Early renal changes in 45° HDT rats

Chris R. Pettis, Matt Drake, Mark L. Witten, Jill Truitt, Eldon Braun, Kim Lindberg, George Mcneil, Jack N. Hall

Research output: Contribution to journalArticlepeer-review


Background: Both microgravity and simulated microgravity models, such as the 45HDT (45° 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. Hypothesis: 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. Methods: 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. Results: 45HDT animals show a significantly (p=0.0001) increased area in the interstitial space of the proximal tubules. Conclusions: 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.

Original languageEnglish (US)
Pages (from-to)393-398
Number of pages6
JournalActa Astronautica
Issue number6
StatePublished - Mar 2002
Externally publishedYes


  • 45° head-down tilt
  • Kidney proximal tubule
  • Microgravity

ASJC Scopus subject areas

  • Aerospace Engineering


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