Early renal changes in 45 degrees HDT rats.
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.
Pettis
Chris R
CR
Department of Pediatrics and Steele Memorial Children's Research Center, Tucson, AZ 85724, USA.
Drake
Matt
M
Witten
Mark L
ML
Truitt
Jill
J
Braun
Eldon
E
Lindberg
Kim
K
McNeil
George
G
Hall
Jack N
JN
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
D013667:Technetium