title: Early renal changes in 45 degrees HDT rats.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Pediatrics and Steele Memorial Children's Research Center, Tucson, AZ 85724, USA.
authors.forename: Chris R
authors.initials: CR
authors.lastname: Pettis
authors.forename: Matt
authors.initials: M
authors.lastname: Drake
authors.forename: Mark L
authors.initials: ML
authors.lastname: Witten
authors.forename: Jill
authors.initials: J
authors.lastname: Truitt
authors.forename: Eldon
authors.initials: E
authors.lastname: Braun
authors.forename: Kim
authors.initials: K
authors.lastname: Lindberg
authors.forename: George
authors.initials: G
authors.lastname: McNeil
authors.forename: Jack N
authors.initials: JN
authors.lastname: Hall
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D005110:Extracellular Space / Q000000981:diagnostic imaging / Q000502:physiology; D018495:Fluid Shifts / Q000502:physiology; D018475:Head-Down Tilt; D006874:Hydrostatic Pressure; D007668:Kidney / Q000502:physiology* / Q000648:ultrastructure*; D007687:Kidney Tubules, Proximal / Q000502:physiology / Q000648:ultrastructure*; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011916:Rats, Inbred F344; D013667:Technetium; D014463:Ultrasonography; D018474:Weightlessness Simulation
chemical_list: D013667:Technetium