during and after the returning to Earth. Current countermeasures against these adverse changes include exercise, the Russian Penguin suit, lower bodynegative pressure (LBNP), fluid loading, nutrition, preflight adaptation training, drugs, and electrical muscle stimulation. Although exercise-based countermeasures have been practiced with some success for years, these countermeasures have their own limitations, such as limited effectiveness, time-consuming (2-4 h/d), exercise consumption of material and energy resources on board, and et al. In the 21st century, in order to achieve the goal of long-duration, exploration-class spaceflights, it is important to develop effective multi-system countermeasures. Intermittent artificial gravity (IAG), by incorporation of a short-arm centrifuge into the spacecraft, has been suggested as an alternative to continuous artificial gravity, provided by spinning the entire spacecraft or a tethered rotating spacecraft. However, a 4-day, -6 head-down bedrest study conducted by scientists at NASA AMES research center, led to the conclusion that various physiological systems benefit differentially from daily short-period +Gz gravitation; i.e., the preventive value appears to be system specific. Before an IAG protocol can be tested in space, a number of ground-based animal studies should be conducted to ascertain whether there is a system specificity in responsiveness to IAG.Hence, the present thesis work was designed to determine whether there was a greater difference in the counteracting effectiveness of daily gravitation in alleviating/preventing the adverse changes in testis, skeletal and cardiac muscles, bones, and vessels during a 4-wk simulated microgravity. Tail-suspended hindlimb -unloaded rat model was used to simulate the microgravity-induced adverse effects on various physiological systems. A total of three kinds of treatment including standing (STD), +45 head-up tilt (HUT), and centrifugation (CEN), were used to provide daily short-periodgravitations varying in G level, vector, and duration. The present thesis work consisted of the following five parts: (1) General feature of the three kinds of simulated IAG rat models was investigated by observations on changes in body weight, testis and adrenal glands. Thus, a suitable simulated IAG rat model was selected and used in subsequent experiments. (2) Effectiveness of daily 4 h STD in alleviating/preventing testis atrophy was evaluated with the rat model without cryptorchidism, which was prevented by inguinal canal ligation. Another aim of this experiment was to exclude in general the possible influences on the results obtained with conventional rat model simulating effects of microgravity. (3) Effeciveness of simulated IAG in alleviating/preventing hindlimb muscle atrophy induced by simulated microgravity was investigated. (4) Effeciveness of simulated IAG in alleviating/preventing myocardial contractility depression induced by simulated microgravity was investigated. (5) Effectiveness of simulated IAG in counteracting vascular structural adaptational changes and the angiotensin II receptor 1 (AT1) protein expression changes induced by simulated weightlessness was investigated.The main results of the present work are as follows: 1. General Features of the IAG simulation models: During the simulation period, the body weight (BW) of SUS rats increased steadily, and showed no significant differences as compared with that of the CON. But less BW gain were found in groups of different countermeasures, especially in SUS+HUT (4 h/d) and CEN (2.6 G) groups. Wet weights of testes among different groups were significantly l...
|
PDF Full Text Request