Pettis Chris R, Drake Matt, Witten Mark L, Truitt Jill, Braun Eldon, Lindberg Kim, McNeil George, Hall Jack N
Department of Pediatrics and Steele Memorial Children's Research Center, Tucson, AZ 85724, USA.
Acta Astronaut. 2002 Mar;50(6):393-8. doi: 10.1016/s0094-5765(01)00186-2.
Both microgravity and simulated microgravity models, such as the 45HDT (45 degrees head-down tilt), cause a redistribution of body fluids indicating a possible adaptive process to the microgravity stressor. Understanding the physiological processes that occur in microgravity is a first step to developing countermeasures to stop its harmful effects, i.e., (edema, motion sickness) during long-term space flights.
Because of the kidneys' functional role in the regulation of fluid volume in the body, it plays a key role in the body's adaptation to microgravity.
Rats were injected intramuscularly with a radioactive tracer and then lightly anesthetized in order to facilitate their placement in the 45HDT position. They were then placed in the 45HDT position using a specially designed ramp (45HDT group) or prone position (control group) for an experimental time period of 1 h. During this period, the 99mTc-DTPA (technetium-labeled diethylenepentaacetate, MW=492 amu, physical half-life of 6.02 h) radioactive tracer clearance rate was determined by measuring gamma counts per minute. The kidneys were then fixed and sectioned for electron microscopy. A point counting method was used to quantitate intracellular spaces of the kidney proximal tubules.
45HDT animals show a significantly (p=0.0001) increased area in the interstitial space of the proximal tubules.
There are significant changes in the kidneys during a 1 h exposure to a simulated microgravity environment that consist primarily of anatomical alterations in the kidney proximal tubules. The kidneys also appear to respond differently to the initial periods of head-down tilt.
微重力和模拟微重力模型，如45度头低位倾斜（45HDT），都会导致体液重新分布，这表明可能存在对微重力应激源的适应性过程。了解微重力环境下发生的生理过程是开发应对措施以阻止其在长期太空飞行中产生有害影响（如水肿、晕动病）的第一步。
由于肾脏在调节体内液体量方面的功能作用，它在身体对微重力的适应中起着关键作用。
给大鼠肌肉注射放射性示踪剂，然后轻度麻醉以便于将其放置在45HDT体位。然后使用专门设计的斜坡将它们置于45HDT体位（45HDT组）或俯卧位（对照组），实验时间为1小时。在此期间，通过测量每分钟的伽马计数来确定99mTc-DTPA（锝标记的二乙三胺五乙酸，分子量 = 492原子质量单位，物理半衰期为6.02小时）放射性示踪剂的清除率。然后将肾脏固定并切片用于电子显微镜检查。采用点计数法对肾近端小管的细胞内间隙进行定量分析。
45HDT组动物近端小管间质空间的面积显著增加（p = 0.0001）。
在暴露于模拟微重力环境1小时期间，肾脏发生了显著变化，主要表现为肾近端小管的解剖学改变。肾脏对头低位倾斜的初始阶段似乎也有不同反应。
