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首页> 外文期刊>American Journal of Physiology >Mechanisms of postspaceflight orthostatic hypotension: low alpha1-adrenergic receptor responses before flight and central autonomic dysregulation postflight.
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Mechanisms of postspaceflight orthostatic hypotension: low alpha1-adrenergic receptor responses before flight and central autonomic dysregulation postflight.

机译：飞行后体位性低血压的机制：飞行前α1-肾上腺素受体反应低和飞行后中枢神经系统调节异常。

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Although all astronauts experience symptoms of orthostatic intolerance after short-duration spaceflight, only approximately 20% actually experience presyncope during upright posture on landing day. The presyncopal group is characterized by low vascular resistance before and after flight and low norepinephrine release during orthostatic stress on landing day. Our purpose was to determine the mechanisms of the differences between presyncopal and nonpresyncopal groups. We studied 23 astronauts 10 days before launch, on landing day, and 3 days after landing. We measured pressor responses to phenylephrine injections; norepinephrine release with tyramine injections; plasma volumes; resting plasma levels of chromogranin A (a marker of sympathetic nerve terminal release), endothelin, dihydroxyphenylglycol (DHPG, an intracellular metabolite of norepinephrine); and lymphocyte beta(2)-adrenergic receptors. We then measured hemodynamic and neurohumoral responses to upright tilt. Astronauts were separated into two groups according to their ability to complete 10 min of upright tilt on landing day. Compared with astronauts who were not presyncopal on landing day, presyncopal astronauts had 1). significantly smaller pressor responses to phenylephrine both before and after flight; 2). significantly smaller baseline norepinephrine, but significantly greater DHPG levels, on landing day; 3). significantly greater norepinephrine release with tyramine on landing day; and 4). significantly smaller norepinephrine release, but significantly greater epinephrine and arginine vasopressin release, with upright tilt on landing day. These data suggest that the etiology of orthostatic hypotension and presyncope after spaceflight includes low alpha(1)-adrenergic receptor responsiveness before flight and a remodeling of the central nervous system during spaceflight such that sympathetic responses to baroreceptor input become impaired.
机译：尽管所有宇航员在短时航天飞行后都会经历体位不耐症的症状，但实际上只有大约20％的人在着陆日直立姿势时会经历晕厥。晕厥前组的特点是飞行前后血管阻力低，着陆日体位压力时去甲肾上腺素释放低。我们的目的是确定晕厥前和非晕厥前组之间差异的机制。我们在发射前10天，着陆日和着陆后3天研究了23名宇航员。我们测量了对苯肾上腺素注射的升压反应。酪胺注射释放去甲肾上腺素;血浆量血浆嗜铬粒蛋白A（交感神经末梢释放的标志物），内皮素，二羟苯基乙二醇（DHPG，去甲肾上腺素的细胞内代谢产物）的血浆水平;和淋巴细胞β（2）-肾上腺素受体。然后，我们测量了对直立倾斜的血液动力学和神经体液反应。根据他们在着陆日完成10分钟直立倾斜的能力，将其分为两组。与在登陆日未晕厥前的宇航员相比，晕厥前的宇航员有1）。飞行前和飞行后对苯肾上腺素的升压反应均明显降低; 2）。降落日基线去甲肾上腺素水平明显降低，但DHPG水平显着升高; 3）。降落日与酪胺的去甲肾上腺素释放明显增加;和4）。去甲肾上腺素释放明显减少，但肾上腺素和精氨酸加压素释放明显增加，着陆日直立倾斜。这些数据表明，航天飞行后体位性低血压和晕厥前的病因包括飞行前低α（1）-肾上腺素能受体的反应性以及航天飞行中中枢神经系统的重塑，从而使对压力感受器输入的共鸣反应受损。

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